Development and Function of the Zebrafish Neuroendocrine System

Zebrafish (Danio rerio) is a small fish of the Cyprinidae family originating in the streams of India and Myanmar. Its small adult size, relative tolerance to husbandry conditions, high fecundity and transparent embryos have made the zebrafish highly appealing for developmental biologists and geneticists. The development of a large array of molecular tools for genetic manipulations and phenotyping has constantly increased the popularity of the zebrafish as a model organism in various biological fields, including neuroendocrinology. One of the biggest advantages of the zebrafish is its larval transparency, which has allowed the characterization of key events of neuroendocrine system development, as well as identification of genes essential for its formation and function during embryogenesis. As in other vertebrates, zebrafish neuroendocrine regulation is mediated either by releasing/release-inhibiting hormones that affect the pituitary gland, or by neurohypophyseal hormones. These neuroendocrine hormones are secreted by neurons of the hypothalamus, a brain area that regulates body homeostasis and affects peripheral organ functions. Hypothalamic neurohormones are either released directly into the general circulation or regulate the release of a variety of hormones from the pituitary, which is located at the interface between the brain and peripheral blood circulation. In this chapter, we summarize the anatomy, development and function of major components of the zebrafish neuroendocrine system. We describe the regulation and function of several neuroendocrine axes, which modulate a variety of physiological functions including stress, reproduction, growth and metabolism. Lastly, we review the current genetic tools for transgenesis and genome editing, as well as available biochemical tools for neuroendocrine research in zebrafish.