Bromocriptine requires D-1 receptor stimulation for the expression of sniffing behaviour in rats

The effect of the mixed D-1/D-2 dopamine agonist apomorphine, the D-2 agonist bromocriptine and the D- 1-selective dopamine agonist SKF 38393 on sniffing behaviour in rats was tested in the present experiments. Apomorphine induced a dose-dependent sniffing, which was decreased by either D-2 or D-1 dopamine antagonist pre-treatment. Atropine (antimuscarinic drug) or phenoxybenzamine and propranolol (α and β- adrenergic blockers, respectively) did not alter the apomorphine response. Apomorphine induced a significant increase in sniffing in reserpine-treated animals. Bromocriptine produced sniffing during the 3rd hour after drug injection. The effect was decreased by sulpiride or SCH 23390 pre-treatment. Phenoxybenzamine or propranolol did not change the bromocriptine effect, while atropine increased the drug response. SKF 38393 also induced a slight but significant sniffing. In rats pre-treated with reserpine, neither bromocriptine nor the D-1-selective agonist SKF 38393 produced any sniffing. However, the combination of bromocriptine with SKF 38393 produced an intense sniffing behaviour. It may be concluded that bromocriptine requires D-1 receptor stimulation for the expression of sniffing.