Interaction between Corticosterone and Alpha-2-Noradrenergic System of the Paraventricular Nucleus in Relation to Feeding Behavior

Abstract

Food consumption elicited by injection of norepinephrine (NE) into the paraventricular nucleus (PVN) of satiated rats has been shown to be dependent on the glucocorticoid corticosterone. To determine the specific nature of this dependence of NE-induced feeding on corticosterone, the efficacy of PVN-injected NE and its interaction with peripherally administered corticosterone was examined in adrenalectomized rats. NE, at doses ranging from 10 to 160 nmol, failed to elicit a reliable feeding response in these adrenalectomized animals. This loss of noradrenergic responsiveness developed at least as early as 4 h after adrenalectomy and continued until the end of the test sequence 6–8 weeks post-surgery. Single subcutaneous injections of corticosterone, administered to adrenalectomized rats, significantly restored the NE feeding response when injected 15–120 min prior to NE PVN injection, but not when administered 5 min before. Corticosterone was effective at doses of 0.5–4.0 mg/kg. Tests with other steroid hormones, namely, the synthetic glucocorticoid dexamethasone, the mineralocorticoid deoxycorticosterone, and the gonadal hormones testosterone and progesterone, were generally ineffective in restoring the sensitivity of the PVN to noradrenergic stimulation. Radioimmunoassay of circulating corticosterone in adrenalectomized rats, as a function of dose and time after injection of corticosterone, indicated that physiological levels of the hormone, at least 3 µg%, are required for a patent behavioral effect. These findings demonstrate a specific, sensitive, and rapid dependence of the PVN α₂-noradrenergic eating response on circulating corticosterone.