Fos induction in selective hypothalamic neuroendocrine and medullary nuclei by intravenous injection of urocortin and corticotropin-releasing factor in rats

CRF and urocortin, administrated systemically, exert peripheral biological actions which may be mediated by brain pathways. We identified brain neuronal activation induced by intravenous (i.v.) injection of CRF and urocortin in conscious rats by monitoring Fos expression 60 min later. Both peptides (850 pmol/kg, i.v.) increased the number of Fos immunoreactive cells in the paraventricular nucleus of the hypothalamus, supraoptic nucleus, central amygdala, nucleus tractus solitarius and area postrema compared with vehicle injection. Urocortin induced a 4-fold increase in the number of Fos-positive cells in the supraoptic nucleus and a 3.4-fold increase in the lateral magnocellular part of the paraventricular nucleus compared with CRF. Urocortin also elicited Fos expression in the accessory hypothalamic neurosecretory nuclei, ependyma lining the ventricles and choroid plexus which was not observed after CRF. The intensity and pattern of the Fos response were dose-related (85, 255 and 850 pmol/kg, i.v.) and urocortin was more potent than CRF. Neither CRF nor urocortin induced Fos expression in the lateral septal nucleus, Edinger-Westphal nucleus, dorsal raphe nucleus, locus coeruleus, or hypoglossal nucleus. These results show that urocortin, and less potently CRF, injected into the circulation at picomolar doses activate selective brain nuclei involved in the modulation of autonomic/endocrine function; in addition, urocortin induces a distinct activation of hypothalamic neuroendocrine neurons.