Potentiometric probes are dyes which, when bound to the membranes of excitable cells, behave as molecular indicators of membrane potential. The optical properties of these molecules vary linearly with voltage and may be used to monitor action potentials, synaptic potentials, or other voltage changes from a large number of sites at once, without the use of electrodes. For nearly thirty years our laboratory has pioneered the technology for using potentiometric probes, and developed new optical methods for use in cellular neurophysiology, including a system for Multiple Site Optical Recording of Transmembrane Voltage (MSORTV). Now we will employ a new and much more sensitive high-resolution camera system and newly designed voltage sensitive dyes, to study the functional role of individual nicotinic acetylcholine receptor (nAChR) subtypes in intact vasodilator reflexes that are fully contained within the gut wall and are mediated by the enteric nervous system (ENS). The ENS is an autonomous network with identified functions, comprising two plexuses, submucous and myenteric, located in distinct planes within the gut wall. Since the effector organs for these plexuses (blood vessels, transporting epithelium, neuroendocrine cells, immune elements, and smooth muscle) are also contained within the gut wall, semi-intact preparations can be dissected that preserve intact reflex pathways. The vasodilator reflexes described here can be evoked by electrical stimulation, balloon-distension or mucosal-stroking, and require activation of myenteric neurons that converge onto vasodilator submucosal neurons whose activity triggers the dilation of submucosal arterioles. The reflex evoked by electrical stimulation will be studied in a myenteric-submucosa semi-intact preparation. The others will be studied in a semi-intact flat-sheet ileal preparation. All of these reflexes exhibit hexamethonium-sensitive myenteric and submucosal components. Thus, by using MSORTV and a novel analytical approach, we will identify the role of individual nAChR subtypes in vasodilation. These reflex pathways, that project through the myenteric plexus to the submucosa, serve as examples of the mechanisms, built into ENS networks, which coordinate mucosal blood flow with specific motor and secretory patterns in the intestine.
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