Regulation of tadpole spinal nerve fiber growth by the regenerating limb blastema in tissue culture.

Explants of frog tadpole spinal cord cocultured with blastemas of regenerating hindlimbs provide in vitro evidence that the mesenchymelike cells of the blastema may serve to elicit nerve fiber growth and sprouting into the limb stump. The present study indicates that (1) blastemal mesenchyme results in enhanced, directed nerve fiber growth and its extended survival in defined tissue culture medium; (2) the amount of nerve growth decreases in the presence of blastemas from limbs incapable of complete regeneration; and (3) the quantity of nerve fiber outgrowth decreases as the developmental stage of the spinal cord increases. It is hypothesized that one of the requisites for limb regeneration is the production of a distal population of dedifferentiated cells capable of eliciting nerve fiber outgrowth from competent neural tissue in an amount that is sufficient to promote nerve-dependent regeneration.