GABRA4 and nicotine dependence: The differentially expressed genes annotated to the nicotine addiction pathway (Table 1) included γ-aminobutyric acid type A receptor subunit alpha2 (Gabra2), γ-aminobutyric acid type A receptor subunit alpha3 (Gabra3), γ-aminobutyric acid type A receptor subunit alpha4 (Gabra4), glutamate ionotropic receptor NMDA type subunit 1 (Grin1), and glutamate ionotropic receptor NMDA type subunit 2A (Grin2a).