Development of neurotransmitter uptake in regions of the chick brain

Abstract

SUMMARYThe uptake of postulated neurotransmitters or their precursors into regions of the developing chick brain and retina has been examined. The transport of low concentrations (around 10-s M) of GABA, glutamic acid, choline, dopamine and serotonin into homogenates was sodium and energy dependent and inhibited by a variety of pharmacological agents that are thought to act presynaptically. After morphological fractionation, the high affinity transport mechanism was concentrated in the nerve ending fraction.Compounds were poorly accumulated by the cerebral regions of the 6 day incubated chick embryo. After this time, the uptake capacity of each brain region studied exhibited a characteristic developmental profile.Mechanisms for GABA transport appeared early in development, while catecholamine and choline systems matured later. Homogenates of the cerebral hemispheres and optic lobes took up all compounds studied, while the retina and cerebellum of the young chick were able to take up only GABA to a significant extent.

Calcium-dependent release of putative neurotransmitters in the chick visual system

“…While the rate of highaffinity uptake is lower in embryonic brain (BONDY & PuRDY, 1977), the proportion of the label released in response to Cal+ was relatively constant after [ 3 H]choline or [ 3 H]GABA accumulation. On the other hand, the Ca 2 +-related release of radioactivity after dopamine transport was not clearly demonstrable in embryos.…”

“…This efflux may have been from micelles of axonal or glial origin but was obviously not from synapses. However, it should be noted that since the high-affinity uptake capacity of optic nerve homogenates is relatively low (BoNDY & PuRDY, 1977), the absolute amounts released from the optic nerve is much less than that of a corresponding chick brain homogenate. Calcium-related release of labeled compounds from the optic nerve also occurred if veratridine or A-23187 was substituted for high K + as a means of enabling Ca 2 + to enter into cytoplasmic particles and encapsulated cellular fragments.…”

“…The quantity of each isotopically labeled compound incorporated by chick retina, optic nerve and optic lobe under these conditions has been previously reported (BONDY & PuRDY, 1977). The percentage of incorporated label remaining after three washes at 0°C that was released by incubation with calcium-free buffer was as follows: 18.1 ± 1.6 (glutamate), 23.8 ± 1.0 (glycine), 18.9 ± 2.9 (GABA), 13.8 ± 1.5 (dopamine), and 13.8 ± 0.9 (choline).…”

“…The bulk of the Ca 2 +-dependent efflux may be relevant to presynaptic neurotransmitter release because the sodium-dependent high-affinity uptake of labeled putative neurotransmitters that precedes release in our system may be predominantly synaptosomal in homogenates (KUHAR, 1973;BONDY & PuRDY, 1977).…”

Effects of prevention of afferentation of the development of the chick optic lobe

“…Thus, parameters of neuronal development (e.g., increased levels of acetylcholinesterase, choline acetyltransferase and the appearance of high affinity transport mechanisms) of several putative neurotransmitters are more dramatically impaired than are indices of glial maturation (e.g., levels of nonspecific cholinesterase) [2,7,8,15].…”