SwePub
Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "L773:0022 3077 ;srt2:(2000-2004)"

Sökning: L773:0022 3077 > (2000-2004)

  • Resultat 1-50 av 54
Sortera/gruppera träfflistan
   
NumreringReferensOmslagsbildHitta
1.
  • Alstermark, Bror, et al. (författare)
  • In vivo recordings of bulbospinal excitation in adult mouse forelimb motoneurons.
  • 2004
  • Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 92:3, s. 1958-62
  • Tidskriftsartikel (refereegranskat)abstract
    • Here we report on pyramidal and reticulospinal excitation in forelimb motoneurons in the adult mouse using intracellular recordings in vivo. The results have been obtained in BALB/C mice, which were anesthetized with midazolam fentanyl/fluanison. In contrast to the rat, only weak and infrequent pyramidal excitation could be evoked with a minimal trisynaptic linkage. Disynaptic reticulospinal excitation could always be evoked, as well as monosynaptic excitation from the medial longitudinal fasciculus. The results suggest that the reticulospinal pathway in the mouse is important in voluntary motor control of the forelimbs and that the role of the corticospinal tract might be different in mouse compared with rat. Our study provides an opening for studying the effect of genetic manipulation on specified descending systems in the mouse in vivo.
  •  
2.
  • Alstermark, Bror, et al. (författare)
  • Lack of monosynaptic corticomotoneuronal EPSPs in rats : disynaptic EPSPs mediated via reticulospinal neurons and polysynaptic EPSPs via segmental interneurons.
  • 2004
  • Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 91:4, s. 1832-9
  • Tidskriftsartikel (refereegranskat)abstract
    • In the rat, some findings have been taken to suggest the existence of monosynaptic corticomotoneuronal (CM) connections. Because this connection is believed to be largely responsible for the ability to make independent digit movements in primates and man, it has been inferred that the monosynaptic CM connection in the rat is likewise important for skilled prehension. Comparison of intra- and extracellular recordings from forelimb motoneurons in anesthetized rats, revealed no monosynaptic CM excitatory postsynaptic potentials (EPSPs). The fastest descending excitation in forelimb motoneurons was disynaptically mediated via a corticoreticulospinal pathway and slowly conducted excitation via corticospinal fibers and segmental interneurons. The findings stress the importance of di- and trisynaptic excitatory corticofugal pathways to forelimb motoneurons in the control of skillful digit movements.
  •  
3.
  • Aoki, F, et al. (författare)
  • Slow dorsal-ventral rhythm generator in the lamprey spinal cord
  • 2001
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 85:1, s. 211-218
  • Tidskriftsartikel (refereegranskat)abstract
    • In the isolated lamprey spinal cord, a very slow rhythm (0.03–0.11 Hz), superimposed on fast N-methyl-d-aspartate (NMDA)-induced locomotor activity (0.26–2.98 Hz), could be induced by a blockade of GABAAor glycine receptors or by administration of (1 s, 3 s)-l-aminocyclopentane-1,3-dicarboxylic acid a metabotropic glutamate receptor agonist. Ventral root branches supplying dorsal and ventral myotomes were exposed bilaterally to study the motor pattern in detail. The slow rhythm was expressed in two main forms: 1) a dorsal-ventral reciprocal pattern was the most common (18 of 24 preparations), in which bilateral dorsal branches were synchronous and alternated with the ventral branches, in two additional cases a diagonal dorsal-ventral reciprocal pattern with alternation between the left (or right) dorsal and the right (or left) ventral branches was observed; 2) synchronous bursting in all branches was encountered in four cases. In contrast, the fast locomotor rhythm occurred always in a left-right reciprocal pattern. Thus when the slow rhythm appeared in a dorsal-ventral reciprocal pattern, fast rhythms would simultaneously display left-right alternation. A longitudinal midline section of the spinal cord during ongoing slow bursting abolished the reciprocal pattern between ipsilateral dorsal and ventral branches but a synchronous burst activity could still remain. The fast swimming rhythm did not recover after the midline section. These results suggest that in addition to the network generating the swimming rhythm in the lamprey spinal cord, there is also a network providing slow reciprocal alternation between dorsal and ventral parts of the myotome. During steering, a selective activation of dorsal and ventral myotomes is required and the neural network generating the slow rhythm may represent activity in the spinal machinery used for steering.
  •  
4.
  • Beierholm, U, et al. (författare)
  • Characterization of reliability of spike timing in spinal interneurons during oscillating inputs
  • 2001
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 86:4, s. 1858-1868
  • Tidskriftsartikel (refereegranskat)abstract
    • The spike timing in rhythmically active interneurons in the mammalian spinal locomotor network varies from cycle to cycle. We tested the contribution from passive membrane properties to this variable firing pattern, by measuring the reliability of spike timing, P, in interneurons in the isolated neonatal rat spinal cord, using intracellular injection of sinusoidal command currents of different frequencies (0.325–31.25 Hz). P is a measure of the precision of spike timing. In general, P was low at low frequencies and amplitudes ( P = 0–0.6; 0–1.875 Hz; 0–30 pA), and high at high frequencies and amplitudes ( P = 0.8–1; 3.125–31.25 Hz; 30–200 pA). The exact relationship between P and amplitude was difficult to describe because of the well-known low-pass properties of the membrane, which resulted in amplitude attenuation of high-frequency compared with low-frequency command currents. To formalize the analysis we used a leaky integrate and fire (LIF) model with a noise term added. The LIF model was able to reproduce the experimentally observed properties of P as well as the low-pass properties of the membrane. The LIF model enabled us to use the mathematical theory of nonlinear oscillators to analyze the relationship between amplitude, frequency, and P. This was done by systematically calculating the rotational number, N, defined as the number of spikes divided by the number of periods of the command current, for a large number of frequencies and amplitudes. These calculations led to a phase portrait based on the amplitude of the command current versus the frequency-containing areas [Arnold tongues (ATs)] with the same rotational number. The largest ATs in the phase portrait were those where N was a whole integer, and the largest areas in the ATs were seen for middle to high (>3 Hz) frequencies and middle to high amplitudes (50–120 pA). This corresponded to the amplitude- and frequency-evoked increase in P. The model predicted that P would be high when a cell responded with an integer and constant N. This prediction was confirmed by comparing N and P in real experiments. Fitting the result of the LIF model to the experimental data enabled us to estimate the standard deviation of the internal neuronal noise and to use these data to simulate the relationship between N and P in the model. This simulation demonstrated a good correspondence between the theoretical and experimental values. Our data demonstrate that interneurons can respond with a high reliability of spike timing, but only by combining fast and slow oscillations is it possible to obtain a high reliability of firing during rhythmic locomotor movements. Theoretical analysis of the rotation number provided new insights into the mechanism for obtaining reliable spike timing.
  •  
5.
  • Beloozerova, IN, et al. (författare)
  • Postural control in the rabbit maintaining balance on the tilting platform
  • 2003
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 90:6, s. 3783-3793
  • Tidskriftsartikel (refereegranskat)abstract
    • A deviation from the dorsal-side-up body posture in quadrupeds activates the mechanisms for postural corrections. Operation of these mechanisms was studied in the rabbit maintaining balance on a platform periodically tilted in the frontal plane. First, we characterized the kinematics and electromyographic (EMG) patterns of postural responses to tilts. It was found that a reaction to tilt includes an extension of the limbs on the side moving down and flexion on the opposite side. These limb movements are primarily due to a modulation of the activity of extensor muscles. Second, it was found that rabbits can effectively maintain the dorsal-side-up body posture when complex postural stimuli are applied, i.e., asynchronous tilts of the platforms supporting the anterior and posterior parts of the body. These data suggest that the nervous mechanisms controlling positions of these parts of the body can operate independently of each other. Third, we found that normally the somatosensory input plays a predominant role for the generation of postural responses. However, when the postural response appears insufficient to maintain balance, the vestibular input contributes considerably to activation of postural mechanisms. We also found that an asymmetry in the tonic vestibular input, caused by galvanic stimulation of the labyrinths, can affect the stabilized body orientation while the magnitude of postural responses to tilts remains unchanged. Fourth, we found that the mechanisms for postural corrections respond only to tilts that exceed a certain (threshold) value.
  •  
6.
  • Buschges, A, et al. (författare)
  • Roles of high-voltage-activated calcium channel subtypes in a vertebrate spinal locomotor network
  • 2000
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 84:6, s. 2758-2766
  • Tidskriftsartikel (refereegranskat)abstract
    • Lamprey spinal cord neurons possess N-, L-, and P/Q-type high-voltage–activated (HVA) calcium channels. We have analyzed the role of the different HVA calcium channels subtypes in the overall functioning of the spinal locomotor network by monitoring the influence of their specific agonists and antagonists on synaptic transmission and on N-methyl-d-aspartate (NMDA)–elicited fictive locomotion. The N-type calcium channel blocker ω-conotoxin GVIA (ω-CgTx) depressed synaptic transmission from excitatory and inhibitory interneurons. Blocking L-type and P/Q-type calcium channels with nimodipine and ω-agatoxin, respectively, did not affect synaptic transmission. Application of ω-CgTx initially decreased the frequency of the locomotor rhythm, increased the burst duration, and subsequently increased the coefficient of variation and disrupted the motor pattern. These effects were accompanied by a depression of the synaptic drive between neurons in the locomotor network. Blockade of L-type channels by nimodipine also decreased the frequency and increased the duration of the locomotor bursts. Conversely, potentiation of L-type channels increased the frequency of the locomotor activity and decreased the duration of the ventral root bursts. In contrast to blockade of N-type channels, blockade or potentiation of L-type calcium channels had no effect on the stability of the locomotor pattern. The P/Q-type calcium channel blocker ω-agatoxin IVA had little effect on the locomotor frequency or burst duration. The results indicate that rhythm generation in the spinal locomotor network of the lamprey relies on calcium influx through L-type and N-type calcium channels.
  •  
7.
