Postnatal changes in enzyme activities in synaptosomes isolated from hamster optic nerve endings

Development and regional distribution of two molecular forms of the catalytic subunit of the Na,K-ATPase in rat brain

Two molecular forms of the catalytic subunit of the Na,K-ATPase can be isolated from brain (1). Only the alpha form was detected in rat embryo brain at 13 days of gestation (E13). The alpha (+) form, which is characteristic of myelinated axons, appeared at E15 before myelination begins. Hence its expression is not dependent on prior myelination. Axonal transport of the alpha (+) form was demonstrated in 4 day-old rats. The ratio of alpha (+): alpha was 1:1 in adult retina, cortex and cerebellum and 10:1 in brain stem. Although alpha (+) is characteristic of myelinated axons, this regional difference was present not only in enzyme extracted from crude microsomes, that contain myelinated axon fragments, but also in enzyme from isolated synaptosomes. Hence, the alpha (+): alpha ratio is an inherent characteristic of the neuron and does not depend on regional differences in myelination.

Postnatal changes in [3H]fucosyl glycoconjugates axonally transported into hamster optic nerve endings

The subsynaptosomal distribution of [3H]fucosyl glycoproteins axonally transported into the optic nerve endings of neonatal and adult hamsters changed dramatically at eye-opening. In 12 day-old previsual hamsters, the highest concentration of incorporated fucose was in the axoplasmic reticulum/synaptic vesicle fraction (51%), with only 6% in the dense synaptic membrane fraction. By the end of the eye-opening period four days later proportional labeling of the dense synaptic membrane fraction had increased four-fold to 23% of total sub-synaptosomal radioactivity. Labeling of the synaptic membrane doubled again in adults (41%). Total synaptosomal radioactivity was greatest in 16 day-olds. These results imply that utilization o [3H]fucose by the retinal ganglion cells, as well as composition of the synaptic membrane, change in association with the onset of functional visual activity.