Rapid decline of stereotyped behavior in rats during constant one week administration of amphetamine via implanted ALZET osmotic minipumps.

Groups of rats were subcutaneously implanted with ALZET 2001 type osmotic minipumps containing d-amphetamine. Three doses of amphetamine (calculated as 0.47, 0.94 and 1.41 mg/kg/hour; measured values were approximately 50% lower), continuously released for 7 days, initially produced locomotor stimulation and stereotyped behavior slightly increasing over the first few days. During the later days, however, locomotor stimulation and stereotyped behavior markedly declined indicating tolerance development. These results contrast the often reported development of sensitization to the behavioral effect of amphetamine observed with repeated injections.