Adolescent and adult male spontaneous hyperactive rats (SHR) respond differently to acute and chronic methylphenidate (Ritalin).

Abstract

Eight groups of male adolescent and adult spontaneous hyperactive rats (SHR) were used in a dose response (saline, 0.6, 2.5, and 10 mg/kg) experiment of methylphenidate (MPD). Four different locomotor indices were recorded for 2 hours postinjection using a computerized monitoring system. Acutely, the 0.6 mg/kg dose of MPD did not elicit an increase in locomotor activity in either the adolescent or in the adult male SHR. The 2.5 and the 10.0 mg/kg doses increased activity in the adolescent and the adult rats. Chronically, MPD treatment when comparing adolescent and adult gave the following results: the 0.6 mg/kg dose of MPD failed to cause sensitization in the adolescent group but caused sensitization in the adult group, while the 2.5 and 10 mg/kg both caused sensitization in the adolescent and adult groups.