Biochemical Specification versus Specific Regrowth in the Innervation of Skin Grafts in Anurans

Abstract

FROM studies of the reflex responses of the adult animal^1–4, it seems that specification of cutaneous nerves in the anuran tadpole depends on the type of skin innervated. In the frog, Rana pipiens, in which specification does not seem to occur much before the onset of metamorphosis, rotation of large patches of back and belly skin through 180° early in larval development results in the development of white belly skin on the frog's back and dark skin on its belly. If the rotation operations are carried out early enough in larval development, the adult wiping reflex responses seem to be permanently misdirected: stimulation of the belly skin grafts results in wiping reflexes directed towards the animal's belly, whereas stimuli applied to the grafted back skin result in a reflex movement directed towards the animal's back. Tadpoles operated on in such a manner after larval stage XV⁵, however, develop only normal reflex behaviour^2,3. Allowing 6–12 days regeneration time (R. E. B., unpublished), specification must occur at the onset of metamorphosis: stages XVIII–XXI. Local cutaneous nerves grow into the nearest available skin^2–4,6 which has led to the suggestion that the maladaptive reflex behaviour results from central readjustment of synapses according to specification from the peripheral skin.