Abdominal pain is the most common gastrointestinal (GI) issue and the most debilitating feature of disorders of gut-brain interaction (DGBI) such as irritable bowel syndrome (IBS) and the inflammatory bowel diseases (IBDs). Abdominal pain is driven by mechanisms that lead to the sensitization of peripheral nerve fibers. However, very little is known about the specific mechanisms that sensitize nerve terminals in the intestine.Nociceptors densely innervate enteric ganglia where they interact with enteric glia. Neuron-glia communication regulates gut reflexes in health and glia contribute to neuroinflammation by releasing mediators that contribute to enteric neuron death. Glial cells are key players in central pain pathways, but whether enteric glia fulfill similar functions during the development of visceral pain is unknown. We recently discovered that communication between nociceptors and enteric glia drives neuroinflammation in the intestine. Nociceptors release mediators that activate enteric glia and promote neuroinflammation by driving reactive gliosis. Enteric glia possess the ability to modulate afferent nociceptor signaling through the release of neuromodulators or through communication with other cell types like enteric neurons and immune cells. This dissertation aimed to define novel glial mechanisms that sensitize visceral afferent nerves during inflammation.℗ To address this question, we used in vivo and in vitro models of acute inflammation in combination with novel transgenic animal models, protein and RNA labeling, Ca2+ imaging techniques, chemogenetics, and visceromotor reflex recordings and assessed the contribution of enteric glia to nociceptive signaling in the myenteric plexus. We discovered that enteric glia sensitize TRPV1-nociceptor activity during acute inflammation, and they do so through mechanisms that involve IL-1Îø and the connexin-43-dependent release of PGE2. In vivo, recordings show that colonic IL-1Îø shifts normal innocuous stimuli toward a noxious range through mechanisms that require glial Cx43, given that glial knock animals did not develop hypersensitivity. We further provide evidence that enteric glia modulate visceral hypersensitivity through mechanisms involving endocannabinoids. Specifically, the endocannabinoid hydrolyzing enzyme, monoacylglycerol lipase (MAGL), expressed by enteric glia, regulates neural-glial signaling in the myenteric plexus, and this effect is altered during inflammation. Visceral hypersensitivity induced in animal models of colitis is ameliorated by either the pharmacological inhibition or genetic ablation of MAGL. Our data also demonstrate that the glial-mediated mechanisms of visceral hypersensitivity during colitis are sexually dimorphic.℗ Our data provide new evidence for the active role of enteric glia in afferent signaling and visceral hypersensitivity. Specifically, we demonstrate that 1) glia-nociceptor signaling in the intestine is required for the sensitization of nociceptors and visceral hypersensitivity, 2) enteric glia can modulate nociceptor sensitivity directly through the release of pro-inflammatory neuromodulators like PGE2 3) or through regulation of endocannabinoid signaling via MAGL, and 4) the glial mechanisms involved in visceral hypersensitivity during acute inflammation are sex-dependent and are predominant in females. Results from these studies identify fundamental glial mechanisms that govern the activity of nociceptors in the intestine. Identifying the mechanisms contributing to the development of visceral pain will facilitate the development of new, more effective therapies for those suffering from chronic abdominal pain.
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