Table 1.

Bacteria release neuromodulators.

Neuro-modulators	Bacterial genera	Brain disease	References
5-Hydroxytryptamine (5-TH)	Candida, Enterococcus, Escherichia, Streptococcus	anxiety, depression, MS, PD	Baganz and Blakely, 2013; Mawe and Hoffman, 2013; O'Mahony et al., 2015; Yano et al., 2015
β-Methylamino-L-alanine (BMAA)	Cyanobacteria	AD, ALS, PD	Meneely et al., 2016; Delcourt et al., 2017
γ-Aminobutyric (GABA)	Bifidobacterium, Lactobacillus	AD, anxiety, depression	Barrett et al., 2012; Lin, 2013; Hu et al., 2016
Acetylcholine	Lactobacillus	AD	Wessler and Kirkpatrick, 2008; Wall et al., 2014
Catecholamine (Adrenaline, Dopamine, Noradrenaline)	Bacillus, Escherichia, Saccharomyces	ASD, depression, PD, schizophrenia	Mayer and Hsiao, 2017; Mittal et al., 2017; Sugama et al., 2017
Histamine	Lactobacillus, Lactococcus, Pediococcus, Streptococcus, Enterococcus spp.	AD, MS	Landete et al., 2008; Thomas et al., 2012; Naddafi and Mirshafiey, 2013; Westfall et al., 2017
Lipopolysaccharide (LPS)	Gram-negative bacteria	AD, anxiety, ASD depression, HD, MS, PD, schizophrenia, etc.	Zhao et al., 2017
Short-chain fatty acids (SCFA, e.g., acetate, propionate and butyrate)	Bacteroides, Bifidobacterium, Clostridium, Eubacterium, Lactobacillus, Propionibacterium, Roseburia Prevotella	AD, ASD, HD, PD	Liu et al., 2015; Verbeke et al., 2015; Bourassa et al., 2016; Ho et al., 2018; Van de Wouw et al., 2018
Gingipains	Porphyromonas gingivalis	AD, PD	Adams et al., 2019; Dominy et al., 2019

Summary of the most important neuropeptides involved in brain disorders such as anxiety, autism, AD, amyotrophic lateral sclerosis, depression, MS, schizophrenia, and PD.