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- Asanuma, H., et al.
(författare)
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Projection of individual pyramidal tract neurons to lumbar motor nuclei of the monkey
- 1979
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Ingår i: Experimental Brain Research. - 0014-4819 .- 1432-1106. ; 34, s. 73-89
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Tidskriftsartikel (refereegranskat)abstract
- The projection of individual pyramidal tract (PT) neurons from the hindlimb area in the precentral gyrus of the cerebral cortex to the lumbar spinal cord was studied in the monkey by systematically searching for sites within identified regions of the spinal gray from which the PT neurons could be antidromically activated by local stimulation. All investigated neurons belonged to the fast conducting fraction of PT neurons. The following results were obtained. 1. Each PT neuron could be activated from more than one region of the spinal gray matter, including identified spinal motor nuclei and areas dorsomedial to these nuclei, but not the intermediate nucleus or regions dorsal to it. "Passage areas" and "termination areas" were defined. 2. Half of the PT neurons with termination areas within motor nuclei had these areas in more than one nucleus. There were thus strong suggestions for synaptic contacts of some PT neurons with motoneurons of more than one muscle. 3. Four groups of three or four neurons were recorded simultaneously by the same cortical electrode. Comparisons of passage and termination areas within groups revealed both similarities and differences in projections of neighboring neurons. Every neuron was activated from some region(s) where others of the group were not. Common passage areas, or passage and termination areas, for two or three neurons of a group within at least one motor nucleus were found for all groups. Termination areas in the same motor nucleus have been found for the majority of the neurons of only one group. These common projection areas are compatible with, but do not prove, that a group of adjacent PT neurons has common target cells in the spinal cord. © 1979 Springer-Verlag.
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- Hongo, T., et al.
(författare)
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Inhibition of dorsal spinocerebellar tract cells by interneurones in upper and lower lumbar segments in the cat.
- 1983
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 342, s. 145-159
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Tidskriftsartikel (refereegranskat)abstract
- The topographical distribution of interneurones mediating disynaptic inhibition of dorsal spinocerebellar tract (d.s.c.t.) cells from group I muscle afferents in the cat was investigated using both physiological and morphological techniques. Lesions of either the dorsal funiculi or of the lateral and ventral funiculi were made between L4 and L5 segments in two groups of cats. I.p.s.p.s. evoked from group I afferents were seen after both these lesions, showing that the i.p.s.p.s were evoked by interneurones located more caudally as well as by interneurones in the same segments as Clarke's column. Distribution of the caudally located interneurones in the lower lumbar segments was investigated after marking these interneurones with horseradish peroxidase retrogradely transported from Clarke's column. The horseradish peroxidase was injected along L3‐L4 segments of Clarke's column in two cats with transected dorsal funiculi. The marked cells were found in L5, L6, L7 and S1 segments, with a highest density in L6 and L7. They were seen in laminae V, VI and VII. A search was made for interneurones which could be antidromically invaded following stimuli applied in Clarke's column and were monosynaptically excited by group I afferents. Such interneurones were found at locations corresponding to laminae V‐VI of Rexed. The latencies of antidromic and orthodromic responses were within ranges allowing them to mediate disynaptic inhibition of d.s.c.t. cells. © 1983 The Physiological Society
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- Hongo, T., et al.
(författare)
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The same interneurones mediate inhibition of dorsal spinocerebellar tract cells and lumbar motoneurones in the cat.
- 1983
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 342, s. 161-180
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the study was to investigate whether inhibition of dorsal spinocerebellar tract (d.s.c.t.) cells evoked from group I afferents is mediated by the same interneurones which mediate the non‐reciprocal inhibition of hind‐limb motoneurones. The origin of inhibition of d.s.c.t. cells from group I afferents was compared in intact preparations, after lesions of the dorsal funiculi (when it could only be mediated by lower lumbar interneurones) and after lesions of the lateral and ventral funiculi (when it would be expected to be evoked by upper lumbar interneurones). In all three preparations extensors were the most common source of inhibition, as in motoneurones. Lower lumbar interneurones inhibiting d.s.c.t. cells were found to be co‐excited by group I (Ia and/or Ib) and cutaneous and joint afferents, and by rubrospinal tract fibres, as are interneurones mediating inhibition of motoneurones. Co‐excitation by group I and rubrospinal fibres was also found for upper lumbar interneurones. I.p.s.p.s were evoked in hind‐limb motoneurones from within Clarke's column in cats with the dorsal funiculi cut between L4 and L5 segments; they were evoked at thresholds as low as 2 microA, i.e. by stimuli with very local actions. The latencies of these i.p.s.p.s were short enough to allow them to be evoked monosynaptically via axonal branches of the same interneurones which projected to Clarke's column. Correspondingly, i.p.s.p.s were evoked in d.s.c.t. cells from within motor nuclei in L7 segments; they were evoked at similarly low thresholds and with similar latencies. In confirmation of previous reports i.p.s.p.s of Ia origin evoked in d.s.c.t. cells were not found to be depressed by Renshaw cells, which excludes their mediation by interneurones responsible for Ia reciprocal inhibition. The study leads to the conclusion that the inhibition of d.s.c.t. cells from group I afferents is, at least in part, collateral to the non‐reciprocal inhibition of lumbar motoneurones. © 1983 The Physiological Society
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