Influence of yohimbine on the ACTH-induced behavioural syndrome, in rats.

In adult male rats, yohimbine at low doses (0.1, 0.5 and 1 mg/kg i.p.) potentiated, and at high doses (30.0 mg/Kg) antagonized, the behavioural syndrome induced by the intracerebroventricular injection of ACTH 1-24 (3 micrograms/rat) (stretching-yawning syndrome and penile erections). These results support the hypothesis that brain catecholaminergic systems play a positive role in the ACTH-induced behavioural syndrome.