BDNF and major depressive disorder: Ongoing research has identified multiple pathogenic factors in depression, including impaired neuroplasticity, inflammatory dysregulation, neuroimmune dysfunction, disrupted BDNF signaling, and HPA axis abnormalities (Chen et al., 2024; Lemogne et al., 2024; He et al., 2024; Köhler et al., 2017; Duman and Aghajanian, 2012; Castrén and Rantamäki, 2010).