THE EFFECTS OF NEONATAL DORSAL-ROOT SECTION ON THE SURVIVAL AND DENDRITIC DEVELOPMENT OF LUMBAR MOTONEURONS IN THE RAT

Peripheral nerve crush during the early neonatal period results in the death of a large proportion of affected motoneurons and abnormal dend ritic development in those which survive. The present study reports th e effects of neonatal dorsal root section on motoneurons supplying the extensor digitorum longus muscle of the rat. This lesion did not resu lt in motoneuron death, but did disrupt subsequent dendritic developme nt. In cells retrogradely labelled with cholera toxin subunit B conjug ated to horseradish peroxidase, there was little change in adult dendr itic morphology in the transverse plane, where abnormalities associate d with loss of efferent contact and cell death have been found. Howeve r, there was a caudal expansion of the dendritic field, an effect seen following nerve crush but not after blockade of neuromuscular transmi ssion alone. The results show that disruption of dorsal root sensory i nputs alone can affect the dendritic development of motoneurons but do es not cause their death. In conjunction with our earlier findings, it is clear that both afferent and efferent connections are required for normal dendritic development, and disruption of either has a characte ristic effect on survival and dendritic morphology.