| 1. |
- Bannatyne, B Anne, et al.
(författare)
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Differential projections of excitatory and inhibitory dorsal horn interneurons relaying information from group II muscle afferents in the cat spinal cord.
- 2006
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Ingår i: The Journal of neuroscience : the official journal of the Society for Neuroscience. - 1529-2401. ; 26:11, s. 2871-80
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Tidskriftsartikel (refereegranskat)abstract
- Dorsal horn interneurons with input from group II muscle spindle afferents are components of networks involved in motor control. Thirteen dorsal horn interneurons with monosynaptic group II input were characterized electrophysiologically and labeled intracellularly with Neurobiotin. Their axonal projections were traced, and neurotransmitter content was established by using immunocytochemistry. Two subpopulations were identified: five interneurons had axons that contained vesicular glutamate transporter 2 and hence were glutamatergic and excitatory. Terminals of the remaining eight interneurons were immunoreactive for the glycine transporter 2 or were apposed to gephyrin but did not contain the GABA-synthesizing enzyme glutamic acid decarboxylase and were therefore glycinergic and inhibitory. Excitatory cells were located mainly in the central region of lamina IV and had relatively small somata and restricted dendritic trees. In contrast, inhibitory interneurons were located more ventrally, in lamina V and had relatively larger somata and more extensive dendritic trees. Axonal projections of the two subpopulations differed considerably. Excitatory interneurons predominantly projected ipsilaterally, whereas most inhibitory interneurons projected both ipsilaterally and contralaterally. Three inhibitory axons formed contacts with large cholinergic cells in motor nuclei, thus revealing a novel direct coupling between inhibitory dorsal horn interneurons and motoneurons. The organization of the excitatory interneurons is consistent with current knowledge of reflex pathways to motoneurons, but the existence and connections of the inhibitory subpopulation could not be predicted from previous data. Our results indicate that these latter interneurons exercise widespread inhibitory control over a variety of cell types located on both sides of the spinal cord.
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| 2. |
- Bannatyne, B A, et al.
(författare)
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Excitatory and inhibitory intermediate zone interneurons in pathways from feline group I and II afferents: differences in axonal projections and input.
- 2009
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Ingår i: The Journal of physiology. - : Wiley. - 1469-7793 .- 0022-3751. ; 587:Pt 2, s. 379-99
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study was to compare properties of excitatory and inhibitory spinal intermediate zone interneurons in pathways from group I and II muscle afferents in the cat. Interneurons were labelled intracellularly and their transmitter phenotypes were defined by using immunocytochemistry. In total 14 glutamatergic, 22 glycinergic and 2 GABAergic/glycinergic interneurons were retrieved. All interneurons were located in laminae V-VII of the L3-L7 segments. No consistent differences were found in the location, the soma sizes or the extent of the dendritic trees of excitatory and inhibitory interneurons. However, major differences were found in their axonal projections; excitatory interneurons projected either ipsilaterally, bilaterally or contralaterally, while inhibitory interneurons projected exclusively ipsilaterally. Terminal projections of glycinergic and glutamatergic cells were found within motor nuclei as well as other regions of the grey matter which include the intermediate region, laminae VII and VIII. Cells containing GABA/glycine had more restricted projections, principally within the intermediate zone where they formed appositions with glutamatergic axon terminals and unidentified cells and therefore are likely to be involved in presynaptic as well as postsynaptic inhibition. The majority of excitatory and inhibitory interneurons were found to be coexcited by group I and II afferents (monosynaptically) and by reticulospinal neurons (mono- or disynaptically) and to integrate information from several muscles. Taken together the morphological and electrophysiological data show that individual excitatory and inhibitory intermediate zone interneurons may operate in a highly differentiated way and thereby contribute to a variety of motor synergies.
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| 3. |
- Bannatyne, B Anne, et al.
(författare)
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Networks of inhibitory and excitatory commissural interneurons mediating crossed reticulospinal actions.
