| 1. |
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| 2. |
- Alstermark, Bror, et al.
(författare)
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Motor command for precision grip in the macaque monkey can be mediated by spinal interneurons
- 2011
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 106:1, s. 122-126
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Tidskriftsartikel (refereegranskat)abstract
- In motor control, the general view is still that spinal interneurons mainly contribute to reflexes and automatic movements. The question raised here is whether spinal interneurons can mediate the cortical command for independent finger movements, like a precision grip between the thumb and index finger in the macaque monkey, or if this function depends exclusively on a direct corticomotoneuronal pathway. This study is a followup of a previous report (Sasaki et al. J Neurophysiol 92: 3142-3147, 2004) in which we trained macaque monkeys to pick a small piece of sweet potato from a cylinder by a precision grip between the index finger and thumb. We have now isolated one spinal interneuronal system, the C3-C4 propriospinal interneurons with projection to hand and arm motoneurons. In the previous study, the lateral corticospinal tract (CST) was interrupted in C4/C5 (input intact to the C3-C4 propriospinal interneurons), and in this study, the CST was interrupted in C2 (input abolished). The precision grip could be performed within the first 15 days after a CST lesion in C4/C5 but not in C2. We conclude that C3-C4 propriospinal interneurons also can carry the command for precision grip.
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| 3. |
- Baugh, Lee A., et al.
(författare)
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Material evidence : interaction of well-learned priors and sensorimotor memory when lifting objects
- 2012
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 108:5, s. 1262-1269
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Tidskriftsartikel (refereegranskat)abstract
- Skilled object lifting requires the prediction of object weight. When lifting new objects, such prediction is based on well-learned size-weight and material-density correlations, or priors. However, if the prediction is erroneous, people quickly learn the weight of the particular object and can use this knowledge, referred to as sensorimotor memory, when lifting the object again. In the present study, we explored how sensorimotor memory, gained when lifting a given object, interacts with well-learned material-density priors when predicting the weight of a larger but otherwise similar-looking object. Different groups of participants 1st lifted 1 of 4 small objects 10 times. These included a pair of wood-filled objects and a pair of brass-filled objects where 1 of each pair was covered in a wood veneer and the other was covered in a brass veneer. All groups then lifted a larger, brass-filled object with the same covering as the small object they had lifted. For each lift, we determined the initial peak rate of change of vertical load-force rate and the load-phase duration, which provide estimates of predicted object weight. Analysis of the 10th lift of the small cube revealed no effects of surface material, indicating participants learned the appropriate forces required to lift the small cube regardless of object appearance. However, both surface material and core material of the small cube affected the 1st lift of the large block. We conclude that sensorimotor memory related to object density can contribute to weight prediction when lifting novel objects but also that long-term priors related to material properties can influence the prediction.
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| 4. |
- Böhme, Rebecca, et al.
(författare)
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Rebound excitation triggered by synaptic inhibition in cerebellar nuclear neurons is suppressed by selective T-type calcium channel block
- 2011
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 106:5, s. 2653-2661
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Tidskriftsartikel (refereegranskat)abstract
- Following hyperpolarizing inputs, many neurons respond with an increase in firing rate, a phenomenon known as rebound excitation. Rebound excitation has been proposed as a mechanism to encode and process inhibitory signals and transfer them to target structures. Activation of low-voltage-activated T-type calcium channels and the ensuing low-threshold calcium spikes is one of the mechanisms proposed to support rebound excitation. However, there is still not enough evidence that the hyperpolarization provided by inhibitory inputs, particularly those dependent on chloride ions, is adequate to deinactivate a sufficient number of T-type calcium channels to drive rebound excitation on return to baseline. Here, this issue was investigated in the deep cerebellar nuclear neurons (DCNs), which receive the output of the cerebellar cortex conveyed exclusively by the inhibitory Purkinje cells and are also known to display rebound excitation. Using cerebellar slices and whole cell recordings of large DCNs, we show that a novel piperidine-based compound that selectively antagonizes T-type calcium channel activity, 3,5-dichloro-N-[1-(2,2-dimethyl-tetrahydropyran-4-ylmethyl)-4-fluoro-piperidin-4-ylmethyl]-benzamide (TTA-P2), suppressed rebound excitation elicited by current injection as well as by synaptic inhibition, whereas other electrophysiological properties of large DCNs were unaltered. Furthermore, TTA-P2 suppressed transient high-frequency rebounds found in DCNs with low-threshold spikes as well as the slow rebounds present in DCNs without low-threshold spikes. These findings demonstrate that chloride-dependent synaptic inhibition effectively triggers T-type calcium channel-mediated rebounds and that the latter channels may support slow rebound excitation in neurons without low-threshold spikes.
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| 5. |
- Condon, M., et al.
(författare)
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Differential sensitivity to surface compliance by tactile afferents in the human finger pad
- 2014
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 111:6, s. 1308-1317
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Tidskriftsartikel (refereegranskat)abstract
- We undertook a neurophysiological investigation of the responses of low-threshold mechanoreceptors in the human finger pad to surfaces of differing softness. Unitary recordings were made from 26 slowly adapting type I (SAI), 17 fast-adapting type I (FAI), and 9 slowly adapting type II (SAII) afferents via tungsten microelectrodes inserted into the median nerve at the wrist. A servo-controlled stimulator applied ramp-and-hold forces (1, 2, 4 N) at a constant loading and unloading rate (2 N/s) via a flat silicone disc over the center of the finger pad. Nine discs were used, which linearly increased in stiffness across the range. Population responses of the SAI afferents showed the greatest sensitivity to compliance, with a steep monotonic increase in mean firing rate with increasing stiffness (decreasing compliance) of the surface during the loading and plateau (but not unloading) phases. FAI afferents also showed a linear increase in firing during the loading but not unloading phase, although the slope was significantly lower than that of the SAI afferents at all amplitudes. Conversely, SAII afferents were influenced by object compliance only in certain conditions. Given their high density in the finger pads and their linear relationship between firing rate and object compliance during the loading and plateau phases, SAI afferents (together with FAI afferents during the loading phase) are ideally suited to contributing information on surface compliance to the overall estimation of softness, but the SAII afferents appear to play only a minor role.
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| 6. |
- Dayanidhi, S, et al.
(författare)
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Developmental improvements in dynamic control of fingertip forces last throughout childhood and into adolescence
- 2013
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 110:7, s. 1583-1592
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Tidskriftsartikel (refereegranskat)abstract
- While it is clear that the development of dexterous manipulation in children exhibits dramatic improvements over an extended period, it is difficult to separate musculoskeletal from neural contributors to these important functional gains. This is in part due to the inability of current methods to disambiguate improvements in hand strength from gains in finger dexterity (i.e., the dynamic control of fingertip force vectors at low magnitudes). We adapted our novel instrumentation to evaluate finger dexterity in 130 typically developing children between the ages of 4 and 16 yr. We find that finger dexterity continues to develop well into late adolescence and musculoskeletal growth and strength are poorly correlated with the improvements in dexterity. Importantly, because these behavioral results seem to mirror the known timelines of neuroanatomical development up to adolescence, we speculate that they reflect the functional benefits of such continual neural maturation. This novel perspective now enables the systematic study of the functional roles of specific neuroanatomical structures and their connectivity, maturity, and plasticity. Moreover, the temporal dynamics of the fingertip force vectors shows improvements in stability that provide a novel way to look at the maturation of finger control. From a clinical perspective, our results provide a practical means to chart functional development of dexterous manipulation in typically developing children and could be adapted for clinical use and for use in children with developmental disorders.
