Scopolamine blocks play fighting behavior in juvenile rats.

Play fighting, social investigation, and locomotor activity of prepubescent male laboratory rats were observed 20 min following administration of scopolamine hydrobromide. Play fighting was inhibited by an intraperitoneal dosage of 0.3 mg/kg and was effectively blocked at all dosages greater than 0.5 mg/kg; activity and social investigatory behavior were increased by scopolamine. Play fighting inhibition following a threshold dosage of 0.3 mg/kg scopolamine was effective at 30 min; after 120 min, drug- and saline-treated groups failed to differ reliably. Behavioral tolerance to scopolamine was observed after five days of daily treatment with 0.5 mg/kg scopolamine; play fighting, following a 0.5 mg/kg dosage of scopolamine, did not differ from that of saline-treated controls. The results are discussed in terms of central and peripheral effects of scopolamine and the competing response hypothesis.