These experiments were performed in Tabac mice backcrossed to the inbred mouse line C57BL/6 (Figure 7C), which has been shown to have a high basal level of self-selection of nicotine (Glatt et al., 2009, Meliska et al., 1995 and Robinson et al., 1996), and in Tabac mice outbred between FBV/N mixed and Swiss Webster (Figure 7D). As shown in Figure 7C, in C57BL/6 Tabac mice, injection of buy Vandetanib the LV-α5N virus reversed their nicotine aversion in comparison to mice injected with the control virus. In outbred Tabac mice injected with the control virus,
we observed no alteration in nicotine aversion (Figure 7D) with respect to uninjected Tabac mice (Figure 6C). Importantly, infection with LV-α5N virus reversed nicotine aversion in Tabac mice (Figure 7D), restoring nicotine consumption in α5 D397N-infected Tabac mice to levels evident in WT mice (Figure 6C). These results demonstrate a major role for the MHb in nicotine consumption. Human genetic studies have established an association between the CHRNB4-CHRNA3-CHRNA5
locus and tobacco use ( Amos et al., 2010b, Saccone et al., 2009, Thorgeirsson et al., 2008 and Weiss et al., 2008). Here we report a mouse model (Tabac mice) with altered nicotine consumption and CPA caused by elevated levels of β4, enhanced nicotine-evoked currents, and increased surface expression of functional nAChRs at endogenous sites. The ability of β4 to enhance nicotine-evoked currents depends on a single critical residue (S435) located in the intracellular vestibule of the receptor. Interestingly, modeling studies revealed that one this website of the most common SNPs associated with tobacco usage, D398N in the α5 subunit, also maps to this domain. Functional analyses of this variant demonstrate that alterations in this domain can result in profound effects on nicotine-evoked currents. many Based on our studies in Tabac mice in which enhanced current is associated with increased aversion to nicotine, we predicted that the α5 variant (corresponding to D397N in
mice) should increase nicotine consumption consistent with its association with smoking. To test this idea, and given that the MHb contains a very high concentration of endogenous α3β4α5 receptors and elevated levels of β4 driven by the Tabac transgene, we introduced the α5 variant by viral-mediated transduction in habenular neurons of Tabac mice. The reversal of the nicotine aversion achieved in Tabac mice observed in these experiments demonstrates that the MHb plays a major regulatory role in nicotine consumption. Three main points are addressed in this study. First, changes both in the coordinated expression of α3β4α5 subunits (i.e., overexpression of the β4 subunit) and in single residues (i.e., in vivo viral-mediated expression of the α5 D397N variant) have a strong influence on nicotine consumption in mice.