Striatal dopamine metabolism in monoamine oxidase B-deficient mice: A brain dialysis study

We have studied striatal dopamine (DA) metabolism in monoamine oxidase (MAO ) B-deficient mice using brain microdialysis. Baseline DA levels were simil ar in wild-type and knock-out (KO) mice. Administration of a selective MAO A inhibitor, clorgyline (2 mg/kg), increased DA levels and decreased levels of its metabolites in all mice, but a selective MAO B inhibitor, I-depreny l (1 mg/kg), had no effect. Administration of 10 and 50 mg/kg L-DOPA, the p recursor of DA, increased the levels of DA similarly in wild-type and KO mi ce. The highest dose of L-DOPA (100 mg/kg) produced a larger increase in DA in KO than wild-type mice. This difference was abolished by pretreating wi ld-type mice with /-deprenyl. These results suggest that in mice, DA is onl y metabolized by MAO A under basal conditions and by both MAO A and B at hi gh concentrations. This is in contrast to the rat, where DA is always metab olized by MAO A regardless of concentration.