The effects of cimetidine on schedule-controlled responding and locomotor activity in rats

The effect of intraperitoneal injections of cimetidine, a selective histaminergic H₂-receptor blocking agent, on operant behavior and locomotor activity were examined in rats. Cimetidine (1–100 mg/kg) failed to show any significant effect on responding maintained under a fixed-ratio (FR) 30 fixed-interval (FI) 5-min schedule of food presentation. A higher dose of cimetidine (300 mg/kg) produced decreases in both FR and FI rates of responding. In contrast, 100 mg/kg of cimetidineincreased the response rate and decreased reinforcement rate in rats performing under a schedule requiring the temporal spacing of responses (DRL-10 sec). Cimetidine (10–300 mg/kg) did not induce significant changes in locomotor activity in the rat. These data suggest that cimetidine is more potent in altering the steady low rate of responding under a DRL schedule of food presentation, than responding maintained under a multiple FR FI schedule, and that cimitidine is even less potent in altering locomotor activity.