- 2003
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Ingår i: The European journal of neuroscience. - 0953-816X. ; 18:8, s. 2273-84
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Tidskriftsartikel (refereegranskat)abstract
- Axonal projections and neurotransmitters used by commissural interneurons mediating crossed actions of reticulospinal neurons were investigated in adult cats. Eighteen interneurons, located in or close to lamina VIII in midlumbar segments, that were monosynaptically excited by reticulospinal tract fibres and projected to contralateral motor nuclei were labelled by intracellular injection of tetramethylrhodamine-dextran and Neurobiotin. The nine most completely labelled interneurons were analysed with combined confocal and light microscopy. None of the stem axons gave off ipsilateral axon collaterals. Seven cells had axon collaterals that arborized in the contralateral grey matter in the ventral horn of the same segments. Transmitters were identified by using antibodies raised against vesicular glutamate transporters 1 and 2, glutamic acid decarboxylase and the glycine transporter 2. The axons of two cells were immunoreactive for the glycine transporter 2 and hence were glycinergic. Three cells were immunoreactive for the vesicular glutamate transporter 2 and hence were glutamatergic. None of the axons displayed immunoreactivity for glutamic acid decarboxylase. Electron microscopy of two cells revealed direct synaptic connections with motoneurons and other neurons. Axonal swellings of one neuron formed synapses with profiles in motor nuclei whereas those of the other formed synapses with other structures, including cell bodies in lamina VII. The results show that this population of commissural interneurons includes both excitatory and inhibitory cells that may excite or inhibit contralateral motoneurons directly. They may also influence the activity of motoneurons indirectly by acting through interneurons located outside motor nuclei in the contralateral grey matter but are unlikely to have direct actions on interneurons in the ipsilateral grey matter.
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| 4. |
- Edgley, S A, et al.
(författare)
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Both dorsal horn and lamina VIII interneurones contribute to crossed reflexes from feline group II muscle afferents.
- 2003
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Ingår i: The Journal of physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 552:Pt 3, s. 961-74
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies have demonstrated that group II muscle afferents exert powerful actions on contralateral motoneurones and that these actions are mediated primarily via lamina VIII commissural interneurones. We examined whether dorsal horn interneurones also contribute to these actions, as they have been shown to contribute to the actions of group II afferents on ipsilateral motoneurones. We tested the susceptibility of IPSPs and EPSPs evoked from group II afferents in contralateral motoneurones to presynaptic inhibition as an indicator of the relative contribution of dorsal horn interneurones to these PSPs, since the monosynaptic activation of dorsal horn interneurones is more weakly and more briefly depressed by presynaptic inhibition than is the monosynaptic activation of lamina VIII and other intermediate zone and ventral horn interneurones. While the earliest components of IPSPs and EPSPs evoked by group II afferents were abolished by conditioning stimulation of group II afferents, consistent with them being evoked disynaptically by commissural interneurones, trisynaptic components of these PSPs were only partly reduced and are therefore attributed to dorsal horn interneurones. The same conditioning stimuli depressed the disynaptic excitation of lamina VIII commissural interneurones by group II afferents much less effectively than they depressed monosynaptic excitation, indicating that dorsal horn interneurones contribute to this disynaptic excitation. On the basis of these observations we conclude that that dorsal horn interneurones contribute to the late actions of group II muscle afferents on contralateral motoneurones through their disynaptic actions on commissural interneurones.
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| 5. |
- Edgley, S A, et al.
(författare)
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Ipsilateral actions of feline corticospinal tract neurons on limb motoneurons.
