Abstract About 50 years after Harris’s first demonstration of its existence, GnRH has strongly stimulated the interest and imagination of scientists, resulting in a high number of studies in an ...increasing number of species. For the endocrinologist, GnRH, via its actions on the synthesis and release of pituitary gonadotrophins, is first an essential hormone for the initiation and maintenance of the reproductive axis, but recent data suggest that GnRH emerged in animals lacking a pituitary. In this context, this review intends to explore the current status of knowledge on GnRH and GnRH receptors in metazoa in order to see if it is possible to draw an evolutive scenario according to which GnRH actions progressively evolved from the control of simple basic functions in early metazoa to an indirect mean of controlling gonadal activity in vertebrates through a sophisticated network of finely tuned neurons developing in a rather fascinating way. This review also intends to provide an evolutive scenario based on the recent advances of whole genome sequencing possibly explaining the number of GnRH and GnRH receptor variants according to the 2R and 3R theories accompanied by gene losses.
The role of gonadotrophin‐inhibitory hormone (GnIH) in the inhibition of the reproductive axis has been well‐established in birds and mammals. However, its role in other vertebrates, such as the ...teleost fish, remains controversial. In this context, the present study aimed to evaluate whether GnIH modulates the release of gonadotrophins and growth hormone (GH) in the cichlid fish Cichlasoma dimerus. First, we partially sequenced the precursor polypeptide for GnIH and identified three putative GnIH peptides. Next, we analysed the expression of this precursor polypeptide via a polymerase chain reaction in the reproductive axis of both sexes. We found a high expression of the polypeptide in the hypothalamus and gonads of males. Immunocytochemistry allowed the observation of GnIH‐immunoreactive somata in the nucleus posterioris periventricularis and the nucleus olfacto‐retinalis, with no differences between the sexes. GnIH‐immunoreactive fibres were present in all brain regions, with a high density in the nucleus lateralis tuberis and at both sides of the third ventricle. Finally, we performed in vitro studies on intact pituitary cultures to evaluate the effect of two doses (10−6 m and 10−8 m) of synthetic C. dimerus (cd‐) LPQRFa‐1 and LPQRFa‐2 on the release of gonadotrophins and GH. We observed that cd‐LPQRFa‐1 decreased β‐luteinising hormone (LH) and β‐follicle‐stimulating hormone (FSH) and also increased GH release to the culture medium. The release of β‐FSH was increased only when it was stimulated with the higher cd‐LPQRFa‐2 dose. The results of the present study indicate that cd‐LPQRFa‐1, the cichlid fish GnIH, inhibits β‐LH and β‐FSH release and stimulates GH release in intact pituitary cultures of C. dimerus. The results also show that cd‐LPQRF‐2 could act as an β‐FSH‐releasing factor in this fish species.
Exposure to environmental stressors, such as high temperature (HT), during early development of fish induces sex reversal of genotypic females. Nevertheless, the involvement of the brain in this ...process is not well clarified. In the present work, we investigated the mRNA levels of corticotropin-releasing hormone b (
) and its receptors (
and
), and found that they were upregulated at HT during the crucial period of gonadal sex determination in medaka. In order to clarify their roles in sex reversal, biallelic mutants for
and
were produced by CRISPR/Cas9 technology. Remarkably, biallelic mutants of both loci (
and
) did not undergo female-to-male sex reversal upon exposure to HT. Inhibition of this process in double corticotropin-releasing hormone receptor mutants could be successfully rescued through the administration of the downstream effector of the hypothalamic-pituitary-interrenal axis, cortisol. Taken together, these results reveal for the first time that the CNS acts as a transducer of masculinization induced by thermal stress.
Although some studies have investigated the effects of dietary
l
-tryptophan on agonistic behavior, research on adult fish specimens is still lacking. Moreover, submissive behaviors have been ...generally overlooked. We focused on agonistic behavior between males of the cichlid fish
Cichlasoma dimerus
, in dyadic encounters held in a novel context after being fed or not with an
l
-tryptophan enriched diet (TRP) for 2 weeks. We arranged three different dyads: control/control (control conditions: not TRP enriched), control/TRP, and TRP/TRP. We also registered the response of the brain serotonergic system in four brain regions. TRP/TRP dyads showed higher latencies to first attack, lower overall aggression, and lower proportions of bites and passive copings (submissive display) compared to control/control. TRP dominant males performed fewer bites with respect to controls, and subordinate males opposed to TRP males showed fewer passive copings. Higher serotonergic activities were found in subordinates’ optic tectum and in the telencephalon and preoptic area/hypothalamus of TRP males. Altogether, results point out that dietary
l
-tryptophan reduced males’ motivation to attack and dominant aggression, which consequently influenced subordinate agonistic repertory. In addition, males within TRP/TRP dyads showed a switch in their behavioral agonistic repertory. These behavioral outcomes were probably due to modifications at brain serotonergic functioning.
