Aversion to Nicotine Is Regulated by the Balanced Activity of β4 and α5 Nicotinic Receptor Subunits in the Medial Habenula

Nicotine dependence is linked to single nucleotide polymorphisms in the CHRNB4-CHRNA3-CHRNA5 gene cluster encoding the alpha 3 beta 4 alpha 5 nicotinic acetylcholine receptor (nAChR). Here we show that the beta 4 subunit is rate limiting for receptor activity, and that current increase by beta 4 is maximally competed by one of the most frequent variants associated with tobacco usage (D398N in alpha 5). We identify a beta 4-specific residue (S435), mapping to the intracellular vestibule of the alpha 3 beta 4 alpha 5 receptor in close proximity to alpha 5 D398N, that is essential for its ability to increase currents. Transgenic mice with targeted overexpression of Chrnb4 to endogenous sites display a strong aversion to nicotine that can be reversed by viral-mediated expression of the alpha 5 D398N variant in the medial habenula (MHb). Thus, this study both provides insights into alpha 3 beta 4 alpha 5 receptor-mediated mechanisms contributing to nicotine consumption, and identifies the MHb as a critical element in the circuitry controlling nicotine-dependent phenotypes.