Chemical lesion of visceral afferents causes transient overconsumption of unfamiliar high-fat diets in rats.

Because it is commonly assumed that the major role of visceral afferents in food intake control is to terminate meals by carrying negative-feedback signals to the brain, we hypothesized that overconsumption should occur in rats with chemically lesioned visceral afferents if they were presented with an unfamiliar diet. Adult male Sprague-Dawley (SD) rats were treated with multiple doses of capsaicin or vehicle as a control. Five weeks later, a series of 3-h feeding tests after 24-h deprivation was carried out, first with chow and then with either a solid (vegetable shortening) or liquid (Ensure) unfamiliar high-fat diet. Both groups consumed similar amounts of their powdered chow maintenance diet, but capsaicin-treated rats consumed at least 50% more of either high-fat diet than vehicle controls (P < 0.01) at the beginning of the first trial. During second and third trials with the now-familiar high-fat diet, intake was no longer significantly different between the two groups, suggesting rapid engagement of redundant control mechanisms. These results support a role of capsaicin-sensitive visceral afferents in providing negative feedback for early meal termination during the ingestion of unfamiliar diets.