Results from numerous in vivo studies have suggested that a new dopamine agonist, B-HT 920, may be selective for stimulation of dopamine autoreceptors. To examine this question, the inhibition of K+stimulated [3H] dopamine and [14C]acetycholine release was used as an in vitro measure of presynaptic and postsynaptic dopamine receptor stimulation, respectively. In contrast to the results of in vivo studies, B-HT 920 was found to be a potent agonist at both pre- and postsynaptic dopamine recetors. Both effects of B-HT 920 were stereospecific and antagnoized by the D2 dopamine antagonist, sulpiride, while the alpha antagonist, tolazoline, was without effect. The presynaptic effect of B-HT 920 was selective to dopamine neurons in that K+-stimulated [3H]serotonin release was not affected.
