Fig. 5.

Ketamine (7.5–30 mg/kg, i.p.) effects on DRL 72-s behavior displayed by scatter plots and associated mean ± S.D. bars. Ketamine increased the number of reinforcers obtained in a group of rats (n = 8), with a 84% increase at the 30-mg/kg dose [(A), P < 0.05]. Ketamine also decreased the total responses made during the hour-long session by about 30% at the 30-mg/kg dose [(B) *P < 0.05]. Vehicle is displayed as black squares, whereas ketamine is expressed by green triangles (7.5 mg/kg), red circles (15 mg/kg), and blue triangles (30 mg/kg). (C) displays the effects of vehicle or ketamine on the cumulative IRT distribution using symbols for the respective treatments as defined for (A) and (C). Although the 7.5- and 15-mg/kg dose conditions largely were without effect on the IRT distribution, for the highest tested subanesthetic dose of 30 mg/kg, the peak of responding in the 48–60-second range was blunted with a modest rightward shift so that the peak was now observed at the 84–90-second time bin.