Enkephalin prevents CCK-induced enhancement of amphetamine-induced locomotor stereotypy.

Enkephalin (ENK) and/or cholecystokinin octapeptide (CCK-8) were infused into nucleus accumbens of rats prior to injection with saline or 1.0 mg/kg amphetamine. Behavior was observed in an open-field paradigm which allowed assessment of locomotor stereotypy (repetitive routes or patterns of locomotion) as well as assessment of lines crossed and rears. Neither CCK nor ENK nor the combination of the two affected the behavior of saline-injected rats in the open field. CCK enhanced the locomotor stereotypy produced by amphetamine without affecting any of the other behaviors recorded. ENK had no effect on the behavior of amphetamine-treated rats when given alone, but ENK prevented the effect of CCK. Thus, enkephalin and CCK interact to modulate amphetamine-induced locomotor stereotypy.