Figure 3.

Release mechanism and activation of enteroendocrine cells. Nutrient (diamonds) activate GPCR (blue) on enteroendocrine cell (pink), which via G-proteins (red) activate mediator release on to receptors (blue) on vagal afferents (yellow). Fluorescence micrograph inset shows cell in human colonic epithelium activated in vitro by lauric acid [phosphorylated extracellular-regulated kinase (pERK) immunohistochemistry, unpublished], Nerve recording insets show direct and modulatory effects on vagal afferents of released mediators. Data from Page et al. (2002), Kentish et al. (2011) and unpublished. Recordings are from gastric mucosal afferents in mice. Square waves indicate timing of mechanical stimuli. Note that ghrelin is probably constitutively released rather than induced by nutrient receptors.