5-HT3 receptor modulation of behavior during withdrawal from continuous or intermittent cocaine.

The present experiments examined alterations in 5-HT3 receptors during withdrawal from continuous or intermittent cocaine. Rats were pretreated with 40 mg/kg/day cocaine for 14 days by either SC injections or osmotic minipumps. The rats were then withdrawn from the pretreatment regimen for 7 days. In Experiment 1, rats received 0-16 mg/kg IP injections of ondansetron, a selective 5-HT3 receptor antagonist. In Experiment 2, the rats received 0-16 mg/kg IP ondansetron in combination with a 15 mg/kg IP injection of cocaine. In Experiment 3, the subjects received 0-16 mg/kg IP injections of ondansetron in combination with a 7.5 mg/kg IP injection of cocaine. Following these injections, the subjects' behavior was rated using the Ellinwood and Balster (18) rating scale. The results of Experiment 1 indicated that ondansetron had no effect on the behavior of the subjects, nor was there a differential effect of pretreatment regimen the effects of ondansetron. The results of Experiment 2 indicated that ondansetron had no effect on cocaine-induced locomotion in the saline control rats, but did have a slight, statistically significant, suppressive effect in the injection rats. In contrast, ondansetron had a robust facilitative effect on cocaine-induced locomotion in the continuous infusion rats. The results of Experiment 3 indicated that ondansetron had no effect on cocaine-induced locomotion in the saline control rats or the cocaine injection pretreatment subjects. In the continuous infusion subjects, ondansetron did have a slight, statistically significant, facilitative effect on cocaine-induced locomotion.(ABSTRACT TRUNCATED AT 250 WORDS)