Effects of an augmented nerve supply on forelimb regeneration in the adult mud frog, Rana rugosa.

Forelimbs of the adult mud frog Rana rugosa, when amputated midway through the zeugopodium, regenerate heteromorphically. The resulting regenerative outgrowths were mostly rod shaped and consisted of a cartilaginous core, in which the base was ossified, and muscle elongated distally along the cartilage, the whole being covered by connective tissue and skin. The tip of the regenerating muscle reached a point distally about one third of the length of the regenerative outgrowths. When the innervation of forelimb stumps was augmented by surgical diversion of the ipsilateral sciatic nerve, the amputated limbs regenerated mostly as spatula-shaped outgrowths, which were longer than those of normally innervated forelimbs. Such hyperinnervated regenerates exhibited less ossification of cartilage, or sometimes none at all. However, the regeneration of muscle was more extensive. That is, it reached more than half way along the regenerative outgrowth. Furthermore, denervation resulted in the absence of regeneration in all cases examined. These results clearly indicate that limb regeneration in Rana rugosa is dependent upon the degree of innervation, not only for the early stages of regeneration, but also for the growth and differentiation of the regenerative outgrowth.