Effects of caerulein + haloperidol on amphetamine-induced locomotor stereotypy in rats

Scopolamine produces locomotor stereotypy in an open field but apomorphine does not

Both dopaminergic and nondopaminergic drugs produce hyperlocomotion in rats. Dopaminergic drugs also produce focused stereotypy (absence of locomotion and intense sniffing or licking/biting of a restricted area of the environment). Some drugs produce repetitive routes of locomotion; this phenomenon might represent a combination of hyperlocomotion and stereotypy. Scopolamine (an acetylcholine antagonist) and apomorphine (a dopamine agonist) both produce hyperlocomotion in rats; apomorphine also produces focused stereotypy but scopolamine does not. This research determines whether these drugs also produce locomotor stereotypy as measured by gamma. Scopolamine (0.5 and 2.0 mg/kg) produced locomotor stereotypy at both doses. Apomorphine (1.0, 2.0, and 3.0 mg/kg) failed to reliably produce locomotor stereotypy. Thus, there is not necessarily a relationship between the ability of a drug to produce focused stereotypy and the ability of the drug to produce locomotor stereotypy.

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.

Time course of amphetamine-induced locomotor stereotypy in an open field

Gamma (gamma) is a recently proposed statistic that quantifies and describes the repetitive patterns of locomotion (locomotor stereotypy) exhibited by amphetamine-treated rats in an open field. The time-course of locomotor stereotypy after 1, 2, 3, and 4 mg/kg amphetamine was investigated in this research. Locomotor stereotypy was often evident during the first observation period after amphetamine. Lower doses of amphetamine produced qualitatively different locomotor stereotypy than higher doses. Rats given higher doses of amphetamine exhibited locomotor stereotypy during the "hyperactivity" phase of the three-phase response produced by higher doses of amphetamine (hyperactivity; absence of locomotions, increased sniffing, biting etc.; hyperactivity). Contrary to expectations, rats injected with 2 mg/kg amphetamine exhibited the highest and most sustained increase in gamma. We conclude that locomotor stereotypy is an important component of the behavioral effects of amphetamine in rats. Whether locomotor stereotypy and focused stereotypy are similar phenomena is still unclear.