Neural Control of Large Intestinal Mucosa

Diarrhea is one of the most common symptoms of inflammatory bowel disease, parasitic infections and food allergies. Substance P which is found in extrinsic and intrinsic neurons is elevated along with its receptor during inflammation. The overall goal is to identify the role of substance P in neural reflex pathways that regulate epithelial function in the colon of guinea pigs. The first aim addresses whether neural secretory reflexes triggered by mucosal stroking and activation of 5-HT1P receptors present on intrinsic afferent neurons stimulate chloride secretion. Submucosa/mucosa preparations would be set up in flux chambers for recording short-circuit current (Isc) which reflects ion transport. Studies would identify whether substance P mediates increases in Isc during reflex activation by stimulating capsaicin-resistant neurons. Release of substance P and the effects of specific antagonists would be used to determine the synaptic coupling to down stream cholinergic or vasoactive intestinal peptide-immunoreactive neurons. The second aim is to determine whether substance P mediates it effects on Isc by releasing prostaglandins. In this phase, antagonism at prostanoid or neurokinin receptors would be examined in conjunction with release of prostaglandins, measured by radioimmunoassay. The third aim addresses the role of mast cells in mediating secretory reflexes by comparing reflexes in a model of mast cell hyperplasia, the Trichinella spiralis model, with the beta-lactoglobulin-sensitized guinea pig model with normal mast cell numbers. The third aim is to determine whether substance P activates neurokinin receptors on epithelial cells to stimulate chloride secretion and prostaglandin synthesis. Gene expression and cellular localization of neurokinin receptors would be examined by reverse transcription-polymerase chain reaction and in situ hybridization. 125 I-Bolton Hunter substance P binding would be done to verify the presence of the neurokinin receptor protein. Cloning the neurokinin receptor genes in guinea pig epithelial cells and their expression in epithelial cells lines would allow study of their function. In general, these studies are expected to provide important insights into the neural reflex pathways that govern the fluidity of the intestinal contents, and in particular, the role of substance P-containing neurons during normal or pathophysiologic states of inflammation.