Fig. 1.

The gut microbiome produces molecules such as SCFAs and 2-BAs that simulate enterochromaffin cells to release 5-HTs. 5-HTs communicate via the vagus nerve, traveling to the nucleus tractus solitarius in the brainstem. The autonomic nervous system also communicates via the vagus nerve and can activate enterochromaffin cells to release 5-HT into the gut.

SCFAs, short-chain fatty acids; 2-BAs, secondary bile acids; 5-HTs, serotonins; DRN, dorsal raphe nucleus; NTS, nucleus tractus solitarii.