Furthermore, several signaling pathways involved in the regulations of oxidative stress, neuroinflammation, neurotransmitter dysfunction, and neurotrophic factors (e.g. brain derived neurotrophic factor, BDNF) also contribute to the pathogenesis of anxiety and depression (Kalueff et al., 2006; Ehsanifar et al., 2019). Here, BDNF is linked to major depressive disorder.