The New World silversides (family Atherinopsidae) are found in marine, estuarine and inland waters of North, Central and South America, where they are ecologically important as forage fishes and ...sometimes economically important for commercial and recreational fisheries. This report reviews the knowledge of the reproductive attributes of temperate and subtropical atherinopsids in relation to temperature and discusses the potential effects of climate change on their reproduction and adaptive responses. Their reproductive cycles are primarily entrained by photoperiod with high temperature acting as a limiting factor. They are generally multiple spawners which release successive batches of eggs in spring, but some species can spawn also in autumn and even summer when temperatures do not increase excessively. The decoupling of temperature patterns and photoperiod with further global warming and associated asymmetric thermal fluctuations could lead to spawning at times or temperatures that are unsuitable for larval development and growth. Many members of this family show temperature‐dependent sex determination (TSD), where the phenotypic sex of an individual is determined partly or wholly by the temperature experienced during gonadal sex differentiation, and high‐temperature induced germ cell degeneration and decreased fertility. The predicted short‐term reproductive responses of atherinopsids to climate change therefore include acceleration, shortening or overall disruption of spawning activity, and also more subtle, but nonetheless equally population‐threatening, dysfunctions such as highly skewed sex ratios and partial or total loss of fertility. In the case of species with TSD, asymmetric thermal fluctuations could also cause larvae to encounter temperatures lower than normal during early development and be feminized. Such dysfunctions have been documented already in natural populations but are confined so far to landlocked, inland water habitats, perhaps because they impose more severe thermal fluctuations and limitations to migration and dispersal. The severity and recurrence of these dysfunctions with further climate change will depend both on the magnitude, speed and pattern of change and on how much (or how fast) physiological and behavioural traits can evolve to match the new conditions imposed by the climate, which is largely unknown. In this regard, compelling evidence is shown that numerous traits, including the sex determination system, are capable of rapid evolution and could mitigate the negative effects of temperature increases on population viability in atherinopsids.
This study confirms the presence of two species of the non‐native mosquitofish Gambusia in Argentina. The risks that they represent to native biota, their potential dispersal in the region, and their ...effectiveness in mosquito larvae control are discussed.
Secretoneurin (SN) is a 33- to 34-amino acid neuropeptide derived from secretogranin-II, a member of the chromogranin family. We previously synthesized a putative goldfish (gf) SN and demonstrated ...its ability to stimulate LH release in vivo. However, it was not known whether goldfish actually produced the free SN peptide or whether SN directly stimulates LH release from isolated pituitary cells. Using a combination of reverse-phase HPLC and mass spectrometry analysis, we isolated for the first time a 34-amino acid free gfSN peptide from the whole brain. Moreover, Western blot analysis indicated the existence of this peptide in goldfish pituitary. Immunocytochemical localization studies revealed the presence of SN immunoreactivity in prolactin cells of rostral pars distalis of the anterior pituitary. Additionally, we found that magnocellular cells of the goldfish preoptic region are highly immunoreactive for SN. These neurons send heavily labeled projections that pass through the pituitary stalk and innervate the neurointermediate and anterior lobes. In static 12-h incubation of dispersed pituitary cells, application of SN antiserum reduced LH levels, whereas 1 and 10 nm gfSN, respectively, induced 2.5-fold (P < 0.001) and 1.9-fold (P < 0.01) increments of LH release into the medium, increases similar to those elicited by 100 nm concentrations of GnRH. Like GnRH, gfSN elevated intracellular Ca2+ in identified gonadotrophs. Whereas we do not yet know the relative contribution of neural SN or pituitary SN to LH release, we propose that SN could act as a neuroendocrine and/or paracrine factor to regulate LH release from the anterior pituitary.
Secretoneurin is a neuroendocrine factor that can affect luteinizing hormone secretion in the pituitary.
In this study we examined the endocrine mediation between environmental factors (temperature and photoperiod) and the brain–pituitary–gonadal axis in females of pejerrey
Odontesthes bonariensis
. ...Changes in the expression of brain gonadotropin-releasing hormones (GnRHs) and gonadotropin (GtH) subunit follicle stimulating-β (FSH-β), luteinizing hormone-β (LH-β), glycoprotein hormone-α (GPH-α) genes, plasma gonadal steroids estradiol (E
2
) and testosterone (T), gonadal histology, and gonadosomatic index (GSI) in adult females exposed to combinations of short-day (8 h) or long-day (16 h) photoperiods and low (12°C) or high (20°C) temperatures after winter conditions (8 h light, 12°C) were analyzed. Pejerrey females kept under the short photoperiod had low GSIs, and their ovaries contained only previtellogenic oocytes regardless of the experimental temperature. In contrast, females exposed to the long photoperiod had high GSIs and ovaries with vitellogenic oocytes at both temperatures. These fish also showed a significantly higher expression of sGnRH, pjGnRH, cGnRH-II (the three different GnRH variants found to date in the pejerrey brain), FSH-β, LH-β and GPH-α genes and plasma E
2
levels than those at the shorter photoperiod. No significant changes were observed in plasma T levels. Based on these results, we concluded that the increase in day length but not that of temperature triggers the maturation of pejerrey females after the winter period of gonadal rest and that this occurs by an integrated stimulation of the various components of the brain–pituitary–gonad axis.
Highlights ► The MCH and GH sequence is reported for the first time in Cichlasoma dimerus . ► Double immunofluorescence showing clear contacts among MCH fibers and GH cells in the proximal pars ...distalis . ► Salmon MCH stimulates GH synthesis and release from C. dimerus pituitaries in culture. ► Fish reared in white background present higher mRNA MCH levels than those reared in black background. ► Fish reared in white background present a body weight gain compared to those reared in black background.
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