BDNF and major depressive disorder: Antibiotic treatment from early adolescence significantly decreased hippocampal BDNF and enhanced learning and memory impairments in a mouse model of multiple sclerosis (Zeraati et al., 2019), and prevented the development of anxiety- and depression-related behaviors, oxidative stress and hypothalamic-pituitary-adrenal axis dysregulation in AD mice (Mosaferi et al., 2021).