The neuroendocrine control of feeding and reproduction in zebrafish (Danio rerio) and glass catfish (Kryptopterus vitreolus)

London, Sydney (2018) The neuroendocrine control of feeding and reproduction in zebrafish (Danio rerio) and glass catfish (Kryptopterus vitreolus). Masters thesis, Memorial University of Newfoundland.

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Abstract

Reproduction and feeding are two critical life processes in all vertebrates, the regulations of which involve a complex network of interactions. It has been suggested that appetite regulators, such as orexin, neuropeptide Y (NPY), and cocaine and amphetamine regulated transcript (CART), and reproductive hormones, like gonadotropin-releasing hormone (GnRH), gonadotropin-inhibitory hormone (GnIH), kisspeptin, and neurokinin B (NKB), interact to regulate both food intake and reproduction. However, this relationship is not well characterized in all vertebrate species, especially fish. The purpose of this study was to examine this relationship and uncover some of the regulating mechanisms underlying these two processes. Specifically, I investigated two species of freshwater fish; glass catfish (Kryptopterus vitreolus) and zebrafish (Danio rerio). In glass catfish, I was able to successfully isolate two reproductive hormones (GnRH1 and GnRH2) and three appetite regulators (orexin, NPY, and CART). I found that fasting affected the relative brain expression levels of all of these peptides, except for GnRH2, suggesting a link between nutritional status and endocrine regulation. In zebrafish, I examined how nutritional status, reproductive stage, gender, and strain affected the brain mRNA expression of certain appetite (orexin and NPY) and reproductive (GnRH, kisspeptin, GnIH, and NKB) hormones. To compare strains, I used both wild-type and transparent Casper zebrafish. My results suggest gender- and reproductive stage-specific, as well as strain-specific variations in the mechanisms that regulate feeding and reproduction in zebrafish. To further investigate these differences, I compared the brain mRNA expression of genes involved in the melanocortin system and melanin pathway between wild-type and Casper zebrafish. I found that the Casper zebrafish had lower levels of several of the genes examined, suggesting that these strain-specific differences may be mediated by the melanocortin system. Overall, I was able to show a clear relationship between appetite and reproduction in both zebrafish and glass catfish, providing new insights into the endocrine mechanisms that regulate these two processes in fish.

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