Recuperation of regeneration in denervated limbs of Ambystoma larvae

Abstract

AbstractThe current neurotrophic theory of amphibian limb regeneration allows for a non‐neural tissue contribution of trophic substance (TS) which during ontogeny is suppressed by the production of large amounts of neural TS. A difficulty has been to account for the inability of denervated limbs to initiate regeneration in the absence of neural TS when non‐neural tissue TS synthesis, no longer “quenched,” might be expected to function. This difficulty has now been overcome in the aneurogenic limb system. Aneurogenic forelimbs of A. maculatum larvae were transplanted orthotopically and homoplastically in place of left forelimbs of normally innervated larvae. The brachial nerves of the host larva were allowed to grow into the grafted aneurogenic limb. When tested by subsequent denervation and amputation, the grafted limbs became progressively nerve‐dependent, for regeneration purposes, between 10 and 13 days post‐transplantation, dependence on nerves being complete at 13 days. Grafted, aneurogenic limbs were allowed to become innervated for periods of 2–3 weeks. Then for at least 30 days the limbs were maintained in a nerveless state by denervations, repeated at five day intervals, with histological checks on effectiveness of denervation. Amputation through the forearm was performed at 30 days with continued denervations to prevent reinnervation. Regeneration occurred in 49% of cases (in 16 of 33 limbs) with histological verification of nerveless or sparsely innervated condition. Thus, regeneration‐competent aneurogenic limbs may become nerve‐dependent after transplantation and then, after prolonged denervation, recover ability to regenerate under essentially nerveless conditions.