FOS EXPRESSION IN FOREBRAIN AFFERENTS TO THE HYPOTHALAMIC PARAVENTRICULAR NUCLEUS FOLLOWING SWIM STRESS

The paraventricular nucleus of the hypothalamus (PVN) serves as the or igin of the final common pathway in the secretion of glucocorticoid ho rmones in response to stress. Various stress-related inputs converge u pon the cells of the medial parvocellular division of the PVN. These n eurons, which synthesize and release corticotropin-releasing hormone, arginine vasopressin, and other secretagogues, are responsible for a c ascade of events which culminates in the adrenocorticotropin-induced r elease of corticosteroids from the adrenal cortex. Previous data have suggested complex afferent relation of PVN neurons, although the neuro nal pathways by which the effects of stress are mediated remain to be fully disclosed. The present experiment sought to identify forebrain a reas potentially involved in afferent regulation of the PVN in respons e to an acute stressor. Discrete injections of the retrograde tracer F luoro-gold were delivered to the PVN, and rats were subsequently subje cted to an acute swim stress. Brains were processed immunocytochemical ly for the simultaneous detection of the tracer and Fos, the protein p roduct of the immediate early gene c-fos, utilized as a marker for neu ronal activation. The majority of Fluoro-gold/Fos labeled neurons were detected in the parastrial nucleus, the medial preoptic area, the ant erior hypothalamic area, the dorsomedial hypothalamic nucleus and adja cent posterior hypothalamic area, and, to a lesser extent, the suprama mmillary nucleus. These findings are discussed in relation to neural p athways mediating activation and inhibition of the hypothalamic-pituit ary-adrenocortical axis. (C) 1996 Wiley-Liss, Inc.