Simple method for evaluation of stimulatory effect of drugs on presynaptic dopamine receptors in mice.

In order to clarify the stimulating activity of presynaptic dopamine (DA) receptors, the ability of drugs to inhibit in vivo accumulation of l-dopa produced by gamma-butyrolactone was estimated in the striatum of mouse treated with an amino acid decarboxylase inhibitor. Apomorphine (0.05-0.5 mg/kg, s.c.) significantly suppressed this accumulation in a dose-related manner. Bromocriptine, lisuride, and ergometrine also reduced it. Methamphetamine (5 and 10 mg/kg, s.c.) diminished striatal l-dopa accumulation and the effects of apomorphine, bromocriptine, and methamphetamine were all blocked by 0.1 mg/kg, i.p., of haloperidol. Ephedrine (100 mg/kg, s.c.) caused a slight decrease in the dopa accumulation although the same dose of cocaine did not change it. These results indicate that the estimation of striatal l-dopa from a single mouse brain is feasible, and dopamine receptor agonists, apomorphine, and ergot alkaloids have stimulatory effects on the activity of presynaptic dopamine receptors of the nigrostriatal dopaminergic neurons of the mouse.