Role of mouse cerebellar nicotinic acetylcholine receptor (nAChR) α4β2- and α7 subtypes in the behavioral cross-tolerance between nicotine and ethanol-induced ataxia

Abstract

We have demonstrated that nicotine attenuated ethanol-induced ataxia via nicotinic-acetylcholine-receptor (nAChR) subtypes α4β2 and α7. In the present study, ethanol (2g/kg; i.p.)-induced ataxia was assessed by Rotorod performance following repeated intracerebellar infusion of α4β2- and α7-selective agonists. Localization of α4β2 and α7 nAChRs was confirmed immunohistochemically. Cerebellar NOx (nitrite+nitrate) was determined flurometrically. Repeated intracerebellar microinfusion of the α4β2-selective agonist, RJR-2403 (for 1, 2, 3, 5 or 7 days) or the α7-selective agonist, PNU-282987 (1, 2, 3 or 5 days), dose-dependently attenuated ethanol-induced ataxia. These results suggest the development of cross-tolerance between ethanol-induced ataxia and α4β2 and α7 nAChR agonists. With RJR-2403, the cross-tolerance was maximal after a 5-day treatment and lasted 48h. Cross-tolerance was maximal after a 1-day treatment with PNU-282987 and lasted 72h. Pretreatment with α4β2- and α7-selective antagonists, dihydro-β-erythroidine and methyllycaconitine, respectively, prevented the development of cross-tolerance confirming α4β2 and α7 involvement. Repeated agonist infusions elevated cerebellar NOx 16h after the last treatment while acute ethanol exposure decreased it. Pretreatment with repeated RJR-2403 or PNU-282987 reversed ethanol-induced decrease in NOx. The NOx data suggests the involvement of the nitric oxide (NO)–cGMP signaling pathway in the cross-tolerance that develops between α4β2- and α7-selective agonists and ethanol ataxia. Both α4β2 and α7 subtypes exhibited high immunoreactivity in Purkinje but sparse expression in molecular and granular cell layers. Our results support a role for α4β2 and α7 nAChR subtypes in the development of cross-tolerance between nicotine and ethanol with the NO signaling pathway as a potential mechanism.