CORTICOTROPIN-RELEASING HORMONE NEURONS IN THE PARAVENTRICULAR NUCLEUS PROJECT TO THE EXTERNAL ZONE OF THE MEDIAN-EMINENCE - A STUDY COMBINING RETROGRADE LABELING WITH IMMUNOCYTOCHEMISTRY

Corticotropin-releasing hormone (CRH) is the major regulator of the pi tuitary-adrenal axis. CRH-immunoreactive perikarya are widely distribu ted in the central nervous system; however, only those which participa te directly in the regulation of adrenocorticotropin are connected to the portal circulation in the external zone of the median eminence. Th e present study describes the identification of these hypophysiotropic neurons using retrograde labeling and CRH immunocytochemistry. Fluoro -Gold was injected peripherally then, 5 days later, the animals were t reated with colchicine. Twenty-four hours later the animals were sacri ficed, and their brains were immunostained for CRH with the indirect i mmunofluorescence technique. The results indicate that the vast majori ty of the Fluoro-Gold-accumulating and CRH-immunopositive perikarya (h ypophysiotropic neurons) are located in the medial parvicellular subdi vision of the paraventricular nucleus (PVN). However, not each CRH-imm unoreactive neuron contains Fluoro-Gold, i.e. a small portion of these neurons project to areas of the brain other than the median eminence. The anterior, lateral and periventricular subdivisions of the PVN als o contain hypophysiotropic CRH-immunoreactive perikarya, however, thei r number is much less than in the medial parvicellular subdivision. Sc attered double-labeled cells are also present in the medial preoptic a rea and the dorsal hypothalamus, just behind the PVN. These results su pport previous observations that the PVN, particularly the medial parv icellular subdivision, is the predominant source of the hypophysiotrop ic CRH neurons.