- 2004
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Ingår i: The Journal of neuroscience : the official journal of the Society for Neuroscience. - 1529-2401. ; 24:36, s. 7804-13
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Tidskriftsartikel (refereegranskat)abstract
- Contralateral pyramidal tract (PT) neurons arising in the primary motor cortex are the major route through which volitional limb movements are controlled. However, the contralateral hemiparesis that follows PT neuron injury on one side may be counteracted by ipsilateral of actions of PT neurons from the undamaged side. To investigate the spinal relays through which PT neurons may influence ipsilateral motoneurons, we analyzed the synaptic actions evoked by stimulation of the ipsilateral pyramid on hindlimb motoneurons after transecting the descending fibers of the contralateral PT at a low thoracic level. The results show that ipsilateral PT neurons can affect limb motoneurons trisynaptically by activating contralaterally descending reticulospinal neurons, which in turn activate spinal commissural interneurons that project back across to motoneurons ipsilateral to the stimulated pyramidal tract. Stimulation of the pyramids alone did not evoke synaptic actions in motoneurons but potently facilitated disynaptic EPSPs and IPSPs evoked by stimulation of reticulospinal tract fibers in the medial longitudinal fascicle. In parallel with this double-crossed pathway, corticospinal neurons could also evoke ipsilateral actions via ipsilateral descending reticulospinal tract fibers, acting through ipsilaterally located spinal interneurons. Because the actions mediated by commissural interneurons were found to be stronger than those of ipsilateral premotor interneurons, the study leads to the conclusion that ipsilateral actions of corticospinal neurons via commissural interneurons may provide a better opportunity for recovery of function in hemiparesis produced by corticospinal tract injury.
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| 6. |
- Hammar, Ingela, 1964, et al.
(författare)
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A comparison of postactivation depression of synaptic actions evoked by different afferents and at different locations in the feline spinal cord.
- 2002
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Ingår i: Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale. - : Springer Science and Business Media LLC. - 0014-4819. ; 145:1, s. 126-9
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Tidskriftsartikel (refereegranskat)abstract
- Postactivation depression of synaptic actions of group I and II muscle afferents and low threshold cutaneous afferents was compared with depression of actions of group Ia afferents on alpha-motoneurones in cats deeply anaesthetised with pentobarbital and alpha-chloralose. The depression was analysed on field potentials (population EPSPs). The degree of depression was evaluated by analysing changes in the monosynaptic components of the field potentials, in areas within 0.4- to 0.6-ms-long time windows from their onset. When intervals between successive stimuli used to evoke field potentials were reduced from 10 s to 0.4 s, the potentials evoked by Ia afferents in motor nuclei were depressed as described previously. Field potentials evoked by group II afferents and cutaneous afferents in the dorsal horn were similarly depressed. In contrast, monosynaptic components of field potentials evoked in the intermediate zone, by group I or II afferents, were only marginally affected. Postactivation depression of synaptic actions of group I afferents in the intermediate zone was not enhanced when test stimuli were applied 30-40 ms after a train of four conditioning stimuli. These observations indicate that the degree of postactivation depression may differ depending on the type of afferent. In addition, if postactivation depression depends on intrinsic properties of afferent terminals, differences in the degree of depression of postsynaptic potentials evoked by the same group of afferents at different locations may indicate that properties of terminals contacting different neurones may differ.
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| 7. |
- Hammar, Ingela, 1964, et al.
(författare)
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A trans-spinal loop between neurones in the reticular formation and in the cerebellum.
- 2011
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Ingår i: The Journal of physiology. - : Wiley. - 1469-7793 .- 0022-3751. ; 589:Pt 3, s. 653-65
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Tidskriftsartikel (refereegranskat)abstract
- Voluntary limb movements are initiated in the brain but the neurones responsible for activating the muscles (motoneurones and interneurones) are located in the spinal cord. The spinal cord also contains neurones that provide the brain, and especially the cerebellum, with continuous information on effects of the descending commands. We show that one population of such neurones provide the cerebellum with information on how likely the brain's commands (mediated by descending reticulospinal neurones) are to be executed as planned, depending on the degree of inhibition of motoneurones. They may therefore play an important role in preventing errors in activation of motoneurones and thereby help the brain to correct its signals to the spinal cord before such errors have been committed.
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| 8. |
- Hammar, Ingela, 1964, et al.
(författare)
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Modulation of responses of feline ventral spinocerebellar tract neurons by monoamines.
