Neurophysiological and behavioral evidence for selective reinnervation in skin-grafted Rana pipiens

Abstract

Rana pipiens with skin dorosoventrally reversed can respond to stimulation of the back with forelimb wipes to the belly and to stimulation of the belly with hindlimb wipes to the back. These "misdirected wiping responses" have been explained in terms of two alternative hypotheses of nerve regeneration: nerve respecification or selective reinnervation. Experimental behavioral and neurophysiological experiments reported here support the selective reinnervation hypothesis. Severing ventral nerves, which normally innervate the belly, greatly reduced the percentage of misdirected responses on stimulation of belly skin grafted to the back, while severing dorsal nerves, which normally innervate the back, increased the percentage of misdirected responses elicited under the same circumstances. Moreover, neurophysiological recordings of grafted animals showed three effects of skin grafting on nerve distributions: (i) termination of dorsal and ventral nerve receptive field at graft edges; (ii) overlap of nonadjacent ventral nerve receptive fields; and (iii) dorsal coursing of ventral nerves to reinnervate target belly skin displaced to the back. These neurophysiological observations, and particularly the third effect, also support selective reinnervation as the mechanism of nerve regeneration in skin-grafted Rana pipiens.