Axonal transport of radioactivity in the goldfish optic system following intraocular injection of labelled RNA precursors
After injection of the tritiated RNA precursors [3H]guanosine, [3H]uridine or [3H]orotic acid into the eye of goldfish, labelled trichloroacetic acid (TCA) soluble material and RNA appeared to be axonally transported to the contralateral optic tectum. From the time courses of arrival in the tectum, 'average' rates of transport of 6 mm/day for the soluble material and 1.7 mm/day for the RNA were calculated. If the optic nerve was cut after the transported material had arrived in the tectum, about 60% of the TCA soluble material disappeared by 7 days after the cut, but almost none of the RNA. After a further 8 to 13 day period, the TCA soluble material had declined by a further 50% from the 7 day value, but the RNA by only 20%. Thus, relatively little RNA was lost when the optic axons degenerated, an observation which suggested that the RNA might be extra axonal. However, if the optic nerve was crushed before the arrival of the transported material, RNA did not appear in the tectum until the regenerating optic nerve fibers arrived. Therefore, the presence of RNA must be dependent on intact nerve fibers. Moreover, in the earliest stages of regeneration the proportion of transported RNA to TCA soluble material was considerably higher than normal, suggesting that the regenerating fibers arrived in the tectum already carrying RNA. This implies that the RNA itself was transported in the optic fibers.