Transient overconsumption of novel foods by deafferentated rats: Effects of novel diet composition

We recently demonstrated that capsaicin-treated rats consume more of an unf amiliar high-fat diet than vehicle-treated controls, but only on initial ex posure (Chavez et al, 1997). We hypothesized that negative feedback signals carried by capsaicin-sensitive visceral afferents are critical for the reg ulation of intake of novel foods, but redundant pathways take over during s ubsequent exposures. To examine the role of nutrient content of the novel d iet, 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 overconsu me familiar chow, but did consume 50% more than controls of both the fat/ol estra diet rand the corn oil on first exposure; this suggests that capsaici n eliminated visceral afferents that normally carry satiety signals. Howeve r, the effect with the fat/olestra mixture was due primarily to depressed i ntake by controls, unlike the pure fat diets; this apparent neophobic respo nse was blunted in treated rats. Because treated rats failed to overconsume the fat-free cakes, the neural system damaged by capsaicin appears to be l inked to energy or fat sensory mechanisms, and possibly to hedonic responsi veness. (C) 1999 Elsevier Science Inc.