EFFECT OF TETRODOTOXIN ON AXONAL TRANSPORT AND REGENERATION IN GOLDFISH OPTIC NERVE

The first part of the thesis examined the effects of intraocular tetrodotoxin (TTX) on anterograde axonal transport in goldfish optic axons. Goldfish were injected in one eye with TTX followed by injection of radioactively labeled precursors for macromolecules carried by axonal transport. TTX was reinjected every 60-65 hours. At varying times after injection of precursor the retinas, optic nerves, or optic tecta were removed and transported radioactivity assayed by liquid scintillation counting. The major findings were: (1) Intraocular TTX did not affect the velocity of fast or slow axonal transport of protein or the amount of protein transported in optic nerves. Axonal transport of glycoprotein labeled with ('3)H-fucose was not affected by TTX, but turnover of ('3)H-glucosamine glycoproteins at the optic tectum may have been reduced. (2) Intraocular TTX reduced the amount of ('3)H-glucosamine gangliosides transported along optic axons and reduced the turnover of gangliosides at the tectum. TTX did not affect the rate or amount of axonal transport of phospholipid labeled with ('3)H-glycerol but seemed to affect transport or turnover of ('3)H-inositol phospholipids. (3) Intraocular TTX reduced the amount of nucleosides (adenosine, uridine, guanosine) and nucleotide derivatives transported to optic nerve terminals and their transfer to tectal neurons and incorporation into RNA. Transfer of nucleosides to glia along the lengths of optic axons was not altered by intraocular TTX.;The second part of the thesis examined effects of intraocular TTX on the time course of regeneration following an optic nerve crush. After receiving right optic nerve crushes, fish were injected in the right eye with TTX at 3-4 day intervals until 28 days post-crush. Regeneration was monitored by tests for recovery of visual function, histological measurements of regenerating retinal ganglion cells and optic nerves, and by electrophysiological studies of retinotectal synapse formation. The results showed that following an optic nerve crush retinal ganglion cell axons treated with intraocular TTX can regenerate and form effective synapses at the optic tectum. TTX did not affect the proper targeting of the optic axons since the polarity of the retinotectal map was normal. However, the size of the multi-unit receptive fields in TTX-treated fish was more than two times those of control regenerating fish. Intraocular TTX may have affected the branching, size, or maturation of the regenerating optic axons.