When 3H-uridine is injected into the eye of fish during regeneration of the optic nerves, large amounts of 3H RNA can be detected within optic axons and axonal growth cones as regenerating fibers re-enter the optic tectum. Biochemical evidence suggests that a large fraction of this 3H-RNA is 4S RNA. It is likely that 4S RNA is synthesized in retinal ganglion cells and then axonally transported into the growing fibers. This study investigates some of the characteristics of axonal 4S RNA in regenerating optic nerves of goldfish. The research proposed for this year (02) involves: (1) EM autoradiographic analysis of the goldfish optic tecta at times up to 60 days after the intraocular injection of 3H-uridine, and 18 days after regeneration has begun. We are attempting to determine if axonal 4S RNA remains in the axon or is transferred to surrounding cells. (2) Another experiment has been designed to determine whether 4S RNA contains amino acid residues and perhaps may function as transfer RNA. (3) A third experiment investigates the possibility that 4S RNA in the axon may be complexed with the polyamine spermidine. We will study this association using 3H-spermidine as a tracer and identify the presumed association of spermidine and 4S RNA by SDS polyacrylamide gel electrophoresis. (4) A series of experiments, currently in progress, compares the axonal transport of adenosine and phosphorylated derivatives with uridine and phosphorylated derivatives in intact and regenerating optic nerves of fish. The object of these experiments is to examine the "needs" of the growing normal axon with respect to these small molecules. The overall goal of these experiments is to identify the biochemical requirements of the growing axon; specifically regarding 4S RNA and its precursors. A better understanding of the biochemistry of regenerating axons may allow us to identify the reason(s) why mature axons in the CNS of mammals have lost their ability to grow while those of low organisms retain this ability.