Central Type 2 Corticotropin-Releasing Hormone Receptor Mediates Hypothalamic-Pituitary-Adrenocortical Axis Activation in the Rat

Abstract

In an attempt to clarify the role of the type 2 corticotropin-releasing hormone (CRH) receptor (CRHR-2) in the brain in activation of the hypothalamic-pituitary-adrenocortical axis, we conducted experiments using male Wistar rats. First, an injection of urocortin-2 (7.5 µg) into the lateral ventricle resulted in transient increases in CRH heteronuclear RNA (hnRNA) in parvocellular paraventricular nucleus (PVN) and in plasma adrenocorticotropic hormone (ACTH), whereas sustained increases in arginine vasopressin (AVP) hnRNA and c-fos mRNA in the parvocellular PVN were observed as compared with vehicle treatment. Pretreatment with the selective CRHR-2 antagonist antisauvagine-30 (20 µg) into the lateral ventricle 15 min prior to agonist injection attenuated the stimulatory effects of urocortin-2 on the above-mentioned hypothalamic-pituitary-adrenal axis variables. These effects were similar or rather more potent than those induced by pretreatment with 50 µg of α-helical CRH. Second, we found longer-lasting increases in CRH and AVP hnRNA and c-fos mRNA in parvocellular PVN and in plasma ACTH following central administration of urocortin-3 (7.5 µg) than following urocortin-2. Pretreatment with antisauvagine-30 antagonized the effects of urocortin-3 on the above-mentioned variables. Finally, central administration of antisauvagine-30 as well as α-helical CRH profoundly attenuated restraint-stress-induced increases in AVP hnRNA. However, α-helical CRH, but not antisauvagine-30, attenuated restraint-stress-induced increases in CRH hnRNA in the PVN. Both antagonists transiently attenuated stress responses of c-fos mRNA in PVN and plasma ACTH. These results indicate that there is a CRHR-2-mediated mechanism in the brain that stimulates CRH- and AVP-producing neurons in the PVN which results in the promotion of plasma ACTH secretion.