Dopamine Inhibits Reproduction in Female Zebrafish (Danio rerio) via Three Pituitary D2 Receptor Subtypes

Abstract

In many teleosts, the stimulatory control of gonadotrope axis by GnRH is opposed by an inhibitory control by dopamine (DA). The functional importance of this inhibitory pathway differs widely from one teleostean species to another. The zebrafish (Danio rerio) is a teleost fish that has become increasingly popular as an experimental vertebrate model. However, the role of DA in the neuroendocrine control of its reproduction has never been studied. Here the authors evaluated in sexually regressed female zebrafish the effects of in vivo treatments with a DA D2 receptor (D2-R) antagonist domperidone, or a GnRH agonist, alone and in combination, on the pituitary level of FSHβ and LHβ transcripts, the gonadosomatic index, and the ovarian histology. Only the double treatment with GnRH agonist and domperidone could induce an increase in the expression of LHβ, in the gonadosomatic index, and a stimulation of ovarian vitellogenesis, indicating that removal of dopaminergic inhibition is required for the stimulatory action of GnRH and reactivation of ovarian function to occur. Using double immunofluorescent staining on pituitary, the authors showed in this species the innervation of LH cells by tyrosine-hydroxylase immunoreactive fibers. Finally, using in situ hybridization and immunofluorescence, the authors showed that the three subtypes of zebrafish DA D2-R (D2a, D2b, and D2c) were expressed in LH-producing cells, suggesting that they all may be involved in mediating this inhibition. These results show for the first time that, in zebrafish, DA has a direct and potent inhibitory action capable of opposing the stimulatory effect of GnRH in the neuroendocrine control of reproduction.

Zebrafish pituitary gene expression before and after sexual maturation

“…In addition to the observed expression patterns of the core hormone signaling molecules in the hypothalamicpituitary-gonadal (HPG) axis, the expression levels of several other relevant neuroendocrine signaling molecules, including grid1, gal, and drd1, were also significantly elevated in the pituitary gland of adult zebrafish (Table 4). These are associated with Lhb production in mammals and/or fish (Flett et al 1994, Wang et al 2011, Garcia-Galiano et al 2012, Fontaine et al 2013. Our observations indicate that these signaling molecules might also be involved in the regulation of Lhb production in the zebrafish pituitary gland during the juvenile-sexual maturity transition.…”

Dopamine receptor agonist bromocriptine restrains the follicular development, hatchling success and puberty in Gambusia affinis

“…In teleosts, the ovarian activity is synchronized by the hormones produced by the BPG-axis (Nagahama, 1997 & Chang, 1986), the tilapia O. mossambicus (Yaron et al, 2003) and the zebra fish Danio rerio (Fontaine et al, 2013). In teleosts, the ovarian activity is synchronized by the hormones produced by the BPG-axis (Nagahama, 1997 & Chang, 1986), the tilapia O. mossambicus (Yaron et al, 2003) and the zebra fish Danio rerio (Fontaine et al, 2013).…”

Identification of the optic recess region as a morphogenetic entity in the zebrafish forebrain

“…Fluorescent in situ hybridization (FISH) was performed as described previously54. Embryos were fixed in fresh 4% paraformaldehyde (PFA) in PBS-tween20 0.1% (PBST) for 24 hours at 4°C, dehydrated and stored at −20°C in methanol for at least 24 hours.…”