Dorsal horn cells that respond to stimulation of distant dorsal roots (cat)

Abstract

Post-synaptic effects produced by impulses in the long ranging primary afferents, shown by Wall and Werman to extend from upper lumbar dorsal roots to the sacral segments, were studied. Dorsal rootlets were stimulated in decerebrate low-spinal adult cats. The dorsal root potential and ventral root reflex were recorded on S1 root filaments, in response to stimulation of dorsal rootlets extending from L1 to S1. With increasing distance between stimulating and recording segments, these potentials became smaller and more delayed. In 2 animals, there was no response at S1 to stimulation of L1 and L2 dorsal roots. In all animals, stimulation of L3 or L4 dorsal roots produced cell responses in dorsal horn segments L7 or S1. The density of such cells was variable, from animal to animal. Responding cells were mainly concentrated laterally in the dorsal horn. The latency and response variability of L7-S1, dorsal horn cells to L3-L4 stimulation was consistent with at least some of them being fired monosynaptically. Cells that responded to stimulation of 1 distant rootlet also responded to many closer rootlets. The receptive fields of L7-S1 dorsal horn cells, responsive to stimulation of L3-L4 rootlets, were typical of those generally found in the L7-S1 segments, and were at some distance from the L4 dermatome. Only 20 cells had receptive fields which extended into the dermatome of the rootlets stimulated. Some L4 cells responded to S1 dorsal root stimulation, just as the main study showed that S1 responded to L4. Substantial numbers of dorsal horn cells, including cells with many types of cutaneous receptive field, apparently respond to 2 classes of synaptic in-put: 1 effective in firing the cell upon natural cutaneous stimulation, and 1 relatively ineffective, capable of driving the cell only when stimulated electrically and thus carrying a synchronous volley from a number of highly convergent axons. The contribution of this secondary afferent channel to normal and pathological cord physiology must now be determined.