Role of oropharyngeal stimulation in cholecystokinin-induced satiety in the sham feeding rat

The belief that oropharyngeal stimulation potentiates the satiety produced by cholecystokinin (CCK) is based on the demonstration that the ability of 20% pure CCK to suppress feeding is enhanced the closer it is injected to a meal. The increase efficacy of CCK with closer temporal proximity to a meal might simply reflect increased peptide levels at the time of feeding. Further, since oropharyngeal synergy has never been demonstrated with pure CCK, studies were performed to evaluate the role of oropharyngeal stimulation in CCK-induced satiety. Rats equipped with gastric fistulae were injected IP with CCK-8 15 min before a test sham feed. In one condition, rats sham fed for 15 min prior to CCK injection; in the other, they did not. CCK-8 suppressed eating in only those cases when its administration was accompanied by oropharyngeal stimulation. Thus, oropharyngeal cues enhance the satiety action of exogenous CCK. A second experiment examined whether oropharyngeal synergy requires oropharyngeal stimulation prior to peptide delivery. CCK-8 was injected into rats coincident with the initation of a test sham feed. Rats had either sham fed, or not sham fed, for 15 min prior to CCK administration. Both conditions produced similar and significant suppressions of eating during the test sham feed. Thus, oropharyngeal cues enhance the action of CCK and oropharyngeal amplification needs only contiguous pairings of oropharyngeal stimulation and feeding.