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| 7. |
- Falck-Ytter, Terje
(författare)
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Predicting other people's action goals with low-level motor information
- 2012
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 107:11, s. 2923-2925
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Tidskriftsartikel (refereegranskat)abstract
- In support for the direct-matching hypothesis, Ambrosini et al. (2011) recently reported that goal-directed saccades during action observation were modulated by manipulations of basic motor information. This finding indicates that motor programs, activated by low-level visual descriptions of others' actions, are involved in predicting other people's action goals. Here, I put this result into a broader context, review alternative interpretations, and suggest strategies for future studies.
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| 8. |
- Felix, RA, et al.
(författare)
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Development of on-off spiking in superior paraolivary nucleus neurons of the mouse
- 2013
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 109:11, s. 2691-2704
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Tidskriftsartikel (refereegranskat)abstract
- The superior paraolivary nucleus (SPON) is a prominent cell group in the auditory brain stem that has been increasingly implicated in representing temporal sound structure. Although SPON neurons selectively respond to acoustic signals important for sound periodicity, the underlying physiological specializations enabling these responses are poorly understood. We used in vitro and in vivo recordings to investigate how SPON neurons develop intrinsic cellular properties that make them well suited for encoding temporal sound features. In addition to their hallmark rebound spiking at the stimulus offset, SPON neurons were characterized by spiking patterns termed onset, adapting, and burst in response to depolarizing stimuli in vitro. Cells with burst spiking had some morphological differences compared with other SPON neurons and were localized to the dorsolateral region of the nucleus. Both membrane and spiking properties underwent strong developmental regulation, becoming more temporally precise with age for both onset and offset spiking. Single-unit recordings obtained in young mice demonstrated that SPON neurons respond with temporally precise onset spiking upon tone stimulation in vivo, in addition to the typical offset spiking. Taken together, the results of the present study demonstrate that SPON neurons develop sharp on-off spiking, which may confer sensitivity to sound amplitude modulations or abrupt sound transients. These findings are consistent with the proposed involvement of the SPON in the processing of temporal sound structure, relevant for encoding communication cues.
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| 9. |
- Gentile, G, et al.
(författare)
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Integration of visual and tactile signals from the hand in the human brain: an FMRI study
- 2011
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 105:2, s. 910-922
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Tidskriftsartikel (refereegranskat)abstract
- In the non-human primate brain, a number of multisensory areas have been described where individual neurons respond to visual, tactile and bimodal visuotactile stimulation of the upper limb. It has been shown that such bimodal neurons can integrate sensory inputs in a linear or nonlinear fashion. In humans, activity in a similar set of brain regions has been associated with visuotactile stimulation of the hand. However, little is known about how these areas integrate visual and tactile information. In this functional magnetic resonance imaging experiment, we employed tactile, visual, and visuotactile stimulation of the right hand in an ecologically valid setup where participants were looking directly at their upper limb. We identified brain regions that were activated by both visual and tactile stimuli as well as areas exhibiting greater activity in the visuotactile condition than in both unisensory ones. The posterior and inferior parietal, dorsal, and ventral premotor cortices, as well as the cerebellum, all showed evidence of multisensory linear (additive) responses. Nonlinear, superadditive responses were observed in the cortex lining the left anterior intraparietal sulcus, the insula, dorsal premotor cortex, and, subcortically, the putamen. These results identify a set of candidate frontal, parietal and subcortical regions that integrate visual and tactile information for the multisensory perception of one's own hand.
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| 10. |
- Hsu, LJ, et al.
(författare)
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Effects of galvanic vestibular stimulation on postural limb reflexes and neurons of spinal postural network
- 2012
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 108:1, s. 300-313
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Tidskriftsartikel (refereegranskat)abstract
- Quadrupeds maintain the dorsal side up body orientation due to the activity of the postural control system driven by limb mechanoreceptors. Binaural galvanic vestibular stimulation (GVS) causes a lateral body sway toward the anode. Previously, we have shown that this new position is actively stabilized, suggesting that GVS changes a set point in the reflex mechanisms controlling body posture. The aim of the present study was to reveal the underlying neuronal mechanisms. Experiments were performed on decerebrate rabbits. The vertebral column was rigidly fixed, whereas hindlimbs were positioned on a platform. Periodic lateral tilts of the platform caused postural limb reflexes (PLRs): activation of extensors in the loaded and flexing limb and a decrease in extensor activity in the opposite (unloaded and extending) limb. Putative spinal interneurons were recorded in segments L4–L5 during PLRs, with and without GVS. We have found that GVS enhanced PLRs on the cathode side and reduced them on the anode side. This asymmetry in PLRs can account for changes in the stabilized body orientation observed in normal rabbits subjected to continuous GVS. Responses to platform tilts (frequency modulation) were observed in 106 spinal neurons, suggesting that they can contribute to PLR generation. Two neuron groups were active in opposite phases of the tilt cycle of the ipsi-limb: F-neurons in the flexion phase, and E-neurons in the extension phase. Neurons were driven mainly by afferent input from the ipsi-limb. If one supposes that F- and E-neurons contribute, respectively, to excitation and inhibition of extensor motoneurons, one can expect that the pattern of response to GVS in F-neurons will be similar to that in extensor muscles, whereas E-neurons will have an opposite pattern. We have found that ∼40% of all modulated neurons meet this condition, suggesting that they contribute to the generation of PLRs and to the GVS-caused changes in PLRs.
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| 11. |
- Igelström, Kajsa, 1980-, et al.
(författare)
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Low-magnesium medium induces epileptiform activity in mouse olfactory bulb slices
- 2011
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Ingår i: Journal of Neurophysiology. - Rockville, MD, United States : American Physiological Society. - 0022-3077 .- 1522-1598. ; 106:5, s. 2593-2605
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Tidskriftsartikel (refereegranskat)abstract
- Magnesium-free medium can be used in brain slice studies to enhance glutamate receptor function, but this manipulation causes seizure-like activity in many cortical areas. The rodent olfactory bulb (OB) slice is a popular preparation, and potentially ictogenic ionic conditions have often been used to study odor processing. We studied low Mg2+-induced epileptiform discharges in mouse OB slices using extracellular and whole cell electrophysiological recordings. Low-Mg2+ medium induced two distinct types of epileptiform activity: an intraglomerular delta-frequency oscillation resembling slow sniff-induced activity and minute-long seizure-like events (SLEs) consisting of large negative-going field potentials accompanied by sustained depolarization of output neurons. SLEs were dependent on N-methyl-d-aspartate receptors and sodium currents and were facilitated by α-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors. The events were initiated in the glomerular layer and propagated laterally through the external plexiform layer at a slow time scale. Our findings confirm that low-Mg2+ medium should be used with caution in OB slices. Furthermore, the SLEs resembled the so-called slow direct current (DC) shift of clinical and experimental seizures, which has recently been recognized as being of great clinical importance. The OB slice may therefore provide a robust and unique in vitro model of acute seizures in which mechanisms of epileptiform DC shifts can be studied in isolation from fast oscillations.
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| 12. |
- Jankowska, Elzbieta, et al.
(författare)
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Collateral actions of premotor interneurons on ventral spinocerebellar tract neurons in the cat.
