Influence of SCH 23390, a DA1-receptor antagonist, on the behavioural responsiveness to small and large doses of apomorphine in rats.

SCH 23390 (SCH), a DA1-receptor antagonist, did not influence the decrease in locomotor activity elicited by a dose of apomorphine (20 micrograms/kg) believed to stimulate DA autoreceptors in rats. Conversely, SCH antagonized the effects on locomotion and the stereotyped behaviour elicited by a dose of apomorphine (1 mg/kg) which stimulates postsynaptic DA receptors. These results showing that the behavioural effects produced by small and large doses of apomorphine are differently affected by SCH, further confirm that DA autoreceptors can be pharmacologically distinguished from postsynaptic DA receptors.