BDNF and depressive disorder: Studies have shown that the use of combined probiotics (e.g., Lactobacillus, Enterococcus, and Bifidobacterium) together with prebiotics (e.g., resistant starch, and inulin), called synbiotic products, produces a high level of neurotransmitters and neuropeptides, e.g., GABA and brain-derived neurotrophic factor, improving CNS function, counting psychiatric disease-related functions, such as anxiety, depression, stress, and memory ability (14, 15, 28).