Fundamental Neurochemistry Review: The role of enteroendocrine cells in visceral pain.

While visceral pain is commonly associated with disorders of the gut-brain axis, underlying mechanisms are not fully understood. Dorsal root ganglion (DRG) neurons innervate visceral structures and undergo hypersensitization in inflammatory models. The characterization of peripheral DRG neuron terminals is an active area of research, but recent work suggests that they communicate with enteroendocrine cells (EECs) in the gut. EECs sense stimuli in the intestinal lumen and communicate information to the brain through hormonal and electrical signaling. In that context, EECs are a target for developing therapeutics to treat visceral pain. Linaclotide is an FDA-approved treatment for chronic constipation that activates the intestinal membrane receptor guanylyl cyclase C (GUCY2C). Clinical trials revealed that linaclotide relieves both constipation and visceral pain. We recently demonstrated that the analgesic effect of linaclotide reflects the overexpression of GUCY2C on neuropod cells, a specialized subtype of EECs. While this brings some clarity to the relationship between linaclotide and visceral analgesia, questions remain about the intracellular signaling mechanisms and neurotransmitters mediating this communication. In this Fundamental Neurochemistry Review, we discuss what is currently known about visceral nociceptors, enteroendocrine cells, and the gut-brain axis, and ongoing areas of research regarding that axis and visceral pain.