ROLE OF GUSTATORY AND POSTINGESTIVE ACTIONS OF SWEETENERS IN THE GENERATION OF POSITIVE AFFECT AS EVALUATED BY PLACE PREFERENCE CONDITIONING

Either an 18% sucrose or a 0.1% saccharin solution was used as reward in a conditioned place preference procedure. The respective solution w as consumed immediately before the subject was confined to the non-pre ferred compartment of a place preference box. In this way only the aff ective reaction produced by the rewarding stimulus participated in pla ce conditioning. Non-deprived rats consumed similar quantities of the two solutions, suggesting that they were equally rewarding. Yet only s ucrose induced place preference. The lack of effect of saccharin may h ave been due to weaker positive affect or to an inability to induce an affective state that outlasted consummatory behavior. The first possi bility was evaluated in the second experiment. Food-deprived rats were subjected to a discrimination learning task in a runway with plain wa ter, sucrose or saccharin as reinforcer. Sucrose sustained running res ponses and produced improvement of discrimination behavior. Saccharin had a small effect at the first sessions only. It was concluded that s accharin is less rewarding than sucrose. In a final experiment, one gr oup of rats was injected with glucose (2 g/kg) 17 min before being int roduced in the non-preferred compartment of a place preference box. An other group was given the same dose of glucose just before drinking sa ccharin for 15 min. Immediately thereafter place conditioning was perf ormed. Glucose alone had no effect, while a place preference was estab lished when glucose injection was combined with saccharin drinking. Th ese results show that the positive affect produced by sweet substances does not outlast consummatory behavior in the absence of postabsorpti ve actions. (C) 1997 Academic Press Limited.