A microstructural analysis of the control of water and isotonic saline ingestion by postingestional stimulation

This study investigated the behavioral expression of the mechanisms of satiation from stimulation of the gastrointestinal tract by water and isotonic saline. We compared the licking behavior of water-deprived rats ingesting water or isotonic saline under real- and sham-drinking conditions. In real-drinking tests the rate of ingestion of both types of fluids declined after about 5 min of drinking, and had virtually ceased by 20 min, while in the sham-drinking tests the rate of drinking remained constant during this period. To assess the impact of postingestional stimulation on the microstructure of licking, we compared the size of the clusters (SC) of licking and the duration of the pauses between them (ICIs), during the 15-min period that began 5 min after the start of drinking in the real- and sham-drinking tests. With both fluids postingestional stimulation significantly reduced the number of clusters. With water, but not with isotonic saline, postingestional stimulation also reduced SC, an effect that was shown to be due to differential postingestional not oropharyngeal stimulation. Postingestional stimulation had no overall effect on the ICIs, but in tests with water, but not saline, it altered the shape of the ICI distribution by increasing the duration of the long ICIs. We concluded that the different mechanisms of satiation stimulated by the postingestional effects of water and isotonic saline are expressed in different patterns of the microstructure of licking.