Physiological Properties of the Spinal Dorsal Horn Cells Receiving Ventral Root Afferent Inputs in the Cat

Abstract

Spinal dorsal horn neurons receiving ventral root afferent inputs were studied in cats anesthetized with a -chloralose. The L7 and S1 spinal ventral roots were stimulated electrically, and after identifying the evoked single cell activities, their receptive fields, cell types and peripheral nerve inputs were determined. Followings are the results obtained. 1. A total of 43 cells receiving ventral root afferent inputs were identified. These were located in lamina IV-VI of the spinal cord. More than half of them were silent or showed spontaneous discharge less than 5 Hz during the resting period. The remaining units discharged spontaneously in the range of 10-20 Hz. 2. In 23 cells, the cell types were determined according to the responses to graded mechanical stimulation applied to receptive fields. Eleven cells were HT cells and seven were WDR cells. 3. All these cells were activated by C-intensity stimulation but not by A0 -stimulation of the ventral roots, while their main peripheral nerve inputs were A0 -inputs. 4. Intravenous morphine inhibited the reponses of these cells to VR stimulation, and naloxone reversed the morphine effect. From the above results it was concluded that afferent inputs carried by the VRA fibers might be associated with still unknown pain pathways.