Learning Objectives

After completion of this module students will be able to:

• Describe components linking the gut to the brain.
• Explore the connection between the gut microbiome, diet quality, and potential risk for obesity.
• Explore the sensory physiological processes involved in taste and smell.
• Explain the relationship between taste and smell and obesity.

Key Concepts - Gut to Brain:

• The gut refers to a portion of the gastrointestinal tract (stomach and intestines) and is located in torso. The gut and brain are connected through the vagus nerve.
• The vagus nerve plays an important role in food intake and obesity.
• Transmitters and hormones are part of the chemical process that sends information from the gut to the brain; motor nerves send information from the brain to the gut creating unconscious stimulation of the GI tract, glands, and muscles.
• Obesity treatments involving changing the vagus nerve have been developed; three types of treatment for obesity:
  1. electrical stimulation of the vagus nerve;
  2. ablation or cutting of the vagus nerve;
  3. sensory denervation of the vagus through capsaicin.

Key Concepts - Sensory and Gut

• Taste, smell, and chemical irritation are chemical senses that we use every day.
• Chemical senses can influence satiety, human quality of life, reproduction, and nutrition.
• A up-close look at the tongue shows mechanisms and chemical functions of taste; the cells that comprise the taste buds receive information from papillae that interact with food chemicals from what we eat.
• The sense of taste may not be limited to the 5 known primary taste categories: umami, sweet, bitter, salty, and sour. A major new event occurring in the senses community is the discovery that free fatty acids can activate the taste system enabling humans to sense a sixth category: fattiness.
• Free fatty acids may actually taste bitter, but this is offset by triglycerides, which give a rich and pleasant sensation. It is this balance between the pleasant and unpleasant conveys our sense of fat taste.

Video Microlectures

• Video: Gut to Brain Connections in Obesity
  Dr. Megan Dailey, Department of Animal Science, University of Illinois at Urbana-Champaign

• Video: Sensory Systems and Obesity
  Dr. Richard K. Mattes, Department of Nutrition Science, Purdue University

Optional Readings

• Daly, D. M., Park, S. J., Valinsky, W. C., & Beyak, M. J. (2011). Impaired intestinal afferent nerve satiety signalling and vagal afferent excitability in diet induced obesity in the mouse. The Journal of Physiology, 589, 2857-2870.
• Yarmolinsky, D. A., Zuker, C. S., & Ryba, N. J. (2009). Common sense about taste: from mammals to insects. Cell, 139, 234-244.