Neuronal responses to systemic nicotine in the solitary tract nucleus: origin and possible relation with nutritional...

Single-unit activity was recorded extracellularly in the caudal part of the solitary tract nucleus of anesthetized rats. Of 60 recorded neurons, 44 (73.3%) responded to intravenous (I.V.) nicotine. The incidence of response was significantly greater in the cells sensitive to moderate changes in blood glucose level, suggesting that the effects of nicotine on food intake and body weight are partly mediated by the glycemia-sensitive neurons in the caudal nucleus tractus solitarius. Only one-fourth of the neurons affected by I.V. nicotine responded in the same direction to iontophoretic nicotine application, suggesting that sensitivity to systemic nicotine results mainly from an indirect mechanism. Based on the observed effects of nicotinic agonists and antagonists unable to cross the blood-brain barrier, a majority of indirect unit responses to I.V. nicotine might be mediated by peripheral receptors, while the remaining ones might involve central or both central and peripheral receptors.