Stage dependency of forelimb regeneration on nerves in postmetamorphic froglets of Xenopus laevis

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Abstract
A morphological and histological analysis of the response of forelimb regenerates of Xenopus laevis to denervation is presented. Following forelimb amputation, young Xenopus froglets (3 months postmetamorphosis) consistently regenerated cartilagenous, heteromorphic spikes under conditions of normal innervation. Denervation of forelimbs at 1 or 2 weeks prior to amputation had little effect on the progress of regeneration. Denervation of regenerates at various weekly stages resulted in the inhibition or delay of further regenerative responses and in the regression of any regenerate tissues present at the time of the ablation. Specifically, the formation of the blastema, the initiation of differentiation, and the maintenance of the differentiated state in Xenopus forelimb regeneration were found to require nerves. Following reinnervation some of the denervated forelimb regenerates subsequently reinitiated regeneration, whereas others remained stumped. Stumping was observed histologically to be a function of dermis intervention. These results with Xenopus are discussed and contrasted with previous well‐documented observations of the influence of nerves on appendage regeneration in urodeles.