Small doses of apomorphine (AP, 31.25-125 micrograms/ kg IP) induced 
dose-dependent catalepsy in rats. However, unlike the stereotyped behavior 
induced by high doses of AP which has a rapid onset and is short-lasting, the 
cataleptic effect induced by small doses of AP was evident 30 min after AP 
injection and was unusually long-lasting. Further, AP (31.25-125 micrograms/kg) 
administered 60 min before methamphetamine was found to significantly antagonize 
the methamphetamine-induced stereotyped behavior. Pretreatment with molindone 
(0.45 and 0.8 mg/kg IP), in doses reported to selectively block the presynaptic 
DA receptors, not only decreased the cataleptic effect of AP but also reversed 
the AP antagonism of methamphetamine stereotypy. The results suggest that small 
doses of AP induce catalepsy and antagonize methamphetamine stereotypy probably 
by an action at presynaptic DA receptor sites.