Expression of kisspeptins in the brain and pituitary of the european sea bass (Dicentrarchus labrax)

Kisspeptins are now considered key players in the neuroendocrine control of puberty and reproduction, at least in mammals. Most teleosts have two kiss genes, kiss1 and kiss2, but their sites of expression are still poorly documented. As a first step in investigating the role of kisspeptins in the European sea bass, a perciform fish, we studied the distribution of kiss1 and kiss2‐expressing cells in the brain of males and females undergoing their first sexual maturation. Animals were examined at early and late in the reproductive season. We also examined the putative expression of estrogen receptors in kiss‐expressing cells and, finally, we investigated whether kisspeptins are expressed in the pituitary gland. We show that kiss1‐expressing cells were consistently detected in the habenula and, in mature males and females, in the rostral mediobasal hypothalamus. In both sexes, kiss2‐expressing cells were consistently detected at the level of the preoptic area, but the main kiss2 mRNA‐positive population was observed in the dorsal hypothalamus, above and under the lateral recess. No obvious sexual differences in kiss1 and kiss2 mRNA expression were detected. Additional studies based on confocal imaging clearly showed that most kiss1 mRNA‐containing cells of the mediobasal hypothalamus strongly express ERα and slightly express ERβ2. At the pituitary level, both sexes exhibited kiss1 mRNA expression in most FSHβ‐positive cells and never in LHβ‐positive cells. J. Comp. Neurol. 521:933–948, 2013. © 2012 Wiley Periodicals, Inc. Kisspeptins are now considered as major actors in the neuroendocrine control of puberty and reproduction, at least in mammals. Most teleost fishes have two kiss genes, kiss1 and kiss2, but their respective functions in reproduction are still unclear. Thus, it is important to study the distribution of kiss1 and kiss2 expressing cells in the brain and to see which populations are subject to change in expression over the sex cycle. In the European sea bass, an economically important fish, we show that kiss1 expressing cells in the mediobasal hypothalamus show clear changes in expression in mature males and females. These data suggest a role for Kiss1 in reproduction of the sea bass. In addition, kiss1 mRNAs were expressed in FSHβ positive cells and never in LHβ positive cells of the pituitary level.