Orexigenic Actions of Ghrelin in Goldfish: Feeding-Induced Changes in Brain and Gut mRNA Expression and Serum Levels, and Responses to Central and Peripheral Injections

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Abstract
In this study, we examined (i) the preprandial, postprandial and starvation-induced changes in the preproghrelin mRNA expression and serum ghrelin levels, and (ii) the effects of intracerebroventricular and intraperitoneal administration of ghrelin on food intake in goldfish. Slot blot analysis revealed a significant postprandial decrease in preproghrelin mRNA expression in the hypothalamus (1 and 3 h after feeding) and gut (3 h after feeding). A similar postprandial decrease (1 and 3 h after feeding) in serum ghrelin levels was also detected. In the fish that were unfed at the regular feeding time, the hypothalamic preproghrelin mRNA expression and the serum ghrelin levels remained unchanged, while the preproghrelin mRNA expression in the gut decreased 3 h after the regular feeding time. Starvation increased preproghrelin mRNA expression in the hypothalamus and gut on the 7th day. Serum ghrelin levels were significantly elevated on days 3 and 5 of starvation. Intracerebroventricular injections of n-octanoylated ghrelin-like peptides (gGRL([1-12])) (10 ng/g body weight) and human ghrelin (1 and 10 ng/g body weight) and intraperitoneal injections of n-octanoylated gGRL([1-12]) (10 ng/g body weight), gGRL([1-19]) (100 ng/g body weight) and human ghrelin (10 and 100 ng/g body weight) stimulated food intake in goldfish. The patterns of synthesis, secretion and actions indicate that ghrelin is an orexigen in goldfish.