SEROTONIN(3) ANTAGONISTS BLOCK AVERSION TO SACCHARIN IN AN AMINO ACID-IMBALANCED DIET

Conditioned taste aversion presumably plays a role in the anorectic re sponses to amino acid-imbalanced diets that induce acute amino acid de ficiency. The serotonins (5-HT3) receptor antagonists, tropisetron (Tr op), MDL-72222 (MDL), and ondansetron, increase intake of imbalanced a mino acid diets. Therefore, we tested whether 5-HT3 receptor antagonis ts would block an aversion to powdered saccharin after it was included in an amino acid-imbalanced diet. Rats were given an intraperitoneal injection of Trop, MDL, or vehicle (Veh), just before introducing one of four diets: imbalanced amino acid diet +/- saccharin (Imb or Imb(Sa c)) or a balanced (corrected) diet +/- saccharin (Cor or Cor(Sac)). Su bsequent aversion to saccharin was shown in preference tests using Cor and Cor(Sac). Saccharin preference was significantly decreased (8.3% on test day 1) in the Veh/Imb(Sac) group, but the Trop/Imb(Sac) group' s saccharin preference (57.8%) was similar to controls (49.6-70.3%); M DL also blocked the aversion to saccharin after Imb(Sac). This confirm s previous reports of conditioned taste aversions with amino acid limi tation and suggests a role for the 5-HT3 receptor in the development o f these aversions.