| 1. |
- Edgley, S. A., et al.
(författare)
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Evidence that mid‐lumbar neurones in reflex pathways from group II afferents are involved in locomotion in the cat.
- 1988
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 403, s. 57-71
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Tidskriftsartikel (refereegranskat)abstract
- 1. A group of interneurons in the mid‐lumbar segments of the cat spinal cord which mediate disynaptic excitation or inhibition of motoneurones from group II muscle afferents have recently been described. To test the possibility that the activity of these interneurones is related to the activity in the neuronal networks which subserve locomotion we have investigated whether they are influenced by two procedures which can induce locomotion. These procedures were electrical stimulation within the cuneiform nucleus (the ‘mesencephalic locomotor region’) in anaesthetized preparations and systemic administration of 3,4‐dihydroxyphenylalanine (DOPA) in decerebrate, spinalized, unanaesthetized preparations. The interneurones we have tested were located in the fourth lumbar (L4) segment and were excited by group II muscle afferents; more than half of them were antidromically activated from the hindlimb motor nuclei. 2. Stimuli applied in the cuneiform nucleus evoked excitatory postsynaptic potentials (EPSPs) in a high proportion of these interneurones. The stimuli also evoked distinct extracellular field potentials in the ventral horn of the L4 segment. The properties and latencies of both the intra‐ and extracellularly recorded potentials show that they were evoked disynaptically, via supraspinally located relay neurones and a fast‐conducting descending tract. 3. Stimulation of the cortico‐ and rubrospinal tracts excited or inhibited some of the L4 neurones, often at latencies suggesting mono‐ or disynaptic coupling. The neurones which appeared to be monosynaptically excited from the cortico‐ and rubrospinal tracts tended to be located dorsal to the neurones which were activated from the cuneiform nucleus. 4. Systemic administration of DOPA depressed the responses evoked by stimulation of group II afferents of L4 interneurones which projected to motor nuclei. DOPA also depressed extracellular field potentials evoked by group II afferents in the intermediate zone and in the ventral horn (at the location of the interneurones) but hardly affected those in the dorsal horn. 5. By showing that both stimulation in the cuneiform nucleus and the administration of DOPA influence activity of L4 interneurones which are excited by group II afferents and which project to motor nuclei, the results of this study support the hypothesis that these neurones are in some way involved in locomotion. However, the opposing effects of DOPA administration and of stimulation in the cuneiform nucleus make the interpretation of their role in locomotion rather difficult before it is known to what extent they are active throughout the step cycle. © 1988 The Physiological Society
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| 2. |
- Cavallari, P., et al.
(författare)
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Post‐synaptic actions of midlumbar interneurones on motoneurones of hind‐limb muscles in the cat.
- 1987
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 389, s. 675-689
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Tidskriftsartikel (refereegranskat)abstract
- 1. The hypothesis that interneurones in the 4th lumbar segment (L4) are interposed between group I and group II afferents and hind‐limb motoneurones has been tested. Action potentials of single interneurones were induced by ionophoretically applied homocysteate and recorded in parallel with post‐synaptic potentials in motoneurones; the latter were recorded from motor axons in the ventral root of the first sacral segment as population potentials, using the sucrose gap technique. 2. The action potentials of twenty‐four L4 interneurones were found to be followed by either e.p.s.p.s. or i.p.s.p.s in motoneurones. The latencies of the majority of these p.s.p.s were consistent with monosynaptically evoked excitation or inhibition of motoneurones since they exceeded the latencies of antidromic activation of the interneurones from the S1 motor nuclei by only a fraction of a millisecond. 3. The dominant input to both the excitatory and the inhibitory interneurones was from group II muscle afferents, in particular from the quadriceps nerve. The latencies of excitation of the interneurones by these afferents indicated a monosynaptic coupling between them. The same interneurones were co‐excited by group I and cutaneous afferents and by descending fibres. 4. We conclude that not only excitation but also inhibition of hind‐limb motoneurones from group II afferents may be mediated disynaptically and that interneurones in the 4th lumbar segment contribute to both. © 1987 The Physiological Society
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| 3. |
- Edgley, S. A., et al.
(författare)
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An interneuronal relay for group I and II muscle afferents in the midlumbar segments of the cat spinal cord.
