Transient overconsumption of novel foods by deafferentated rats: effects of novel diet composition.

We recently demonstrated that capsaicin-treated rats consume more of an unfamiliar high-fat diet than vehicle-treated controls, but only on initial exposure (Chavez et al, 1997). We hypothesized that negative feedback signals carried by capsaicin-sensitive visceral afferents are critical for the regulation of intake of novel foods, but redundant pathways take over during subsequent exposures. To examine the role of nutrient content of the novel diet, rats were systemically treated with capsaicin (n = 15) or vehicle (n = 10), and exposed to 1) a fat/olestra diet that was isocaloric with chow; 2) a readily accepted fat-free cake; and 3) pure corn oil. Each 3-h feeding trial was preceded by 24-h food deprivation. Treated rats did not overconsume familiar chow, but did consume 50% more than controls of both the fat/olestra diet and the corn oil on first exposure; this suggests that capsaicin eliminated visceral afferents that normally carry satiety signals. However, the effect with the fat/olestra mixture was due primarily to depressed intake by controls, unlike the pure fat diets; this apparent neophobic response was blunted in treated rats. Because treated rats failed to overconsume the fat-free cakes, the neural system damaged by capsaicin appears to be linked to energy or fat sensory mechanisms, and possibly to hedonic responsiveness.