Localization of GABA(B) receptors in midbrain monoamine containing neurons in the rat

The localization of gamma-aminobutyric acid (GABA)(B) receptors in the midbrain of the rat was examined in multiple labeling studies using antibodies directed against the GABA(B) receptor and either tryptophan hydroxylase or tyrosine hydroxylase. Almost all of the serotonergic and dopaminergic cell bodies in the midbrain displayed GABA(B) receptor-like immunoreactivity. Conversely, most neurons in the raphe nuclei and ventral tegmentum which exhibited intense immunoreactivity for GABA(B) receptors were also immunopositive for serotonergic or dopaminergic markers. These results demonstrate directly that GABA(B) receptors are present in monoaminergic neurons in certain regions of the midbrain.