  • Cangiano, L, et al. (författare)
  • Fast and slow locomotor burst generation in the hemispinal cord of the lamprey
  • 2003
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 89:6, s. 2931-2942
  • Tidskriftsartikel (refereegranskat)abstract
    • A fundamental question in vertebrate locomotion is whether distinct spinal networks exist that are capable of generating rhythmic output for each group of muscle synergists. In many vertebrates including the lamprey, it has been claimed that burst activity depends on reciprocal inhibition between antagonists. This question was addressed in the isolated lamprey spinal cord in which the left and right sides of each myotome display rhythmic alternating activity. We sectioned the spinal cord along the midline and tested whether rhythmic motor activity could be induced in the hemicord with bath-applied d-glutamate or N-methyl-d-aspartate (NMDA) as in the intact spinal cord or by brief trains of electrical stimuli. Fast rhythmic bursting (2–12 Hz), coordinated across ventral roots, was observed with all three methods. Furthermore, to diminish gradually the crossed glycinergic inhibition, a progressive surgical lesioning of axons crossing the midline was implemented. This resulted in a gradual increase in burst frequency, linking firmly the fast hemicord rhythm [6.6 ± 1.7 (SD) Hz] to fictive swimming in the intact cord (2.4 ± 0.7 Hz). Ipsilateral glycinergic inhibition was not required for the hemicord burst pattern generation, suggesting that an interaction between excitatory glutamatergic neurons suffices to produce the unilateral burst pattern. In NMDA, burst activity at a much lower rate (0.1–0.4 Hz) was also encountered, which required the voltage-dependent properties of NMDA receptors in contrast to the fast rhythm. Swimming is thus produced by pairs of unilateral burst generating networks with reciprocal inhibitory connections that not only ensure left/right alternation but also downregulate frequency.
  •  
8.
  • Cangiano, L, et al. (författare)
  • Role of apamin-sensitive k(ca) channels for reticulospinal synaptic transmission to motoneuron and for the afterhyperpolarization
  • 2002
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 88:1, s. 289-299
  • Tidskriftsartikel (refereegranskat)abstract
    • Single motoneurons and pairs of a presynaptic reticulospinal axon and a postsynaptic motoneuron were recorded in the isolated lamprey spinal cord, to investigate the role of calcium-dependent K+ channels (KCa) during the afterhyperpolarization following the action potential (AHP), and glutamatergic synaptic transmission on the dendritic level. The AHP consists of a fast phase due to transient K+ channels (fAHP) and a slower phase lasting 100–200 ms (sAHP), being the main determinant of spike frequency regulation. We now present evidence that the sAHP has two components. The larger part, around 80%, is abolished by superfusion of Cd2+ (blocker of voltage-dependent Ca2+ channels), by intracellular injection of 1,2-bis-( 2-aminophenoxy)-ethane- N,N,N′,N′-tetraacetic acid (BAPTA; fast Ca2+ chelator), and by apamin (selective toxin for KCa channels of the SK subtype). While 80% of the sAHP is thus due to KCa channels, the remaining 20% is not mediated by Ca2+, either entering through voltage-dependent Ca2+ channels or released from intracellular Ca2+ stores. This Ca2+-independent sAHP component has a similar time course as the KCa portion and is not due to a Cl− conductance. It may be caused by Na+-activated K+ channels. Glutamatergic excitatory postsynaptic potentials (EPSPs) evoked by single reticulospinal axons give rise to a local Ca2+ increase in the postsynaptic dendrite, mediated in part by N-methyl-d-aspartate (NMDA) receptors. The Ca2+ levels remain elevated for several hundred milliseconds and could be expected to activate KCa channels. If so, this activation should cause a local conductance increase in the dendrite that would shunt EPSPs following the first EPSP in a spike train. We have tested this in reticulospinal/motoneuronal pairs, by stimulating the presynaptic axon with spike trains at different frequencies. We compared the first EPSP and the following EPSPs in the control and after blockade with apamin. No difference was observed in EPSP amplitude or shape before and after apamin, either in normal Ringer or in Mg2+-free Ringer removing the voltage-dependent block of NMDA receptors. In conclusion, the local Ca2+ entry during reticulospinal EPSPs does not cause an activation of KCa channels sufficient to affect the efficacy of synaptic transmission. Thus the integration of synaptic signals at the dendritic level in motoneurons appears simpler than would otherwise have been the case.
  •  
9.
  •  
10.
  •  
11.
  • Compte, A., et al. (författare)
  • Temporally Irregular Mnemonic Persistent Activity in Prefrontal Neurons of Monkeys during a Delayed Response Task
  • 2003
  • Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 90:5, s. 3441-3454
  • Tidskriftsartikel (refereegranskat)abstract
    • An important question in neuroscience is whether and how temporal patterns and fluctuations in neuronal spike trains contribute to information processing in the cortex. We have addressed this issue in the memory-related circuits of the prefrontal cortex by analyzing spike trains from a database of 229 neurons recorded in the dorsolateral prefrontal cortex of 4 macaque monkeys during the performance of an oculomotor delayed-response task. For each task epoch, we have estimated their power spectrum together with interspike interval histograms and autocorrelograms. We find that 1) the properties of most (about 60%) neurons approximated the characteristics of a Poisson process. For about 25% of cells, with characteristics typical of interneurons, the power spectrum showed a trough at low frequencies (<20 Hz) and the autocorrelogram a dip near zero time lag. About 15% of neurons had a peak at <20 Hz in the power spectrum, associated with the burstiness of the spike train, 2) a small but significant task dependency of spike-train temporal structure: delay responses to preferred locations were characterized not only by elevated firing, but also by suppressed power at low (<20 Hz) frequencies, and 3) the variability of interspike intervals is typically higher during the mnemonic delay period than during the fixation period, regardless of the remembered cue. The high irregularity of neural persistent activity during the delay period is likely to be a characteristic signature of recurrent prefrontal network dynamics underlying working memory.
  •  
12.
  • Deliagina, TG, et al. (författare)
  • Activity of reticulospinal neurons during locomotion in the freely behaving lamprey
  • 2000
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 83:2, s. 853-863
  • Tidskriftsartikel (refereegranskat)abstract
    • The reticulospinal (RS) system is the main descending system transmitting commands from the brain to the spinal cord in the lamprey. It is responsible for initiation of locomotion, steering, and equilibrium control. In the present study, we characterize the commands that are sent by the brain to the spinal cord in intact animals via the reticulospinal pathways during locomotion. We have developed a method for recording the activity of larger RS axons in the spinal cord in freely behaving lampreys by means of chronically implanted macroelectrodes. In this paper, the mass activity in the right and left RS pathways is described and the correlations of this activity with different aspects of locomotion are discussed. In quiescent animals, the RS neurons had a low level of activity. A mild activation of RS neurons occurred in response to different sensory stimuli. Unilateral eye illumination evoked activation of the ipsilateral RS neurons. Unilateral illumination of the tail dermal photoreceptors evoked bilateral activation of RS neurons. Water vibration also evoked bilateral activation of RS neurons. Roll tilt evoked activation of the contralateral RS neurons. With longer or more intense sensory stimulation of any modality and laterality, a sharp, massive bilateral activation of the RS system occurred, and the animal started to swim. This high activity of RS neurons and swimming could last for many seconds after termination of the stimulus. There was a positive correlation between the level of activity of RS system and the intensity of locomotion. An asymmetry in the mass activity on the left and right sides occurred during lateral turns with a 30% prevalence (on average) for the ipsilateral side. Rhythmic modulation of the activity in RS pathways, related to the locomotor cycle, often was observed, with its peak coinciding with the electromyographic (EMG) burst in the ipsilateral rostral myotomes. The pattern of vestibular response of RS neurons observed in the quiescent state, that is, activation with contralateral roll tilt, was preserved during locomotion. In addition, an inhibition of their activity with ipsilateral tilt was clearly seen. In the cases when the activity of individual neurons could be traced during swimming, it was found that rhythmic modulation of their firing rate was superimposed on their tonic firing or on their vestibular responses. In conclusion, different aspects of locomotor activity—initiation and termination, vigor of locomotion, steering and equilibrium control—are well reflected in the mass activity of the larger RS neurons.
  •  
13.
  • Deliagina, TG, et al. (författare)
  • Asymmetrical effect of GABA on the postural orientation in Clione
  • 2000
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 84:3, s. 1673-1676
  • Tidskriftsartikel (refereegranskat)abstract
    • The marine mollusk Clione limacina, when swimming, normally stabilizes the vertical body orientation by means of the gravitational tail reflexes. Horizontal swimming or swimming along inclined ascending trajectories is observed rarely. Here we report that GABA injection into intact Clione resulted in a change of the stabilized orientation and swimming with a tilt of ∼45° to the left. The analysis of modifications in the postural network underlying this effect was done with in vitro experiments. The CNS was isolated together with the statocysts. Spike discharges in the axons of two groups of motoneurons responsible for the left and right tail flexion, as well as in the axons of CPB3 interneurons mediating signals from the statocyst receptors to the motoneurons, were recorded extracellularly when the preparation was rotated in space. Normally the tail motoneurons of the left and right groups were activated with the contralateral tilt of the preparation. Under the effect of GABA, the gravitational responses in the right group of motoneurons and in the corresponding interneurons were dramatically reduced while the responses in the left group remained unchanged. The most likely site of the inhibitory GABA action is the interneurons mediating signals from the statocysts to the right group of tail motoneurons. The GABA-induced asymmetry of the left and right gravitational tail reflexes, observed in the in vitro experiments, is consistent with a change of the stabilized orientation caused by GABA in the intact Clione.
  •  
14.
