Properties of Clarke's Column Neurones

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164

SUMMARY1. The properties of interneurones located in the 4th lumbar segment of the cat spinal cord (L4 interneurones) have been investigated by intracellular and extracellular recording from individual neurones. The study focused on interneurones projecting to hind-limb motor nuclei and/or interposed in pathways from group II muscle afferents. The projection to motor nuclei was assessed from antidromic activation of the neurones by stimuli applied in the motor nuclei of the 7th lumbar (L7) segment.2. Interneurones which projected to gastrocnemius-soleus or hamstring motor nuclei were found in laminae VI and VII and at the border between laminae VII and VIII. The dominant peripheral input to most of them was from group II muscle afferents, but they were also influenced by group I muscle afferents and by afferents in cutaneous, joint and interosseous nerves. Both excitatory post-synaptic potentials (e.p.s.p.s) and inhibitory post-synaptic potentials (i.p.s.p.s) were evoked from all of these fibre systems.3. The same kind of multimodal input was also found in other interneurones in laminae VI and VII. However, their axonal projections were not identified and they might have included neurones projecting to motor nuclei (though outside the areas which were stimulated) as well as neurones with more local actions.4. Interneurones located in laminae IV and V of the dorsal horn appeared to constitute a separate functional population since both their projections and their input differed from those of the more ventrally located interneurones; none of the dorsal horn interneurones were found to project to motor nuclei and none had input from group I afferents, although they were influenced by group II muscle afferents and by afferents in cutaneous, joint and interosseous nerves.5. Many of the excitatory actions from group I and II afferents upon L4 interneurones were found to be evoked monosynaptically. A high proportion of L4 neurones synapsing upon motoneurones would thus be interposed in disynaptic reflex pathways from these afferents. In comparison to actions evoked via interneurones of the caudal lumbar segments, any post-synaptic potentials (p.s.p.s) * Present address:

Section: Preparationmentioning

confidence: 99%

An interneuronal relay for group I and II muscle afferents in the midlumbar segments of the cat spinal cord.

Edgley

Jankowska

1987

215

164

“…in firing regulation it is also necessary to know how the a.h.p.s of successive spikes interact. It has previously been demonstrated (Eide, Fedina, Jansen, Lundberg & Vyklicky, 1969;Kuno, Miyahara & Weakly, 1970) that the a.h.p. in DSCT neurones, at high frequency activation, increases with an increasing number of spikes.…”

Section: Introductionmentioning

confidence: 99%

“…conductance, leads to a linear steady state frequency-current relationship (see Gustafsson et al 1978b). This would seem appropriate for a relay cell such as the DSCT neurone (Eide et al 1969). The depression will cause a small or even negative initial adaptation (Gustafsson et al 1978b), which would presumably be disadvantageous for the muscle contraction.…”

mentioning

confidence: 99%

Effect of repetitive activation on the afterhyperpolarization in dorsal spinocerebellar tract neurones.

Gustafsson¹,

Zangger²

1978

1. The changes in the afterhyperpolarization (a.h.p.) with repetitive activation have been studied in dorsal spinocerebellar tract cells of the cat using intracellular recording techniques. 2. The a.h.p. following a single spike was conditioned at different interspike intervals by a single preceding spike. In the majority of neurones the a.h.p. following a spike added approximately linearly with that generated by a preceding spike. 3. In other cells the a.h.p. following a spike was instead depressed by a preceding spike. THis depression was approximately constant at interspike intervals less than the a.h.p. duration (50‐100 msec). Thereafter the a.h.p. slowly recovered during the next 100‐300 msec. There was no associated decrease in the initial brief hyperpolarizing undershoot. 4. With shortlasting repetitive activation at high frequency (greater than 100 impulses/sec) the a.h.p, peak amplitude increased progressively with successive spikes (5‐15 spikes). No change in the time constant of decay was observed. A good correspondence was found between the observed increase in peak amplitude of the a.h.p.s and that given by a theoretical linear superposition of the successive a.h.p.s. 5. Changes in the brief hyperpolarizing undershoot with repetitive activation is also described.

“…cells, for their identification by antidromic activation, and rubrospinal tract fibres, for adjusting location of an electrode in the red nucleus according to antidromic field potentials. In the cats in which no lesions were made at the level of the lumbar cord (referred to as intact preparations), small holes were made in the dura over areas of the ipsilateral dorsal funiculus which were free from blood vessels (Eide et al 1969). Through these holes pia was torn away before micro-electrodes were inserted.…”

Section: Introductionmentioning

confidence: 99%

Inhibition of dorsal spinocerebellar tract cells by interneurones in upper and lower lumbar segments in the cat.

Hongo¹,

Jankowska²,

Ohno³

et al. 1983

3. 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 transacted dorsal funiculi. The marked cells were found in L5, L6, L7 and SI segments, with a highest density in L6 and L7. They were seen in laminae V, VI and VII. 4. 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.