d-Amphetamine differentially affects low, but not high response rates of male and female Wistar rats

The present experiments investigated sex differences in the effects of d-amphetamine on schedule-controlled behavior. Male and female Wistar rats were exposed to either a differential reinforcement of low rate 15 s schedule, or a differential reinforcement of high rate 0.75 s schedule and challenged with different doses of d-amphetamine (0.2, 0.4, 0.8, 1.6 and 3.2 mg/kg). d-Amphetamine in low to moderate doses increased low response rates. High doses of d-amphetamine decreased low and high response rates in both males and females. The response rate increasing effects of d-amphetamine on low baseline rates were significantly higher for females than for males. Sex differences for high baseline rates were not observed. The results of these experiments show not only that hormonal and neurochemical variables influence the effects of d-amphetamine administration on schedule-controlled behavior, but also that environmental contingencies maintaining the behavior can modify these effects.