Inhibitory role of cholinergic system mediated via α7 nicotinic acetylcholine receptor in LPS-induced neuro-inflammation

This study investigated the influence of the cholinergic system on neuro-inflammation using nicotinic and muscarinic receptor agonists and antagonists. Intracerebroventricular (ICV) injection of lipopolysaccharide (LPS, 50 mu g) was used to induce neuro-inflammation in rats and estimations of pro-inflammatory cytokines, alpha 7 nicotinic acetylcholine receptor (nAChR) mRNA expression were done in striatum, cerebral cortex, hippocampus and hypothalamus at 24 h after LPS injection. Nicotine (0.2, 0.4 and 0.8 mg/kg, i.p.) or oxotremorine (0.2, 0.4 and 0.8 mg/kg, i.p.) were administered 2 h prior to sacrifice. We found that only nicotine was able to block the proinflammatory cytokines induced by LPS whereas, oxotremorine was found ineffective. Methyllycaconitine (MLA; 1.25, 2.5 and 5 mg/kg, i.p.), an alpha 7 nAChR antagonist or dihydro-beta-erythroidine (DHbE; 1.25, 2.5 and 5 mg/kg, i.p.), an alpha 4 beta 2 nAChR antagonist, was given 20 min prior to nicotine in LPS-treated rats. Methyllycaconitine antagonized the anti-inflammatory effect of nicotine whereas DHbE showed no effect demonstrating that alpha 7 nAChR is responsible for attenuation of LPS-induced pro-inflammatory cytokines. This study suggests that the inhibitory role of the central cholinergic system on neuro-inflammation is mediated via alpha 7 nicotinic acetylcholine receptor and muscarinic receptors are not involved.