Binding and functional activity of nicotinic cholinergic receptors in selected rat brain regions are increased following long-term but not short-term nicotine treatment.
Nguyen, Henry N. 1; Rasmussen, Bruce A.; Perry, David C.
[Article] Journal of Neurochemistry. 90(1):40-49, July 2004.

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Chronic nicotine exposure up-regulates neuronal nicotinic receptors, but the functional consequences for these receptors is less well understood. Following 2 weeks of nicotine or saline treatment by osmotic minipump, the functional activity of nicotinic receptors was measured by concentration-response curves for epibatidine-stimulated 86Rb efflux. Nicotine-treated animals had a significantly higher maximal efflux in cerebral cortex and superior colliculus, but not in thalamus or interpeduncular nucleus plus medial habenula. This increase was confirmed in a separate experiment with stimulation by single concentrations of epibatidine (cortex, superior colliculus) or nicotine (cortex only). Chronic nicotine did not alter 86Rb efflux stimulated by cytisine, an [alpha]3[beta]4-selective agonist, or by potassium chloride, in any region. Short-term (16 h) nicotine exposure caused no changes in either 86Rb efflux or receptor binding measured with [3H]epibatidine. Binding was significantly increased after 2 weeks nicotine exposure in cortex, superior colliculus and thalamus, but not in interpeduncular nucleus plus medial habenula. The increases in epibatidine-stimulated 86Rb efflux in the four regions tested was linearly correlated with the increases in [3H]epibatidine binding in these regions (R2 = 0.91), suggesting that rat brain receptors up-regulated by chronic nicotine are active. These results have important consequences for understanding nicotinic receptor neurobiology in smokers and users of nicotine replacement therapy.

(C) 2004 International Society for Neurochemistry