Elevated postmortem monoamine oxidase B activity in the caudate nucleus in Huntington's disease compared to schizophrenics and controls.

Activity (Vmax) of monoamine oxidase (MAO) B in necropsy samples from the head of the caudate nucleus was 260% higher in patients dying with Huntington's disease (HD) than in controls (P less than 0.05). No differences in MAO A enzyme kinetics were found. MAO B, but not MAO A, was increased (26%) in the frontal cortex from patients dying with HD compared to control subjects. MAO A and B kinetics in caudate nucleus and frontal cortex from a group of schizophrenics did not differ from controls. Postmortem delay, the effect of neuroleptics, or nonspecific degeneration artifacts did not explain these findings. It is suggested that the increase in MAO B activity in the caudate nucleus may reflect neurochemical changes that are responsible for the choreiform movements of Huntington's disease. Lower cortical MAO B activity in the schizophrenic group may reflect the effects of neuroleptics.