CHRNA7 and major depressive disorder: Overall, VD supplementation holds an effective therapeutic strategy for an enhancement of cholinergic signaling and α7nAChRs gene expression as demonstrated in several animal models of MDD, PD, HD, and AD (Suzuki et al. 2013; Bordia et al. 2015; Liu et al. 2015; Takata et al. 2018; Potasiewicz et al. 2020; Kouba et al. 2022, 2023; Manjari et al. 2023; Takizawa et al. 2024; Skv et al. 2024; Rabie et al. 2024; Lykhmus et al. 2024).