BDNF and mental disorder: It is well known that the pathogenesis of mental disorders could be explained by a variety of hypotheses, such as the neuroinflammation hypothesis (Dey and Hankey Giblin, 2018; Li et al., 2022), the cyclic adenosine monophosphate response element binding protein (CREB)-brain-derived neurotrophic factor (BDNF) signaling impairment hypothesis (Koch et al., 2009; Tan et al., 2022), and the neurotransmission dysfunction hypothesis (Wang et al., 2021; Yan and Rein, 2022).