The touchy business of gastrointestinal (GI) mechanosensitivity

The gastrointestinal (GI) tract's normal function depends on its ability to propel, mix, and store contents in a highly coordinated fashion. An ability to sense mechanical forces is therefore fundamental to normal GI tract operation. There are several mechanosensory circuits distributed throughout the GI tract. These circuits rely on a range of proposed specialized and non-specialized mechanosensory cells that include epithelial enterochromaffin (EC) cells, both intrinsic and extrinsic sensory neurons, glia, interstitial cells of Cajal (ICC), and smooth muscle cells. While the anatomy of these circuits is established, the molecular mechanisms and functions are still poorly understood. In this review, we focus on the neuro-epithelial mechanosensory circuit in the gut, composed of epithelial EC cells and sensory neurons, both intrinsic and extrinsic. Intriguingly, this circuit closely resembles the light touch circuit in the skin that is composed of an epithelial Merkel cell and an afferent sensory neuron, suggesting that the basic building blocks may be retained in diverse mechanosensory systems. We compare the gross and molecular anatomy and physiology of these circuits and dissect the roles of GI neuro-epithelial mechanosensory, or "GI touch", circuitry in GI health and disease.