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1 Department of Nutritional Sciences, College of Health and Human Development, The Pennsylvania State University, University Park, PA, USA
* To whom correspondence should be addressed. E-mail: mrh212{at}psu.edu.
Serotonin type-3 (5-HT3) receptors have been shown to participate in the negative feedback control of food intake. We have previously reported that cholecystokinin (CCK)-induced suppression of food intake is partly mediated through 5-HT3 receptors when rats were tested on a preferred liquid diet, but whether such an effect occurs when tested on a solid maintenance diet is unknown. In the present study, we examined the effects of ondansetron, a selective 5-HT3 antagonist, on CCK-induced suppression of solid chow intake. Intraperitoneal administration of ondansetron significantly attenuated 30- and 60-min CCK-induced reduction of food intake, with suppression being completely reversed by 120 min. It is not known whether 5-HT3 receptors directly mediate CCK-induced satiation or whether their participation depends on CCK acting as part of a feedback cascade to inhibit ongoing intake. Since CCK-induced inhibition of sham feeding does not depend on additive gastric/post-gastric feedback signals, we examined the ability of ondansetron to reverse CCK-induced satiation in sham feeding rats. Ondansetron did not attenuate reduction of sham feeding by CCK, suggesting that ondansetron does not directly antagonize CCK-satiation signals. CCK suppresses real feeding through a delay in gastric emptying. Ondansetron could attenuate CCK-induced reduction of food intake by reversing CCK-induced inhibition of gastric emptying. We found that blockade of 5-HT3 receptors attenuates CCK-induced inhibition of gastric emptying of a solid meal, as well as saline and glucose loads. We conclude that 5-HT3 receptors mediate CCK-induced satiation through indirect mechanisms as part of a feedback cascade involving inhibition of gastric emptying.
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