Cervical and reticular projections of neurones located in S1 and S2 segments of the cat's spinal cord.

Sacral neurones (S1 and S2 segments) projecting to the cervical cord (C6 segment) and to the contralateral gigantocellular reticular nucleus (coGRN) were electrophysiogically studied on 7 adult cats under alpha-chloralose anaesthesia. Antidromic action potentials were recorded from 48 neurones following stimulation of their axons in both the C6 segment and coGRN. Two groups of investigated cells were distinguished in the gray matter of sacral segments: one distributed in laminae V-VI (12 neurones), the other located in medial part of lamina VII and lamina VIII (36 neurones). All cells from the first group projected to C6. The latter group consisted of three types of neurones: projecting to C6 (n = 9), to coGRN (n = 1) as well as to both C6 and coGRN (n = 26). Axons of all identified neurones ran in lateral funiculi ipsilaterally, contralaterally or bilaterally. Conduction velocities were comprised in the ranges 35-81 m/s and 34-70 m/s for neurones projecting to the reticular formation and the cervical spinal cord, respectively. Decrease in conduction velocities was found in some axons in their distal parts suggesting more extensive divergence to various segments in the spinal cord or supraspinal centres.