Two paradigm-shifting discoveries in taste research in recent years have realigned our thinking as to how taste perception is linked to mechanisms of appetite and satiety. The first was that many cells in the gut express the same molecular machinery required for nutrient detection as that found in taste cells. We now know these receptors in the gut detect ingested nutrients and mediate the secretion of gastric hormones. More recently, it was learned that these 'gastric'hormones together with their cognate receptors are also expressed in taste cells in the peripheral gustatory system. This latest discovery has raised a fundamental challenge to the field to understand how these peripheral 'gastric'hormones affect taste function and ingestive behavior. Given the worldwide rising incidence of diabetes, obesity and related metabolic disorders, we are proposing research that addresses our dearth of knowledge regarding the hormonal modulation of chemosensory perception and how disruption of hormonal signaling in the taste system can impact upon food intake and energy homeostasis. We have recently reported that the gut hormone, glucagon-like peptide 1 (GLP-1), can modulate sweet taste sensitivity. We have also reported that another GI peptide, glucagon, which plays a major role in the regulation of glucose homeostasis, can also act to modulate taste sensitivity to sweeteners. These results, when placed in the context of our preliminary findings on the hormone peptide YY (PYY) suggest that the gustatory system is indeed being dynamically modulated through hormonal action. The neuropeptide Y (NPY) family peptides, NPY and PYY, play a major role in the regulation of satiety when expressed by gut cells and/or in CNS tissues. Currently, PYY is being viewed as a candidate treatment for obesity and has been through clinical trials because of its ability to reduce food intake. However, unfortunately, high doses of PYY given systemically also cause conditioned taste aversion (CTA). Our data suggesting that PYY introduced into the oral cavity, while leading to significant weight loss in animal models, does not induce CTA, reintroduces PYY as a putative treatment for obesity. The presence of these NPY family peptides in the oral cavity, along with the expression of their cognate receptor(s) in gustatory tissues suggests that they may be influencing ingestive behavior by affecting the functioning of the peripheral gustatory system. Using a combination of genetic and pharmacological models, the proposed studies focus on investigating the general hypothesis that taste-related behavior can be modulated by metabolic hormones such as PYY and/or NPY.
Emerging research and our recent studies suggest that the taste system is intimately linked with endocrine systems that regulate energy balance. During regular cycles of food intake or during disorders of endocrine function, chemoreception may be modulated in response to changing levels of gastric hormones. We are proposing research that addresses our dearth of knowledge regarding the hormonal modulation of chemosensory perception and how disruption of hormonal signaling in the taste system can impact upon food intake and energy homeostasis;! an understanding that can lead to novel therapeutic strategies aimed at reducing food intake and controlling obesity and other lifestyle-related diseases that increasingly plague our society.