Hepato-vagal pathway associated with nicotine's anorectic effect in the rat

Nicotine reduces appetite and body weight. Because the hepato-portal area s enses different types of nutrients that transmit signals via vagal afferent nerves to the hypothalamus to modify food intake and feeding pattern, we i nvestigated the effect of nicotine on a hepato-vagal-hypothalamic pathway. Low doses of nicotine (< 10 ng) injected into portal vein (ipv) decreased. while high doses of nicotine increased (greater than or equal to 10 ng) ele ctrophysiological activity of hepatic vagal afferents. Stimulatory effect o f high dose of nicotine on vagal hepatic afferents was blocked by a prior i pv injection of curare (30 mug) or hexamethonium (1 mg). Furthermore. activ ities of gastric vagal and adrenal sympathetic efferents were suppressed by low-dose, but stimulated by high-dose ipv nicotine, These reflex effects d id not occur in hepatic vagotomized rats. Results of experiments demonstrat e that in addition to nicotine's anorectic effect being mediated via a dire ct central action, nicotine also acts peripherally via hepatic vagal affere nts from sensors of nicotine in the hepato-portal region. (C) 2001 Elsevier Science B.V. All rights reserved.