Differential effects of para-chlorophenylalanine on amphetamine-induced locomotion and stereotypy

Amphetamine-induced locomotion and stereotypy were concurrently evaluated in order to determine if pretreatment with para-chlorophenylalanine (PCPA) (which is reported to facilitate some of the effects of amphetamine) results in a behavioral pattern similar to the augmentation previously reported to occur with repeated amphetamine administration. In the present study the behavioral response of rats was characterized after administration of saline or various doses of D-amphetamine (0.5, 2.5 and 4.0 mg/kg) for 48 h following PCPA (300 mg/kg) or vehicle injection. The predominant effects produced by the low dose of D-amphetamine (0.5 mg/kg), i.e., enhanced crossovers and rearings, were found to be significantly elevated after PCPA administration. This effect persisted (relative to PCPA controls) when the response of non-PCPA pretreated animals returned to corresponding control levels, thus indicating that the two drugs acted synergistically. However, while the locomotor component of the amphetamine response was potentiated by PCPA pretreatment, the more focused stereotypies produced by higher doses of amphetamine (2.5 and 4.0 mg/kg) were significantly displaced by enhanced crossovers and rearings. These differential effects of PCPA on amphetamine-induced locomotion and stereotypy are in contrast to the uniform pattern of behavioral augmentation resulting from repeated amphetamine administration. The relationship between the various behavioral components of the amphetamine response and the possible neurochemical mechanisms subserving their interaction are discussed.