Gustation as a factor in the ingestion of sweet and fat emulsions by the rat

This paper was written to pay honor to Professor Gerard P. Smith because of his strong influence on me to study the ingestion of sweet and fat mixtures. Three experiments are reported here, in which the laboratory rat was given an emulsion of a glucose+saccharin mixture with corn oil. In the first experiment, a two-bottle, 24-h test was given comparing the emulsion with water. Over 6 weeks, the concentration of the corn oil was gradually increased. When given only food and water, or the glucose/saccharin solution, the rats regulated their caloric intake and grew at a normal rate. In contrast, when the corn oil was present, the rats significantly increased their caloric intake, resulting in a marked increase in body weight. In the second experiment, a detailed analysis of the ingestion revealed that the rate of licking the emulsion during drinking bouts increased in a linear manner as the concentration of the corn oil was increased. In the third experiment, a conditioned taste aversion to the sweet/fat emulsion generalized to the fat more than to the sweet solutions. The implications for a gustatory input are discussed.