Synaptosomal neurotransmitter uptake systems in the retina and brain nuclei of light- and dark-adapted rabbits

High affinity uptake rate for [14C]aspartate and [3H]dopamine by retinal homogenate (H), Pl (outer plexiform layer, OPL), and P2 (inner plexiform layer, IPL) retinal synaptosomal fractions were not significantly different between light- and dark-adapted rabbits. However, there were significant increases in the dark in [3H]gamma-aminobutyric acid high affinity uptake rate by retinal H and P2 but not that of Pl. There was a significantly higher [3H]choline uptake rate by retinal H, Pl and P2 in the dark-adapted compared to light-adapted rabbits, but there was no significant change in this rate for synaptosomal fractions from the lateral geniculate body, superior colliculus, visual cortex (VA I + II), caudate nucleus (CN) and hippocampus (HP). Data obtained in this study, along with reports of others, indicate that the change in retinal neurotransmission functions may not always be parallel with the change in high affinity uptake rates of neurotransmitters by retinal synaptosomal fractions. Data obtained indicate an increase in retinal cholinergic neuronal activities in the dark and indicate that optic nerves are not cholinergic and cholinergic neurons in brain nuclei, such as VA, CN and HP, are not significantly influenced by optic nerve inputs in light and dark conditions.