- 2010
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 104:4, s. 1872-83
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Tidskriftsartikel (refereegranskat)abstract
- Strong evidence that premotor interneurons provide ventral spinocerebellar tract (VSCT) neurons with feedback information on their actions on motoneurons was previously found for Ia inhibitory interneurons and Renshaw cells, while indications for similar actions of other premotor interneurons were weaker and indirect. Therefore the aim of the present study was to reexamine this possibility with respect to interneurons relaying actions of group Ib afferents from tendon organs and group II afferents from muscle spindles. In all, 133 VSCT neurons in the L3-L5 segments (including 41 spinal border neurons) were recorded from intracellularly in deeply anesthetized cats to verify that stimuli applied in motor nuclei evoked monosynaptic inhibitory postsynaptic potentials (IPSPs) attributable to stimulation of axon collaterals of premotor interneurons. IPSPs were found in over two thirds of the investigated neurons. When intraspinal stimuli were preceded by stimuli applied to a muscle nerve at critical intervals, IPSPs evoked from motor nuclei were considerably reduced, indicating a collision of nerve volleys in axons of interneurons activated by group I and group II afferents. In individual VSCT neurons monosynaptic IPSPs were evoked from both biceps-semitendinosus and gastrocnemius-soleus motor nuclei, in parallel with disynaptic IPSPs from group Ib and group II as well as group Ia afferents. These observations indicate that individual VSCT neurons may monitor the degree of inhibition of both flexor and extensor motoneurons by premotor interneurons in inhibitory pathways from group Ib and group II afferents to motoneurons. They may thus be providing the cerebellum with feedback information on actions of these premotor interneurons on motoneurons.
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| 13. |
- Johansson, Anders Sixten, et al.
(författare)
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Biting intentions modulate digastric reflex responses to sudden unloading of the jaw
- 2014
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 112:5, s. 1067-1073
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Tidskriftsartikel (refereegranskat)abstract
- Reflex responses in jaw opening muscles can be evoked when a brittle object cracks between the teeth and suddenly unloads the jaw. We hypothesized that this reflex response is flexible and, as such, is modulated according to the instructed goal of biting through an object. Study participants performed two different biting tasks when holding a peanut-half stacked on a chocolate piece between their incisors. In one task, they were asked to split the peanut-half only (single-split task) and, in the other task, they were asked to split both the peanut and the chocolate in one action (double-split task). In both tasks, the peanut split evoked a jaw opening muscle response, quantified from EMG recordings of the digastric muscle in a window 20-60 ms following peanut split. Consistent with our hypothesis, we found that the jaw opening muscle response in the single-split trials was about twice the size of the jaw opening muscle response in the double-split trials. A linear model that predicted the jaw opening muscle response on a single trial basis indicated that task settings played a significant role in this modulation but also that the pre-split digastric muscle activity contributed to the modulation. These findings demonstrate that, like reflex responses to mechanical perturbations in limb muscles, reflex responses in jaw muscles not only show gain-scaling but also are modulated by subject intent.
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| 14. |
- Johansson, Anders, 1975-, et al.
(författare)
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Task-dependent control of the jaw during food splitting in humans
- 2014
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Ingår i: Journal of Neurophysiology. - : The American Physiological Society. - 0022-3077 .- 1522-1598. ; 111, s. 2614-2623
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Tidskriftsartikel (refereegranskat)abstract
- Although splitting of food items between the incisors often requires high bite forces, rarely do the teeth harmfully collide when the jaw quickly closes after split. Previous studies indicate that the force-velocity relationship of the jaw closing muscles principally explains the prompt dissipation of jaw closing force. Here, we asked whether people could regulate the dissipation of jaw closing force during food splitting. We hypothesized that such regulation might be implemented via differential recruitment of masseter muscle portions situated along the anteroposterior axis because these portions will experience a different shortening velocity during jaw closure. Study participants performed two different tasks when holding a peanut-half stacked on a chocolate piece between their incisors. In one task, they were asked to split the peanut-half only (single-split trials) and, in the other, to split both the peanut and the chocolate in one action (double-split trials). In double-split trials following the peanut split, the intensity of the tooth impact on the chocolate piece was on average 2.5 times greater than in single-split trials, indicating a substantially greater loss of jaw closing force in the single-split trials. We conclude that control of jaw closing force dissipation following food splitting depends on task demands. Consistent with our hypothesis, converging neurophysiological and morphometric data indicated that this control involved a differential activation of the jaw closing masseter muscle along the anteroposterior axis. These latter findings suggest that the regulation of jaw closing force after sudden unloading of the jaw exploits masseter muscle compartmentalization.
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| 15. |
- Klement, Göran, et al.
(författare)
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Spontaneous ryanodine-receptor-dependent Ca2+-activated K+ currents and hyperpolarizations in rat medial preoptic neurons
- 2010
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 103:5, s. 2900-2911
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study was to clarify the identity of slow spontaneous currents, the underlying mechanism and possible role for impulse generation in neurons of the rat medial preoptic nucleus (MPN). Acutely dissociated neurons were studied with the perforated patch-clamp technique. Spontaneous outward currents, at a frequency of approximately 0.5 Hz and with a decay time constant of approximately 200 ms, were frequently detected in neurons when voltage-clamped between approximately -70 and -30 mV. The dependence on extracellular K(+) concentration was consistent with K(+) as the main charge carrier. We concluded that the main characteristics were similar to those of spontaneous miniature outward currents (SMOCs), previously reported mainly for muscle fibers and peripheral nerve. From the dependence on voltage and from a pharmacological analysis, we concluded that the currents were carried through small-conductance Ca(2+)-activated (SK) channels, of the SK3 subtype. From experiments with ryanodine, xestospongin C, and caffeine, we concluded that the spontaneous currents were triggered by Ca(2+) release from intracellular stores via ryanodine receptor channels. An apparent voltage dependence was explained by masking of the spontaneous currents as a consequence of steady SK-channel activation at membrane potentials > -30 mV. Under current-clamp conditions, corresponding transient hyperpolarizations occasionally exceeded 10 mV in amplitude and reduced the frequency of spontaneous impulses. In conclusion, MPN neurons display spontaneous hyperpolarizations triggered by Ca(2+) release via ryanodine receptors and SK3-channel activation. Thus such events may affect impulse firing of MPN neurons.
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| 16. |
- Krutki, Piotr, et al.
(författare)
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Do premotor interneurons act in parallel on spinal motoneurons and on dorsal horn spinocerebellar and spinocervical tract neurons in the cat?
- 2011
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 105:4, s. 1581-93
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Tidskriftsartikel (refereegranskat)abstract
- It has previously been established that ventral spinocerebellar tract (VSCT) neurons and dorsal spinocerebellar tract neurons located in Clarke's column (CC DSCT neurons) forward information on actions of premotor interneurons in reflex pathways from muscle afferents on α-motoneurons. Whether DSCT neurons located in the dorsal horn (dh DSCT neurons) and spinocervical tract (SCT) neurons are involved in forwarding similar feedback information has not yet been investigated. The aim of the present study was therefore to examine the input from premotor interneurons to these neurons. Electrical stimuli were applied within major hindlimb motor nuclei to activate axon-collaterals of interneurons projecting to these nuclei, and intracellular records were obtained from dh DSCT and SCT neurons. Direct actions of the stimulated interneurons were differentiated from indirect actions by latencies of postsynaptic potentials evoked by intraspinal stimuli and by the absence or presence of temporal facilitation. Direct actions of premotor interneurons were found in a smaller proportion of dh DSCT than of CC DSCT neurons. However, they were evoked by both excitatory and inhibitory interneurons, whereas only inhibitory premotor interneurons were previously found to affect CC DSCT neurons [as indicated by monosynaptic excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) in dh DSCT and only IPSPs in CC DSCT neurons]. No effects of premotor interneurons were found in SCT neurons, since monosynaptic EPSPs or IPSPs were only evoked in them by stimuli applied outside motor nuclei. The study thus reveals a considerable differentiation of feedback information provided by different populations of ascending tract neurons.
