Paradoxical effects of low doses of d-amphetamine in rats

Two experiments were conducted to examine the behavioral effects of low doses of d-amphetamine in rats. In contrast to previous studies showing depression of fixed-ratio 30 lever pressing by doses of d-amphetamine greater than 0.5 mg/kg, lower doses of the drug were found to facilitate such lever pressing. A low dose (0.05 mg/kg) of d-amphetamine was also found to enhance the amount of prandial drinking following food deprivation. These results indicated that the dose-response curve for d-amphetamine is generally non-monotonic and usually in the shape of an inverted U.