Axonal transport in the optic system of neonatal and adult hamsters

Abstract

The axonal transport of [ 3H]proline-labeled protein was determined in the optic system of neonatal and adult hamsters. Proline was injected intravitreally at three stages of visual development: before eye opening (10 days), early functional (16, 21, and 30 days), and adult. The rate of fast axonal transport increased with age from 140 to 220 mm/day. There were two peaks of slowly transported radioactivity in neonatal optic nerve (∼8 and 1.4 mm/day), the earlier being the dominant component. With maturation, the later slow component became larger. There were also two slow-transport peaks in the optic nuclei of adults. The earlier of these turned over rapidly and was apparently produced by the later of the two slow-transport components in the optic nerve. The ratio of radioactivity in optic nerve to that in nerveending samples was much higher in adult than in neonatal nerve, possibly reflecting a larger diameter of adult axons. Slowly transported radioactivity disappeared more slowly from adult than from neonatal nerve endings, although there was no difference in optic nerve samples. Possible explanations for slower decay in the adult include increased stability of nerve-ending proteins, enhanced reutilization of proline, and diminished retrograde transport and/or transneuronal transfer.