  • Deliagina, TG, et al. (författare)
  • Modifications of vestibular responses of individual reticulospinal neurons in lamprey caused by unilateral labyrinthectomy
  • 2002
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 87:1, s. 1-14
  • Tidskriftsartikel (refereegranskat)abstract
    • A postural control system in the lamprey is driven by vestibular input and maintains the dorsal-side-up orientation of the animal during swimming. After a unilateral labyrinthectomy (UL), the lamprey continuously rolls toward the damaged side. Normally, a recovery of postural equilibrium (“vestibular compensation”) takes about 1 mo. However, illumination of the eye contralateral to UL results in an immediate and reversible restoration of equilibrium. Here we used eye illumination as a tool to examine a functional recovery of the postural network. Important elements of this network are the reticulospinal (RS) neurons, which are driven by vestibular input and transmit commands for postural corrections to the spinal cord. In this study, we characterized modifications of the vestibular responses in individual RS neurons caused by UL and the effect exerted on these responses by eye illumination. The activity of RS neurons was recorded from their axons in the spinal cord by chronically implanted electrodes, and spikes in individual axons were extracted from the population activity signals. The same neurons were recorded both before and after UL. Vestibular stimulation (rotation in the roll plane through 360°) and eye illumination were performed in quiescent animals. It was found that the vestibular responses on the UL-side changed only slightly, whereas the responses on the opposite side disappeared almost completely. This asymmetry in the bilateral activity of RS neurons is the most likely cause for the loss of equilibrium in UL animals. Illumination of the eye contralateral to UL resulted, first, in a restoration of vestibular responses in the neurons inactivated by UL and in an appearance of vestibular responses in some other neurons that did not respond to vestibular input before UL. These responses had directional sensitivity and zones of spatial sensitivity similar to those observed before UL. However, their magnitude was smaller than before UL. Second, the eye illumination caused a reduction of the magnitude of vestibular responses on the UL side. These two factors tend to restore symmetry in bilateral activity of RS neurons, which is the most likely cause for the recovery of equilibrium in the swimming UL lamprey. Results of this study are discussed in relation to the model of the roll control system proposed in our previous studies as well as in relation to the vestibular compensation.
  •  
15.
  • Deliagina, TG, et al. (författare)
  • Neuronal mechanisms for the control of body orientation in clione II. Modifications in the activity of postural control system
  • 2000
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 83:1, s. 367-373
  • Tidskriftsartikel (refereegranskat)abstract
    • The marine mollusk Clione limacina, when swimming, can stabilize different body orientations in the gravitational field. The stabilization is based on the reflexes initiated by activation of the statocyst receptor cells and mediated by the cerebro-pedal interneurons that produce excitation of the motoneurons of the effector organs; tail and wings. Here we describe changes in the reflex pathways underlying different modes of postural activity; the maintenance of the head-up orientation at low temperature, the maintenance of the head-down orientation at higher temperature, and a complete inactivation of the postural mechanisms during defense reaction. Experiments were performed on the CNS-statocyst preparation. Spike discharges in the axons of different types of neurons were recorded extracellularly while the preparation was rotated in space through 360° in different planes. We characterized the spatial zones of activity of the tail and wing motoneurons and the CPB3 interneurons mediating the effects of statocyst receptor cells on the tail motoneurons. This was done at different temperatures (10 and 20°C). The “fictive” defense reaction was evoked by electrical stimulation of the head nerve. At 10°C, a tilt of the preparation evoked activation in the tail motoneurons and wing retractor motoneurons contralateral to the tilt and in the wing locomotor motoneurons ipsilateral to the tilt. At 20°C, the responses in the tail motoneurons and in the wing retractor motoneurons occurred reversed; these neurons were now activated with the ipsilateral tilt. In the wing locomotor motoneurons the responses at 20°C were suppressed. During the defense reaction, gravitational responses in all neuron types were suppressed. Changes in the chains of tail reflexes most likely occurred at the level of connections from the statocyst receptor cells to the CPB3 interneurons. The changes in gravitational reflexes revealed in the present study are sufficient to explain the corresponding modifications of the postural behavior in Clione.
  •  
16.
  • Deliagina, TG, et al. (författare)
  • Responses of reticulospinal neurons in intact lamprey to vestibular and visual inputs
  • 2000
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 83:2, s. 864-878
  • Tidskriftsartikel (refereegranskat)abstract
    • A lamprey maintains the dorsal-side-up orientation due to the activity of postural control system driven by vestibular input. Visual input can affect the body orientation: illumination of one eye evokes ipsilateral roll tilt. An important element of the postural network is the reticulospinal (RS) neurons transmitting commands from the brain stem to the spinal cord. Here we describe responses to vestibular and visual stimuli in RS neurons of the intact lamprey. We recorded activity from the axons of larger RS neurons with six extracellular electrodes chronically implanted on the surface of the spinal cord. From these multielectrode recordings of mass activity, discharges in individual axons were extracted by means of a spike-sorting program, and the axon position in the spinal cord and its conduction velocity were determined. Vestibular stimulation was performed by rotating the animal around its longitudinal axis in steps of 45° through 360°. Nonpatterned visual stimulation was performed by unilateral eye illumination. All RS neurons were classified into two groups depending on their pattern of response to vestibular and visual stimuli; the groups also differed in the axon position in the spinal cord and its conduction velocity. Each group consisted of two symmetrical, left and right, subgroups. In group 1neurons, rotation of the animal evoked both dynamic and static responses; these responses were much larger when rotation was directed toward the contralateral labyrinth, and the dynamic responses to stepwise rotation occurred at any initial orientation of the animal, but they were more pronounced within the angular zone of 0–135°. The zone of static responses approximately coincided with the zone of pronounced dynamic responses. The group 1 neurons received excitatory input from the ipsilateral eye and inhibitory input from the contralateral eye. When vestibular stimulation was combined with illumination of the ipsilateral eye, both dynamic and static vestibular responses were augmented. Contralateral eye illumination caused a decrease of both types of responses. Group 2neurons responded dynamically to rotation in both directions throughout 360°. They received excitatory inputs from both eyes. Axons of the group 2 neurons had higher conduction velocity and were located more medially in the spinal cord as compared with the group 1 neurons. We suggest that the reticulospinal neurons of group 1 constitute an essential part of the postural network in the lamprey. They transmit orientation-dependent command signals to the spinal cord causing postural corrections. The role of these neurons is discussed in relation to the model of the roll control system formulated in our previous studies.
  •  
17.
  • Dickson, C. T., et al. (författare)
  • Properties and role of I-h in the pacing of subthreshold oscillations in entorhinal cortex layer II neurons
  • 2000
  • Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 83:5, s. 2562-2579
  • Forskningsöversikt (refereegranskat)abstract
    • Various subsets of brain neurons express a hyperpolarization-activated inward current (I-h) that has been shown to be instrumental in pacing oscillatory activity at both a single-cell and a network level. A characteristic feature of the stellate cells (SCs) of entorhinal cortex (EC) layer II, those neurons giving rise to the main component of the perforant path input to the hippocampal formation, is their ability to generate persistent, Na+-dependent rhythmic subthreshold membrane potential oscillations, which are thought to be instrumental in implementing theta rhythmicity in the entorhinal-hippocampal network. The SCs also display a robust time-dependent inward rectification in the hyperpolarizing direction that may contribute to the generation of these oscillations. We performed whole cell recordings of SCs in in vitro slices to investigate the specific biophysical and pharmacological properties of the current underlying this inward rectification and to clarify its potential role in the genesis of the subthreshold oscillations. In voltage-clamp conditions, hyperpolarizing voltage steps evoked a slow, noninactivating inward current, which also deactivated slowly on depolarization. This current was identified as I-h because it was resistant to extracellular Ba2+, sensitive to Cs+, completely and selectively abolished by ZD7288, and carried by both Na+ and K+ ions. I-h in the SCs had an activation threshold and reversal potential at approximately -45 and -20 mV, respectively. Its half-activation voltage was -77 mV. Importantly, bath perfusion with ZD7288, but not Ba2+ gradually and completely abolished the subthreshold oscillations, thus directly implicating I-h in their generation. Using experimentally derived biophysical parameters for I-h and the low-threshold persistent Na+ current (I-NaP) present in the SCs, a simplified model of these neurons was constructed and their subthreshold electroresponsiveness simulated. This indicated that the interplay between I-NaP and I-h can sustain persistent subthreshold oscillations in SCs. I-NaP and I-h operate in a push-pull fashion where the delay in the activation/deactivation of I-h gives rise to the oscillatory process.
  •  
18.
  • Edin, Benoni (författare)
  • Quantitative analyses of dynamic strain sensitivity in human skin mechanoreceptors.
  • 2004
  • Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 92:6, s. 3233-43
  • Tidskriftsartikel (refereegranskat)abstract
    • Microneurographical recordings from 24 slowly adapting (SA) and 16 fast adapting (FA) cutaneous mechanoreceptor afferents were obtained in the human radial nerve. Most of the afferents innervated the hairy skin on the back of the hand. The afferents' receptive fields were subjected to controlled strains in a ramp-and-hold fashion with strain velocities from 1 to 64%.s(-1), i.e., strain velocities within most of the physiological range. For all unit types, the mean variation in response onset approached 1 ms for strain velocities >8%.s(-1). Except at the highest strain velocities, the first spike in a typical SAIII unit was evoked at strains <0.5% and a typical SAII unit began to discharge at <1% skin strain. Skin strain velocity had a profound effect on the discharge rates of all classes of afferents. The "typical" peak discharge rate at the highest strain velocity studied was 50-95 imp/s(-1) depending on unit type. Excellent fits were obtained for both SA and FA units when their responses to ramp stretches were modeled by simple power functions (r2 > 0.9 for 95% of the units). SAIII units grouped with SAII with respect to onset latency and onset variation but with SAI units with respect to dynamic strain sensitivity. Because both SA and FA skin afferents respond strongly, quickly, and accurately to skin strain changes, they all seem to be able to provide useful information about movement-related skin strain changes and therefore contribute to proprioception and kinesthesia.
  •  
19.
  • Ehrsson, HH, et al. (författare)
  • Cortical activity in precision- versus power-grip tasks: an fMRI study
  • 2000
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 83:1, s. 528-536
  • Tidskriftsartikel (refereegranskat)abstract
    • Most manual grips can be divided in precision and power grips on the basis of phylogenetic and functional considerations. We used functional magnetic resonance imaging to compare human brain activity during force production by the right hand when subjects used a precision grip and a power grip. During the precision-grip task, subjects applied fine grip forces between the tips of the index finger and the thumb. During the power-grip task, subjects squeezed a cylindrical object using all digits in a palmar opposition grasp. The activity recorded in the primary sensory and motor cortex contralateral to the operating hand was higher when the power grip was applied than when subjects applied force with a precision grip. In contrast, the activity in the ipsilateral ventral premotor area, the rostral cingulate motor area, and at several locations in the posterior parietal and prefrontal cortices was stronger while making the precision grip than during the power grip. The power grip was associated predominately with contralateral left-sided activity, whereas the precision-grip task involved extensive activations in both hemispheres. Thus our findings indicate that in addition to the primary motor cortex, premotor and parietal areas are important for control of fingertip forces during precision grip. Moreover, the ipsilateral hemisphere appears to be strongly engaged in the control of precision-grip tasks performed with the right hand.