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| 17. |
- Lyalka, VF, et al.
(författare)
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Facilitation of postural limb reflexes in spinal rabbits by serotonergic agonist administration, epidural electrical stimulation, and postural training.
- 2011
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598.
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Tidskriftsartikel (refereegranskat)abstract
- In quadrupeds, spinalization in the thoracic region severely impairs postural control in the hindquarters. The goal of this study was to improve postural functions in chronic spinal rabbits by regular application of different factors: intrathecal injection of the 5-HT(2) agonist (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI), epidural electrical spinal cord stimulation (EES), and specific postural training (SPT). The factors were used either alone (SPT group) or in combination (DOI+SPT, EES+SPT, and DOI+EES+SPT groups) or not used (control group). It was found that in none of these groups did normal postural corrective movements in response to lateral tilts of the supporting platform reappear within the month of treatment. In control group, reduced irregular electromyographic (EMG) responses, either correctly or incorrectly phased in relation to tilts, were observed. By contrast, in DOI+SPT and EES+SPT groups, a gradual threefold increase in the proportion of correctly phased EMG responses (compared with control) was observed. The increase was smaller in DOI+EES+SPT and SPT groups. Dissimilarly to these long-term effects, short-term effects of DOI and EES were weak or absent. In addition, gradual development of oscillatory EMG activity in the responses to tilts, characteristic for the control group, was retarded in DOI+SPT, EES+SPT, DOI+EES+SPT, and SPT groups. Thus regular application of the three tested factors and their combinations caused progressive, long-lasting plastic changes in the isolated spinal networks, resulting in the facilitation of spinal postural reflexes and in the retardation of the development of oscillatory EMG activity. The facilitated reflexes, however, were insufficient for normal postural functions.
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| 18. |
- Malinina, Evgenya, et al.
(författare)
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Differential control of spontaneous and evoked GABA release by presynaptic L-type Ca(2+) channels in the rat medial preoptic nucleus
- 2010
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 104:1, s. 200-209
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Tidskriftsartikel (refereegranskat)abstract
- To clarify the role of presynaptic L-type Ca(2+) channels in GABA-mediated transmission in the medial preoptic nucleus (MPN), spontaneous, miniature, and impulse-evoked inhibitory postsynaptic currents (sIPSCs, mIPSCs, and eIPSCs, respectively) were recorded from MPN neurons in a slice preparation from rat brain. The effects of different stimulus protocols and pharmacological tools to detect contributions of L-type Ca(2+) channels and of Ca(2+)-activated K(+) (K(Ca)) channels were analyzed. Block of L-type channels did not affect the sIPSC and mIPSC properties (frequency, amplitude, decay time course) in the absence of external stimulation but unexpectedly potentiated the eIPSCs evoked at low stimulus frequency (0.1-2.0 Hz). This effect was similar to and overlapping with the effect of K(Ca)-channel blockers. High-frequency stimulation (50 Hz for 10 s) induced a substantial posttetanic potentiation (PTP) of the eIPSC amplitude and of the sIPSC frequency. Block of L-type channels still potentiated the eIPSC during PTP, but in contrast, reduced the sIPSC frequency during PTP. It was concluded that L-type channels provide a means for differential control of spontaneous and impulse-evoked GABA release and that this differential control is prominent during short-term synaptic plasticity. Functional coupling of the presynaptic L-type channels to K(Ca) channels explains the observed effects on eIPSCs.
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| 19. |
- Marlinski, V, et al.
(författare)
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Signals from the ventrolateral thalamus to the motor cortex during locomotion
- 2012
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 107:1, s. 455-472
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Tidskriftsartikel (refereegranskat)abstract
- The activity of the motor cortex during locomotion is profoundly modulated in the rhythm of strides. The source of modulation is not known. In this study we examined the activity of one of the major sources of afferent input to the motor cortex, the ventrolateral thalamus (VL). Experiments were conducted in chronically implanted cats with an extracellular single-neuron recording technique. VL neurons projecting to the motor cortex were identified by antidromic responses. During locomotion, the activity of 92% of neurons was modulated in the rhythm of strides; 67% of cells discharged one activity burst per stride, a pattern typical for the motor cortex. The characteristics of these discharges in most VL neurons appeared to be well suited to contribute to the locomotion-related activity of the motor cortex. In addition to simple locomotion, we examined VL activity during walking on a horizontal ladder, a task that requires vision for correct foot placement. Upon transition from simple to ladder locomotion, the activity of most VL neurons exhibited the same changes that have been reported for the motor cortex, i.e., an increase in the strength of stride-related modulation and shortening of the discharge duration. Five modes of integration of simple and ladder locomotion-related information were recognized in the VL. We suggest that, in addition to contributing to the locomotion-related activity in the motor cortex during simple locomotion, the VL integrates and transmits signals needed for correct foot placement on a complex terrain to the motor cortex.
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| 20. |
- Musienko, PE, et al.
(författare)
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Facilitation of postural limb reflexes with epidural stimulation in spinal rabbits
- 2010
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 103:2, s. 1080-1092
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Tidskriftsartikel (refereegranskat)abstract
- It is known that after spinalization animals lose their ability to maintain lateral stability when standing or walking. A likely reason for this is a reduction of the postural limb reflexes (PLRs) driven by stretch and load receptors of the limbs. The aim of this study was to clarify whether spinal networks contribute to the generation of PLRs. For this purpose, first, PLRs were recorded in decerebrated rabbits before and after spinalization at T12. Second, the effects of epidural electrical stimulation (EES) at L7 on the limb reflexes were studied after spinalization. To evoke PLRs, the vertebrate column of the rabbit was fixed, whereas the hindlimbs were positioned on the platform. Periodic lateral tilts of the platform caused antiphase flexion–extension limbs movements, similar to those observed in intact animals keeping balance on the tilting platform. Before spinalization, these movements evoked PLRs: augmentation of extensor EMGs and increase of contact force during limb flexion, suggesting their stabilizing postural effects. Spinalization resulted in almost complete disappearance of PLRs. After EES, however, the PLRs reappeared and persisted for up to several minutes, although their values were reduced. The post-EES effects could be magnified by intrathecal application of quipazine (5-HT agonist) at L4–L6. Results of this study suggest that the spinal cord contains the neuronal networks underlying PLRs; they can contribute to the maintenance of lateral stability in intact subjects. In acute spinal animals, these networks can be activated by EES, suggesting that they are normally activated by a tonic supraspinal drive.
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| 21. |
- Nanou, E, et al.
