Extrahypothalamic corticotropin-releasing hormone mediates (−)-nicotine-induced elevation of plasma corticosterone in rats

Abstract

(−)-Nicotine activates the hypothalamic–pituitary–adrenal axis via an activation of the brainstem catecholaminergic neurons in rats. The present study was undertaken to clarify the mechanisms involved in the (−)-nicotine-induced activation of brainstem catecholaminergic neurons in anesthetized rats. Physostigmine (a cholinesterase inhibitor) (0.31 and 0.77 μmol/animal, i.p.) dose-dependently elevated plasma corticosterone in the presence of scopolamine (a muscarinic receptor antagonist) (2.3 μmol/animal, i.p.). (−)-Nicotine (250 and 500 nmol/animal, i.c.v.) dose-dependently elevated plasma corticosterone with concomitant noradrenaline release in the hypothalamic paraventricular nucleus. The (−)-nicotine (500 nmol/animal, i.c.v.)-induced elevation of corticosterone was abolished by phentolamine (an α-adrenoceptor antagonist) (0.66 μmol/animal, i.c.v.), and attenuated by (±)-sotalol (a β-adrenoceptor antagonist) (0.97 μmol/animal, i.c.v.). The (−)-nicotine-induced increases of plasma corticosterone and hypothalamic noradrenaline release were abolished either by hexamethonium (a nicotinic acetylcholine receptor antagonist) (1.8 μmol/animal, i.c.v.), CP-154,526 (butyl-ethyl-[2,5-dimethyl-7-(2,4,6-trimethylphenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-yl]amine) (a selective CRF-1 receptor antagonist) (1.3 μmol/animal, i.c.v.) or indomethacin (a cyclooxygenase inhibitor) (1.2 μmol/animal, i.c.v.). These results suggest that (−)-nicotine elevates plasma corticosterone by CRF-1 receptor- and prostaglandin-mediated noradrenaline release in the paraventricular nucleus in rats.