The Use of Selective Monoamine Oxidase Inhibitor Drugs for Evaluating Pharmacological and Physiological Mechanisms. Ciba Foundation Symposium 39 - Monoamine Oxidase and its Inhibition. Chichester: John Wiley & Sons, Ltd.; 1976. pp. 163-79. [DOI: 10.1002/9780470720219.ch9]

Neurochemical insights into monoamine oxidase inhibitors, with special reference to deprenyl (selegiline)

Monoamine oxidase (MAO) is distributed in neurons and non-neuronal tissue in the human central nervous system. It occurs there as MAO type A and MAO type B. It is not, however, established where both types are located intra- and/or extra-neuronally. Recently, the use of selective MAO-B blockers has shown beneficial effects in the treatment of Parkinson's disease (PD). Knowledge about the locus of action of MAO inhibitors is therefore of great importance. Our findings indicate that MAO-B inhibitors like deprenyl act by blocking neuronal and extra-neuronal MAO-B. This demonstrates that in the early stages of PD the action of deprenyl improves dopamine neurotransmission and hormonal action, whereas in the advanced stages of the disease, when there is progressive loss of dopaminergic neurons accompanied by gliosis, the drug seems to exert beneficial effects via the hormonal route.

Conjugated dopamine in superfusates of slices of rat striatum

An acid-hydrolyzable conjugate of 3,4-dihydroxyphenylethylamine (dopamine, DA) was detected in superfusates from slices from rat striatum. The concentrations of endogenous free and conjugated DA, and of the acid metabolites (3,4-dihydroxyphenylacetic acid [DOPAC] and homovanillic acid [HVA]) in superfusates were measured using HPLC with electrochemical detection. Conjugated DA in superfusates represented 10-20% of the free DA under basal conditions and during release evoked by p-tyramine (5 X 10(-6) M to 5 X 10(-4) M); much smaller amounts of conjugated DA overflowed into superfusate when DA was released by equimolar concentrations of beta-phenylethylamine. Surprisingly, inhibition of monoamine oxidase by the inhibitors N-methyl-N-propargyl-3-(2,4-dichlorophenoxy)propylamine hydrochloride (clorgyline) or N-methyl-N-2-propynylbenylamine (pargyline) had little effect on the amounts of conjugated DA present in superfusate. Under basal conditions, the amounts of conjugated DA in superfusate were always less than the amounts of DOPAC but quite similar to the amounts of HVA. However, during release of DA evoked by p-tyramine the concentrations of conjugated DA in superfusate showed much more pronounced increases than those of the acidic metabolites.