Role of type A and Type B MAO in the metabolism of epinephrine in rat brain

Abstract

Three different catecholamines appear to be neurotrans-mitters in brain: dopamine, norepinephrine and epinephrine. Dopamine and norepinephrine have been extensively studied as brain neurotransmitters during the past two decades. Less work has been done on brain epinephrine, which became a focus of attention only after Hokfelt et al (1974) showed that the epinephrine-forming enzyme, norepinephrine N-methyltransferase (EC 2.1.1.28), was present in rat brain in discrete tracts of neurons. These neurons presumably make and use epinephrine as their neurotransmitter and were suggested to have specific functions separate from those of dopamine and norepinephrine neurons (Hokfelt et al, 1974). Since then, various drug effects on brain epinephrine neurons have been described, including an increase in epinephrine concentration in rat brain following monoamine oxidase (MAO) inhibition (Fuller et al, 1979; Fuller et al, 1980; Scatton and Bartholini, 1980).