| 1. |
- Bannatyne, B Anne, et al.
(author)
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Networks of inhibitory and excitatory commissural interneurons mediating crossed reticulospinal actions.
- 2003
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In: The European journal of neuroscience. - 0953-816X. ; 18:8, s. 2273-84
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Journal article (peer-reviewed)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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| 2. |
- Edgley, S A, et al.
(author)
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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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In: The Journal of physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 552:Pt 3, s. 961-74
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Journal article (peer-reviewed)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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| 3. |
- Edgley, S A, et al.
(author)
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Ipsilateral actions of feline corticospinal tract neurons on limb motoneurons.
- 2004
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In: The Journal of neuroscience : the official journal of the Society for Neuroscience. - 1529-2401. ; 24:36, s. 7804-13
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Journal article (peer-reviewed)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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| 4. |
- Gladden, M H, et al.
(author)
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Coupling between serotoninergic and noradrenergic neurones and gamma-motoneurones in the cat.
- 2000
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In: The Journal of physiology. - 0022-3751. ; 527 Pt 2, s. 213-23
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Journal article (peer-reviewed)abstract
- Noradrenaline is known to suppress transmission from group II muscle afferents when locally applied to gamma-motoneurones, and serotonin (5-HT) facilitates the transmission. The purpose of this investigation was to search for evidence of monoaminergic innervation of gamma-motoneurones. Eight gamma-motoneurones were labelled with rhodamine-dextran, and 50 micrometer thick sagittal sections of the spinal cord containing them were exposed to antibodies against dopamine beta-hydroxylase (DBH) and 5-HT. All the cells were directly and/or indirectly excited by muscle group II afferents from the muscle they innervated and/or other muscles. Appositions between monoaminergic fibres and the labelled somata and dendrites were located with three-colour confocal laser scanning microscopy by examining series of optical sections at 1 or 0.5 micrometer intervals. DBH and 5-HT varicosities formed appositions with the somata and dendrites of all the gamma-motoneurones. The mean packing densities for 5-HT (1.12 +/- 0.11 appositions per 100 micrometer(2) for somata and 0.91 +/- 0.07 per 100 micrometer(2) for dendrites) were similar to the densities of contacts reported for alpha-motoneurones. Monoaminergic varicosities in apposition to dendrites greatly outnumbered those on the somata. The density of DBH appositions was consistently lower - corresponding means were 53% and 62% of those for 5-HT on the somata and dendrites, respectively. It is concluded from an analysis of the distribution and density of varicosities in apposition to the gamma-motoneurones compared with the density in the immediate surround of the dendrites that there is indeed both a serotoninergic and noradrenergic innervation of gamma-motoneurones.
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| 5. |
- Gladden, M. H., et al.
(author)
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Coupling between serotoninergic and noradrenergic neurones and γ-motoneurones in the cat
- 2000
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In: Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 527, s. 213-223
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Journal article (peer-reviewed)abstract
- 1. Noradrenaline is known to suppress transmission from group II muscle afferents when locally applied to γ-motoneurones, and serotonin (5-HT) facilitates the transmission. The purpose of this investigation was to search for evidence of monoaminergic innervation of γ-motoneurones. 2. Eight γ-motoneurones were labelled with rhodamine-dextran, and 50 μm thick sagittal sections of the spinal cord containing them were exposed to antibodies against dopamine β-hydroxylase (DBH) and 5-HT. All the cells were directly and/or indirectly excited by muscle group II afferents from the muscle they innervated and/or other muscles. 3. Appositions between monoaminergic fibres and the labelled somata and dendrites were located with three-colour confocal laser scanning microscopy by examining series of optical sections at 1 or 0·5 μm intervals. 4. DBH and 5-HT varicosities formed appositions with the somata and dendrites of all the γ-motoneurones. The mean packing densities for 5-HT (1·12 ± 0·11 appositions per 100 μm2 for somata and 0·91 ± 0·07 per 100 μm2 for dendrites) were similar to the densities of contacts reported for α-motoneurones. Monoaminergic varicosities in apposition to dendrites greatly outnumbered those on the somata. 5. The density of DBH appositions was consistently lower - corresponding means were 53% and 62% of those for 5-HT on the somata and dendrites, respectively. 6. It is concluded from an analysis of the distribution and density of varicosities in apposition to the γ-motoneurones compared with the density in the immediate surround of the dendrites that there is indeed both a serotoninergic and noradrenergic innervation of γ-motoneurones.
