BDNF and depressive disorder: In addition, LGG implantation can also activate epithelial growth factor receptor expression, enhance serotonin transporter protein expression, modulate the serotonergic system in the gut, and increase the levels of BDNF and GABA receptors in the amygdala and hippocampus (Cui et al., 2014; Johnson and Foster, 2018), which can alleviate anxiety and depression symptoms (Xu J. et al., 2022).