Neurochemical Studies of the Mesolimbic Dopaminergic Pathway: Somatodendritic Mechanisms and GABAergic Neurones in the Rat Ventral Tegmentum

The rat ventral tegmentum (containing dendrites and somata of mesolimbic neurones) contained 1.3 μg/g of dopamine, which was reduced to 40% of the control level by reserpine. Slices of ventral tegmentum were able to accumulate and release (elevated potassium or protoveratrine A) exogenous [3H]dopamine. In parallel studies the uptake mechanism in ventral tegmentum was shown to be virtually identical to the nerve terminal uptake of [3H]dopamine by slices of nucleus accumbens. The release of [3H]dopamine was indistinguishable from that observed in substantia nigra, where there is substantial evidence for dendritic mechanisms. Basal adenylate cyclase activity was present, but dopamine‐stimulated activity was not detected. A high GABA concentration (7.7 μmol/g) was present in ventral tegmentum, in conjunction with an uptake and a release mechanism for [3H]GABA. GABA and muscimol elicited a small, reproducible efflux of [3H]dopamine, but an interaction between dopamine and [3H]GABA efflux was not observed. The results are in accord with transmitter roles for dopamine and GABA in the somatoden‐dritic area of mesolimbic dopaminergic neurons.