Melatonin effects on Fundulus heteroclitus reproduction

Abstract

This study aimed to investigate the effects of two different doses (100nM (M1) and 1µM (M2)) of exogenous melatonin on the reproductive capacity of Fundulus heteroclitus. Eight days of melatonin exposure significantly increased the fecundity and embryo survival of F. heteroclitus only in the M2 group compared with the control; the hatching rate was unaffected. Moreover, increases in the local expression of the melatonin receptor (mtnr) gene during follicle maturation were found; however, there were no differences between the experimental groups. Furthermore, in vitro melatonin-treated follicles showed a significantly higher germinal vesicle break down percentage compared with the control, while SDS-PAGE showed no difference in the electrophoretic pattern of the major yolk proteins. Nevertheless, densitometry revealed a greater intensity of the 118-, 95- and 40-kDa components in groups treated with melatonin. Finally, Fourier transform infrared microspectroscopy was applied to classify the different stages of oocyte development (Stages I-II, III and IV) on the basis of their macromolecular composition. The effects induced by melatonin on oogenesis were investigated by comparing vibrational spectra of females exposed to melatonin with those of controls. Changes to the Amide I band, corresponding to an increase in β-structure, were found in oocytes of females exposed to the highest melatonin dose. These results highlight the positive role of melatonin, which is able to enhance the reproductive capacity of F. heteroclitus. Further studies are in progress to better explain the molecular mechanisms by which melatonin treatment affects reproduction in this marine species.

Melatonin actions on ovaprim (synthetic GnRH and domperidone)-induced oocyte maturation in carp

“…The earliest effects in carp oocytes were observed about 7 h after the injection of ovaprim, which need melatonin priming for 2 h prior to ovaprim injection. A 7 h latency period could be sufficient for melatonin to regulate intracellular signaling or to act via genomic actions on the ovary (Carnevali et al 2011, Lombardo et al 2012. Thus, the observed changes in the latency period as well as in the rate of GVBD and MPF formation in the oocytes between females treated with melatonin and ovaprim at different time intervals might be due to ovaprim actions on gonadotropic hormone (GtH) release from the pituitary glands and the cascade of molecular events occurring thereafter in the ovary .…”

“…However, the data obtained from the studies on zebrafish (Carnevali et al 2011) and killifish (Lombardo et al 2012) have opened up the possibility that melatonin may stimulate the release of hypothalamic GnRH. The present study by showing the stimulatory response of carp oocytes to melatonin when administered with or before ovaprim promotes an idea that the employed regimen of melatonin treatment may elicit the ovarian response by exerting major effects on the hypothalamic part of the brain, where the melatonin receptors are known to be present (Gaildrat et al 2002).…”

“…The study on zebrafish reports that melatonin plays a critical role in promoting seasonal reproduction by activating the cascade starting from the kiss peptide, which, in turn, stimulates hypothalamic neurons to produce gonadotropin-releasing hormone (GnRH), and by acting directly on gonads that regulate the transcription of two important genes whose proteins are involved in oocyte competence and maturation (Carnevali et al 2011). Likewise, a study on killifish (Lombardo et al 2012) provides evidence that endogenously synthesized or exogenously added melatonin acts on steroidogenesis by regulating steroidogenic enzyme activities in theca and granulosa cells of the ovary (Tamura et al 2009). Moreover, the discovery that melatonin due to its lipophilic nature can easily cross the plasma membrane of cells to act directly as a scavenger of free radicals (Tan et al 1993) followed by studies demonstrating the stimulation of antioxidative enzymes by melatonin (Rodriguez et al 2004) and even scavenging actions of its metabolites on free radicals (Galano et al 2013) added a new dimension to the current understanding on the physiological role of melatonin as a potent antioxidant (Zhang & Zhang 2014) in the regulation of ovarian functions in at least mammals (Tamura et al 2014).…”

The Role of Melatonin as a Hormone and an Antioxidant in the Control of Fish Reproduction

“…The mechanism by which melatonin regulates fish reproduction is one of the major areas that received serious attention in the studies on different fish, but is not yet clearly understood. Possibly, melatonin interacts with the brain–pituitary–gonad axis, or with one or more of a variety of peripheral and/or central sites, including the brain ( 38 ), the pituitary ( 39 ), and the gonads ( 35 , 40 ). It seems likely that melatonin acts on the HPG axis and on the ovary itself ( 36 , 38 , 40 ).…”

A comparison of techniques for studying oogenesis in the European eel Anguilla anguilla

“…In addition, Fourier transform infrared (FT‐IR) microspectroscopy was employed, possibly for the first time with A. anguilla . This technique, previously used in the study of zebrafish Danio rerio (Hamilton 1882) and mummichog Fundulus heteroclitus (L. 1766) ovaries and single oocytes, is considered a novel and powerful tool for analysing the macromolecular composition of ovarian structures (Carnevali et al ., ; Giorgini et al ., ; Lombardo et al ., ). Plasma FT‐IR has also been shown to be effective in determining the stage of sexual development in sturgeon Acipenser transmontanus Richardson 1836 (Lu et al ., ).…”