(författare)
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Differential regulation of synaptic transmission by pre- and postsynaptic SK channels in the spinal locomotor network
- 2013
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 109:12, s. 3051-3059
-
Tidskriftsartikel (refereegranskat)abstract
- The generation of activity in the central nervous system requires precise tuning of cellular properties and synaptic transmission. Neural networks in the spinal cord produce coordinated locomotor movements. Synapses in these networks need to be equipped with multiple mechanisms that regulate their operation over varying regimes to produce locomotor activity at different frequencies. Using the in vitro lamprey spinal cord, we explored whether Ca2+ influx via different routes in postsynaptic soma and dendrites and in presynaptic terminals can activate apamin-sensitive Ca2+-activated K+ (SK) channels and thereby shape synaptic transmission. We show that postsynaptic SK channels are tightly coupled to Ca2+ influx via NMDA receptors. Activation of these channels by synaptically induced NMDA-dependent Ca2+ transients restrains the time course of the synaptic current and the amplitude of the synaptic potential. In addition, presynaptic SK channels are activated by Ca2+ influx via voltage-gated channels and control the waveform of the action potential and the resulting Ca2+ dynamics in the axon terminals. The coupling of SK channels to different Ca2+ sources, pre- and postsynaptically, acts as a negative feedback mechanism to shape synaptic transmission. Thus SK channels can play a pivotal role in setting the dynamic range of synapses and enabling short-term plasticity in the spinal locomotor network.
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| 22. |
- Nanou, E, et al.
(författare)
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Mechanisms of modulation of AMPA-induced Na+-activated K+ current by mGluR1
- 2010
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 103:1, s. 441-445
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Tidskriftsartikel (refereegranskat)abstract
- Na+-activated K+ (KNa) channels can be activated by Na+ influx via ionotropic receptors and play a role in shaping synaptic transmission. In expression systems, KNa channels are modulated by G protein–coupled receptors, but such a modulation has not been shown for the native channels. In this study, we examined whether KNa channels coupled to AMPA receptors are modulated by metabotropic glutamate receptors (mGluRs) in lamprey spinal cord neurons. Activation of mGluR1 strongly inhibited the AMPA-induced KNa current. However, when intracellular Ca2+ was chelated with 1,2-bis(2-aminophenoxy)ethane- N,N,N′, N′-tetraacetic acid (BAPTA), the KNa current was enhanced by mGluR1. Activation of protein kinase C (PKC) mimicked the inhibitory effect of mGluR1 on the KNa current. Blockade of PKC prevented the mGluR1-induced inhibition of the KNa current, but did not affect the enhancement of the current seen in BAPTA. Together these results suggest that mGluR1 can differentially modulate AMPA-induced KNa current in a Ca2+- and PKC-dependent manner.
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| 23. |
- Omrani, Mohsen, et al.
(författare)
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Perturbation-evoked responses in primary motor cortex are modulated by behavioral context
- 2014
-
Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 112:11, s. 2985-3000
-
Tidskriftsartikel (refereegranskat)abstract
- Corrective responses to external perturbations are sensitive to the behavioral task being performed. It is believed that primary motor cortex (M1) forms part of a transcortical pathway that contributes to this sensitivity. Previous work has identified two distinct phases in the perturbation response of M1 neurons, an initial response starting similar to 20 ms after perturbation onset that does not depend on the intended motor action and a task- dependent response that begins similar to 40 ms after perturbation onset. However, this invariant initial response may reflect ongoing postural control or a task- independent response to the perturbation. The present study tested these two possibilities by examining if being engaged in an ongoing postural task before perturbation onset modulated the initial perturbation response in M1. Specifically, mechanical perturbations were applied to the shoulder and/ or elbow while the monkey maintained its hand at a central target or when it was watching a movie and not required to respond to the perturbation. As expected, corrective movements, muscle stretch responses, and M1 population activity in the late perturbation epoch were all significantly diminished in the movie task. Strikingly, initial perturbation responses (<40 ms postperturbation) remained the same across tasks, suggesting that the initial phase of M1 activity constitutes a task- independent response that is sensitive to the properties of the mechanical perturbation but not the goal of the ongoing motor task.
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| 24. |
- Panarese, Alessandro, et al.
(författare)
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Human ability to discriminate direction of three-dimensional force stimuli applied to the finger pad
- 2011
-
Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 105:2, s. 541-547
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Tidskriftsartikel (refereegranskat)abstract
- Sensory information from tactile mechanoreceptors located in the glabrous skin of the hand is crucial for skillful object exploration and manipulation. These mechanoreceptors reliably encode the direction of fingertip forces, and the brain certainly relies on this information in both sensorimotor and cognitive tasks. In this study, we examined human ability to discriminate the direction of force stimuli applied to the volar surface of the index fingertip on the basis of tactile information only. We show that humans can discriminate three-dimensional (3D) force stimuli whose directions differ by an angle as small as 7.1 ° in the plane tangential to the skin surface. Moreover, we found that the discrimination ability was mainly affected by the time-varying phases of the stimulus, because adding a static plateau phase to the stimulus improved the discrimination threshold only to a limited extent.
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| 25. |
- Perez, CT, et al.
(författare)
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Modulation of calcium currents and membrane properties by substance P in the lamprey spinal cord
- 2013
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 110:2, s. 286-296
-
Tidskriftsartikel (refereegranskat)abstract
- Substance P is endogenously released within the locomotor network of the adult lamprey, accelerates the burst frequency of fictive locomotion, and reduces the reciprocal inhibition. Previous studies have shown that dopamine, serotonin, and GABA regulate calcium channels, which control neurotransmitter release, action potential duration, and slow afterhyperpolarization (sAHP). Here we examine the effect of substance P on calcium channels in motoneurons and commissural interneurons using whole cell patch clamp in the lamprey spinal cord. This study analyzed the effects of substance P on calcium currents activated in voltage clamp. We examined the calcium-dependent sAHP in current clamp, to determine the involvement of three calcium channel subtypes modulated by substance P. The effects of substance P on membrane potential and during N-methyl-d-aspartic acid (NMDA) induced oscillations were also analyzed. Depolarizing voltage steps induced inward calcium currents. Substance P reduced the currents carried by calcium by 61% in commissural interneurons and by 31% in motoneurons. Using specific calcium channel antagonists, we show that substance P reduces the sAHP primarily by inhibiting N-type (CaV2.2) channels. Substance P depolarized both motoneurons and commissural interneurons, and we present evidence that this occurs due to an increased input resistance. We also explored the effects of substance P on NMDA-induced oscillations in tetrodotoxin and found it caused a frequency increase. Thus the reduction of calcium entry by substance P and the accompanying decrease of the sAHP amplitude, combined with substance P potentiation of currents activated by NMDA, may both contribute to the increase in fictive locomotion frequency.
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| 26. |
- Perfiliev, Sergei, 1957, et al.
(författare)
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Reflexive limb selection and control of reach direction to moving targets in cats, monkeys, and humans.
- 2010
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 104:5, s. 2423-32
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Tidskriftsartikel (refereegranskat)abstract
- When we reach for an object, we have to decide which arm to use and the direction in which to move. According to the established view, this is voluntarily controlled and programmed in advance in time-consuming and elaborate computations. Here, we systematically tested the motor strategy used by cats, monkeys, and humans when catching an object moving at high velocity to the left or right. In all species, targets moving to the right selectively initiated movement of the right forelimb and vice versa for targets moving to the left. Movements were from the start directed toward a prospective target position. In humans, the earliest onset of electromyographic activity from start of motion of the target ranged from 90 to 110 ms in different subjects. This indicates that the selection of the arm and specification of movement direction did not result from the subject's voluntary decision, but were determined in a reflex-like manner by the parameters of the target motion. As a whole the data suggest that control of goal-directed arm movement relies largely on an innate neuronal network that, when activated by the visual signal from the target, automatically guides the arm throughout the entire movement toward the target. In the view of the present data, parametric programming of reaching in advance seems to be superfluous.
