DIFFERENT EFFECTS OF AMPHETAMINE ON REINFORCED VARIATIONS VERSUS REPETITIONS IN SPONTANEOUSLY HYPERTENSIVE RATS (SHR)

The spontaneously hypertensive rat (SHR) may serve as an animal model of human attention deficit hyperactivity disorder (ADHD). We compared performances of SHRs and Wystar-Kyoto normotensive controls rats (WKY) in two experiments. When rewarded for varying sequences of responses across two manipulanda, the SHRs were more likely to vary than the WKY s. On the other hand, when rewarded for repetitions of a small number of sequences, the WKYs were more likely to learn to repeat. Both of th ese results confirm previous findings. Injecting 0.75 mg/kg d-amphetam ine facilitated learning by SHRs to repeat the required sequences, wit h amphetamine-injected SHRs learning as rapidly as saline-injected, co ntrol WKYs. On the other hand, amphetamine tended to increase variabil ity in both strains when high levels of variations were required for r eward, and to decrease it in both strains when low levels of variabili ty were required. Thus, amphetamine may have different effects on rein forced repetitions vs. reinforced variations.