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- Jankowska, Elzbieta, et al.
(författare)
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Disynaptic inhibition of spinal motoneurones from the motor cortex in the monkey.
- 1976
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 258, s. 467-487
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Tidskriftsartikel (refereegranskat)abstract
- 1. The neuronal mechanism of disynaptic inhibition of spinal motoneurones by the corticospinal tract was investigated in Macaca irus. Surface stimulation or weak intracortical stimulation was used in order to evoke the inhibition. Intracellular records were taken from motoneurones in lumbar segments. 2. Both the disynaptic i.p.s.p.s evoked from group Ia afferents and the disynaptic i.p.s.p.s evoked from corticospinal fibres were found to be depressed by conditioning stimulation of motor axons to antagonistic muscles. Mutual facilitation of the actions from these two fibre systems occurred when nerve impulses set up in them reached the explored spinal segment synchronously. These observations led to the conclusion that disynaptic i.p.s.p.s from group Ia afferents and from the motor cortex are mediated by common interneurones. 3. No evidence either for or against projections of the same pyramidal tract cells to motoneurones of one motor nucleus and to interneurones interposed between group Ia afferents and motoneurones of an antagonistic muscle could be obtained by comparing cortical areas from which monosynaptic e.p.s.p.s and disynaptic i.p.s.p.s were evoked in the different motor nuclei. 4. The areas from which the disynaptic i.p.s.p.s were evoked in individual motoneurones appeared to be similar in size to the areas of cortical monosynaptic projections to motoneurones and showed similar degrees of overlap, indicating that the projections of pyramidal tract cells to Ia inhibitory interneurones are as extensive as to motoneurones and that they are similarly organized. © 1976 The Physiological Society
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| 2. |
- Jankowska, Elzbieta, et al.
(författare)
-
Projections of pyramidal tract cells to alpha‐motoneurones innervating hind‐limb muscles in the monkey.
- 1975
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 249, s. 637-667
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Tidskriftsartikel (refereegranskat)abstract
- 1. We have investigated the spatial organization of monosynaptic corticospinal projections to hind‐limb motoneurones, using near threshold stimulation of the surface of the precentral gyrus to activate pyramidal tract (PT) cells and intracellular recording from motoneurones to detect the resulting e.p.s.p.s. 2. Monosynaptic e.p.s.p.s. of cortical origin were seen in all motoneurone species investigated, those of distal as well as of proximal hind‐limb muscles. The proportion of motoneurones in which the e.s.p.s. were evoked and the amplitudes of the latter indicated a more extensive cortical projection to motor nuclei for distal than for proximal muscles, as previously found for forelimb motoneurones. 3. Cortical areas from which monosynaptic e.p.s.p.s. were evoked in individual motoneurones were remarkably large, most often between 3 and 7 mm2. Several motoneurones appeared to have two or three separate areas within the hind‐limb division of the motor cortex. 4. Areas of location of pyramidal tract cells projecting to various motoneurones innervating one muscle were usually not identical. They overlapped often only partially or did not overlap at all. 5. Areas of location of pyramidal tract cells projecting to motor nuclei for different muscles often showed an extensive overlap. When it occurred, various motoneurones of a given motor nucleus had common cortical projection areas with motoneurones of other motor nuclei, either to synergistic or to antagonistic muscles. Our results give further evidence for overlapping of areas of cortical projections to motoneurones and speak against a mosaic‐like organization of pyramidal tract cells projecting to different motor nuclei. 6. The rise times of cortically evoked e.p.s.p.s. indicate that the corticospinal tract fibres terminate on motoneurones at approximately similar distances from the soma as group Ia afferents. The small amplitudes of the majority of e.p.s.p.s. evoked by near threshold cortical stimulation therefore suggest that unitary e.p.s.p.s of cortical origin are small and that the density of pyramidal tract cells projecting to individual motoneurones is usually low, even in the centrum of projection areas. 7. Effects of intracortical stimulation depended on the stimulus strength. With currents of 2‐3 muA, e.p.s.p.s were usually evoked in one motoneurone species or in close synergists. With currents of 5‐10 muA, largest e.p.s.p.s a number of other motoneurones. Latencies of descending volleys in the lumbar corticospinal tract indicated that intracortical stimuli activated pyramidal tract cells indirectly; the effects of these stimuli could thus not be used to indicate the location of pyramidal tract cells responsible for them. © 1975 The Physiological Society
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| 3. |
- Jankowska, Elzbieta, et al.
(författare)
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The mode of activation of pyramidal tract cells by intracortical stimuli.
- 1975
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 249, s. 617-636
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Tidskriftsartikel (refereegranskat)abstract
- 1. Direct and indirect effects of intracortical stimulattion on pyramidal tract cells were compared in the monkey and in the cat under barbiturate or chloralose anaesthesia. The hind‐limb motor areas were explored, that in the monkey only within the convex part of the precentral gyrus. The intracortical stimuli were applied in the nearest vicinity of pyramidal tract cells, where antidromic spike potentials of single cells were recorded. 2. Average records of descending volleys in corticospinal tract fibres were taken from the surface of the lateral funiculus or from its dissected fascicles. The sensitivity of the recording was sufficient to detect responses in single fibres. 3. The latencies of the earliest descending volleys evoked by weak intracortical stimuli were compared with the latencies of the antidromic spike potentials of pyramidal tract cells evoked by stimulation of the lateral funiculus at a low lumbar level (same conduction distance). Only in about one third of cases these latencies were similar and compatible with a direct activation of pyramidal tract cells. In the remaining cases they indicated mono‐ or polysynaptic activation of pyramidal tract cells. 4. Latencies of the later components of the descending volleys indicated that they were due to indirect activation of pyramidal tract cells in practically all cases. 5. The components of the descending volleys attributable to the indirect activation of pyramidal tract cells were greatly increased when repetitive intracortical stimuli were applied instead of single ones. 6. The investigation leads to the conclusion that a weak intracortical stimulation is relatively ineffective in a direct excitation of pyramidal tract cells and that the effects of such a stimulation are mainly indirect, especially when repetitive stimuli are used. © 1975 The Physiological Society
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