THE EFFECTS OF NEONATAL MEDIAN NERVE INJURY ON THE RESPONSIVENESS OF TACTILE NEURONS WITHIN THE CUNEATE NUCLEUS OF THE CAT

1. The capacity of cuneate neurones to attain normal functional proper ties following neonatal median nerve injury was investigated with sing le neurone recording in anaesthetized cats, 12-24 months subsequent to a controlled crush injury. Effectiveness of the Peripheral nerve inju ry was confirmed by the abolition of the median nerve compound action potential following the crush. 2. Cuneate recording was carried out af ter denervation of the forearm, apart from the median nerve, to ensure that neurones studied had receptive fields within the distribution zo ne of the regenerated median nerve. Controlled and reproducible tactil e stimuli were used to evaluate the functional capacities of neurones to determine whether they were consistent with those reported earlier for cuneate neurones in cats that had normal peripheral nerve developm ent. 3. Twenty-two cuneate neurones with well-defined tactile receptiv e fields within the distribution zone of the regenerated median nerve were classified according to their adaptation characteristics and func tional properties. Slowly adapting: neurones responded throughout stat ic skin indentations and had graded and approximately linear stimulus- response relations over indentation ranges up to 1.5 mm. Rapidly adapt ing neurones responded to the dynamic phases of skin indentations and could be divided into two broad classes, one most sensitive to vibrota ctile stimuli at 200-400 Hz which appeared to receive a predominant in put from Pacinian corpuscle receptors, and a non-Pacinian group that i ncluded neurones most sensitive to skin vibration at 5-50 Hz which app eared to receive glabrous skin input from the rapidly adapting class o f afferent fibres. 4. Based on the stimulus-response relations and on measures of phase locking in the responses to vibrotactile stimuli, it appears that the functional properties of cuneate neurones activated from the field of a regenerated median nerve subsequent to a neonatal nerve crush injury were consistent with those reported previously for 'control' cuneate neurones. The results indicate that cuneate neurones can acquire normal tactile coding capacities despite the disruption c aused by prior crush injury to their peripheral nerve source.