Figure 3.

The potential mechanisms by which the brain senses and responds to microbial changes.

The ascending transmission involves vagal afferents terminating in the DMV and dorsal root afferents of the spinal cord, whose terminals are equipped with molecular sensors to detect inflammatory mediators and microbiota alterations. The secretions and metabolites produced by bacteria can also activate nociceptors and induce an increase in intracellular calcium flux, which in turn, stimulates the nociceptors to release neurotransmitters (such as CGRP) for signal transmission to the host brain. Additionally, EECs possess intrinsic sensory conduction properties, enabling the formation of neural circuits with vagal afferents to facilitate the transmission of alterations in the GI milieu upwards. Created with BioRender.com. CGRP: Calcitonin-gene–related peptide; DMV: dorsal nucleus of vagus nerve; EECs: enteroendocrine cells.