Effect of nicotine on cerebellar granule neuron development

To assess the role of nicotinic cholinergic receptors (nAChR) on neuronal m aturation, nAChR expression and the direct effects of nAChR activation were examined in cerebellar external granular layer (EGL) precursors isolated i n vitro. Treatment of EGL neuroblasts with nicotine elicited a concentratio n-dependent increase in DNA content and synthesis, implying an increase in cell numbers. Pretreatment of cultures with the nAChR antagonist dihydro-be ta -erythroidine (DHBE) attenuated nicotine-induced changes in DNA abundanc e and synthesis. Furthermore, chronic nicotine treatment for 4-7 days promo ted EGL cell survival. Epibatidine but not cytisine stimulated granule neur oblast DNA synthesis and survival. Survival effects mediated by nicotine an d epibatidine were attenuated by pretreating cultures with DHBE. Immunocyto chemical analysis revealed that EGL neurons possessed alpha3, but not alpha 4, nAChR immunoreactivity. Quantitative autoradiography was used to determi ne which nAChRs are present during the period of granule cell neurogenesis in vivo. On postnatal day 5, the EGL was intensely labelled by [H-3]-epibat idine but virtually devoid of [H-3]-A85380 binding, suggesting that a high concentration of alpha3 AChRs is present in granule neuroblasts. The pharma cology of [H-3]-epibatidine displacement from EGL neurons also suggested an interaction with the alpha3-nAChR subunits. Together these data provide no vel evidence that the activation of nAChRs directly affect the development of primary cerebellar neuroblasts and further suggest that the effects are mediated through the alpha3-nAChR subtype.