Differential effects of d-amphetamine on impulsive choice in spontaneously hypertensive and Wistar-Kyoto rats

The spontaneously hypertensive rat (SHR) has been shown to exhibit three of the behavioral characteristics of attention-deficit/hyperactivity disorder: hyperactivity, attention deficit and impulsivity. This study used SHRs and a control strain to assess the effects of the commonly prescribed psychomotor stimulant, d-amphetamine, on impulsivity, defined as choice for a small, immediate over a large, delayed reinforcer. d-Amphetamine (1.0, 3.2 and 5.6 mg/kg) was administered to SHR and Wistar-Kyoto rats (WKY; their progenitor strain) before sessions of a choice task involving small, immediate and larger, delayed food reinforcers. As reported earlier, SHRs were more impulsive than WKYs (they preferred the smaller, immediate reinforcer). d-Amphetamine had no effect on preference for the SHRs, but increased choices for the small, immediate reinforcer for the WKYs at the 1.0 and 3.2 doses. Thus, d-amphetamine did not reduce impulsivity in the already impulsive SHRs, but did increase impulsivity in rats that were not already impulsive.