Effects of phencyclidine and methylphenidate on d-amphetamine-induced behaviors in reserpine pretreated rats

The effects and interactions of phencyclidine (PCP), methylphenidate and d-amphetamine on locomotor activity, stereotyped behavior and ataxia in reserpine- and vehicle-pretreated rats were examined. The behaviors of rats receiving PCP alone or in combination with other drugs were quantified along three dimensions (locomotor activity, stereotyped behavior, and ataxia) on scales developed in this laboratory. The behaviors of groups receiving methylphenidate and/or d-amphetamine in treatment combinations other than those including PCP were quantified using a well known d-amphetamine behavioral rating scale. PCP, methylphenidate and d-amphetamine each induced significant increases in locomotor activity and stereotyped behavior when administered alone. Reserpine was found to antagonize PCP-induced locomotor activity and stereotyped behavior, and methylphenidate-induced stereotyped behavior at a dose which either potentiated or had no significant effect upon d-amphetamine-induced behavior (depending upon the scale used). Reserpine also potentiated PCP-induced ataxia. Whereas PCP potentiated the locomotor activity induced by d-amphetamine in both reserpine- and vehicle-pretreated subjects, methylphenidate marginally antagonized d-amphetamine-induced stereotypy in reserpine-pretreated subjects. PCP-induced ataxia in reserpine pretreated subjects appeared moderately reduced in subjects also receiving d-amphetamine. In general, the behavioral effects of PCP appear to be more similar to those of methylphenidate than to those of d-amphetamine, but differences are also found between PCP and methylphenidate. The results are discussed in relation to a behavioral model recently proposed as a method for differentiating indirect dopamine agonists on the basis of their neurochemical mechanisms of action.