Inputs to spinocerebellar tract neurones located in stilling's nucleus in the sacral segments of the rat spinal cord.

Spinocerebellar neurones located in the sacral segments of the rat spinal cord have been identified electrophysiologically. The neurones studied were located 0.7-1.1 mm deep to the cord dorsum, lateral and dorsal to the central canal in the medial part of lamina VII. Neurones were identified as spinocerebellar by antidromic activation from the cerebellar surface, the lowest threshold stimulation sites being near the midline on the posterior lobe vermis (lobule VIII). Estimates of conduction velocities of the axons ranged from 15-32 m/s (mean 22.8 m/s) and are directly comparable to velocities of presumed ventral spinocerebellar tract neurones recorded in the same animals. In intact animals, activity was most strongly influenced by passive movement of the tail. Activation by proprioceptors was confirmed with nerve stimulation: all of the neurones studied were discharged by stimulation of nerves which innervate ipsilateral tail muscles. In many cases responses appeared close to the threshold of the nerve, indicating that the largest, fastest conducting afferents (group Ia muscle spindle primary afferents) were responsible for them. Latencies of EPSPs or spikes were brief and in many cases indicative of a monosynaptic connection. We conclude that this group of neurones is powerfully and monosynaptically excited by group I muscle afferents and thus resemble the cells of Clarke's column and cells of the central cervical nucleus, both of which occupy a similar location in the grey matter of more rostral segments.