"We found that compared to the LETO rats, the OLETF rats had about 50 percent fewer neurons firing when their tongues were exposed to sucrose, suggesting that obese rats are overall less sensitive to sucrose," explained Hajnal, whose findings appeared in a recent issue of the Journal of Neurophysiology. The response to salt was the same for both strains.
However, when the obese rats were fed a stronger concentration of sucrose, their nerve cells fired more vigorously than in the lean rats. In other words, obese rats have a weaker response to weak concentrations and a stronger response to strong concentrations.
"These findings tell us that there is a difference in activation of neurons between lean and obese rats when they are exposed varying concentrations of sucrose," noted Hajnal. "If you sense sweetness less, you may be inclined to eat sweeter foods."
The Penn State researchers believe that the increased consumption of sweet foods over time could be influencing the brain's reward center by relaying progressively weaker nerve signals, which affects the perception of taste of the meals through the PBN.
In obese humans, an increase in the weight-height ratio is usually accompanied by a decrease in dopamine, which is a neurotransmitter associated with the brain's pleasure system.
"In these obese rats, like in humans, the dopamine system is suppressed and it is very possible that the obese rats are seeking a hedonistic experience or reward by eating larger meals and when they have a chance they also eat more sweets," Hajnal added.
The findings linking taste responses and obesity could hold an important message for a condition that affects more than 60 percent of adult Americans.
For instance, Hajnal points to an ever-increasing amount of
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