creased gastric mechanodetection, but preserved gastric emptying, in CCK-1 receptor-deficient OLETF rats. Am J Physiol Gastrointest Liver Physiol 291: G640 -G649, 2006. First published May 25, 2006 doi:10.1152/ajpgi.00109.2006.-Obese CCK-1 receptor-lacking Otsuka Long Evans Tokushima fatty (OLETF) rats are hyperphagic relative to control, nonmutant Long Evans Tokushima Otsuka (LETO) rats. This study sought to assess whether the overeating observed in OLETF rats is associated with changes in gastric emptying rates or detection of gastric volume. We performed experiments in both 12-and 29-wk-old OLETF and LETO rats to address possible alterations in gastric functions during the development of increased body weight and blood glucose abnormalities in OLETF rats. Gastric emptying of a 5-g solid chow test meal was not significantly different between strains at either 1, 2, or 4 h postmeal. When rats with ad libitum access to chow were tested, there were no significant differences in gastric emptying between strains at any time period despite OLETF rats consuming significantly more chow than LETO rats. Similar to solid food, 5-min gastric emptying of a 5-ml isosmotic and hyperosmotic saline or glucose load was not significantly different between strains. When the stomach was distended with a 15-ml semisolid chow load, there was no significance difference in emptying at either 1 or 2 h. No significant differences in gastric emptying were detected between 12-and 29-wk-old rats under any conditions. Both young and old OLETF rats, however, reduced sham intake significantly less compared with LETO rats during a brief period of gastric distension by 5-or 10-ml balloon inflation. Finally, OLETF rats showed decreased Fos expression in the nucleus of the solitary tract relative to LETO rats after an 8-ml gastric distension. These findings demonstrate that OLETF rats do not express deficits in controlling gastric emptying rates; however, they exhibit decreased behavioral and vagal responsiveness to gastric distension that may contribute to the increased meal size in these animals.cholecystokinin; hyperphagia; cholecystokinin-1 receptor; c-Fos; gastric distension; sucrose; sham feeding THE OTSUKA LONG-EVANS TOKUSHIMA FATTY (OLETF) rat is an outbred mutant strain of the Long Evans Tokushima Otsuka (LETO) rat that lacks CCK-1 receptor expression entirely due to a spontaneous 6.8-kb mutation spanning the promoter and first two exon regions of the CCK-1 receptor gene (46). In addition to the use of these animals as a model of insulin resistance, due to their natural manifestation of hyperglycemia and non-insulin-dependent diabetes mellitus relative to agematched LETO rats (16), OLETF rats are also currently under investigation as a model of obesity. OLETF rats exhibit an increased rate of weight gain relative to controls across their lifespan, with a marked elevation in body weight seen as early as 2-4 postnatal days (2, 27, 43). It is also known that OLETF rats are hyperphagic via increased meal size. This behavior has been attribu...