  •  
20.
  • Ehrsson, HH, et al. (författare)
  • Differential fronto-parietal activation depending on force used in a precision grip task: an fMRI study
  • 2001
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 85:6, s. 2613-2623
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent functional magnetic resonance imaging (fMRI) studies suggest that the control of fingertip forces between the index finger and the thumb (precision grips) is dependent on bilateral frontal and parietal regions in addition to the primary motor cortex contralateral to the grasping hand. Here we use fMRI to examine the hypothesis that some of the areas of the brain associated with precision grips are more strongly engaged when subjects generate small grip forces than when they employ large grip forces. Subjects grasped a stationary object using a precision grip and employed a small force (3.8 N) that was representative of the forces that are typically used when manipulating small objects with precision grips in everyday situations or a large force (16.6 N) that represents a somewhat excessive force compared with normal everyday usage. Both force conditions involved the generation of time-variant static and dynamic grip forces under isometric conditions guided by auditory and tactile cues. The main finding was that we observed stronger activity in the bilateral cortex lining the inferior part of the precentral sulcus (area 44/ventral premotor cortex), the rostral cingulate motor area, and the right intraparietal cortex when subjects applied a small force in comparison to when they generated a larger force. This observation suggests that secondary sensorimotor related areas in the frontal and parietal lobes play an important role in the control of fine precision grip forces in the range typically used for the manipulation of small objects.
  •  
21.
  • Ehrsson, H Henrik, et al. (författare)
  • Evidence for the involvement of the posterior parietal cortex in coordination of fingertip forces for grasp stability in manipulation
  • 2003
  • Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 90:5, s. 2978-2986
  • Tidskriftsartikel (refereegranskat)abstract
    • Grasp stability during object manipulation is achieved by the grip forces applied normal to the grasped surfaces increasing and decreasing in phase with increases and decreases of destabilizing load forces applied tangential to the grasped surfaces. This force coordination requires that the CNS anticipates the grip forces that match the requirements imposed by the self-generated load forces. Here, we use functional MRI (fMRI) to study neural correlates of the grip-load force coordination in a grip-load force task in which six healthy humans attempted to lift an immovable test object held between the tips of the right index finger and thumb. The recorded brain activity was compared with the brain activity obtained in two control tasks in which the same pair of digits generated forces with similar time courses and magnitudes; i.e., a grip force task where the subjects only pinched the object and did not apply load forces, and a load force task, in which the subjects applied vertical forces to the object without generating grip forces. Thus neither the load force task nor the grip force task involved coordinated grip-load forces, but together they involved the same grip force and load force output. We found that the grip-load force task was specifically associated with activation of a section of the right intraparietal cortex, which is the first evidence for involvement of the posterior parietal cortex in the sensorimotor control of coordinated grip and load forces in manipulation. We suggest that this area might represents a node in the network of cortical and subcortical regions that implement anticipatory control of fingertip forces for grasp stability.
  •  
22.
  • Ehrsson, HH, et al. (författare)
  • Imagery of voluntary movement of fingers, toes, and tongue activates corresponding body-part-specific motor representations
  • 2003
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 90:5, s. 3304-3316
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate whether imagery of voluntary movements of different body parts activates somatotopical sections of the human motor cortices. We used functional magnetic resonance imaging to detect the cortical activity when 7 healthy subjects imagine performing repetitive (0.5-Hz) flexion/extension movements of the right fingers or right toes, or horizontal movements of the tongue. We also collected functional images when the subjects actually executed these movements and used these data to define somatotopical representations in the motor areas. In this study, we relate the functional activation maps to cytoarchitectural population maps of areas 4a, 4p, and 6 in the same standard anatomical space. The important novel findings are 1) that imagery of hand movements specifically activates the hand sections of the contralateral primary motor cortex (area 4a) and the contralateral dorsal premotor cortex (area 6) and a hand representation located in the caudal cingulate motor area and the most ventral part of the supplementary motor area; 2) that when imagining making foot movements, the foot zones of the posterior part of the contralateral supplementary motor area (area 6) and the contralateral primary motor cortex (area 4a) are active; and 3) that imagery of tongue movements activates the tongue region of the primary motor cortex and the premotor cortex bilaterally (areas 4a, 4p, and 6). These results demonstrate that imagery of action engages the somatotopically organized sections of the primary motor cortex in a systematic manner as well as activating some body-part-specific representations in the nonprimary motor areas. Thus the content of the mental motor image, in this case the body part, is reflected in the pattern of motor cortical activation.
  •  
23.
  • Fagergren, Anders, et al. (författare)
  • Control strategies correcting inaccurately programmed fingertip forces : Model predictions derived from human behavior
  • 2003
  • Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 89:6, s. 2904-2916
  • Tidskriftsartikel (refereegranskat)abstract
    • When picking up a familiar object between the index finger and the thumb, the motor commands are predetermined by the CNS to correspond to the frictional demand of the finger-object contact area. If the friction is less than expected, the object will start to slip out of the hand, giving rise to unexpected sensory information. Here we study the correction strategies of the motor system in response to an unexpected frictional demand. The motor commands to the mononeuron pool are estimated by a novel technique combining behavioral recordings and neuromuscular modelling. We first propose a mathematical model incorporating muscles, hand mechanics, and the action of lifting an object. A simple control system sends motor commands to and receives sensory signals from the model. We identify three factors influencing the efficiency of the correction: the time development of the motor command, the delay between the onset of the grip and load forces (GF-LF-delay), and how fast the lift is performed. A sensitivity analysis describes how these factors affect the ability to prevent or stop slipping and suggests an efficient control strategy that prepares and corrects for an altered frictional condition. We then analyzed fingertip grip and load forces (GF and LF) and position data from 200 lifts made by five healthy subjects. The friction was occasionally reduced, forcing an increase of the GF to prevent the object being dropped. The data were then analyzed by feeding it through the inverted model. This provided an estimate of the motor commands to the motoneuron pool. As suggested by the sensitivity analysis the GF-LF-delay was indeed used by the subjects to prevent slip. In agreement with recordings from neurons in the primary motor cortex of the monkey, a sharp burst in the estimated GF motor command (NGF) efficiently arrested any slip. The estimated motor commands indicate a control system that uses a small set of corrective commands, which together with the GF-LF-delay form efficient correction strategies. The selection of a strategy depends on the amount of tactile information reporting unexpected friction and how long it takes to arrive. We believe that this technique of estimating the motor commands behind the fingertip forces during a precision grip lift can provide a powerful tool for the investigation of the central control of the motor system.
  •  
24.
  • Fagerstedt, P, et al. (författare)
  • Lateral turns in the Lamprey. I. Patterns of motoneuron activity
  • 2001
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 86:5, s. 2246-2256
  • Tidskriftsartikel (refereegranskat)abstract
    • The activity of motoneurons during lateral turns was studied in a lower vertebrate, the lamprey, to investigate how a supraspinal command for the change of direction during locomotion is transmitted from the brain stem and integrated with the activity of the spinal locomotor pattern generator. Three types of experiments were performed. 1) The muscular activity during lateral turns in freely swimming adult lampreys was recorded by electromyography (EMG). It was characterized by increased cycle duration and increased duration, intensity, and cycle proportion of the bursts on the side toward which the animal turns. 2) Electrical stimulation of the skin on one side of the head in a head-spinal cord preparation of the lamprey during fictive locomotion elicited asymmetric ventral root burst activity with similar characteristics as observed in the EMG of intact lampreys during lateral turns. The cycle duration and ventral root burst intensity, duration, and cycle proportion on the side of the spinal cord contralateral to the stimulus were increased; hence a fictive lateral turn away from the stimulus could be produced. The fictive turn propagated caudally with decreasing amplitude. The increase in burst duration during the turn correlated well with the increase in cycle duration, while changes in contralateral burst intensity and burst duration did not co-vary. Turning responses varied depending on the timing (phase) of the skin stimulation: stimuli in the first two-thirds of a cycle evoked a turn in the same cycle, whereas stimuli in the last third gave a turn in the following cycle. The largest turns were evoked by stimuli in the first third of a cycle. 3) Fictive turns were abolished after transection of the trigeminal nerve or a rhombencephalic midline split, but not in a rhombencephalic preparation with transected cerebellar commissure. High spinal hemisection was sufficient to block turning toward the lesioned side, while turns toward the intact side remained. Taken together these findings suggest that the reticulospinal turn command is essentially unilateral and generated in the rhombencephalon.
  •  
25.
  • Fagerstedt, P, et al. (författare)
  • Lateral turns in the Lamprey. II. Activity of reticulospinal neurons during the generation of fictive turns
  • 2001
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 86:5, s. 2257-2265
  • Tidskriftsartikel (refereegranskat)abstract
    • We studied the neural correlates of turning movements during fictive locomotion in a lamprey in vitro brain–spinal cord preparation. Electrical stimulation of the skin on one side of the head was used to evoke fictive turns. Intracellular recordings were performed from reticulospinal cells in the middle (MRRN) and posterior (PRRN) rhombencephalic reticular nuclei, and from Mauthner cells, to characterize the pattern of activity in these cell groups, and their possible functional role for the generation of turns. All recorded reticulospinal neurons modified their activity during turns. Many cells in both the rostral and the caudal MRRN, and Mauthner cells, were strongly excited during turning. The level of activity of cells in rostral PRRN was lower, while the lowest degree of activation was found in cells in caudal PRRN, suggesting that MRRN may play a more important role for the generation of turning behavior. The sign of the response (i.e., excitation or inhibition) to skin stimulation of a neuron during turns toward (ipsilateral), or away from (contralateral) the side of the cell body was always the same. The cells could thus be divided into four types: 1) cells that were excited during ipsilateral turns and inhibited during contralateral turns; these cells provide an asymmetric excitatory bias to spinal networks and presumably play an important role for the generation of turns; these cells were common ( n = 35; 52%) in both MRRN and PRRN; 2) cells that were excited during turns in either direction; these cells were common ( n = 19; 28%), in particular in MRRN; they could be involved in a general activation of the locomotor system after skin stimulation; some of the cells were also more activated during turns in one direction and could contribute to an asymmetric turn command; 3) one cell that was inhibited during ipsilateral turns and excited during contralateral turns; and 4) cells ( n = 12; 18%) that were inhibited during turns in either direction. In summary, our results show that, in the lamprey, the large majority of reticulospinal cells have responses during lateral turns that are indicative of a causal role for these cells in turn generation. This also suggests a considerable overlap between the command system for lateral turns evoked by skin stimulation, which was studied here, and other reticulospinal command systems, e.g., for lateral turns evoked by other types of stimuli, initiation of locomotion, and turns in the vertical planes.
