The Contribution of Taste to Nutrient-Related Ingestive Behavior

PROJECT SUMMARY/ABSTRACT
Nutrient intake is a key factor in both maintaining and restoring good health but compliance with nutrition
guidelines remains low. A better understanding of the factors controlling food choice and intake could inform
more precisely designed dietary recommendations, thus improving compliance, and ultimately curtailing the
personal and public health burdens of chronic disease. Chief among the factors that influence food intake is
taste. Taste buds are distributed in relatively segregated fields in the oral cavity, with ~70% of taste buds located
on the tongue. Taste buds of the anterior tongue are innervated by the chorda tympani (CT) branch of CN VII
and the posterior field is innervated by the glossopharyngeal nerve (GL; CN IX). Decades of taste nerve
transection studies in rodent models suggest that the signals in these nerves do not contribute equally to taste
functions. Input from the CT, along with that from the greater superficial petrosal branch of CN VII which
innervates palatal taste buds, is essential for taste identification and discrimination. Input from the GL, in contrast,
is critical to both oromotor rejection reflexes and, combined with the CT, avoidance responses to bitter tastes.
Central to this proposal, in rats, the GL is critical for maintenance of normal corn oil preference. Although the
lingual gustatory nerves are among the first to provide sensory information about food as it enters the alimentary
tract, there is little research investigating how the information these nerves provide affects critical nutritionally
relevant behaviors like food selection and meal patterning. Recently, we found that, in male rats, combined CT
and GL transection (2Nx) alters food choices, leading to increased fat intake and reduced carbohydrate intake,
concurrent with an increase in meal size and decrease in meal number. Thus, in rats, 2Nx affects the choice of
foods and how those foods are consumed. Here, we propose to use our custom 5-Item Food Choice Monitor
(FCM) to assess intake and meal patterns in rats of both sexes offered a cafeteria diet after transection of the
CT (CTx), GL (GLx), 2Nx, or sham surgery to determine the relative role each nerve plays and how they interact
to produce the changes in macronutrient intake and meal patterns that were revealed in our preliminary study
after 2Nx. In an intriguing contrast to our preliminary study, earlier research found that after GLx, rats had lower
corn oil (i.e., fat) intake with no change in chow intake. The disparity between this earlier study and our
preliminary findings suggest food form or energy density could be a factor. Therefore, we will additionally
compare meal patterns and intake of foods varying in form/consistency, fat content, and energy density in rats
after CTx, GLx, 2Nx, or sham surgery to determine the role food characteristics may play. The combination of
selective lingual gustatory nerve transections with meal-by-meal intake data from our state-of-the-art FCM
analysis will provide a direct readout of how selective changes in sensory input affect motor output in the service
of nutritional regulation while generating both publications and strong preliminary data to support a future R01
application.

Grant Number: 5R21DC021498-03
NIH Institute/Center: NIH
Principal Investigator: Carolina Cawthon