Modulation of Fat Taste by Diet and Hormones

The prevalence of obesity worldwide continues to rise despite efforts to reverse the trend. While many factors contribute to the onset and maintenance of obesity, caloric intake and dietary composition have been shown be primary contributors. The oral cavity is one of the first systems to encounter food and determine its hedonic value. As the gateway to ingestion, the taste system plays a unique role in the initial decisions surrounding the control of food intake. Nutrients like carbohydrates, protein, minerals, and fat all have dedicated systems to allow their recognition at this outermost site of the enteric nervous system. Recent research has shown this system to have a high degree of plasticity, where it may tune itself to the nutritional needs of an organism. The work in this dissertation examined how circulating hormones and dietary changes alter fatty acid detection in the oral cavity thereby altering fat intake. Firstly, we examined the role high dietary fat intake has on fatty acid taste responses. We concluded that high dietary fat intake significantly increases inward currents elicited by linoleic acid (LA) in taste cells, these changes are dependent on the type of dietary fatty acids consumed, and only occur in a subset of fatty acid responding taste cells that are not thought to be the classical receptor cells of the taste bud. Additionally, to better understand physiological factors modulating fat taste sensing, we examined the effects of the orexigenic hormone ghrelin in the taste system. Through a conditioned taste aversion assay, systemic Ghrl-/- male mice exhibit diminished fat taste sensitivity compared to wild type (WT) mice with corresponding decreased calcium responses to fatty acids in taste cells. Lastly, ghrelin receptor (GHSR) agonists increased calcium responses to taste cells in WT mice. These data suggest that ghrelin plays a modulatory role in fat taste sensitivity. To further examine these effects using Ghsr-/- mice we observed Ghsr-/- females consume significantly less high fat diet than their WT counterparts. Ghsr-/- females also showed a significant reduction in fatty acid detection via a conditioned taste aversion assay with no threshold changes observed in males. Collectively, these studies demonstrate that the taste system is plastic and is modulated by diet, circulating hormone levels, and sex to selectively alter food intake