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| 27. |
- Rossant, C, et al.
(författare)
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A calibration-free electrode compensation method
- 2012
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 108:9, s. 2629-2639
-
Tidskriftsartikel (refereegranskat)abstract
- In a single-electrode current-clamp recording, the measured potential includes both the response of the membrane and that of the measuring electrode. The electrode response is traditionally removed using bridge balance, where the response of an ideal resistor representing the electrode is subtracted from the measurement. Because the electrode is not an ideal resistor, this procedure produces capacitive transients in response to fast or discontinuous currents. More sophisticated methods exist, but they all require a preliminary calibration phase, to estimate the properties of the electrode. If these properties change after calibration, the measurements are corrupted. We propose a compensation method that does not require preliminary calibration. Measurements are compensated offline by fitting a model of the neuron and electrode to the trace and subtracting the predicted electrode response. The error criterion is designed to avoid the distortion of compensated traces by spikes. The technique allows electrode properties to be tracked over time and can be extended to arbitrary models of electrode and neuron. We demonstrate the method using biophysical models and whole cell recordings in cortical and brain-stem neurons.
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| 28. |
- Stöckl, Anna, et al.
(författare)
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Encoding of social signals in all three electrosensory pathways of Eigenmannia virescens.
- 2014
-
Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 112:9, s. 2076-2091
-
Tidskriftsartikel (refereegranskat)abstract
- Extracting complementary features in parallel pathways is a widely used strategy for a robust representation of sensory signals. Weakly electric fish offer the rare opportunity to study complementary encoding of social signals in all of its electrosensory pathways. Electrosensory information is conveyed in three parallel pathways: two receptor types of the tuberous (active) system and one receptor type of the ampullary (passive) system. Modulations of the fish's own electric field are sensed by these receptors and used in navigation, prey-detection and communication. We studied the neuronal representation of electric communication signals (called chirps) in the ampullary and the two tuberous pathways of Eigenmannia virescens. We first characterized different kinds of chirps observed in behavioral experiments. Since Eigenmannia chirps simultaneously drive all three types of receptors, we studied their responses in in vivo electrophysiological recordings. Our results demonstrate that different electroreceptor types encode different aspects of the stimuli and each appears best suited to convey information about a certain chirp type. A decoding analysis of single neurons and small populations shows that this specialization leads to a complementary representation of information in the tuberous and ampullary receptors. This suggests that a potential readout mechanism should combine information provided by the parallel processing streams to improve chirp detectability.
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| 29. |
- Svensson, Pär, et al.
(författare)
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Effect of conditioned stimulus parameters on timing of conditioned purkinje cell responses
- 2010
-
Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 103:3, s. 1329-1336
-
Tidskriftsartikel (refereegranskat)abstract
- Pavlovian eyeblink conditioning is a useful experimental model for studying adaptive timing, an important aspect of skilled movements. The conditioned response (CR) is precisely timed to occur just before the onset of the expected unconditioned stimulus (US). The timing can be changed immediately, however, by varying parameters of the conditioned stimulus (CS). It has previously been shown that increasing the intensity of a peripheral CS or the frequency of a CS consisting of a train of stimuli to the mossy fibers shortens the latency of the CR. The adaptive timing of behavioral CRs probably reflects the timing of an underlying learned inhibitory response in cerebellar Purkinje cells. It is not known how the latency of this Purkinje cell CR is controlled. We have recorded form Purkinje cells in conditioned decerebrate ferrets while increasing the intensity of a peripheral CS or the frequency of a mossy fiber CS. We observe changes in the timing of the Purkinje cell CR that match the behavioral effects. The results are consistent with the effect of CS parameters on behavioral CR latency being caused by corresponding changes in Purkinje cell CRs. They suggest that synaptic temporal summation may be one of several mechanisms underlying adaptive timing of movements.
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| 30. |
- Säfström, Daniel, et al.
(författare)
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Skill learning involves optimizing the linking of action phases
- 2013
-
Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 110:6, s. 1291-1300
-
Tidskriftsartikel (refereegranskat)abstract
- Many manual tasks involve object manipulation and are achieved by an evolving series of actions, or action phases, recruited to achieve task subgoals. The ability to effectively link action phases is an important component of manual dexterity. However, our understanding of how the effective linking of sequential action phases develops with skill learning is limited. Here, we addressed this issue using a task in which participants applied forces to a handle to move a cursor on a computer screen to successively acquire visual targets. Target acquisition required actively holding the cursor within the target zone (hold phase) for a required duration, before moving to the next target (transport phase). If the transport phase was initiated prematurely, before the end of the required hold duration, participants had to return to the target to acquire it. The goal was to acquire targets as quickly as possible. Distinct visual and auditory sensory events marked goal completion of each action phase. During initial task performance, the transport phase was reactively triggered by sensory events signaling hold phase completion. However, with practice, participants learned to initiate the transport phase based on a prediction of the time of hold phase completion. Simulations revealed that participants learned to near-optimally compensate for temporal uncertainty, presumably related to estimation of time intervals and execution of motor commands, so as to reduce the average latency between the end of the required hold phase duration and the start of the transport phase, while avoiding an excess of premature exits.
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| 31. |
- Tigerholm, Jenny, et al.
(författare)
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Modeling activity-dependent changes of axonal spike conduction in primary afferent C-nociceptors
- 2014
-
Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 111:9, s. 1721-1735
-
Tidskriftsartikel (refereegranskat)abstract
- Action potential initiation and conduction along peripheral axons is a dynamic process that displays pronounced activity dependence. In patients with neuropathic pain, differences in the modulation of axonal conduction velocity by activity suggest that this property may provide insight into some of the pathomechanisms. To date, direct recordings of axonal membrane potential have been hampered by the small diameter of the fibers. We have therefore adopted an alternative approach to examine the basis of activity-dependent changes in axonal conduction by constructing a comprehensive mathematical model of human cutaneous C-fibers. Our model reproduced axonal spike propagation at a velocity of 0.69 m/s commensurate with recordings from human C-nociceptors. Activity-dependent slowing (ADS) of axonal propagation velocity was adequately simulated by the model. Interestingly, the property most readily associated with ADS was an increase in the concentration of intra-axonal sodium. This affected the driving potential of sodium currents, thereby producing latency changes comparable to those observed for experimental ADS. The model also adequately reproduced post-action potential excitability changes (i.e., recovery cycles) observed in vivo. We performed a series of control experiments replicating blockade of particular ion channels as well as changing temperature and extracellular ion concentrations. In the absence of direct experimental approaches, the model allows specific hypotheses to be formulated regarding the mechanisms underlying activity-dependent changes in C-fiber conduction. Because ADS might functionally act as a negative feedback to limit trains of nociceptor activity, we envisage that identifying its mechanisms may also direct efforts aimed at alleviating neuronal hyperexcitability in pain patients.
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| 32. |
- Trulsson, M, et al.
