Responses of dorsal horn cells of Gallus domesticus to cutaneous and peroneal nerve stimuli

Single dorsal horn neurons have been recorded extracellularly in the lumbar spinal cord of chickens anesthetized with sodium pentobarbital and anemically decerebrated. The location of units in the dorsal horn was marked by the electrophoretic deposition of fast green dye from the recording electrode. Seventy percent of 125 units studied were activated by mechanical, thermal, and/or electrical stimulation. Thirty percent were responsive only to electrical stimulation of the ipsilateral peroneal nerve. Some units fired spontaneously with brief bursts of 2 to 4 spikes per burst with varying interburst intervals. Frequently, spontaneously firing units could be inhibited by noxious pinch on the distal region of the comb. Chicken dorsal horn cell responses bear some resemblance to those of mammals, though with certain differences. Some may fire spontaneously in an irregular manner and show properties of convergence. Continuous background activity was uncommon in cells that were excited exclusively by electrical stimulation. Evidence of a prolonged discharge was apparent when the peroneal nerve was stimulated at A-Δ intensity. A progressive increase in frequency and duration of discharge with controlled repetitive C-fiber stimulation, i.e., “windup”, was nerver seen. Several units responded to restricted feather movement. There was no physiological evidence of identifiable zones of concentration of dorsal horn cells in the various laminae (IV to VI) investigated. The present studies provide physiological evidence that supraspinal descending influences are capable of modulating afferent input from chicken dorsal horn cells. The data further suggest that the filtering effect of dorsal horn cells is seen early in phylogeny. The results are described with reference to similarities to and differences from mammalian dorsal horn cell responses.