- 2002
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Ingår i: The Journal of comparative neurology. - 0021-9967. ; 443:3, s. 298-309
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Tidskriftsartikel (refereegranskat)abstract
- Ventral spinocerebellar tract neurons located in laminae V-VII of cat lumbar spinal cord were tested for the effects of ionophoretically applied monoamines and receptor selective agonists. Extracellularly recorded responses, monosynaptically evoked by group I afferents in a muscle nerve, were compared before, during, and after ionophoresis. They were analyzed with respect to changes in the number of evoked spikes and in the latency. Both serotonin (5-HT) and noradrenaline (NA) were found to facilitate responses of all neurons tested. Ionophoresis of three serotonin subtype receptor agonists (5-carboxamidotryptamine maleate, 5 methoxytryptamine HCl, and alpha-methyl 5-hydroxytryptamine) and of two NA receptor agonists (phenylephrine and isoproterenol) likewise had a facilitatory effect. However, three other 5-HT receptor agonists (8-hydroxy-dipropylaminotetraline hydrobromide), 2-methyl 5-hydroxytryptamine, and 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl and two NA receptor agonists (tizanidine and clonidine) had the opposite effect because they depressed responses of the tested neurons. These results show that information forwarded by means of the ventral spinocerebellar tract may be modulated by monoamines and that several receptor subtypes, located pre- or postsynaptically, may be involved. The results also demonstrate that transmission by means of group I muscle afferents may not only be facilitated by monoamines but also depressed by selective receptor subtype activation.
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| 9. |
- Hammar, Ingela, 1964, et al.
(författare)
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Modulatory effects of alpha1-,alpha2-, and beta -receptor agonists on feline spinal interneurons with monosynaptic input from group I muscle afferents.
- 2003
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Ingår i: The Journal of neuroscience : the official journal of the Society for Neuroscience. - 1529-2401. ; 23:1, s. 332-8
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies have shown that monoamines may modulate operation of spinal neuronal networks by depressing or facilitating responses of the involved neurons. Recently, activation of interneurons mediating reciprocal inhibition from muscle spindle (Ia) afferents and nonreciprocal inhibition from muscle spindle and tendon organ (Ia/Ib) afferents in the cat was found to be facilitated by noradrenaline (NA). However, which subclass membrane receptors are involved in mediating this facilitation was not established; the aim of the present experiments was to investigate this. Individual Ia- and Ia/Ib-inhibitory interneurons were identified in the cat lumbar spinal cord, and NA agonists were applied close to these neurons by ionophoresis. The agonists included the alpha1-receptor agonist phenylephrine, the alpha2-receptor agonists clonidine and tizanidine, and the beta-receptor agonist isoproterenol. Effects were measured by comparing changes in the number of extracellularly recorded spike potentials evoked by electrical stimulation of muscle nerves and changes in the latency of these potentials before, during, and after application of the tested compounds. Results show that the facilitatory effect of phenylephrine is as strong as that of NA, whereas the facilitatory effect of isoproterenol is weaker. Clonidine depressed activity of both Ia- and Ia/Ib-inhibitory interneurons, whereas tizanidine had no effect. These findings lead to the conclusion that beneficial antispastic effects of clonidine and tizanidine in humans are unlikely to be associated with an enhancement of the actions of Ia- and Ia/Ib-inhibitory interneurons, and the findings also support previous proposals that these compounds exert their antispastic actions via effects on other neuronal populations.
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| 10. |
- Hammar, Ingela, 1964, et al.
(författare)
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New observations on input to spino-cervical tract neurons from muscle afferents.
- 1994
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Ingår i: Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale. - 0014-4819. ; 100:1, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- Peripheral input to spino-cervical tract (SCT) neurons located in the L4 and L5 segments of the cat spinal cord was investigated using both extracellular and intracellular recording. The main aim was to find out whether midlumbar SCT neurons are excited monosynaptically not only by cutaneous afferents but also by group II muscle afferents, as in the sacral segments but apparently not in the caudal lumbar segments. Input from group II muscle afferents was found in 73% of investigated neurons; the latencies of excitation by group II afferents were compatible with a monosynaptic coupling between these afferents and 62% of neurons. The majority of the midlumbar SCT neurons were excited by group II afferents of the quadriceps and deep peroneal nerves. The predominant monosynaptic input from cutaneous afferents to the same neurons was from the saphenous nerve.
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