Axonal transport in the asymmetric optic axons of flatfish

Abstract

Axonal transport of protein was studied in the asymmetric optic axons of adult flounders, Pseudopleuronectes americanus. In these animals, the right optic nerve averaged 36% longer than the left optic nerve. There was no significant difference between the two sides in optic tract length or retinal ganglion cell body size. 3H-Proline was injected into the eyes and the amount of labeled protein accumulating in the optic tectum at selected intervals was measured by liquid scintillation counting. The rate at which proteins traveled with the fast component was estimated at 20–24 mm/day in both long and short axons; labeled protein, therefore, arrived in the right tectum earlier than in the left tectum. No such difference in accumulation of labeled protein could be demonstrated in the two tecta at longer intervals, suggesting that the rate of slow transport is not identical in the long and short axons, but that the net rate is greater in the longer axons. A consistently greater amount of labeled protein reached the right tectum at the longer intervals, indicating a greater utilization of the newly synthesized protein by the longer axons. The rate of slow transport thus seems to be influenced by the length of axon, perhaps in response to a greater rate of utilization of transported material required by the longer anox.