  •  
26.
  • Fridberger, Anders, 1966-, et al. (författare)
  • Loud sound-induced changes in cochlear mechanics
  • 2002
  • Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 88:5, s. 2341-2348
  • Tidskriftsartikel (refereegranskat)abstract
    • To investigate the inner ear response to intense sound and the mechanisms behind temporary threshold shifts, anesthetized guinea pigs were exposed to tones at 100-112 dB SPL. Basilar membrane vibration was measured using laser velocimetry, and the cochlear microphonic potential, compound action potential of the auditory nerve, and local electric AC potentials in the organ of Corti were used as additional indicators of cochlear function. After exposure to a 12-kHz intense tone, basilar membrane vibrations in response to probe tones at the characteristic frequency of the recording location (17 kHz) were transiently reduced. This reduction recovered over the course of 50 ms in most cases. Organ of Corti AC potentials were also reduced and recovered with a time course similar to the basilar membrane. When using a probe tone at either 1 or 4 kHz, organ of Corti AC potentials were unaffected by loud sound, indicating that transducer channels remained intact. In most experiments, both the basilar membrane and the cochlear microphonic response to the 12-kHz overstimulation was constant throughout the duration of the intense stimulus, despite a large loss of cochlear sensitivity. It is concluded that the reduction of basilar membrane velocity that followed loud sound was caused by changes in cochlear amplification and that the cochlear response to intense stimulation is determined by the passive mechanical properties of the inner ear structures.
  •  
27.
  • Granseth, Björn, 1973-, et al. (författare)
  • Unitary EPSCs of corticogeniculate fibers in the rat dorsal lateral geniculate nucleus in vitro
  • 2003
  • Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 89:6, s. 2952-2960
  • Tidskriftsartikel (refereegranskat)abstract
    • To investigate unitary corticogeniculate excitatory postsynaptic currents (EPSCs), whole cell patch-clamp recordings were obtained from 20 principal cells in slices of the dorsal lateral geniculate nucleus (dLGN) of DA-HAN rats. EPSCs, evoked by electrical stimulation of corticogeniculate axons, had size distributions with one or more quantal peaks. Gaussian curves fitted to such distributions gave a mean quantal size (q) of -5.0 ± 0.7 (SD) pA for the EPSCs. Paired-pulse ratio (EPSC2/EPSC1) was 3.3 ± 0.9 for stimuli separated by 40 ms. The mean quantal size was similar for facilitated EPSCs (-5.2 ± 0.8 pA), implying an increase in mean quantal content (m). Most corticogeniculate axons were capable of releasing only one or two quanta onto individual principal cells. Mean resting release probability (p) was low, 0.09 ± 0.04. Binomial models, with the same n but increased p, could account for both the basal and facilitated EPSC size distributions in 6/8 cells. It is suggested that the low resting efficacy of corticogeniculate synapses serves to stabilize this excitatory feedback system. The pronounced facilitation in conjunction with large convergence from many corticogeniculate cells would provide a transient, potent excitation of dLGN cells, compliant with the idea of a visually driven neuronal amplifier.
  •  
28.
  • Hao, JX, et al. (författare)
  • Response characteristics of spinal cord dorsal horn neurons in chronic allodynic rats after spinal cord injury
  • 2004
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 92:3, s. 1391-1399
  • Tidskriftsartikel (refereegranskat)abstract
    • The physiological mechanisms of chronic pain in patients with spinal cord injury (SCI) are poorly understood. In the present study, we explored response characteristics of dorsal horn neurons of spinally injured rats exhibiting chronic pain (pain-like response to innocuous mechanical and cold stimulation). Several abnormalities were found in the distribution and response characteristics of dorsal horn neurons in chronic allodynic rats. First, 17% of the recorded neurons (vs. 0% in control animals) had no receptive field. Most of these units were located at or close to the lesioned spinal segment, and they discharged spontaneously at high frequencies. Allodynic rats also showed a significant decrease in the proportion of low-threshold (LT) neurons and an increase in the proportion of wide dynamic range (WDR) neurons. The rate of spontaneous activity of high-threshold (HT) neurons was significantly higher in allodynic compared with control rats. Moreover, HT neurons in allodynic animals showed increased neuronal responses to mechanical stimulation. WDR neurons responded with higher discharge rates to innocuous von Frey hair stimulation in allodynic compared with control rats. The percentage of WDR and HT neurons showing afterdischarges to noxious pinch was also significantly increased in the allodynic rats. The proportion of WDR and HT neurons responding to innocuous cold stimulation respectively increased from 53 and 25% in control rats to 91 and 75% in allodynic animals. These results suggest that the chronic pain-like behaviors in spinally injured rats may be generated and maintained by abnormalities in dorsal horn neurons.
  •  
29.
  • Hu, GY, et al. (författare)
  • Intracellular QX-314 causes depression of membrane potential oscillations in lamprey spinal neurons during fictive locomotion
  • 2002
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 87:6, s. 2676-2683
  • Tidskriftsartikel (refereegranskat)abstract
    • Spinal neurons undergo large cyclic membrane potential oscillations during fictive locomotion in lamprey. It was investigated whether these oscillations were due only to synaptically driven excitatory and inhibitory potentials or if voltage-dependent inward conductances also contribute to the depolarizing phase by using N-(2,6-dimethylphenyl carbamoylmethyl)triethylammonium bromide (QX-314) administered intracellularly during fictive locomotion. QX-314 intracellularly blocks inactivating and persistent Na+ channels, and in some neurons, effects on certain other types of channels have been reported. To detail the effects of QX-314 on Na+ and Ca2+ channels, we used dissociated lamprey neurons recorded under whole cell voltage clamp. At low intracellular concentrations of QX-314 (0.2 mM), inactivating Na+ channels were blocked and no effects were exerted on Ca2+ channels (also at 0.5 mM). At 10 mM QX-314, there was, however a marked reduction of I Ca. In the isolated spinal cord of the lamprey, fictive locomotion was induced by superfusing the spinal cord with Ringer's solution containing N-methyl-d-aspartate (NMDA), while recording the locomotor activity from the ventral roots. Simultaneously, identified spinal neurons were recorded intracellularly, while infusing QX-314 from the microelectrode. Patch electrodes cannot be used in the intact spinal cord, and therefore “sharp” electrodes were used. The amplitude of the oscillations was consistently reduced by 20–25% in motoneurons ( P < 0.05) and unidentified spinal neurons ( P < 0.005). The onset of the effect started a few minutes after impalement and reached a stable level within 30 min. These effects thus show that QX-314 causes a reduction in the amplitude of membrane potential oscillations during fictive locomotion. We also investigated whether QX-314 could affect glutamate currents by applying short pulses of glutamate from an extracellular pipette. No changes were observed. We also found no evidence for a persistent Na+ current in dissociated neurons, but these cells have a much-reduced dendritic tree. The results indicate that there is an inward conductance, which is sensitive to QX-314, during membrane potential oscillations that “boosts” the synaptic drive during fictive locomotion. Taken together, the results suggest that inactivating Na+ channels contribute to this inward conductance although persistent Na+channels, if present on dendrites, could possibly also contribute to shaping the membrane potential oscillations.
  •  
30.
  • Ivarsson, Magnus, et al. (författare)
  • Conditioned eyeblink response consists of two distinct components
  • 2000
  • Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 83:2, s. 796-807
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of these experiments was to obtain a detailed knowledge of how the orbicularis oculi muscle is activated during the execution of a conditioned eyeblink response (CR). This is the first critical step to understand the underlying neural mechanisms involved in the control of the CR. Decerebrate ferrets were trained in a classical conditioning paradigm. The conditioned stimulus (CS) was a train of electrical stimuli (15 pulses, 50 Hz, 1 mA) applied to the forelimb, and the unconditioned stimulus (US) was a train of electrical stimuli (3 pulses, 50 Hz, 3-4 mA) to the periorbital region. The CRs were studied by recording electromyograms (EMGs) from the orbicularis oculi muscle. The eyeblink CR in all animals showed a similar topography with at least two different components, CR1 and CR2, which were expressed at different rates. CR1 appeared first during acquisition, had a shorter onset latency, and was more phasic and more resistant to extinction than CR2. A marked pause in the muscle activity separated the two components. To control that the two-component CR were not species, paradigm or preparation specific, awake rabbits were trained with a tone CS (300 ms, 4 kHz, 64 dB) and a train of periorbital stimuli as US (3 pulses, 50 Hz, 3 mA). CR1 and CR2 were present in the rabbit eyeblink CR. The cerebellum is implicated in the control of CRs and to study whether separate neural pathways were responsible for CR1 and CR2, direct brachium pontis stimulation was used to replace the forelimb CS. CR1 and CR2 were present in the CR elicited by the brachium pontis CS. The presence of CR1 and CR2 after a unilateral lesion of the brachium conjunctivum shows that output from the contralateral cerebellar hemisphere was not the cause for any of the components. Other mechanisms that might be involved in the separation of the CR into two components are discussed. The results show that the eyeblink CR consists of at least two components, CR1 and CR2, which most likely originate either as a direct central command from the cerebellum or in the output pathway before the facial nucleus.
  •  
31.
  • Jensen, Kimmo, et al. (författare)
  • GABA Transporter-1 (GAT1) Deficient Mice: Differential Tonic Activation of GABAA versus GABAB Receptors in the Hippocampus.
