A functional separation of behavioral stereotypy based on naloxone-reversible effects of seryl enkephalinamide: comparison with morphine.

Amphetamine's stereotypic behavioral actions, produced by the stimulant at a moderate dose, were inhibited by the systemic administration of seryl enkephalinamide, D-Ser2-D-Ser5-enkephalinamide, (Wy 42,896). The classical sequelae of stimulatory behavioral events: sniffing, head bobbing, rearing and locomotor activity, were significantly inhibited by the seryl enkephalinamide. Subsequently, pretreatment with the opiate receptor antagonist, naloxone, significantly blocked the inhibitory effects of the seryl enkephalinamide on the stereotypic and locomotor components. Concomitantly, the behavioral stereotypic component, licking, a behavior usually produced by opiates and only high doses of amphetamine, was significantly induced by the seryl enkephalinamide. Pretreatment with naloxone on the stimulatory behavioral effect of licking, produced a significant inhibitory effect. The combination treatment, consisting of both the seryl enkephalinamide and the stimulant amphetamine, caused a naloxone-reversible synergistic effect. These data show that the seryl enkephalinamide, produced concomitant, naloxone-reversible, inhibitory and stimulatory behavioral stereotypic effects. These data are discussed within the context of current neuronal theories which might underly the observed dose-related continuum of behavioral stereotypies produced by morphine and amphetamine.