DETECTION OF MAO-A AND MAO-B MESSENGER-RNAS IN MONKEY BRAIN-STEM BY CROSS-HYBRIDIZATION WITH HUMAN OLIGONUCLEOTIDE PROBES

The distribution of mRNAs encoding the isoenzymes monoamine oxidase A and B (MAO-A and MAO-B) in monkey locus coeruleus and dorsal raphe nuc leus was studied by in situ hybridization histochemistry using S-35-la belled oligodeoxynucleotide probes complementary to cloned human seque nces. MAO-A mRNA was highly expressed in noradrenergic neurons of the locus coeruleus while MAO-B mRNA was abundantly and exclusively locali zed in serotoninergic neurons of the raphe. However, upon emulsion rad ioautography raphe neurons showed a level of MAO-A mRNA signal noticea bly above the background. Our results indicate the utility of human MA O oligodeoxynucleotide probes to identify homologous species of transc ripts in the brain of a non-human primate. They also suggest the coexi stence of the isoenzymes in raphe neurons as well as the potential rol e of MAO-A in metabolizing serotonin in vivo.