- 1987
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 389, s. 647-674
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Tidskriftsartikel (refereegranskat)abstract
- 1. 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) evoked via L4 interneurones would be delayed. These delays would amount to 0.4‐0.9 ms for p.s.p.s. from group I afferents and by 0.5‐2.5 ms for group II p.s.p.s. 6. In many interneurones, particularly those located ventrally, i.p.s.p.s. were evoked by group I and II muscle afferents at latencies which indicated that they were evoked disynaptically. They may therefore reflect inhibitory interactions between subpopulations of L4 interneurones.(ABSTRACT TRUNCATED AT 400 WORDS) © 1987 The Physiological Society
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| 4. |
- Edgley, S. A., et al.
(författare)
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Field potentials generated by group II muscle afferents in the middle lumbar segments of the cat spinal cord.
- 1987
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 385, s. 393-413
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Tidskriftsartikel (refereegranskat)abstract
- 1. A powerful projection from group II muscle afferents of hind‐limb muscles to the 3rd, 4th and 5th segments of the lumbar spinal cord has been demonstrated by focal synaptic field potential recording. 2. Field potentials were found at two locations: one in the dorsal horn (Rexed's laminae IV and V) and the other in the intermediate zone and ventral horn (Rexed's laminae VII and VIII). In the dorsal horn the field potentials were exceptionally large and were evoked only by group II afferents. At more ventral locations, they were smaller and were sometimes preceded by small field potentials evoked by group I afferents. 3. At both locations field potentials could be evoked by stimulation of a number of hind‐limb muscle nerves at strengths sufficient to activate group II afferents. However, some nerves consistently evoked more powerful effects than others and the largest potentials were from the nerves to quadriceps, sartorius and to the pretibial flexor muscles (tibialis anterior and extensor digitorum longus). Activation of articular afferents (from the knee joint nerve) or Pacinian corpuscle afferents (from the interosseous nerve) evoked small field potentials at some locations. 4. In the dorsal horn the latency of the field potentials was so short that they must have been generated monosynaptically. Field potentials in the ventral horn had longer latencies, by 0.5‐1.0 ms, but they also appear to have been monosynaptically evoked by slowly conducting intraspinal collaterals. This conclusion is based primarily on the effects of intraspinal stimulation which was found to antidromically activate afferents with the appropriate latencies and thresholds. 5. Evidence is presented that the dorsal and ventral field potentials are generated by afferents whose receptors can be activated by small (less than 100 micron) muscle stretches. © 1987 The Physiological Society
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| 5. |
- Edgley, S. A., et al.
(författare)
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Information processed by dorsal horn spinocerebellar tract neurones in the cat.
- 1988
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 397, s. 81-97
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Tidskriftsartikel (refereegranskat)abstract
- 1. A group of spinocerebellar tract neurones located in the dorsal horn of the mid‐lumbar segments of the spinal cord but outside of Clarke's column have been investigated by intracellular and extracellular recording from their somata. The existence of these neurones has been demonstrated previously using anatomical methods, but their properties have not been investigated in detail. In contrast to the cells of Clarke's column, these neurones were found to process information from both exteroceptors and proprioceptors. 2. All of the investigated neurones were powerfully excited following stimulation of muscle nerves at strengths sufficient to activate group II afferents while there was no evidence for actions from group I afferents onto any of them. Most were excited by group II afferents from many different nerves, including those from muscles acting on different joints. The latencies and properties of the excitatory postsynaptic potentials (EPSPs) suggest that at least a large proportion of them were monosynaptically evoked. 3. All of the neurones were powerfully excited following electrical stimulation of cutaneous afferents. The most potent effects were evoked from the saphenous and sural nerves which innervate the skin of the leg and thigh. In many cases these EPSPs had latencies indicative of a monosynaptic connection. The superficial peroneal and tibial nerves which innervate the skin of the foot evoked EPSPs which were usually smaller and of longer latency. 4. Responses to adequate stimulation of cutaneous afferents were examined in twenty extracellularly recorded neurones. All but one of them could be discharged by weak mechanical stimulation of the skin over the proximal part of the leg and thigh. None were activated from the skin of the foot. 5. Some of the neurones were influenced by stimulation of the posterior knee joint or interosseous nerves. These actions were relatively weak, however, suggesting that the powerful effects seen on stimulation of muscle nerves were unlikely to have been mediated by articular or Pacinian afferents which contaminate them. 6. Excitation from group II afferents was sometimes followed by inhibition (in 27% of the neurones). In almost all cases the inhibitory postsynaptic potentials (IPSPs) were evoked from the same nerves which evoked EPSPs. The minimal latencies of the IPSPs were approximately 1.0 ms longer than those of the EPSPs, suggesting that they were evoked disynaptically. 7. The possibility that these neurones provide information regarding limb position is discussed. © 1988 The Physiological Society
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