Serotonin receptor blocking effect of SCH 23390.

The effect of SCH 23390 administration on the serotonin system-dependent head twitch behavior was studied in the rat. A small dose of SCH 23390 (1.25 micrograms/kg), injected 20 min before the test, decreased the number of quipazine-induced head twitches. Repeated treatment with SCH 23390 (0.5 mg/kg, SC), once a day for 18 days, increased the number of spontaneously occurring and quipazine-induced head twitches. The enhancing effect of repeated administration of SCH 23390 was blocked by cyproheptadine (0.4 mg/kg). The results indicate that acute injection of SCH 23390 blocks central serotonin receptors, whereas repeated treatment induces their functional supersensitivity.