  • 2003
  • Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 90:4, s. 701-2690
  • Tidskriftsartikel (refereegranskat)abstract
    • After its release from interneurons in the CNS, the major inhibitory neurotransmitter GABA is taken up by GABA transporters (GATs). The predominant neuronal GABA transporter GAT1 is localized in GABAergic axons and nerve terminals, where it is thought to influence GABAergic synaptic transmission, but the details of this regulation are unclear. To address this issue, we have generated a strain of GAT1-deficient mice. We observed a large increase in a tonic postsynaptic hippocampal GABAA receptor-mediated conductance. There was little or no change in the waveform or amplitude of spontaneous inhibitory postsynaptic currents (IPSCs) or miniature IPSCs. In contrast, the frequency of quantal GABA release was one-third of wild type (WT), although the densities of GABAA receptors, GABAB receptors, glutamic acid decarboxylase 65 kDa, and vesicular GAT were unaltered. The GAT1-deficient mice lacked a presynaptic GABAB receptor tone, present in WT mice, which reduces the frequency of spontaneous IPSCs. We conclude that GAT1 deficiency leads to enhanced extracellular GABA levels resulting in an overactivation of GABAA receptors responsible for a postsynaptic tonic conductance. Chronically elevated GABA levels also downregulate phasic GABA release and reduce presynaptic signaling via GABAB receptors thus causing an enhanced tonic and a diminished phasic inhibition.
  •  
32.
  • Johnsen, SE, et al. (författare)
  • Receptive field properties of human periodontal afferents responding to loading of premolar and molar teeth
  • 2003
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 89:3, s. 1478-1487
  • Tidskriftsartikel (refereegranskat)abstract
    • Impulses in 45 single mechanoreceptive afferents were recorded from the human inferior alveolar nerve with permucosally inserted tungsten microelectrodes. All afferents responded to mechanical stimulation of one or more premolar or molar teeth and most likely innervated their periodontal ligaments. For each afferent, isolated “ramp-and-hold” shaped force profiles of similar magnitudes (252 ± 24 mN; mean ± SD) were applied to the lower first premolar, the second premolar, and the first molar on the recording side. The tooth loads were applied in six directions: lingual, facial, mesial, and distal in the horizontal plane and up and down in the vertical direction of the tooth. The afferents response during the static phase of the stimulus was analyzed. All afferents were slowly adapting, discharging continuously in response to static forces in at least one stimulation direction. Twenty-nine afferents (64%) were spontaneously active, exhibiting an ongoing discharge in the absence of external stimulation. Stimulation of a single tooth was found to excite each afferent most strongly. The most sensitive tooth (MST) was the first premolar for 23, the second premolar for 13, and the first molar for 9 afferents. About half of the afferent population also responded to loading of one or two more teeth. The response profiles of these afferents indicated that the multiple-teeth receptive fields were due to mechanical coupling between the teeth rather than branching of single afferents to innervate several teeth. The afferent responses to loading the mesial and distal halves of the first molars were very similar. Thus both intensive and directional aspects of the afferent response when loading one side of the tooth was preserved to a great extent when loading the other side. When loading the MST, the afferents typically showed excitatory responses in two to four of the six stimulation directions, i.e., the afferents were broadly tuned to direction of tooth loading. In the horizontal plane, the afferent populations at the premolar teeth expressed no clear directional preferences. The afferents at the molar, however, showed a strong directional bias in the distal-lingual direction. In the vertical plane, there was a preference for downward-directed forces with a gradually decreasing sensitivity distally along the dental arch. The present results demonstrate that human periodontal afferents supplying anterior and posterior teeth differ in their capacity to signal horizontal and vertical forces, respectively.
  •  
33.
  • Kettunen, P, et al. (författare)
  • mGluR1, but not mGluR5, mediates depolarization of spinal cord neurons by blocking a leak current
  • 2003
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 90:4, s. 2341-2348
  • Tidskriftsartikel (refereegranskat)abstract
    • The modulation of neuronal excitability by group I metabotropic glutamate receptors (mGluRs) was studied in isolated lamprey spinal cord. At resting potential, application of the group I mGluR agonist ( R,S)-3,5-dihydroxyphenylglycine (DHPG) slightly depolarized the cells. However, at depolarized membrane potentials, this agonist induced repetitive firing. When Na+channels were blocked by TTX, DHPG induced a slight depolarization at rest that increased in amplitude as the neurons were held at more depolarized membrane potentials. In voltage-clamp conditions, DHPG application induced an inward current associated with a decrease in membrane conductance when cells were held at –40 mV. At resting membrane potential, no significant change in the current was induced by DHPG, although a decrease in membrane conductance was seen. The conductance blocked by DHPG corresponded to a leak current, since DHPG had no effect on the voltagegated current elicited by a voltage step from –60 to –40 mV, when leak currents were subtracted. The leak current blocked by DHPG is mediated by fluxes of both K+and Na+. The subtype of group I mGluR mediating the block of the leak current was characterized using specific antagonists for mGluR1 and mGluR5. The inhibition of the leak current was blocked by the mGluR1 antagonist LY 367385 but not by the mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP). The DHPG-induced blockage of the leak current required phospholipase C (PLC)-activation and release of Ca2+from internal stores as the effect of DHPG was suppressed by the PLC-blocker U-73122 and after depletion of intracellular Ca2+pools by thapsigargin. Our results thus show that mGluR1 activation depolarizes spinal neurons by inhibiting a leak current. This will boost membrane depolarization and result in an increase in the excitability of spinal cord neurons, which could contribute to the modulation of the activity of the spinal locomotor network.
  •  
34.
  •  
35.
  • Matsuyama, Kiyoji, et al. (författare)
  • Coupling between feline cerebellum (fastigial neurons) and motoneurons innervating hindlimb muscles.
  • 2004
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 91:3, s. 1183-92
  • Tidskriftsartikel (refereegranskat)abstract
    • The aims of the study were twofold: (1) to verify the hypothesis that neurons in the fastigial nucleus excite and inhibit hindlimb alpha-motoneurons and (2) to determine both the supraspinal and spinal relays of these actions. Axons of fastigial neurons were stimulated at the level of their decussation in the cerebellum, within the hook bundle of Russell, in deeply anesthetized cats with only the right side of the spinal cord intact. The resulting excitatory postsynaptic potentials and inhibitory postsynaptic potentials were analyzed in motoneurons on the left side of the lumbar enlargement. Postsynaptic potentials evoked by the first effective stimulus were induced at latencies <2 ms from descending volleys and <1 ms from interneuronally relayed volleys, indicating a trisynaptic coupling between the fastigial neurons and alpha-motoneurons, via commissural interneurons on the right side. Cerebellar stimulation facilitated the synaptic actions of both vestibulospinal and reticulospinal tract fibers. However, the study leads to the conclusion that trisynaptic fastigial actions are mediated via vestibulospinal rather than reticulospinal tract fibers [stimulated within the lateral vestibular nucleus (LVN) and the medial longitudinal fascicle (MLF), respectively]. This is indicated firstly by collision between descending volleys induced by cerebellar stimulation and volleys evoked by LVN stimuli but not by MLF stimuli. Second, similar cerebellar actions were evoked before and after a transection of MLF. Mutual facilitation between the fastigial and reticulospinal, as well as between the fastigial and vestibulospinal actions, could be due to the previously reported integration of descending vestibulospinal and reticulospinal commands by spinal commissural interneurons.
  •  
36.
  • Naito, E, et al. (författare)
  • Fast reaction to different sensory modalities activates common fields in the motor areas, but the anterior cingulate cortex is involved in the speed of reaction
  • 2000
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 83:3, s. 1701-1709
  • Tidskriftsartikel (refereegranskat)abstract
    • We examined which motor areas would participate in the coding of a simple opposition of the thumb triggered by auditory, somatosensory and visual signals. We tested which motor areas might be active in response to all three modalities, which motor structures would be activated specifically in response to each modality, and which neural populations would be involved in the speed of the reaction. The subjects were required to press a button with their right thumb as soon as they detected a change in the sensory signal. The regional cerebral blood flow (rCBF) was measured quantitatively with 15O-butanol and positron emission tomography (PET) in nine normal male subjects. Cytoarchitectural areas were delimited in 10 post mortem brains by objective and quantitative methods. The images of the post mortem brains subsequently were transformed into standard anatomic format. One PET scanning for each of the sensory modalities was done. The control condition was rest with the subjects having their eyes closed. The rCBF images were anatomically standardized, and clusters of significant changes in rCBF were identified. These were localized to motor areas delimited on a preliminary basis, such as supplementary motor area (SMA), dorsal premotor zone (PMD), rostral cingulate motor area (CMAr), and within areas delimited by using microstructural i.e., cytoarchitectonic criteria, such as areas 4a, 4p, 3a, 3b, and 1. Fields of activation observed as a main effect for all three modalities were located bilaterally in the SMA, CMAr, contralateral PMD, primary motor (M1), and primary somatosensory cortex (SI). The activation in M1 engaged areas 4a and 4p and expanded into area 6. The activation in SI engaged areas 3b, 1, and extended into somatosensory association areas and the supramarginal gyrus posteriorly. We identified significant activations that were specific for each modality in the respective sensory association cortices, though no modality specific regions were found in the motor areas. Fields in the anterior cingulate cortex, rostral to the CMAr, consistently showed significant negative correlation with mean reaction time (RT) in all three tasks. These results show that simple reaction time tasks activate many subdivisions of the motor cortices. The information from different sensory modalities converge onto the common structures: the contralateral areas 4a, 4p, 3b, 1, the PMD, and bilaterally on the SMA and the CMAr. The anterior cingulate cortex might be a key structure which determine the speed of reaction in simple RT tasks.
  •  
37.
