LIMITED IMPORTANCE OF A LEARNED AVERSION IN THE HYPOPHAGIC EFFECT OF INTERLEUKIN-1-BETA

This study addressed the possible role of a learned aversion in the hy pophagic effect of interleukin-1 beta (IL-1 beta) in the rat. Two repe titive intraperitoneal injections of IL-1 beta (2 mu g/kg body weight = b.wt.) progressively reduced intake of a novel-tasting saccharin die t (SD) presented immediately after injection. When SD and the familiar diet were offered some days after an injection, SD selection was in s ome but not all trials reduced by IL-1 beta pretreatment. When SD was offered alone several days after an injection, SD intake was not affec ted by the initial pairing of SD presentation with IL-1 beta injection . In further experiments, the novelty of a flavor added to the diet fe d immediately after injection proved to be crucial for the aversive ef fect of IL-1 beta, and enhanced its hypophagic effect. Finally, lesion of the area postrema and the adjacent nucleus of the solitary tract f ailed to affect the hypophagia induced by IL-1 beta (1 mu g/kg b.wt.). The results indicate that, under certain conditions, IL-1 beta can in duce an aversion to the taste and flavor of the food consumed after in jection. This aversive effect of IL-1 beta appears to be rather weak a nd is presumably not involved in the hypophagic effect of IL-1 beta un der normal feeding conditions. It may however enhance IL-1 beta's hypo phagic effect under certain conditions, for instance after repeated in jections.