Catecholamines in the Median Eminence: New Evidence for a Major Noradrenergic Input

THE median eminence of the hypothalamus contains large amounts of hypothalamic hormones (releasing factors) 1 , but the cellular localization of these hormones is unknown. In contrast, there is convincing evidence, from fluorescence histochemical studies, for the existence of a dopaminergic system with neuronal cell bodies in the arcuate nucleus, whose axons project into the external layer of the median eminence 2 . Deafferentation studies combined with fluorescence 3,4 or electron microscopy 5 have suggested that there may also be a noradrenergic component in the innervation of the median eminence. We now report additional biochemical evidence supporting the existence of a substantial noradrenergic input to this brain area. We also describe the properties of a dopamine (DA) uptake system in the median eminence.