Gastrointestinal factors in the acquisition of oral sensory control of satiation

Rats were given a series of starch meals. Half the meals were of a 65% starch solution with one taste added and the other meals were 5% carbohydrate which had been given another taste. After a few meals of each type, the dilute starch began to be taken in larger volumes. The rats were then given test meals of 35% starch having either flavour. The rate of intake towards the end of a meal decelerated more slowly in the presence of the taste given to dilute starch than in the presence of the flavour given to concentrated starch. The taste of dilute starch was not systematically preferred in a two-stimulus test. Thus there was a conditioned differentiation of the oral control of satiation: the onset of satiety was slowed in the presence of oral cues which had been associated with the passage of very little carbohydrate. The oral control of satiety was acquired even when meals differed in starch concentration during their first 5 min only. In contrast, concentration differences after the first 5 min did not generate an adequate unconditioned stimulus. It appeared therefore that the unconditioned stimulus was related to the phase of rapid starch clearance and glucose absorption which occurs early in the meal. This conclusion was supported by the additional finding that rats conditioned faster after bilateral subdiaphragmatic vagotomy, when fat-free diets are cleared faster than in intact rats. This result also indicated that the conditioned oral stimuli did not reduce the satiating power of ingested nutrients via motor control of the stomach or by interacting with vagal afferent information.