Recent studies have provided a relatively complete picture of the manner in which sodium (Na) salts are transduced by taste receptor cells. One mechanism, described 20 years ago, is by Na diffusion through apically located, passive, epithelial sodium channels. Na influx through these channels can be competitively inhibited by amiloride, but saturating concentrations only inhibit about 60% of the NaCI-evoked response in the chorda tympani nerve, implicating amiloride-insensitive transduction mechanism(s) as well. This second transduction mechanism is inhibited by cetylpiridinium chloride (CPC), an over-the-counter surface disinfectant used in mouthwashes, fluoride rinses, and snore-relief sprays. Thus, for the first time, experimenters studying central nervous system processing of the afferent gustatory signal have a relatively complete understanding of that signal for one tastant, NaCI. The ability to selectively interfere with this signal using amiloride and CPC provide powerful empirical tools to address very old but unsettled questions in gustatory neuroscience; e.g., the relative contribution of labeled line versus across neuron coding schemes in the representation of taste quality. Experiments proposed will assess CPC's inherent taste (Aim #1) so that any effect of mixing CPC in with salts can be properly attributed to CPC's pharmacological interference with salt transduction. Later experiments will characterize the specificity of orally-applied CPC on central nervous system responses to salts and the extent to which CPC elevates detection thresholds for salts (Aim #2). Finally, the role of CPC-sensitive pathways in allowing organisms to appreciate the distinctive taste quality of salts will be probed in behavioral and electrophysiological studies (Aim #3). In addition to addressing basic questions about how the nervous system can represent the distinctiveness of important environmental stimuli, these studies have the potential to aid in the design of salt taste enhancers, a desirable goal given Na's palatability, but also its association with hypertension and other conditions. ? ?
