BDNF and depressive disorder: Furthermore, psychobiotics have demonstrated efficacy in reducing some physiological outputs of anxiety and depression such as immune function, corticosterone/cortisol, neurotransmitters, and brain-derived neurotrophic factor (BDNF) in animal and human studies (Bercik et al., 2011; Bravo et al., 2011; Buffington et al., 2016; Messaoudi et al., 2011).