LOCALIZATION OF MONOAMINE-OXIDASE-A AND MONOAMINE-OXIDASE-B MESSENGER-RNA IN THE RAT-BRAIN BY IN-SITU HYBRIDIZATION

Monoamine oxidases A and B (MAOA and MAOB) are the major catabolic iso enzymes of catecholamines and serotonin in the mammalian brain. Althou gh the distribution of the monoamine oxidase protein has been mapped b y ligand binding and immunohistochemistry, the sites of MAOA and MAOB synthesis have not been precisely determined. In this study, we used i n situ hybridization to visualize MAOA and MAOB mRNAs in the rat brain by using specific cDNA and oligonucleotide probes. MAOA mRNA was loca lized in major monoaminergic cell groups, such as the dorsal vagal com plex, the C1/A1 groups, the locus ceruleus, the raphe nuclei, the subs tantia nigra, and the ventral tegmental area. MAOA mRNA was also found in forebrain structures, such as the cortex, the hippocampus, the tha lamus, and the hypothalamus. In contrast to the distribution of MAOA m RNA, high levels of MAOB mRNA were present in only three brain regions : the area postrema, the subfornical organ, and the dorsal raphe. The in situ visualization of MAO mRNA demonstrates that MAOA mRNA synthesi s is wide spread in many catecholaminergic and serotonergic cell group s, whereas MAOB mRNA synthesis is far more discrete and limited. The d ifferent expression patterns of MAOA and MAOB suggests that may also h ave different physiological functions. (C) 1997 Wiley-Liss, Inc.