Amino acid incorporation into proteins of degenerating and regenerating goldfish optic tracts

Abstract

The goldfish optic system was used to examine the patterns of incorporation of 3H-amino acid into proteins of the degenerating and regenerating optic tract. On various days after unilateral enucleation, groups of fish were injected intraperitoneally with [ 3H]-leucine and the contralateral optic tracts were examined for protein specific radioactivity 5.5 h later. Labeling of proteins in experimental tracts showed a biphasic increase over unoperated controls with the greatest increments occurring at 1 to 5 days and again at 10 to 14 days. Labeling increases of approximately 2.5-fold and 4- to 5-fold were observed in the first and second phase, respectively. Enhanced labeling was shown not to be due to increases in precursor pools and sham-operated animals showed only minimal increases in tract labeling. Parallel experiments were conducted on fish receiving optic nerve crush in which degeneration is followed by tract reinnervation. Results showed a biphasic pattern of isotope incorporation that was very similar in time course and magnitude to that seen in the totally degenerating tracts. The second phase was found to correspond in time of the entry of regenerating axons into the tract. These results have implications with reference to the probable origin of labeled cells, the possible function of the first and second phase of labeling, and the similarity in metabolic pattern between the degenerating and regenerating tracts.