Physiology & Behavior, Vol. 18, pp. 1039-1045. Pergamon Press and Brain Research Publ., 1977. Printed in the U.S.A. Origin of Olfacto-Gustatory Alliesthesia: Intestinal Sensitivity to Carbohydrate Concentration? MICHEL CABANAC AND MARC FANTINO Universitd Claude Bernard, Facult~ de M~decine Lyon Sud-Ouest Laboratoire de Psycho-Physiologic, B.P. 12, 69600 Oullins, France (Received 21 December 1976) CABANAC, M. AND M. FANTINO. Origin of olfacto-gustatory alliesthesia: intestinal sensitivity to carbohydrate concentration? PHYSIOL. BEHAV. 18(6) 1039-1045, 1977. - Gustatory and olfactory alliesthesia was observed in nine healthy adult humans who received on three different days an intragastric load of 50 g glucose dissolved into various amounts of water in order to make 100, 200 and 400 ml of solution. Maximal alliesthesia to sweet stimuli was observed with the smallest volume, i.e., highest concentration. Comparison of these results with previous results [7], obtained not by varying the volume but by varying the glucose mass, shows identity. Maximal alliesthesia to olfactory anchovy and Viandox(R) was also observed after ingestion of the most concentrated gastric load. Maximal negative aUiesthesia was observed about 45 rain after the gastric load; thereafter alliesthesia tended to decrease. A gastric 200 ml load containing 40 g Mannitol, a nonabsorbed sugar, was followed by a strong negative alliesthesia to alimentary stimuli. Ten g glucose in 20 ml solution produced a more intense and rapid alliesthesia when injected into the duodenum than when injected into the stomach. It may be concluded that postinjective negative alliesthesia for alimentary stimuli can be caused by intraduodenal concentration of nutrients, probably sensed by duodenal nervous chemoreceptors. Alliesthesia Intestinal chemoreceptors Duodenum Mannitol Glucose concentration CABANAC, M. AND M. FANTINO. Origin of olfacto.gustatory alliesthesia: intest&al sensitivity to carbohydrate concentration? PHYSIOL. BEHAV. 18(6) 1039-1045, 1977. - L'alliesth6sie olfacto-gustative a 6t6 mesur6e chez neuf humains adultes en bonne sant6, apr6s des charges gastriques de 50 g de glucose dissout dans 100, 200 et 400 ml d'eau, donn6es trois jours diff6rents. L'alliesth&ie maximale, en r6ponse A des stimulus sucres, a ~t~ observ& avec le plus petit volume, i.e. la plus forte concentration. Les r6sultats sont superposables ~ ceux d'une exp&ience pr6c6dente [71 off la concentration des charges gastriques variait non par le volume mais par la masse de glucose dissoute. L'alliesth~sie maximale, en r~ponse A des odeurs d'anchoix et de Viandox R, a 6t6 obtenue aprbs la charge la plus concentr&. "L'atliesth6sie n~gative maximale a ~t6 observ~e environ 45 min apr& la charge gastrique, puis elle tendait A d~croitre. Une charge gastrique de 200 ml contenant 40 g de Mannitol, un sucre non absorbS, fur suivie par une alliesth~sie n~gative importante pour les stimulus alimentaires. L'injection de 10 g de glucose dans le duodenum porduisit une alliesth~sie plus intense et plus rapide que la m6me injection dans L'estomac; il est permis de conclure que l'alliesth6sie n6gative postingestive pour les stimulus alimentaires peut trouver son origine dans la concentration du bol duodenal, probablement par l'interm6diaire de chemor~cepteurs nerveux. Alliesth~sie Chemor~cepteurs Duodenum Mannitol Concentration en glucose ALIMENTARY stimuli are rated as pleasant by fasting subjects and as unpleasant by satieted subjects. Thus, the same stimulus can appear pleasant or unpleasant according to the subject's internal state. Alliesthesia is this depen- dance of the affective component of sensation, not only upon the stimulus, but also upon inner signals. Negative alliesthesia is the evolution of the sensation toward less pleasure and/or more displeasure, and positive alliesthesia the opposite. Negative alliesthesia toward sweet solutions and alimentary odors was observed after a meal [10] and gastric glucose loads, whether the load was drunk or directly injected via a nasogastric tube [5,6]. Deglutition, therefore, does not seem to be necessary for its production. Negative alliesthesia seemed also to be nonaffected by repetition of sweet oral stimuli, provided these were separated by intervals of several minutes. Negative allies- thesia was also independent of the following factors: - gastric distension: up to 1000ml water [6]; -osmotic pressure of the gastric load: 15 g NaC1 in 200 ml [6]; - systemic hyperglycemia: up to 170 mg per cent [6]; - 1039