Assessment of dopamine autoreceptor agonist properties of apomorphine, (+)-3-PPP and (-)-3-PPP by recording of yawning behaviour in rats.

Yawning behaviour in rats was studied by direct observation. Apomorphine dose dependently induced yawning: 0.05 mg/kg was most effective, 0.2 mg/kg induced locomotor and sniffing behaviour but less yawning. Sulpinide (2 and 10 mg/kg) dose dependently blocked the apomorphine (0.05 mg/kg)-induced yawning. (+)-3-PPP (1-10 mg/kg) induced yawning in a manner similar to that of apomorphine but (-)-3-PPP (1-10 mg/kg) did so only weakly. Yawning induced by (+)-3-PPP was blocked by sulpiride 10 mg/kg. It is concluded that (+)-3-PPP but not (-)-3-PPP is at least as effective as apomorphine to induce yawning in rats, indicating that (+)-3-PPP, but not (-)-3-PPP, is a pure agonist on dopamine autoreceptors.