(författare)
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Brain activations in response to vibrotactile tooth stimulation: a psychophysical and fMRI study
- 2010
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 104:4, s. 2257-2265
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Tidskriftsartikel (refereegranskat)abstract
- The tactile sensitivity of the teeth, and associated periodontium, serves important sensory and motor functions. Microneurographic recordings from human periodontal ligament mechanoreceptor (PDLM) nerves, in response to tooth loading, reveal discharge patterns with sole slowly adapting (SA) II-type characteristics, highlighting the unique role of PDLMs in oral sensory processes. Here we investigate these receptors' properties, psychophysically and with neuroimaging (fMRI), in response to varying frequencies of dynamic (vibrotactile) stimulation. The finding of increased activity in primary (SI) and secondary (SII) somatosensory cortices (SI and SII) at low frequencies of stimulation (20 Hz) as compared with higher frequencies (50 and 100 Hz), shows an increased entrainment of the PDLMs at this lower frequency in line with expected SA II-type response properties. At the highest frequency (100 Hz), no significant activity was found in SI or SII, suggesting this frequency is outside the range of activity of PDLMs. An activation matrix is mapped that includes SI, SII, insular, inferior frontal gyrus, inferior parietal lobe and supplementary motor area as well as middle frontal gyrus and cerebellum. We compared the responses to tooth stimulation with those produced by identical vibrotactile stimulation of the finger. The results strongly suggest that the PDLMs play a significant role in the specification of the forces used to hold and manipulate food between teeth, and in these respects, the masticatory system appears analogous to fine finger-control mechanisms used during precision manipulation of small objects. Because fMRI reveals activations in posterior insular cortex, we also speculate that PDLMs, and SA II-type receptors in general, may be involved in one aspect of the feeling of body ownership.
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| 33. |
- Trulsson, M, et al.
(författare)
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Sensations evoked by microstimulation of single mechanoreceptive afferents innervating the human face and mouth
- 2010
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 103:4, s. 1741-1747
-
Tidskriftsartikel (refereegranskat)abstract
- Intraneural microneurography and microstimulation were performed on single afferent axons in the inferior alveolar and lingual nerves innervating the face, teeth, labial, or oral mucosa. Using natural mechanical stimuli, 35 single mechanoreceptive afferents were characterized with respect to unit type [fast adapting type I (FA I), FA hair, slowly adapting type I and II (SA I and SA II), periodontal, and deep tongue units] as well as size and shape of the receptive field. All afferents were subsequently microstimulated with pulse trains at 30 Hz lasting 1.0 s. Afferents recordings whose were stable thereafter were also tested with single pulses and pulse trains at 5 and 60 Hz. The results revealed that electrical stimulation of single FA I, FA hair, and SA I afferents from the orofacial region can evoke a percept that is spatially matched to the afferent's receptive field and consistent with the afferent's response properties as observed on natural mechanical stimulation. Stimulation of FA afferents typically evoked sensations that were vibratory in nature; whereas those of SA I afferents were felt as constant pressure. These afferents terminate superficially in the orofacial tissues and seem to have a particularly powerful access to perceptual levels. In contrast, microstimulation of single periodontal, SA II, and deep tongue afferents failed to evoke a sensation that matched the receptive field of the afferent. These afferents terminate more deeply in the tissues, are often active in the absence of external stimulation, and probably access perceptual levels only when multiple afferents are stimulated. It is suggested that the spontaneously active afferents that monitor tension in collagen fibers (SA II and periodontal afferents) may have the role to register the mechanical state of the soft tissues, which has been hypothesized to help maintain the body's representation in the central somatosensory system.
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| 34. |
- Wang, D, et al.
(författare)
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5-HT and dopamine modulates CaV1.3 calcium channels involved in postinhibitory rebound in the spinal network for locomotion in lamprey
- 2011
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 105:3, s. 1212-1224
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Tidskriftsartikel (refereegranskat)abstract
- Postinhibitory rebound (PIR) can play a significant role for producing stable rhythmic motor patterns, like locomotion, by contributing to burst initiation following the phase of inhibition, and PIR may also be a target for modulatory systems acting on the network. The current aim was to explore the PIR in one type of interneuron in the lamprey locomotor network and its dependence on low voltage-activated (LVA) calcium channels, as well as its modulation by 5-HT and dopamine. PIR responses in commissural interneurons, mediating reciprocal inhibition and left-right alternation in the network, were significantly larger than in motoneurons. The L-type calcium channel antagonist nimodipine reduced PIR amplitude by ∼50%, whereas the L-channel agonist BAY K 8644 enhanced PIR amplitude, suggesting that LVA calcium channels of the L-subtype (CaV1.3) participate in the PIR response. The remainder of the response was blocked by nickel, indicating that T-type (CaV3) LVA calcium channels also contribute. No evidence was obtained for the involvement of a hyperpolarization-activated current. Furthermore, 5-HT, acting via 5-HT1Areceptors, reduced PIR, as did dopamine, acting via D2receptors. Coapplication of nimodipine caused no further PIR reduction, indicating that these modulators target CaV1.3 channels specifically. These results suggest that PIR may play a prominent role in the generation of alternating network activity and that the CaV1.3 and CaV3 subtypes of LVA calcium channels together underlie the PIR response. 5-HT and dopamine both target PIR via CaV1.3 channels, which may contribute significantly to their modulatory influence on locomotor network activity.
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| 35. |
- Wang, D, et al.
(författare)
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Endogenous release of 5-HT modulates the plateau phase of NMDA-induced membrane potential oscillations in lamprey spinal neurons
- 2014
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 112:1, s. 30-38
-
Tidskriftsartikel (refereegranskat)abstract
- The lamprey central nervous system has been used extensively as a model system for investigating the networks underlying vertebrate motor behavior. The locomotor networks can be activated by application of glutamate agonists, such as N-methyl-D-aspartic acid (NMDA), to the isolated spinal cord preparation. Many spinal neurons are capable of generating pacemaker-like membrane potential oscillations upon activation of NMDA receptors. These oscillations rely on the voltage-dependent properties of NMDA receptors in interaction with voltage-dependent potassium and calcium-dependent potassium (KCa) channels, as well as low voltage-activated calcium channels. Upon membrane depolarization, influx of calcium will activate KCachannels, which in turn, will contribute to repolarization and termination of the depolarized phase. The appearance of the NMDA-induced oscillations varies markedly between spinal cord preparations; they may either have a pronounced, depolarized plateau phase or be characterized by a short-lasting depolarization lasting approximately 200–300 ms without a plateau. Both types of oscillations increase in frequency with increased concentrations of NMDA. Here, we characterize these two types of membrane potential oscillations and show that they depend on the level of endogenous release of 5-HT in the spinal cord preparations. In the lamprey, 5-HT acts to block voltage-dependent calcium channels and will thereby modulate the activity of KCachannels. When 5-HT antagonists were administered, the plateau-like oscillations were converted to the second type of oscillations lacking a plateau phase. Conversely, plateau-like oscillations can be induced or prolonged by 5-HT agonists. These properties are most likely of significance for the modulatory action of 5-HT on the spinal networks for locomotion.
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| 36. |
- Wienecke, J, et al.