  • Parker, D (författare)
  • Presynaptic and interactive peptidergic modulation of reticulospinal synaptic inputs in the lamprey
  • 2000
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 83:5, s. 2497-2507
  • Tidskriftsartikel (refereegranskat)abstract
    • The modulatory effects of neuropeptides on descending inputs to the spinal cord have been examined by making paired recordings from reticulospinal axons and spinal neurons in the lamprey. Four peptides were examined; peptide YY (PYY) and cholecystokinin (CCK), which are contained in brain stem reticulospinal neurons, and calcitonin-gene–related peptide (CGRP) and neuropeptide Y (NPY), which are contained in primary afferents and sensory interneurons, respectively. Each of the peptides reduced the amplitude of monosynaptic reticulospinal-evoked excitatory postsynaptic potentials (EPSPs). The modulation appeared to be presynaptic, because postsynaptic input resistance and membrane potential, the amplitude of the electrical component of the EPSP, postsynaptic responses to glutamate, and spontaneous miniature EPSP amplitudes were unaffected. In addition, none of the peptides affected the pattern of N-methyl-d-aspartate (NMDA)–evoked locomotor activity in the isolated spinal cord. Potential interactions between the peptides were also examined. The “brain stem peptides” CCK and PYY had additive inhibitory effects on reticulospinal inputs, as did the “sensory peptides” CGRP and NPY. Brain stem peptides also had additive inhibitory effects when applied with sensory peptides. However, sensory peptides increased or failed to affect the amplitude of reticulospinal inputs in the presence of the brain stem peptides. These interactive effects also appear to be mediated presynaptically. The functional consequence of the peptidergic modulation was investigated by examining spinal ventral root responses elicited by brain stem stimulation. CCK and CGRP both reduced ventral root responses, although in interaction both increased the response. These results thus suggest that neuropeptides presynaptically influence the descending activation of spinal locomotor networks, and that they can have additive or novel interactive effects depending on the peptides examined and the order of their application.
  •  
38.
  • Pavlova, EL, et al. (författare)
  • Asymmetry in the pitch control system of the lamprey caused by a unilateral labyrinthectomy
  • 2003
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 89:5, s. 2370-2379
  • Tidskriftsartikel (refereegranskat)abstract
    • A postural control system in the lamprey is driven by vestibular input and maintains a definite orientation of the animal during swimming. After a unilateral labyrinthectomy (UL), the lamprey continuously rolls toward the damaged side. Important elements of the postural network are the reticulospinal (RS) neurons that are driven by vestibular input and transmit commands for postural corrections to the spinal cord. We characterized the effect of UL on vestibular responses in RS neurons elicited by rotation of the animal in the pitch plane. The activity of RS neurons was recorded from their axons in the spinal cord before and after UL. The neurons can be classified into the Up and Down groups activated preferentially with nose-up or nose-down rotation, respectively. After UL, vestibular responses in the group Up changed only slightly on the damaged side and disappeared almost completely on the opposite side. In the group Down, responses on both sides persisted after UL. These results indicate that the left and right subgroups of the group Up neurons receive excitatory input mainly from the contralateral labyrinth. In contrast, the group Down neurons receive excitatory input from both labyrinths. We conclude that the UL-induced changes in vestibular responses to pitch tilt will disturb the normal activity of the postural control system. The UL-induced asymmetry in the bilateral activity of the group Up neurons seems to be an important factor contributing to the loss of equilibrium in UL animals and to their rotation during swimming.
  •  
39.
  • Pavlova, EL, et al. (författare)
  • Responses of reticulospinal neurons in intact lamprey to pitch tilt
  • 2002
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 88:3, s. 1136-1146
  • Tidskriftsartikel (refereegranskat)abstract
    • In the swimming lamprey, a postural control system maintains a definite orientation of the animal's longitudinal axis in relation to the horizon (pitch angle). Operation of this system is based on vestibular reflexes. Important elements of the postural network are the reticulospinal (RS) neurons, which are driven by vestibular input and transmit commands for postural corrections from the brain stem to the spinal cord. Here we describe responses to vestibular stimulation (rotation of the animal in the pitch plane) in RS neurons of intact lampreys. The activity of neurons was recorded from their axons in the spinal cord by chronically implanted arrays of macroelectrodes. From the multielectrode recordings of mass activity, discharges in individual axons were extracted by means of a spike-sorting program, and the axon position in the spinal cord and its conduction velocity were determined. Vestibular stimulation was performed by rotating the animal in steps of 45° throughout 360° or by periodical “trapezoid” tilts between the nose-up and -down positions. Typically, the RS neurons exhibited both dynamic responses (activity during movement) and static responses (activity in a new sustained position). The neurons were classified into two groups according to their pattern of response. Group up neurons responded preferentially to nose-up rotation with maximal activity at 0–135° up. Group down neurons responded preferentially to nose-down rotation with maximal activity at 0–135° down. Neurons of the two groups also differed in the position of their axons in the spinal cord and axonal conduction velocity. An increase in water temperature, which presumably causes a downward turn in swimming lampreys, affected the activity in the up anddown groups differently, so that the ratio upresponses to down responses increased. We suggest that theup and down groups mediate the opposing vestibular reflexes and cause the downward and upward turns of the animal, respectively. The lamprey will stabilize the orientation in the pitch plane at which the effects of up and downgroups are equal to each other. In addition to the main test (rotation in the pitch plane), the animals were also tested by rotation in the transverse (roll) plane. It was found that 22% of RS neurons responding to pitch tilts also responded to roll tilts. The overlap between the pitch and roll populations suggests that the RS pathways are partly shared by the pitch and roll control systems.
  •  
40.
  • Petersson, Per, et al. (författare)
  • Properties of an adult spinal sensorimotor circuit shaped through early postnatal experience.
  • 2004
  • Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 92:1, s. 280-288
  • Tidskriftsartikel (refereegranskat)abstract
    • During development, information about the three-dimensional shape and mechanical properties of the body is laid down in the synaptic connectivity of sensorimotor systems through adaptive mechanisms. This functional adaptation occurs through alteration of connection properties. Here, we characterize the differences between strong and weak connections in the nociceptive withdrawal reflex in adult decerebrate spinal rats, representing the preserved end product of the developmental adaptation process. Stronger excitatory reflex connections from the skin onto a muscle had relatively higher gain in their input-output relations, shorter onset latencies ( up to similar to 150 ms) and lower trial-to-trial variability in relation to response amplitude (SD similar to mean(1/2)) than weaker pathways. Although inhibitory and excitatory nociceptive receptive fields of a muscle overlap to some degree, the results indicate that the inhibitory input is not a major determinant of the gain distribution within the excitatory receptive field and vice versa. The N-methyl-D-aspartate ( NMDA) receptor antagonist, D-2-amino-5-phosphonovalerate (0.1 - 1 mug), applied topically on the spinal cord reduced the gain, whereas the response amplitude was mainly reduced by an absolute number by the alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor antagonist, 6-nitro-7-sulfamoylbenzo(f) quinoxaline-2,3- dione ( 1 - 10 mug). The results indicate that NMDA receptors have a critical role in gain regulation in the nociceptive withdrawal reflex system. It is suggested that after normal postnatal experience-dependent adaptation, the number of connections from a given skin site onto the reflex encoding interneurons is a major determinant of the difference in gain.
  •  
41.
  •  
42.
  • Sasaki, S, et al. (författare)
  • Dexterous finger movements in primate without monosynaptic corticomotoneuronal excitation
  • 2004
  • Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 92:5, s. 3142-3147
  • Tidskriftsartikel (refereegranskat)abstract
    • It is generally accepted that the precision grip and independent finger movements (IFMs) in monkey and man are controlled by the direct (monosynaptic) corticomotoneuronal (CM) pathway. This view is based on previous observations that pyramidotomy causes near permanent deficits of IFMs. However, in addition to the direct CM pathway, pyramidotomy interrupts several corticofugal connections to the brain stem and upper cervical segments. Indirect (oligosynaptic) CM pathways, which are phylogenetically older, have been considered to be of little or no importance in prehension. In three adult macaque monkeys, complete transection of the direct CM pathway was made in C4/C5, which is rostral to the forelimb segments (C6–Th1). Electrophysiological recordings revealed lack of the direct lateral corticospinal tract (LCST) volley, monosynaptic extracellular field potentials in the motor nuclei, and monosynaptic CM excitation. However, a disynaptic volley, disynaptic field potentials and disynaptic CM excitation mediated via C3–C4 propriospinal neurons remained after the lesion. Thus the lesion interrupted the monosynaptic CM pathway and oligosynaptic LCST pathways mediated by interneurons in the forelimb segments. Precision grip and IFMs were observed already after 1–28 days postoperatively. Weakness in force and deficits in preshaping remained for an observation period of 3 mo. Indirect CM pathways may be important for neuro-rehabilitation.
  •  
43.
  • Schmelz, M., et al. (författare)
  • Chemical response pattern of different classes of C-nociceptors to pruritogens and algogens
  • 2003
  • Ingår i: Journal of Neurophysiology. - Washington : The American Physiological Society. - 0022-3077 .- 1522-1598. ; 89:5, s. 2441-2448
  • Tidskriftsartikel (refereegranskat)abstract
    • Vasoneuroactive substances were applied through intradermal microdialysis membranes and characterized as itch- or pain-inducing in psychophysical experiments. Histamine always provoked itching and rarely pain, capsaicin always pain but never itching. Prostaglandin E[2] (PGE[2]) led preferentially to moderate itching. Serotonin, acetylcholine, and bradykinin induced pain more often than itching. Subsequently the same substances were used in microneurography experiments to characterize the sensitivity profile of human cutaneous C-nociceptors. The responses of 89 mechanoresponsive (CMH, polymodal nociceptors), 52 mechanoinsensitive, histamine-negative (CMi[H][i][s][-]), and 24 mechanoinsensitive, histamine-positive (CMi[H][i][s][+]) units were compared. CMi[H][i][s][+] units were most responsive to histamine and to PGE[2] and less to serotonin, ACh, bradykinin, and capsaicin. CMH units (polymodal nociceptors) and CMi[H][i][s] units showed significantly weaker responses to histamine, PGE[2], and acetylcholine. Capsaicin and bradykinin responses were not significantly different in the two classes of mechano-insensitive units. We conclude that CMi[H][i][s][+]units are "selective," but not "specific" for pruritogenic substances and that the pruritic potency of a mediator increases with its ability to activate CMi[H][i][s][+] units but decreases with activation of CMH and CMi[H][i][s] units.
  •  
44.
