Fig. 1.

Effects of cocaine, d-amphetamine, and the κ-agonist U-50488 in mice trained to discriminate cocaine from saline. Abscissae, drug dose in mg/kg; “V” indicates vehicle. Ordinates, percentage cocaine-appropriate responses (top), response rate in responses per second (bottom). Data are groups means ± S.E.M. Groups sizes: cocaine, n = 30; amphetamine, n = 7; U-50488, n = 6. In the top, exceptions to these group sizes are indicated when some mice failed to respond at the highest drug doses. **, p < 0.01 versus vehicle.