Effects of B-HT 920 and B-HT 933 on dopamine and noradrenaline autoreceptors in the rat brain.

B-HT 920 at low doses inhibited the accumulation of DOPA following treatment with reserpine and a DOPA decarboxylase inhibitor in the dopamine-, but not in the noradrenaline-predominant regions of the rat brain. B-HT 933 selectively inhibited this DOPA accumulation in the noradrenaline-predominant regions. These effects of B-HT 920 and B-HT 933 were completely antagonized by haloperidol and yohimbine, respectively. The rat motor activity was reduced by B-HT 920 and it was restored following apomorphine. B-HT 933 decreased the motor activity by a yohimbine-sensitive mechanism. The results indicate that B-HT 920 can selectively and potently stimulate the dopamine autoreceptors whereas B-HT 933 can selectively stimulate the noradrenaline autoreceptors.