Stimulation of postsynaptic D2− dopamine receptors by B‐HT 958 is revealed by co‐treatment with the D1− receptor agonist SKF 38393

Abstract— The motor activity of reserpine‐treated mice was used to study effects of B‐HT958 (2‐amino‐6‐(p‐chlorobenzyl)‐4H‐5,6, 7, 8‐tetrahydrothiazolo‐[5, 4‐d]‐azepine) on postsynaptic dopamine and noradrenaline receptors. The motor activity was only slightly stimulated by B‐HT 958 or by the D1− receptor agonist SKF 38393 but it was markedly increased by the two drugs given in combination. The effect of B‐HT 958 peaked earlier following low rather than high doses. The enhanced motor activity was inhibited by the D2− receptor antagonist sulpiride or the D1− receptor antagonist SCH 23390, indicating that it was caused by stimulation of both receptor types. The results suggest that B‐HT 958 stimulates postsynaptic D2− receptors in addition to D2− autoreceptors and that its blockade of postsynaptic α2‐adrenoceptors is of no importance for the motor activity.