Characterization of appetite-­‐regulating factors in platyfish, Xiphophorus maculatus (Cyprinodontiformes Poeciliidae) and cunner, Tautogolabrus adspersus

Pitts, Paul (2016) Characterization of appetite-­‐regulating factors in platyfish, Xiphophorus maculatus (Cyprinodontiformes Poeciliidae) and cunner, Tautogolabrus adspersus. Masters thesis, Memorial University of Newfoundland.

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Abstract

The regulation of energy in fish, like most vertebrates, is a complex process that involves a number of chemical signals originating and networking in different parts of the brain and throughout the body. These signals include anorexigenic hormones that suppress feeding and hunger [e.g. cholecystokinin (CCK) and cocaine-­‐and amphetamine-­‐regulated transcript (CART)] as well as orexigenic peptides that stimulate feeding behaviour and food intake [e.g. orexin and neuropeptide Y (NPY)]. Platyfish, Xiphophorus maculatus, are freshwater viviparous fish found in tropical waters from South America to northern Mexico. Although these fish have been the object of numerous physiology and behavioural studies, very little is known about the endocrine mechanisms regulating their feeding. In order to elucidate the role of these peptides in the regulation of feeding, we examined the effects of peripheral injections of CCK and orexin on feeding behaviour and food intake. Injections of CCK decreased both food intake and searching behaviour, while injections of orexin increased searching behaviour but did not seem to have an effect on food consumption. In order to better characterize these peptides, we performed tissue distribution and gene expression studies. Tissue distribution studies show that CCK, CART, NPY and orexin all show a widespread distribution in brain and several peripheral tissues, including intestine. In addition, we compared the expression of these peptides in brain and gut between fed and 10-­‐day fasted platyfish using qPCR. Fasting caused decreases in both CCK and CART mRNA expressions in the brain and a decrease in CCK expression in the intestine. There was also a significant increase in orexin mRNA expression in the brain as a result of fasting. Cunners, Tautogolabrus adspersus, are cold-­‐water oviparous (egg laying) marine fish that can be found from Northern Newfoundland to all along the coast of the western North Atlantic. In cunner, fasting for 10 days caused a decrease in CCK in the brain, and a significant increase in orexin expression in the brain. Fasting had no significant effect on either NPY or CART expression. Furthermore, fasting had no effect on the expression of the peptides studies in the intestine. We also compared the expression of these peptides as a result of fasting in males and females of both species. In platyfish, there was no significant gender specific differences found in the expression of the peptides. In cunner, females showed a significantly higher NPY expression in the brain than males, although this was unique to NPY. The widespread distribution and the fasting-­‐induced changes in expression of these peptides suggest that they might have several physiological roles in platyfish, including the regulation of feeding.

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