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| 6. |
- Hammar, Ingela, 1964, et al.
(author)
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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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In: Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale. - : Springer Science and Business Media LLC. - 0014-4819. ; 145:1, s. 126-9
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Journal article (peer-reviewed)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.
(author)
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Modulation of responses of feline ventral spinocerebellar tract neurons by monoamines.
- 2002
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In: The Journal of comparative neurology. - 0021-9967. ; 443:3, s. 298-309
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Journal article (peer-reviewed)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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| 8. |
- Hammar, Ingela, 1964, et al.
(author)
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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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In: The Journal of neuroscience : the official journal of the Society for Neuroscience. - 1529-2401. ; 23:1, s. 332-8
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Journal article (peer-reviewed)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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| 9. |
- Hammar, Ingela, 1964, et al.
(author)
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The actions of monoamines and distribution of noradrenergic and serotoninergic contacts on different subpopulations of commissural interneurons in the cat spinal cord.
- 2004
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In: The European journal of neuroscience. - : Wiley. - 0953-816X .- 1460-9568. ; 19:5, s. 1305-16
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Journal article (peer-reviewed)abstract
- Modulatory actions of monoamines were investigated on spinal commissural interneurons which coordinate left-right hindlimb muscle activity through direct projections to the contralateral motor nuclei. Commissural interneurons located in Rexed lamina VIII, with identified projections to the contralateral gastrocnemius-soleus motor nuclei, were investigated in deeply anaesthetized cats. Most interneurons had dominant input from either the reticular formation or from group II muscle afferents; a small proportion of neurons had input from both. Actions of ionophoretically applied serotonin and noradrenaline were examined on extracellularly recorded spikes evoked monosynaptically by group II muscle afferents or reticulospinal tract fibres. Activation by reticulospinal fibres was facilitated by both serotonin and noradrenaline. Activation by group II afferents was also facilitated by serotonin but was strongly depressed by noradrenaline. To investigate the possible morphological substrates of this differential modulation, seven representative commissural interneurons were labelled intracellularly with tetramethylrhodamine-dextran and neurobiotin. Contacts from noradrenergic and serotoninergic fibres were revealed by immunohistochemistry and analysed with confocal microscopy. There were no major differences in the numbers and distributions of contacts among the interneurons studied. The findings suggest that differences in modulatory actions of monoamines, and subsequent changes in the recruitment of subpopulations of commissural interneurons in various behavioural situations, depend on intrinsic interneuron properties rather than on the patterns of innervation by monoaminergic fibres. The different actions of noradrenaline on different populations of interneurons might permit reconfiguration of the actions of the commissural neurons according to behavioural context.
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| 10. |
- Jankowska, Elzbieta, et al.
(author)
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Areas of operation of interneurons mediating presynaptic inhibition in sacral spinal segments.
- 2000
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In: Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale. - : Springer Science and Business Media LLC. - 0014-4819. ; 133:3, s. 402-6
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Journal article (peer-reviewed)abstract
- Sources of primary afferent depolarization (PAD) of skin afferents in the sural (Sur) nerve and of group-II muscle afferents in the posterior biceps and semitendinosus (PBST) nerve were compared at several sites, about 2 mm apart, within the L7-S2 segments in order to define areas of projection of sacral interneurons mediating PAD of these afferents. Just rostral to the pudendal nucleus, strong PAD of Sur afferents was evoked by stimulation of skin nerves, while stimulation of muscle nerves had only marginal effects. This indicates that sacral PAD interneurons co-excited by skin and muscle afferents operate primarily within the regions overlying the pudendal nucleus. Furthermore, PAD evoked by muscle afferents was weaker over the rostral part of the pudendal nucleus than over the caudal part of this nucleus, where hamstring afferents became its main source, both in Sur and in PBST group-II afferents. By correlating the relative strength of PAD at the levels of the rostral and caudal parts of the pudendal nucleus with the previously established input from muscle and cutaneous afferents to interneurons at these levels, it is therefore proposed that sacral PAD interneurons operate over shorter distances than indicated by previous experiments: over either rostral or caudal parts of the pudendal nucleus, i.e., about 2 mm, rather than over the whole length of this nucleus, i.e., 4-5 mm. Sacral PAD interneurons may, thus, modulate synaptic transmission to even more spatially restricted neuronal populations than previously proposed.
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