Target dependent and independent stages in regeneration.

Goldfish retinae deprived of their target by tectal ablation showed characteristics of regeneration, such as sprouting activity in culture and changes in protein synthesis. These features resemble changes occurring in regenerating retinae of optic nerves which were subjected only to crush injury. Retinae of tectal ablated nerves maintained their ability to sprout in culture longer than retinae of crushed-injured optic nerves. This may indicate a possible absence of the machinery which regulates growth termination as reflected in this case, by the enduring growth activity in culture. Among the changes in protein synthesis which occurred in retinae following either tectal ablation or crush injury, the most pronounced were in tubulin and in some other polypeptides of the following molecular weights: 46-49, 65 and 74 kdalton. Results are discussed with respect to the possible role of the target in initiating regeneration upon disconnection of the nerve, and in terminating growth upon reconnection.