Table 1.

Bacteria and the enteric nervous system.

Field of Interest	Key Findings
Gut Microbiota
Social behavior	Social events allow horizontal transmission of microbes between individuals of the same species (as observed in Blattodea or baboons). Rodent models with high-fat diets and reduction of Lactobacillus spp. give birth to offspring with reduced ability to discriminate between familiar and unknown individuals of the same species. Dysbiosis promotes drastic changes in social behavior in rodents and supplementation with Bifidobacteria and Lactobacilli leads to improvement in early life and adulthood.
Sleep cycle and mood dysorders	Gut microbiota can alter sleep cycles through the systemic production of inflammatory cytokines, which have been proven to alter non-REM sleep and alter cortisol and norepinephrine production. These phenomena are related to gut permeability and systemic translocation of gut bacteria.
Alzheimer’s disease (AD)	Several bacteria promote neuro-inflammatory response typical of AD. Increased phosphorylated tau in patients with microbiota metabolites in cerebrospinal fluid.
Parkinson’s disease (PD)	High microbial density in the olfactory bulbs of patients with PD. Postural instability and gait symptoms can be associated with abundance of particular species.
Pathogenic bacteria
Toxin-producing bacteria	Toxin-induced diarrhea is favored by the promotion of serotonin (5-HT) from the mucosa, resulting in activation of the secretomotor reflex pathways through local 5-HT receptors. In cases of emesis, 5-HT receptors are located in vagus nerve (VN) sensory terminals that project up to the emetic center in the brainstem.

Given the broad abundancy of information on the topic of interactions between bacteria (being pathogens or commensal bacteria), only key findings have been reported.