Difference in monoamine oxidase B activity between C57 black and albino NMRI mouse strains may explain differential effects of the neurotoxin MPTP.

Monoamine oxidase B (MAO-B) is the key enzyme in the conversion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP) to N-methyl-4-phenyl-pyridinium ion (MPP+) which causes degeneration of dopaminergic nigral neurons. Using a histochemical tetrazolium method for MAO-B with tyramine as substrate and chlorgyline for the inhibition of MAO-A, black C57 mice were found to have a higher brain MAO-B activity than similar aged albino NMRI mice. The difference, which was in general density rather than distribution, included the basal ganglia and the substantia nigra. The higher activity in C57 mice may explain differences in the susceptibility to MPTP.