Corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) play a central role in regulating the stress response. In response to stress, CRF and AVP neurons in the hypothalamic paraventricular nucleus secrete the peptides to stimulate the release of adrenocorticotropic hormone from the anterior pituitary. Ghrelin, an endogenous ligand of the growth hormone-releasing peptide receptors (GHSR), has been shown to stimulate the release of CRF and AVP by rat hypothalamic explants. However, little is known about the ability of the ghrelin signaling pathways to activate the CRF and AVP genes in the hypothalamus. In the present study, we examined the direct effect of ghrelin on CRF and AVP gene expression in hypothalamic 4B cells, which show the characteristics of the hypothalamic parvocellular paraventricular nucleus neurons. Cells were transfected with CRF or AVP promoter to examine the activity of each promoter. Ghrelin stimulated the promoter activities and mRNA levels for both CRF and AVP. The involvement of a protein kinase pathway was examined using inhibitors. Protein kinase A and phospholipase C pathways were shown to be involved in ghrelin-induced increases in both CRF and AVP promoter activities. GHSR type 1a (GHSR1a) mRNA levels were also increased by ghrelin, and these ghrelin-induced levels were suppressed by a GHSR1a antagonist. Thus, ghrelin-dependent pathways are involved in the regulation of CRF and AVP gene expression in the hypothalamus: ghrelin, an orexigenic hormone, stimulates CRF, an anorexigenic/anxiogenic factor in the hypothalamus, resulting in hypothalamic-pituitary-adrenal axis activation to stimulate the release of glucocorticoids.

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Corticotrophin-releasing factor (CRF) plays a central role in controlling the hypothalamic-pituitary-adrenal axis during stressful periods. CRF neurones are activated in the hypothalamic paraventricular nucleus (PVN) in response to stress, whereas the activated CRF neurones in the PVN are suppressed by glucocorticoids. Glucocorticoids may act directly on CRF neurones because glucocorticoid receptors are expressed highly on these neurones in the PVN. CRF expression levels in the PVN are also increased by adrenalectomy in vivo. The signalling pathways involved in the control of CRF gene transcription in the hypothalamus when negative feedback by glucocorticoids after adrenalectomy is lost remain undetermined. We investigated whether CRF gene transcription is regulated by both glucocorticoids and glucocorticoid withdrawal in hypothalamic cells. The present study demonstrates that CRF gene transcription activity and mRNA levels in the hypothalamic 4B cells were not modulated by incubation with dexamethasone for a short 2-h period, although they were stimulated by incubation for longer than 5 h. CRF gene transcription activity and mRNA levels were increased after 2 h of dexamethasone deprivation. The cAMP-response element (CRE) on the promoter was the main region that is regulated by both glucocorticoids and glucocorticoid withdrawal. We observed that the intracellular cAMP production levels were transiently increased 30 min after the removal of dexamethasone, whereas they were also increased 2.5 h after incubation with dexamethasone without the removal. Phosphorylated-CRE-binding protein (CREB)/CREB protein levels were also increased rapidly after the deprivation of glucocorticoids via an adenylate cyclase pathway. Therefore, the phosphorylation of CREB contributes to the activation of CRF gene transcription after the deprivation of glucocorticoids in hypothalamic cells.

Corticotropin-releasing factor (CRF) activates the pituitary-adrenal axis during stress, and shows anorectic effects via CRF type 1 receptors in the hypothalamus.Both urocortin (Ucn) 2 and Ucn3 also act as anorectic neuropeptides via CRF type 2 receptors. Leptin, a product of the obesity gene secreted mainly from adipose tissue, reduces food intake and increases energy expenditure. A possible interaction between leptin and CRF/Ucns has been suggested, as leptin can regulate expression and activation of CRF and Ucns in the hypothalamus. This study aimed to explore the possible function of leptin in the hypothalamus, and its effects in regulating CRF and Ucns. The study identified mRNA expression of the leptin receptor (Ob-R) and its subtypes, CRF, and Ucn2/3 in mouse hypothalamic N39 cells. Leptin stimulated signal transducer and activators of transcription type 3 (STAT3) phosphorylation, directly increased the mRNA levels of both CRF and Ucn2/3 in hypothalamic cells, and increased Ob-Rb mRNA levels. A Janus kinase inhibitor inhibited the leptin-mediated increase in STAT3 phosphorylation, and then the increases in CRF and Ucn2/3 mRNA levels. Leptin may contribute to a stress response or anorectic effect via the regulation 2 of CRF and Ucn2/3 in the hypothalamus.