CAPSAICIN ATTENUATES FEEDING SUPPRESSION BUT NOT REINFORCEMENT BY INTESTINAL NUTRIENTS

During and after a meal, the presence of nutrients in the intestine ca n be rapidly detected and signaled to the brain via visceral afferents . Intestinal infusions of carbohydrate and fat suppress food intake, a nd this satiety action is inhibited by capsaicin, a neurotoxin that pr oduces a partial visceral deafferentation. This study determined if th e postingestive reinforcing action of nutrients is also suppressed by capsaicin treatment. Food-restricted control and capsaicin-treated rat s were trained to drink a flavored solution paired with intraduodenal infusions of carbohydrate (Polycose solution) on some days and, on oth er days, a differently flavored solution paired with intraduodenal wat er infusions. In a choice test, both groups displayed a strong prefere nce for the Polycose-paired flavor. In a subsequent satiety test, howe ver, intraduodenal Polycose suppressed sucrose sham feeding in the con trols but not in capsaicin-treated rats. The same rats were next train ed to associate new flavors with intraduodenal fat (corn oil emulsion) and intraduodenal water infusions. During training, oil infusions red uced oral intakes in the controls much more than in the capsaicin-trea ted rats. Both groups reliably preferred the oil-paired flavor in the subsequent choice test. These results indicate that, unlike the satiat ing effect of intestinal carbohydrate and fat, the reinforcing actions of these nutrients are not mediated by capsaicin-sensitive visceral a fferents. The data also imply that the postingestive reinforcement pro duced by nutrients is not dependent on the nutrients' satiating qualit y.