Domperidone treatment attenuates stress‐induced suppression of reproduction in viviparous mosquitofish Gambusia affinis

Abstract

The aim of this study was to determine the effect of stress on reproduction and the possible involvement of dopaminergic systems in the reproductive stress response in the mosquitofish Gambusia affinis. Exposure of fish to aquaculture stressors (four 10 min episodes of stress, each corresponding to a different stressor such as handling, chasing, frequent netting and low water levels), for a period of 30 days caused reduction in the mean numbers of stage I–IV follicles associated with lower number of pregnant females and embryos in most of the developmental stages compared with experimental controls. Besides, increase in the intensity of labelling and the per cent area of tyrosine hydroxylase (TH; a rate‐limiting enzyme in the biosynthetic pathway of catecholamines)‐ immunoreactive (ir) neurons was observed in the preoptic area (POA) and the nucleus preopticus (NPO) regions of the brain concomitant with reduction in the labelling of gonadotropin releasing hormone–immunoreactive (GnRH‐ir) fibres in the proximal pars distalis (PPD) of the pituitary gland in stressed fish compared with experimental controls. Treatment of domperidone (DOM) caused an increase in the number of stage II and V follicles and promoted pregnancy rate concomitant with an increase in the number of embryos at various developmental stages compared with those of experimental controls. Similar treatment to stressed fish caused an increase in the number of stages I–V follicles compared with those in stress alone group. The GnRH fibres showed increased immunolabelling in stress + DOM treated fish compared with stress alone fish. On the other hand, TH‐immunoreactivity in the POA and the NPO regions was reduced in stress + DOM treated fish compared with stress‐alone group. These results suggest that stress inhibits follicular development and subsequent hatching success through the suppression of GnRH and that the inhibition appears to be mediated through dopamine, for the first time in a viviparous fish.

Dopamine system in the fish brain: A review on current knowledge

“…Fish gonadal stimulation by dopamine agonists and antagonists demonstrated the role of dopamine in the reproduction. Number of ovarian follicles (Stage V) in the female fish significantly increase in the tilapia following domperidone (DA receptor antagonist) in the tilapia (Chabbi and Ganesh, 2015) [11] , similar reports were also noticed in the viviparous fish G. affinis with increase doses of domperidone (Bhat and Ganesh, 2020) [4] . In contrast to this, Pham and Arukwe, (2013) [35] findings suggest that DOM may not be needed for the induction of maturation and spawning of waigieu seaperch.…”

“…In fish exposed to aqua cultural stressors noticed densely labeled DA-ir cells in the POA and the NPO regions, concomitant with weak LHexpression and increased TH immunoreactivity fibres in the PPD. Further in mosquito fish, Bhat and Ganesh (2020) [4] has demonstrated the neuroanatomical relationship between DA and GnRH during stress condition in fish.…”

Ontogenetic changes in the tyrosine hydroxylase immunoreactive preoptic area in the small-spotted catshark Scyliorhinus canicula (L., 1758) females: catecholaminergic involvement in sexual maturation

“…This drop, simultaneously with GnRH and T enhancement, causes an increase in the synthesis of LH as well as in vitellogenin plasma levels and stimulation of ovarian vitellogenesis (Dufour et al, 2003(Dufour et al, , 2005Vidal et al, 2004). The CAminergic inhibition on the onset of puberty is also known in other teleostean species, such as the viviparous mosquitofish Gambusia affinis (Bhat and Ganesh, 2019), the gray mullet Mugil cephalus (Aizen et al, 2005), and the spadefish Chaetodipterus faber (Marcano et al, 1995), in which administration of dopamine's antagonists blocked D2-like receptors' action with subsequent gonadal maturation.…”

“…The changes here described are not documented among Chondrichthyes, but they are rather similar to what occurs in Osteichthyes, in which a further fall of CAaminergic action triggers the last steps of the oocyte's maturity and the eventual spontaneous spawning (Dufour et al, 2005 , 2010 ). This pattern has also been described in the most phylogenetically ancient Chondrosteans as the white sturgeon Acipenser transmontanus (Pavlick and Moberg, 1997 ; Dufour et al, 2020 ) and in the teleosts as cyprinids (Peter et al, 1986 , 1991 ; Lin et al, 1988 ; Fontaine et al, 2013 ), silurids (De Leeuw et al, 1986 ), percomorphs (Yaron et al, 2003 ), pleuronectiforms (Guzmán et al, 2011 ) and cyprinodontiforms (Bhat and Ganesh, 2019 ). However, the intensity of the CAminergic inhibitory tone at the time of spawning varies according to the studied species, from a drastic barrier in gray mullet Mugil cephalus (Aizen et al, 2005 ) to a milder control in salmonids and in the rainbow trout Oncorhynchus mykiss (Linard et al, 1995 ; Saligaut et al, 1999 ; Vacher et al, 2000 ).…”

The opioid peptide dynorphin suppresses pituitary‐ovary axis in the tilapia Oreochromis mossambicus

“…The photomicrographs were captured using a CCD camera and an image analysing system connected to a BX53 microscope (Olympus; www.olympus-ims.com). The intensity and the percent area of LH-labelled sections were evaluated using ImageJ, version 1.46 (NIH; www.imagej.nih.gov) as described previously (Bhat & Ganesh, 2020). Briefly, the threshold pixel intensities of immunoreactive and non-immunoreactive areas were measured.…”