The ability of homogenates of the chick optic lobe to accumulate a series of possible neurotransmitters has been studied. High affinity uptake of several possible neurotransmitters was examined in optic lobes of 21-day-old embryos that had a single eye removed on the third day of incubation and in 23-day-old chicks that had an eye removed at hatch. Embryonic enucleation resulted in severe reduction of development of the ability of the contralateral optic lobe to take up tritiated GABA, dopamine, choline, serotonin and glutamate from solutions around 10(-8)M. Unilateral eye removal of new-hatched chicks caused failure of the denervated optic lobe to grow, but only the uptake capacity for glutamate was significantly recuced. This deficit was apparent as early as 4 days after enucleation. The transport of other compounds was unimpaired. The uptake of glutamate by homogenates of the optic tract was 43% of that or the optic lobe. This was a much greater fraction than the corresponding value for other postulated neurotransmitters. These data suggest that glutamate may be the primary neurotransmitter of the fibers of the optic tract originating in the retinal ganglion cells.

The production of cytoplasmic RNA that contains polyadenylic acid is increased, relative to total cytoplasmic RNA, in a neuroblastoma clone, NBE-(A), after induction of differentiation by 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone, an inhibitor of adenosine 3',5'-monophosphate phosphodiesterase. The amount of RNA that contains polyadenylic acid in cytoplasm may be greater in such differentiated neuroblastoma cells than in proliferating control cells.

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.

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SummaryThe axoplasmic migration of ribosomes has been detected in the visual system of the chick. Monocular injection of radioactive uridine or an amino acid mixture was followed by sedimentation analysis in sucrose or cesium sulfate density gradients, of ribosomes prepared from the retinae of injected eyes and the left and right optic lobes. By this means both RNA and protein components of ribosomes were found to migrate from the retina to the innervated contralateral optic lobe. Following denervation of the distal nerve segment by eye removal, the stability of the transported RNA was reduced, suggesting its presynaptic location. The transport of RNA was not significantly impaired by intraocular injection of inhibitors of informational RNA or mitochondrial RNA synthesis prior to injection of radioactive uridine but was depressed by a low dose of actinomycin D.