Regulation of A8 dopamine neurons by somatostatin

The effects of depletion of somatostatin in the region of the retrorubral field on in vivo tyrosine hydroxylation in the A8 cell group were assessed. Local injections of cysteamine into the central amygdaloid nucleus, source of a somatostatin input to the A8 cell group region, or directly into the retrorubral field resulted in an increase in in vivo tyrosine hydroxylation in the A8 cell group. Levels of somatostatin-like immunoreactivity in the retrorubral field were decreased by approximately 50% by the cysteamine treatment. These data suggest that somatostatin may hold A8 dopamine neurons under tonic inhibition.