The effects of dorsal root lesions on Clarke neurons in cats of different ages

Abstract

AbstractThe transneuronal effects of dorsal root lesions on Clarke neurons in cats of varying ages were studied. Chromatolytic and degenerative lumbar Clarke neurons were observed 5 to 15 days following dorsal rhizotomy from the lower thoracic to the coccygeal levels in the adult cat. Fiber degeneration was seen in the ipsilateral dorsal and dorsolateral columns in the cervical spinal cord. The finding of fiber degeneration in dorsolateral columns is supportive evidence for the hypothesis that the chromatolytic and neurofibrillar hypertrophic neurons are the result of ischemic myelopathy or direct surgical trauma to the lateral columns during the dorsal root surgery. Within 15 days post‐operatively, degenerative changes were not seen in lumber Clarke neurons when the dorsal root lesions were begun at the L 4 level.The effects of dorsal root lesions at different ages with an increased postoperative survival period were studied. Unilateral dorsal rhizotomies were done beginning at the L 4 level in kittens of two, four, and six weeks of age and adult cats. The degree of mean perikaryal and nuclear shrinkage in Clarke neurons was determined from Nissl preparations after these cells were partially denervated. The kittens of each age group showed approximately the same area reduction, and the adult cats did not show this shrinkage. It is deduced that the differentiation of Clarke neurons is almost completed by two weeks of age and that partial dorsal root denervation causes an arrest of growth rather than a transneuronal atrophy.