Neurochemical studies of the mesolimbic dopaminergic pathway: glycinergic mechanisms and glycinergic-dopaminergic interactions in the rat ventral tegmentum.

The rat ventral tegmentum (containing somata and dendrites of mesolimbic dopaminergic neurones) contained 1.3 mumol/g wet weight of glycine. Slices of ventral tegmentum accumulated exogenous [3H]glycine by an energy-, temperature- and sodium-dependent mechanism. The uptake was medicated by two different transport systems; one system with relatively low affinity for glycine (Km approximately 400 microM) and the other a higher affinity for glycine (Km approximately 10 microM). Small amino acid analogues of glycine inhibited the uptake process, the most potent being taurine and beta-alanine (47% and 44% inhibition, respectively, at 1 mM). Release of exogenous [3H]glycine by elevated potassium and by protoveratrine A was calcium-dependent and tetrodotoxin-sensitive. Glycine (500 microM--2mM) potentiated the protoveratrine A-induced release of exogenous [3H]dopamine from slices of ventral tegmentum; this potentiation was blocked by atrychnine (10 microM). A convulsant dose of strychnine elevated the concentration of 3,4-dihydroxyphenylacetic acid in the ventral tegmentum. Glycine is likely to be a transmitter in the ventral tegmentum and to have a role regulating the activity of somatodendritic regions of mesolimbic dopaminergic neurones.