  • Schmitt, DE, et al. (författare)
  • The spinal GABAergic system is a strong modulator of burst frequency in the lamprey locomotor network
  • 2004
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 92:4, s. 2357-2367
  • Tidskriftsartikel (refereegranskat)abstract
    • The spinal network coordinating locomotion is comprised of a core of glutamate and glycine interneurons. This network is modulated by several transmitter systems including spinal GABA interneurons. The purpose of this study is to explore the contribution of GABAergic neurons to the regulation of locomotor burst frequency in the lamprey model. Using gabazine, a competitive GABAAantagonist more specific than bicuculline, the goal was to provide a detailed analysis of the influence of an endogenous activation of GABAAreceptors on fictive locomotion, as well as their possible interaction with GABABand involvement of GABACreceptors. During N-methyl-d-aspartate (NMDA)-induced fictive locomotion (ventral root recordings in the isolated spinal cord), gabazine (0.1–100 μM) significantly increased the burst rate up to twofold, without changes in regularity or “burst quality.” Gabazine had a proportionately greater effect at higher initial burst rates. Picrotoxin (1–7.5 μM), a less selective GABAAantagonist, also produced a pronounced increase in frequency, but at higher concentrations, the rhythm deteriorated, likely due to the unspecific effects on glycine receptors. The selective GABABantagonist CGP55845 also increased the frequency, and this effect was markedly enhanced when combined with the GABAAantagonist gabazine. The GABACantagonist (1,2,5,6-tetrahydropyridine-4-yl)methylphosphinic acid (TPMPA) had no effect on locomotor bursting. Thus the spinal GABA system does play a prominent role in burst frequency regulation in that it reduces the burst frequency by ≤50%, presumably due to presynaptic and soma-dendritic effects documented previously. It is not required for burst generation, but acts as a powerful modulator.
  •  
45.
  •  
46.
  • Svensson, E, et al. (författare)
  • Synaptically evoked membrane potential oscillations induced by substance P in lamprey motor neurons
  • 2002
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 87:1, s. 113-121
  • Tidskriftsartikel (refereegranskat)abstract
    • Short-lasting application (10 min) of tachykinin neuropeptides evokes long-lasting (>24 h) modulation of N-methyl-d-aspartate (NMDA)-evoked locomotor network activity in the lamprey spinal cord. In this study, the net effects of the tachykinin substance P on the isolated spinal cord have been examined by recording from motor neurons in the absence of NMDA and ongoing network activity. Brief bath application of substance P (30 s to 2 min) induced irregular membrane potential oscillations in motor neurons. These oscillations consisted of depolarizing and hyperpolarizing phases and were associated with phasic ventral-root activity. The oscillations were blocked by the tachykinin antagonist spantide II. They were also blocked by tetrodotoxin (TTX), suggesting that they were not dependent on intrinsic membrane properties of the motor neurons but were synaptically mediated. Substance P could also have a direct effect, however, because a membrane potential depolarization persisted in the presence of TTX. Protein kinase agonists and antagonists were used to investigate the intracellular pathways through which substance P acted. The oscillations were blocked by the selective protein kinase C (PKC) antagonist chelerythrine. However, the TTX-resistant membrane potential depolarization was not significantly affected by blocking PKC. The protein kinase A and G antagonist H8 did not affect either the oscillations or the direct TTX-resistant membrane potential depolarization. The glutamate receptor antagonist kynurenic acid abolished the substance-P-evoked oscillations, suggesting that they were dependent on glutamate release. The oscillations were abolished or reduced by the AMPA/kainate receptor antagonist 6-cyano-7-nitroquinoxalene-2,3-dione but were only reduced by the NMDA receptor antagonist d-AP5. The oscillations were thus mediated by glutamatergic inputs with a greater dependence on non-NMDA receptors. Blocking glycinergic inputs with strychnine resulted in large depolarizing plateaus and bursts of spikes. The glutamatergic and glycinergic inputs underlying the oscillations are apparently evoked through direct and indirect excitatory effects on inhibitory and excitatory premotor interneurons. Substance P thus has a distributed excitatory effect in the spinal cord. While it can activate premotor networks, this activation alone is not able to evoke a coordinated behaviorally relevant motor output.
  •  
47.
  • Terao, Yasuo, et al. (författare)
  • Engagement of gaze in capturing targets for future sequential manual actions.
  • 2002
  • Ingår i: Journal of Neurophysiology. - 0022-3077 .- 1522-1598. ; 88:4, s. 1716-25
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigated the role of saccadic gaze fixations in encoding target locations for planning a future manual task consisting of a sequence of discrete target-oriented actions. We hypothesized that fixations of the individual targets are necessary for accurate encoding of target locations and that there is a transfer of sequence information from visual encoding to manual recall. Subjects viewed four targets presented at random positions on a screen. After various delays following target extinction, the subjects marked the remembered target locations on the screen with the tip of a hand-held stick. When the targets were presented simultaneously among distracting elements, the overall accuracy of marking increased with presentation time and total number of targets fixated because the subjects had to serially fixate the individual targets to locate them. Without distractors, the marking accuracy was similarly high regardless of duration of target presentation (0.25-8 s) and number of targets fixated; it was comparable to that with distractors when all four targets had been fixated. This indicates parallel encoding of target locations largely based on peripheral vision. Location memory was stable in these tasks over the delay periods investigated (0.5-8 s). With parallel encoding there was a "shrinkage" in the visuomotor transformation, i.e., the distances between the markings were systematically smaller than the corresponding inter-target distances. When the targets were presented sequentially without distractors, marking accuracy improved with the total number of targets fixated and shrinkage in the visuomotor transformation occurred only with parallel encoding, i.e., when subjects did not fixate the targets. In all experimental conditions for trials in which targets were fixated during encoding, there was little correspondence between the marking sequence and the sequence in which the targets were fixated. We conclude that subjects benefit from fixating targets for subsequent target-oriented manual actions when the targets are presented among distractors and when presented sequentially; when distinct targets are presented simultaneously against a blank background, they are efficiently encoded in parallel largely by peripheral vision.
  •  
48.
  • Ullen, F, et al. (författare)
  • Independent processing of the temporal and ordinal structure of movement sequences
  • 2003
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 90:6, s. 3725-3735
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigated if the temporal and ordinal structures of sequences can be represented and learned independently. In Experiment 1, subjects learned three rhythmic sequences of key presses with the right index finger: Combined consisted of nine key presses with a corresponding temporal structure of eight intervals; Temporal had the temporal structure of Combined but was performed on one key; Ordinal had the ordinal structure of Combined but an isochronous rhythm. Subjects were divided into two groups. Group 1 first learned Combined, then Temporal and Ordinal; Group 2 first learned Temporal and Ordinal, then Combined. Strong transfer effects were seen in both groups. In Group 1, having learned combined facilitated the learning of the temporal ( Temporal) or ordinal ( Ordinal) sequence alone; in Group 2, having learned Temporal and Ordinal facilitated the learning of Combined, where the two are combined. This supports that subjects had formed independent temporal and ordinal representations. In Experiment 2, we investigated if these can be learned independently. Subjects repeatedly reproduced sequences with fixed temporal and random ordinal structure; random temporal and fixed ordinal structure; and random temporal and ordinal structures. Temporal and ordinal learning was seen only in the first and second sequences, respectively. In summary, we provide evidence for the existence of independent systems for learning and representation of ordinal and temporal sequences and for implicit learning of temporal sequences. This may be important for fast learning and flexibility in motor control.
  •  
49.
  • Ullen, F, et al. (författare)
  • Neural networks for the coordination of the hands in time
  • 2003
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 89:2, s. 1126-1135
  • Tidskriftsartikel (refereegranskat)abstract
    • Without practice, bimanual movements can typically be performed either in phase or in antiphase. Complex temporal coordination, e.g., during movements at different frequencies with a noninteger ratio (polyrhythms), requires training. Here, we investigate the organization of the neural control systems for in-phase, antiphase, and polyrhythmic coordination using functional magnetic resonance imaging (fMRI). Brisk rhythmic tapping with the index fingers was used as a model behavior. We demonstrate different patterns of brain activity during in-phase and antiphase coordination. In-phase coordination was characterized by activation of the right anterior cerebellum and cingulate motor area (CMA). Antiphase coordination was accompanied by extensive fronto-parieto-temporal activations, including the supplementary motor area (SMA), the preSMA, and the bilateral inferior parietal gyri, premotor cortex, and superior temporal gyri. When contrasting polyrhythmic tapping with in-phase tapping, activity was seen in the same set of brain regions, and in the posterior cerebellum and the CMA. Antiphase and polyrhythmic coordination may thus to a large extent use common neural control circuitry. In a separate experiment, we analyzed the neural control of the rhythmic structure and the serial order of finger movements during polyrhythmic tapping. Polyrhythmic tapping was compared with an isochronous coordination pattern that retained the same serial order of finger movements as the polyrhythm. This experiment showed that the preSMA and the bilateral superior temporal gyri may be crucial for the rhythmic control of polyrhythmic tapping, while the cerebellum, the CMA, and the premotor cortices presumably are more involved in the ordinal control of the sequence of finger movements.
  •  
50.
  • Wasling, Pontus, 1970, et al. (författare)
  • Developmental changes in release properties of the CA3-CA1 glutamate synapse in rat hippocampus.
  • 2004
  • Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 92:5, s. 2714-24
  • Tidskriftsartikel (refereegranskat)abstract
    • Developmental changes in release probability (Pr) and paired-pulse plasticity at CA3-CA1 glutamate synapses in hippocampal slices of neonatal rats were examined using field excitatory postsynaptic potential (EPSP) recordings. Paired-pulse facilitation (PPF) at these synapses was, on average, absent in the first postnatal week but emerged and became successively larger during the second postnatal week. This developmental increase in PPF was associated with a reduction in Pr, as indicated by the slower progressive block of the N-methyl-D-aspartate (NMDA) EPSP by the noncompetitive NMDA receptor antagonist MK-801. This developmental reduction in Pr was not homogenous among the synapses. As shown by the MK-801 analysis, the Pr heterogeneity observed among adult CA3-CA1 synapses is present already during the first postnatal week, and the developmental Pr reduction was found to be largely selective for synapses with higher Pr values, leaving Pr of the vast majority of the synapses essentially unaffected. A reduction in Pves, the release probability of the individual vesicle, possibly caused by reduction in Ca2+ influx, seems to explain the reduction in Pr. In vivo injection of tetanus toxin at the end of the first postnatal week did not prevent the increase in PPF, indicating that this developmental change in release is not critically dependent on normal neural activity during the second postnatal week.
  •  
Skapa referenser, mejla, bekava och länka
  • Resultat 1-50 av 54

Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.

 
pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy