DOPAMINE-DEGRADING ACTIVITY OF MONOAMINE-OXIDASE IN LOCUS-COERULEUS AND DORSAL RAPHE NUCLEUS NEURONS - A HISTOCHEMICAL-STUDY IN THE RAT

Dopamine-degrading activity of monoamine oxidase (MAO) was detected in the rat using a new histochemical method, with dopamine as the substr ate. Our new method, designed to minimise the non-enzymatic oxidation of dopamine, was applied in combination with tyrosine hydroxylase (TH) and serotonin immunohistochemistry. We showed that the distribution p attern of MAO neurons was similar to that of TH-immunoreactive neurons (i.e. noradrenergic neurons) in the locus coeruleus (LC) and to that of serotonergic neurons in the dorsal raphe nucleus (DR). Since LC neu rons form dopamine during noradrenaline biosynthesis, and DR neurons p roduce dopamine from exogenously administered L-dopa, our results indi cate that dopamine produced in LC and DR neurons may be degraded, at l east in part, by MAO. (C) 1998 Elsevier Science Ireland Ltd. All right s reserved.