Rewarding and aversive effects of stimulant drugs in infant rats.

Four experiments investigated the reinforcing effects of cocaine, amphetamine, and phenylpropanolamine using odor as the conditioned stimulus and infant rats as the subjects. At the age of 2 days the rats were injected with saline or with one of the three drugs and placed for 30 min in a plastic bag with almond-scented shavings. At the age of 18 days the rats were deprived of water for 12 hr and then given two tests that required different responses. In the consumption test they were given 30 min access to two water spouts, one surrounded by almond-scented cotton and the other surrounded by plain cotton. In the place test, they spent 5 min in a shuttle box with almond-scented shavings under one side and plain shavings under the other side. Compared to saline, all three drugs decreased water intake from the almond-scented spout and increased time spent over the almond-scented shavings.