Background & Aims: Enteric glia are increasingly recognized as an important
functional component of the enteric nervous system. They have been indirectly implicated in the regulation of epithelial ion transport, which regulates homeostatic water and ion balance, through the release of the gaseous neurotransmitter nitric oxide, which has multifaceted roles in the physiological regulation and pathophysiological dysregulation of ion transport. However, the roles of enteric glia and nitric oxide in the regulation of ion transport are poorly understood in health and disease. Using nitric oxide synthase inhibition and a model of glial metabolic inhibition, the primary aims of this work were to investigate the physiological regulation of epithelial ion transport by nitric oxide and enteric glia, and how this regulation is altered during intestinal inflammation. Methods: Ion transport was measuring using full-thickness segments of mouse colon in an Ussing chamber apparatus. The release of nitric oxide from enteric glia and neurons within the myenteric plexus was assessed using amperometry and the cellular sites of nitric oxide release were investigated using nitric oxide imaging. Results: Under physiological conditions, nitric oxide release from enteric glia and neurons within the myenteric plexus regulates the nicotinically-mediated biphasic stimulation of epithelial ion transport in a concentration-dependent manner, while nitric oxide and enteric glia are not involved in the regulation of electrically-evoked stimulation of ion transport. Following intestinal inflammation, ion transport is hyporesponsive to stimulation, as the biphasic nicotinic response is reduced, and the response to electrically-evoked stimulation is absent. The inhibition of nitric oxide synthase or
the metabolic inhibition of enteric glia further inhibits the nicotically-mediated response, and restores the electrically-evoked secretory response. Conclusions: This work demonstrates novel functional roles for nitric oxide released from enteric glia in the nicotinically-mediated physiological regulation and electrically-evoked pathophysiological dysregulation of intestinal ion transport. Additionally, a previously unappreciated role for the myenteric plexus in the regulation of nicotinically-mediated ion transport under physiological conditions is described. The data presented in this thesis highlight and extend the important roles of nitric oxide and enteric glia within the myenteric plexus in gastrointestinal health and disease.