(författare)
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Global gene expression analysis of rodent motor neurons following spinal cord injury associates molecular mechanisms with development of postinjury spasticity
- 2010
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 103:2, s. 761-778
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Tidskriftsartikel (refereegranskat)abstract
- Spinal cord injury leads to severe problems involving impaired motor, sensory, and autonomic functions. After spinal injury there is an initial phase of hyporeflexia followed by hyperreflexia, often referred to as spasticity. Previous studies have suggested a relationship between the reappearance of endogenous plateau potentials in motor neurons and the development of spasticity after spinalization. To unravel the molecular mechanisms underlying the increased excitability of motor neurons and the return of plateau potentials below a spinal cord injury we investigated changes in gene expression in this cell population. We adopted a rat tail-spasticity model with a caudal spinal transection that causes a progressive development of spasticity from its onset after 2 to 3 wk until 2 mo postinjury. Gene expression changes of fluorescently identified tail motor neurons were studied 21 and 60 days postinjury. The motor neurons undergo substantial transcriptional regulation in response to injury. The patterns of differential expression show similarities at both time points, although there are 20% more differentially expressed genes 60 days compared with 21 days postinjury. The study identifies targets of regulation relating to both ion channels and receptors implicated in the endogenous expression of plateaux. The regulation of excitatory and inhibitory signal transduction indicates a shift in the balance toward increased excitability, where the glutamatergic N-methyl-d-aspartate receptor complex together with cholinergic system is up-regulated and the γ-aminobutyric acid type A receptor system is down-regulated. The genes of the pore-forming proteins Cav1.3 and Nav1.6 were not up-regulated, whereas genes of proteins such as nonpore-forming subunits and intracellular pathways known to modulate receptor and channel trafficking, kinetics, and conductivity showed marked regulation. On the basis of the identified changes in global gene expression in motor neurons, the present investigation opens up for new potential targets for treatment of motor dysfunction following spinal cord injury.
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| 37. |
- Zelenin, PV, et al.
(författare)
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Activity of motor cortex neurons during backward locomotion
- 2011
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 105:6, s. 2698-2714
-
Tidskriftsartikel (refereegranskat)abstract
- Forward walking (FW) and backward walking (BW) are two important forms of locomotion in quadrupeds. Participation of the motor cortex in the control of FW has been intensively studied, whereas cortical activity during BW has never been investigated. The aim of this study was to analyze locomotion-related activity of the motor cortex during BW and compare it with that during FW. For this purpose, we recorded activity of individual neurons in the cat during BW and FW. We found that the discharge frequency in almost all neurons was modulated in the rhythm of stepping during both FW and BW. However, the modulation patterns during BW and FW were different in 80% of neurons. To determine the source of modulating influences (forelimb controllers vs. hindlimb controllers), the neurons were recorded not only during quadrupedal locomotion but also during bipedal locomotion (with either forelimbs or hindlimbs walking), and their modulation patterns were compared. We found that during BW (like during FW), modulation in some neurons was determined by inputs from limb controllers of only one girdle, whereas the other neurons received inputs from both girdles. The combinations of inputs could depend on the direction of locomotion. Most often (in 51% of forelimb-related neurons and in 34% of the hindlimb-related neurons), the neurons received inputs only from their own girdle when this girdle was leading and from both girdles when this girdle was trailing. This reconfiguration of inputs suggests flexibility of the functional roles of individual cortical neurons during different forms of locomotion.
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| 38. |
- Zelenin, PV
(författare)
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Reticulospinal neurons controlling forward and backward swimming in the lamprey
- 2011
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 105:3, s. 1361-1371
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Tidskriftsartikel (refereegranskat)abstract
- Most vertebrates are capable of two forms of locomotion, forward and backward, strongly differing in the patterns of motor coordination. Basic mechanisms generating these patterns are located in the spinal cord; they are activated and regulated by supraspinal commands. In the lamprey, these commands are transmitted by reticulospinal (RS) neurons. The aim of this study was to reveal groups of RS neurons controlling different aspects of forward (FS) and backward (BS) swimming in the lamprey. Activity of individual larger RS neurons in intact lampreys was recorded during FS and BS by chronically implanted electrodes. It was found that among the neurons activated during locomotion, 27% were active only during FS, 3% only during BS, and 70% during both FS and BS. In a portion of RS neurons, their mean firing frequency was correlated with frequency of body undulations during FS (8%), during BS (34%), or during both FS and BS (22%), suggesting their involvement in control of locomotion intensity. RS activity was phasically modulated by the locomotor rhythm during FS (20% of neurons), during BS (29%), or during both FS and BS (16%). The majority of RS neurons responding to vestibular stimulation (and presumably involved in control of body orientation) were active mainly during FS. This explains the absence of stabilization of the body orientation observed during BS. We discuss possible functions of different groups of RS neurons, i.e., activation of the spinal locomotor CPG, inversion of the direction of propagation of locomotor waves, and postural control.
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| 39. |
- Zelenin, PV, et al.
(författare)
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Use of galvanic vestibular feedback to control postural orientation in decerebrate rabbits
- 2012
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 107:11, s. 3020-3026
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Tidskriftsartikel (refereegranskat)abstract
- In quadrupeds, the dorsal-side-up body orientation during standing is maintained due to a postural system that is driven by feedback signals coming mainly from limb mechanoreceptors. In caudally decerebrated (postmammillary) rabbits, the efficacy of this system is considerably reduced. In this paper, we report that the efficacy of postural control in these animals can be restored with galvanic vestibular stimulation (GVS) applied transcutaneously to the labyrinths. In standing intact rabbits, GVS causes a lateral body sway towards the positive electrode. We used this GVS-caused sway to counteract the lateral body sway resulting from a mechanical perturbation of posture. Experiments were performed on postmammillary rabbits that stood on the tilting platform with their hindlimbs. To make the GVS value dependent on the postural perturbation (i.e., on the lateral body sway caused by tilt of the platform), an artificial feedback loop was formed in the following ways: 1) Information about the body sway was provided by a mechanical sensor; 2) The GVS current was applied when the sway exceeded a threshold value; the polarity of the current was determined by the sway direction. This simple algorithm allowed the “hybrid” postural system to maintain the dorsal-side-up orientation of the hindquarters when the platform was tilted by ± 20°. Thus, an important postural function, i.e., securing lateral stability during standing, can be restored in decerebrate rabbits with the GVS-based artificial feedback. We suggest that such a control system can compensate for the loss of lateral stability of various etiologies, and can be used for restoration of balance control in patients with impaired postural functions.
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- Zelenin, Pavel V, et al.
(författare)
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Activity of motor cortex neurons during backward locomotion.
- 2011
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Ingår i: Journal of Neurophysiology. - 0022-3077.
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Tidskriftsartikel (refereegranskat)abstract
- Forward walking (FW) and backward walking (BW) are two important forms of locomotion in quadrupeds. Participation of the motor cortex in the control of FW has been intensively studied, while cortical activity during BW has never been investigated. The aim of this study was to analyze locomotion-related activity of the motor cortex during BW, and compare it to that during FW. For this purpose, we recorded activity of individual neurons in the cat during BW and FW. We found that the discharge frequency in almost all neurons was modulated in the rhythm of stepping during both FW and BW. However, the modulation patterns during BW and FW were different in 80% of neurons. To determine the source of modulating influences (forelimb controllers versus hindlimb controllers), the neurons were recorded not only during quadrupedal locomotion, but also during bipedal locomotion (with either forelimbs or hindlimbs walking), and their modulation patterns were compared. We found that during BW (like during FW), modulation in some neurons was determined by inputs from limb controllers of only one girdle, while the other neurons received inputs from both girdles. The combinations of inputs could depend on the direction of locomotion. Most often (in 51% of forelimb-related neurons and in 34% of the hindlimb-related neurons), the neurons received inputs only from their own girdle when this girdle was leading, and from both girdles when this girdle was trailing. This reconfiguration of inputs suggests flexibility of the functional roles of individual cortical neurons during different forms of locomotion.
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