The boundary of proximal hindlimb representation in the dorsal horn following peripheral nerve lesions in cats: a reevaluation of plasticity in the somatotopic map.

Abstract

Some investigators have reported that deafferentation markedly alters the somatotopic organization of the dorsal horn in adult mammals, whereas others, including the present investigator, have not. Failure to observe changes in somatotopy might be attributable to insufficient deafferentation, inadequate sampling, limitation of the observations to a population of neurons that does not exhibit the phenomenon, or a variety of technical factors. The most striking changes in somatotopy have been reported following total deafferentation of the medial dorsal horn by sciatic and saphenous nerve lesions (Devor and Wall, 1981a; Lisney, 1983). The present study was an attempt to replicate this result to determine which explanations might account for the failure of some earlier investigations to observe changes in somatotopic organization. Other variables to be considered include type of anesthesia, type of electrode, and mapping and reconstruction procedures. The somatotopic organization of the lumbar dorsal horn in the adult cat was examined ipsilateral to sciatic and saphenous nerve lesions at postoperative survival times of 1-98 days. Half of these experiments were performed using chloralose anesthesia and half using pentobarbital. Microelectrodes were used to record single and multiunit activity in transverse rows of penetrations across the dorsal horn of L6 and adjacent segments. The results of these experiments were compared with data taken from dorsal horns ipsilateral to intact nerves. Sciatic and saphenous nerve lesions completely abolished dorsal horn neuronal responses to foot and toe stimulation at all survival times, yet there was no significant shift of proximal hindlimb representation into the medial dorsal horn following these lesions at any survival time. It is suggested that the method of anatomical reconstruction of recording sites used by investigators reporting such changes might best explain their findings.