Morphological evidence that serotonin-immunoreactive neurons in the nucleus dorsomedialis hypothalami could be under catecholaminergic influence.

In the nucleus dorsomedialis hypothalami (NDM), it has so far been possible to visualize serotonin (5-HT) neurons by 5-HT immunohistochemistry only after inhibition of the monoamine oxidase and loading with tryptophan. We report here that the intraventricular administration of dopamine, noradrenaline (NA) and adrenaline as well as isoproterenol and, to a lesser extent, apomorphine, similarly permitted 5-HT immunostaining of these neurons in pargyline-pretreated rats, and that additional pretreatment with propranolol prevented the NA-induced effect. Hence, it is proposed that the 5-HT content in the presumed serotoninergic neurons of the NDM could be under dopaminergic and/or beta-adrenergic receptor-mediated catecholaminergic influence.