Obesity occurs because individuals regularly ingest more calories than they expend. This takes place when the reward value of the food is greater than the sum of the satiety signals arising in the gut. Nevertheless, the neural mechanisms that assign hedonic value to taste remain unknown. The neural substrates for the decision to whether ingest or reject a food are complete in the brainstem. In rats, the brainstem contains the first and second central relays for both the gustatory and vagal visceral afferent systems, the motoneurons responsible for ingestive behavior, and sufficient integrative capacity to make this decision. Nevertheless, control of ingestion requires connections to and from the forebrain because disconnecting it from the brainstem eliminates voluntary eating. Writ large, the goal of this research is to understand how the forebrain interacts with these hindbrain mechanisms to bring about the smooth, nuanced control of feeding behavior that characterizes omnivores such as rats and humans. Using behavioral, neuroanatomical, neurochemical, and electrophysiological analysis, this project will test hypotheses about how the reward value of gustatory stimuli is elaborated in the brain.
The first Aim i s to further determine the specific ventral forebrain projections from the parabrachial nuclei that are critical for modulating dopamine release as a function of the rewarding (and aversive) properties of taste stimuli.
Aim 2 addresses functional correlates of those connections by comparing dopamine release in the nucleus accumbens and the central nucleus of the amygdala -- putative nodes in the forebrain reward system -- during homeostatic and hedonic ingestion.
Aim 3 focuses on gustatory neural activity in the pontine taste relays while varying both oral and postoral taste stimulation. The findings will aid in understanding basic regulatory mechanisms that fail to control intake in individuals susceptible to developing dietary obesity due to increased stimulation from augmented palatability of the modern diet.
Palatable foods stimulate intake beyond physiological needs, an effect that leads to obesity. To understand the sensory integration responsible for such hedonic eating, we will examine gustatory neural responses and central dopamine release during oral sucrose stimulation. This project will help us determine how a normally well regulated behavior, such as eating, can go so far awry as to cause an epidemic.
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