Distribution of monoamine oxidase (MAO) was histochemically determined in the hypothalamo-hypophysial region of the dogfish, Triakis scyllia. MAO positive neurons, which seemed to be monoaminergic, were observed in the nucleus medius hypothalamicus (NMH) and the nucleus tuberis (NT). NMH was mainly innervated by the MAO-positive fibers arising from the tractus strio-thalamicus et hypothalamicus...