Abstract
Gonadotropin-releasing hormone (GnRH) is an evolutionarily conserved neuropeptide with 10 amino acid residues, of which several structural variants exist. A molecular form known as GnRH2 ([His5 Trp7 Tyr8]GnRH, also known as chicken GnRH II) is widely distributed in vertebrates except for rodents, and has recently been implicated in the regulation of feeding behavior in goldfish. However, the influence of GnRH2 on feeding behavior in other fish has not yet been studied. In the present study, therefore, we investigated the role of GnRH2 in the regulation of feeding behavior in a zebrafish model, and examined its involvement in food intake after intracerebroventricular (ICV) administration. ICV injection of GnRH2 at 0.1 and 1 pmol/g body weight (BW) induced a marked decrease of food consumption in a dose-dependent manner during 30 min after feeding. Cumulative food intake was significantly decreased by ICV injection of GnRH2 at 1 pmol/g BW during the 30-min post-treatment observation period. The anorexigenic action of GnRH2 was completely blocked by treatment with the GnRH type I receptor antagonist Antide at 25 pmol/g BW. We also examined the effect of feeding condition on the expression level of the GnRH2 transcript in the hypothalamus. Levels of GnRH2 mRNA obtained from fish that had been provided excess food for 7 days were higher than those in fish that had been fed normally. These results suggest that, in zebrafish, GnRH2 acts as an anorexigenic factor, as is the case in goldfish.
Highlights
Gonadotropin-releasing hormone (GnRH) is an evolutionarily conserved decaneuropeptide that plays a crucial role in the regulation of reproduction in vertebrates (Sherwood et al, 1993; Fernald and White, 1999, Millar et al, 2004)
EFFECT OF FEEDING CONDITION ON GnRH2 mRNA EXPRESSION IN THE HYPOTHALAMUS Figure 3 shows the expression levels of GnRH2 mRNA in the hypothalamus of zebrafish supplied an excessive amount of food corresponding to 9% of their body weight (BW), and normal amount of food corresponding to 3% of their BW
Because GnRH2 is implicated in the regulation of reproductive behavior and energy balance in the female musk shrew, sparrow, and goldfish (Maney et al, 1997; Temple et al, 2003; Kauffman, 2004; Kauffman and Rissman, 2004a; Kauffman et al, 2005a,b; Hofmann, 2006; Hoskins et al, 2008; Matsuda et al, 2008; Kang et al, 2011), it is likely that, in zebrafish, GnRH2 is involved in both feeding control and reproductive behavior
Summary
Gonadotropin-releasing hormone (GnRH) is an evolutionarily conserved decaneuropeptide that plays a crucial role in the regulation of reproduction in vertebrates (Sherwood et al, 1993; Fernald and White, 1999, Millar et al, 2004). The demonstration of GnRH structural variants in vertebrates, and even in invertebrates, has resulted in the identification of 29 molecules (Guilgur et al, 2006; Kah et al, 2007; Roch et al, 2011). In vertebrates, these peptides are distributed in a wide range of tissues, and have diverse functions as hypophysiotropic hormones, paracrine or autocrine mediators and neuromodulators/neurotransmitters in the central and peripheral nervous systems and tissues (Gore, 2002; Millar, 2005; Kim et al, 2007; Millar et al, 2007). The involvement of GnRH in the regulation of feeding behavior had not been studied in other animal models
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