Choline

MPP⁺ (methylpyridinium ion) was purchased as MPP⁺ iodide from Sigma-Aldrich, dissolved in water to a stock concentration of 500 mM, and wrapped with foil to protect from light. Choline, nicotine and methyllycaconitine (MLA) were purchased from Tocris Bioscience. nicotine was used at a concentration of 2 mM for in vitro experiments based on previous reports (Ke et al., 1998 (link); Wang et al., 2011 (link)). We used MLA at a concentration of 20 µM based on a previous report that MLA at 5 µM and 10 µM could alleviate amyloid- β peptide-induced cytotoxicity in SH-SY5Y cells, without affecting cell viability (Zheng et al., 2014 (link)). At 20 µM, MLA could theoretically interact with α4β2 and α6β2 receptors, but no α4 and α6 receptor subunit mRNA was detected in SH-SY5Y cells (Gould et al., 1992 (link); Lukas, Norman & Lucero, 1993 (link)). The α7 acetylCholine receptor subunit has good expression levels in SH-SY5Y cells (Peng et al., 1994 (link)).