Alterations in activity and energy expenditure contribute to lean phenotype in Fischer 344 rats lacking the cholecystokinin-1 receptor gene

1VA Puget Sound Health Care System.
AJP Regulatory Integrative and Comparative Physiology (Impact Factor: 3.11). 10/2012; 303(12). DOI: 10.1152/ajpregu.00393.2012
Source: PubMed


Cholecystokinin (CCK) is hypothesized to inhibit meal size by acting at CCK1 receptors (CCK1R) on vagal afferent neurons that innervate the gastrointestinal tract and project to the hindbrain. Earlier studies have shown that obese Otsuka Long-Evans Tokushima Fatty (OLETF) rats, which carry a spontaneous null mutation of the CCK1R, are hyperphagic and obese. Recent findings show that rats with CCK1R-null gene on a Fischer 344 background (Cck1r(-/-)) are lean and normophagic. In this study, the metabolic phenotype of this rat strain was further characterized. As expected, the CCK1R antagonist, devazepide, failed to stimulate food intake in the Cck1r(-/-) rats. Both Cck1r(+/+) and Cck1r(-/-)rats became diet-induced obese (DIO) when maintained on a high fat diet relative to chow fed controls. Cck1r(-/-) rats consumed larger meals than controls during the dark cycle and smaller meals during the light cycle. These effects were accompanied by increased food intake, total spontaneous activity and energy expenditure during the dark cycle and an apparent reduction in respiratory quotient (RQ) during the light cycle. To assess if enhanced responsiveness to anorexigenic factors may contribute to the lean phenotype we examined the effects of melanotan II (MTII) on food intake and body weight. We found an enhanced effect of MTII in Cck1r(-/-) rats to suppress food intake and body weight following both central and peripheral administration. These results suggest that, despite the increases in meal size and food intake during the dark period, the lean phenotype is potentially driven by increases in total spontaneous activity and energy expenditure.

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