Reinnervation of glabrous skin in baboons: properties of cutaneous mechanoreceptors subsequent to nerve crush

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Abstract
A total of 791 fibers were isolated from the ulnar nerves of 5 baboons [Papio anubis]. Over half of these were obtained from the right ulnar nerves subsequent to reinnervation following a nerve crush; the other fibers were obtained from the undamaged left ulnar nerves. The conduction velocities in the proximal portion of the injured axons dropped below normal, and this reduction persisted until reinnervation appeared nearly complete. The response properties of 65 cutaneous afferent fibers serving reinnervated glabrous skin were compared to 80 fibers from normal skin. Of the afferent fibers reinnervating skin, the proportion judged to have abnormal response properties was not significantly greater than the proportion in normal skin. After reinnervation, cutaneous rapidly adapting fibers displayed tuning curves characteristics of their submodality, while some cutaneous slowly adapting fibers could still be differentiated into type I and type II fibers. Both types of slowly adapting fibers displayed an increased rate of adaptation and a lowered sensitivity to sustained displacements even at 5 mo. following reinnervation. The cutaneous mechanoreceptors in reinnervated glabrous skin regained response properties that allowed them to be assigned to the same submodalities found in normal skin. Submodality was recognizable at an early stage when receptive field was still immature and when the threshold was elevated. With time, the receptive-field sizes and shapes returned to normal, the thresholds approached normal, and the remaining differences from normal cutaneous afferent fibers became minor.