Cocaine discrimination and time-course effects in male and female Wistar rats

Previously, sex differences have been observed in the behavioral effects of acute and chronic cocaine administration. In the present experiment, male and female rats were trained to discriminate intraperitoneal injections of 10.0 mg/kg cocaine from its vehicle. It was hypothesized that the subjective effects of cocaine might differ between male and female rats. It was further hypothesized that generalization gradients between male and female rats might differ as a function of the time since cocaine administration. In addition, we were interested to see whether multiple generalization gradients could be determined within the same experimental session. For that purpose, two different types of generalization tests were conducted in extinction, one in which subjects were tested both 10 min and 30 min following cocaine administration (vehicle, 1.0, 3.0, 5.6, 10 or 17 mg/kg) and one in which subjects were only tested 30 min after cocaine administration. The generalization gradients obtained 30 min following drug administration were shifted to the right of the gradient obtained 10 min following drug administration. The two 30-min gradients were not different from one another, showing that multiple generalization gradients can be obtained within the same experimental session.