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E Jankowska

Publications and source records attributed to E Jankowska.

At least 163 records · Page 9Linked to original sources
PubMed1975

The mode of activation of pyramidal tract cells by intracortical stimuli.

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.

Animals↗
PubMed1975

Projections of pyramidal tract cells to alpha-motoneurones innervating hind-limb muscles in the monkey.

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.

Animals↗
PubMed1975

Cortical motor representation in view of recent experiments on cortico-spinal relations.

The results of recent experiments using either intracortical stimulation or stimulation of the surface of the motor cortex were reviewed from the point of view of "muscle" and "movement" cortical representation. It has been concluded that there is no satisfactory evidence for location of the pyramidal tract (PT) cells which project directly (monosynaptically) to motoneurones of one muscle in primates within small and separate cortical areas; such evidence is even weaker for PT cells which exert their effects via polysynaptic pathways in other species. The available evidence shows in contrast a very pronounced overlap of cortical areas of projection to different motor nuclei.

Animals↗
PubMed1972

An electrophysiological demonstration of the axonal projections of single spinal interneurones in the cat.

1. Single interneurones excited from group Ia afferents and located in the ventral horn of the spinal cord in the cat were activated antidromically by stimulation of their axons with one micro-electrode while recording extracellularly close to their somas with a second micro-electrode. The interneurones studied were those which, according to previous indirect evidence, should mediate the reciprocal Ia inhibition of motoneurones.2. Two subgroups of these interneurones were studied: those excited from group Ia afferents in the quadriceps (Q) and posterior bicepssemitendinosus (PBSt) nerves. Most of them could be activated from a number of separate loci in the PBSt and Q motor nuclei respectively and from the ventral or lateral funiculi.3. The location of the axonal branches and the extent of their branching in the motor nuclei were reconstructed by comparing the latencies of the responses and the thresholds (0.1-5 muA) for antidromic activation of single interneurones from different electrode positions in a number of tracks, having previously established the relation between the threshold and the distance from the stimulated fibres. For the main branches in the white matter the conduction velocity was found to be about 70 m/sec.4. The axonal projections of the investigated interneurones were found to be fully consistent with the hypothesis that they mediate reciprocal inhibition of motoneurones.

Action Potentials↗
PubMed1972

Synaptic actions of single interneurones mediating reciprocal Ia inhibition of motoneurones.

1. The investigation was aimed at defining the function of the interneurones which, according to indirect evidence, mediate the reciprocal Ia inhibition of motoneurones (Hultborn, Jankowska & Lindstrom, 1971 b) by studying their direct synaptic actions. These actions were tested by recording post-synaptic potentials in motoneurones following spike activity of single interneurones activated by iontophoretic application of glutamate. The interneurones were found to produce unitary monosynaptic IPSPs in those motoneurones in which disynaptic IPSPs are evoked by the group Ia afferents which monosynaptically excite the interneurones.2. Unitary IPSPs were found in more than 80% of the motoneurones impaled in the immediate vicinity of the axonal branches of the investigated Q interneurones in the PBSt motor nucleus. It is estimated that each interneurone might inhibit about every fifth PBSt motoneurone. The amplitudes of the unitary IPSPs ranged between 8 and 220 muV and were 10-200 times smaller than the maximal Ia IPSPs evoked in the same motoneurones.3. The synaptic delay in the generation of unitary IPSPs was measured in relation to the spike potentials recorded from the terminal branches of interneurones in the immediate vicinity of the impaled motoneurones. The synaptic delays ranged between 0.28 and 0.42 msec.4. From chloride reversal tests and an analysis of the time course of the unitary IPSPs it was concluded that the terminals of the investigated interneurones make synaptic contact predominantly on the soma and/or on the proximal parts of the dendrites of the motoneurones, their distribution being, however, not quite uniform.

Action Potentials↗