Molecular neuroanatomy of monoamine oxidases in human brainstem

Specific, high-resolution techniques (quantitative enzyme radioautography and in situ hybridisation histochemistry) have revealed distribution, abundance and cellular localization of the isoenzymes MAO-A and MAO-B and their mRNAs in human post-mortem brainstem. Whereas MAO-A protein and mRNA are expressed by noradrenergic neurons of the locus coeruleus, MAO-B protein and mRNA are expressed by serotoninergic neurons of the raphé nuclei. In the substantia nigra, MAO-B was more abundant than MAO-A; the former was localized in the reticular zone and the latter in the compact zone (where melanin-containing dopaminergic neurons are found). To date, it has not been possible to detect mRNA for either MAO-A or MAO-B in the substantia nigra or in glial cells of the brain regions investigated, suggesting either that the technique has limited sensitivity, or the possible existence of MAO-A and MAO-B subtypes.