Hypophysectomy prevents yawning and penile erection but not hypomotility induced by apomorphine.

A small dose of apomorphine (25 or 50 micrograms/kg, SC) induced repeated episodes of yawning, penile erection, genital grooming and a decrease in locomotor activity in rats. Hypophysectomy almost completely abolished yawning, penile erection and genital abolished yawning, penile erection and genital grooming but failed to modify the hypomotility induced by apomorphine. These results suggest that pituitary hormones are directly or indirectly involved in the apomorphine-induced yawning, penile erection and genital grooming but not in the sedative response to this drug.