Gustatory Processing of Free Fatty Acids

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DESCRIPTION (provided by applicant): Fat is crucial for life as it promotes the growth and development of organs, including the brain. However, over consumption of fats can result in the development of obesity. In this regard, most animals (including humans) prefer savory foods that, not coincidental; have a high fat content. Thus, the taste of fat may enhance the favor of foods. Surprisingly, little research has investigated the taste of fat. Moreover, most research on fat taste has focused on behavioral responses to free fatty acids (FFAs), the building blocks of fats, rather than on neural coding of FFAs. The gustatory chorda tympani nerve (CT) has been implicated in FFA detection, as bilateral transection of the CT (CTX) significantly impairs the discrimination of linoleic acid (LA), a polvunsaturated free fatty acid and main component of some kinds of dietary fat (Stratford et al., 2006). Yet, the CT is unresponsive to lingual application of LA. Thus, a paradox exists and the exact role of the CT in LA taste discrimination remains unknown. This is particularly pertinent because an understanding of the mechanisms involved in fatty acid perception can provide insight into the development of obesity. The following experiments are designed to determine the role of the CT in LA gustatory responses using parallel behavioral and electrophvsiological methods. Because CTX disrupts:neural control of salivary secretion, Specific Aim 1 will determine the contribution of the salivary glands and salivary sodium concentration specifically to fat taste. Moreover, because fat is traditionally considered an enhancer for other tastes, Specific Aim 1 will also test the hypothesis that the addition of LA will modulate CT electrophysiological activity to other taste stimuli. In fact, LA may require a background of saliva (dilute saline) to activate taste cells (i.e., taste cells are incapable of responding to LA unless there is some low level of sodium in the environment). This would explain, in part, the discrepancy between my behavioral data (in which saliva is present) and CT electrophysiological data (in which salivary sodium is rinsed off during water rinses). Changes in CT responses to taste stimuli when LA is added would suggest that LA modulates CT responses to other taste stimuli. Finally, CTX does not abolish LA detection, suggesting that other gustatory nerves may also be involved. Specific Aim 2 will determine the role of peripheral gustatory nerves in LA taste using a conditioned taste aversion protocol with gustatory nerve transections. Impairment of LA taste discrimination following a specific gustatory nerve transection will implicate that gustatory nerve in LA taste detection. Thus, these data provide insight into the role of fat taste in the development of obesity.