Peripheral injections of cholecystokinin, apelin, ghrelin and orexin in cavefish (Astyanax fasciatus mexicanus): Effects on feeding and on the brain expression levels of tyrosine hydroxylase, mechanistic target of rapamycin and appetite-related hormones

• CCK injections decreased feeding and apelin brain expression.
• Apelin injections increased feeding and TH, mTOR and orexin brain expressions.
• Orexin (OX) treatment increased feeding and brain TH expression.
• Ghrelin injections increased feeding and mTOR and orexin brain expressions.
• CCK, apelin, OX, ghrelin, TH and mTOR might regulate feeding in cavefish.

The effects of intraperitoneal injections of cholecystokinin (CCK), apelin, ghrelin, and orexin on food intake were examined in the blind cavefish Astyanax fasciatus mexicanus. CCK (50 ng/g) induced a decrease in food intake whereas apelin (100 ng/g), orexin (100 ng/g), and ghrelin (100 ng/g) induced an increase in food intake as compared to saline-injected control fish. In order to better understand the central mechanism by which these hormones act, we examined the effects of injections on the brain mRNA expression of two metabolic enzymes, tyrosine hydroxylase (TH), and mechanistic target of rapamycin (mTOR), and of appetite-regulating peptides, CCK, orexin, apelin and cocaine and amphetamine regulated transcript (CART). CCK injections induced a decrease in brain apelin injections, apelin injections induced an increase in TH, mTOR, and orexin brain expressions, orexin treatment increased brain TH expression and ghrelin injections induced an increase in mTOR and orexin brain expressions. CART expression was not affected by any of the injection treatments. Our results suggest that the enzymes TH and mTOR and the hormones CCK, apelin, orexin, and ghrelin all regulate food intake in cavefish through a complex network of interactions.