Yawning produced by dopamine agonists in rhesus monkeys

Yawning was recorded from five rhesus monkeys restrained in a chair after i.m. injection of dopaminergic compounds: apomorphine (0.03 mg/kg), quinpirole (0.01 mg/kg), and (-)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine (1 mg/kg). SKF 38393 or physostigmine produced no yawning. Yawning from apomorphine was blocked by chlorpromazine or SCH 23390 (0.03 mg/kg). Sulpiride (10 mg/kg) was ineffective. The difference between rats and monkeys in their yawning response to dopaminergic compounds is discussed.