ROLE OF MONOAMINE-OXIDASE TYPE-A AND TYPE-B ON THE DOPAMINE METABOLISM IN DISCRETE REGIONS OF THE PRIMATE BRAIN

The role of monoamine oxidase (MAO) type A and B on the metabolism of dopamine (DA) in discrete regions of the monkey brain was studied. Mon keys were administered (-)-deprenyl (0.25 mg/kg) or clorgyline (1.0 mg /kg) or deprenyl and clorgyline together by intramuscular injections f or 8 days. Levels of DA and its metabolites, dihydroxy phenylacetic ac id (DOPAC) and homovanillic acid (HVA) were estimated in frontal corte x (FC), motor cortex (MC), occipital cortex (OC), entorhinal cortex (E C), hippocampus (I-II), hypothalamus (HY), caudate nucleus (CN), globu s pallidus (GP) and substantia nigra (SN). (-)-Deprenyl administration significantly increased DA levels in FC, HY, CN, GP and SN (39-87%). This was accompanied by a reduction in the levels of DOPAC (37-66%) an d HVA (27-79%). Clorgyline administration resulted in MAO-A inhibition by more than 87% but failed to increase DA levels in any of the brain regions studied. Combined treatment of(-)-deprenyl and clorgyline inh ibited both types of MAO by more than 90% and DA levels were increased (57-245%) in all brain regions studied with a corresponding decrease in the DOPAC (49-83%) and HVA (54-88%) levels. Our results suggest tha t DA is metabolized preferentially, if not exclusively by MAO-B in som e regions of the monkey brain.