Differences between monoamine oxidase concentrations in striatum and forebrain of aged and young rats

The MAO-A and MAO-B activities in the striatum and the rest of the forebrain of young adult and aged rats were determined and compared. There was no significant difference in Km values of MAO-A for 5-HT or of -B for benzylamine in any of the brain regions of both rat groups. With increase in age, the Vmax value of MAO-A in the forebrain decreased; in the striatum the Vmax values of MAO-A and -B increased with age. The MAO-A concentrations, measured by enzyme titration with clorgyline or 1-deprenyl as the titre, were the same in both brain regions of young and aged rats, but in both brain regions of aged rats, MAO-B concentrations were greater than those in young rats. The MAO-B concentrations increased in parallel with the increases in Vmax indicating that the increase with age was due to increase in the number of MAO molecules.