Differential effects of ketamine on schedule-controlled responding and motility.

Male Sprague-Dawley reats were trained to bar press for food reinforcement on an FI-300 sec schedule. Ketamine (7.5 mg/kg, IP) significantly increased response rates of both drug-naive and drug-experienced rats for the first 10 min after injection. With a 15.0 mg/kg dose of ketamine, response rates decreased significantly during the first 10 min after injection, irrespective of prior drug experience, but increased significantly above control thereafter in drug-experienced animals. Both doses of ketamine enhanced spontaneous locomotor activity significantly, irrespective of prior drug experience. Differences in the time course and dose dependency of these effects suggest that ketamine stimulates schedule-controlled responding and spontaneous locomotor activity via different neuropharmacologic mechanisms.