Reproduction In Goldfish Research Articles

Hormone-Driven Temperature Optimization for Elevated Reproduction in Goldfish (Carassius auratus) under Laboratory Conditions.

This study investigates the efficacy of hormone-induced artificial reproduction in goldfish (Carassius auratus) under controlled temperatures. Ovaprim injections significantly enhanced ovulation and sperm production compared to controls. Medium temperature (22 °C) produced the highest ovulation rates, fastest ovulation timing, and optimal sperm quality (motility and morphology) compared to high (28 °C) and low (16 °C) temperature groups. The low-temperature group exhibited reduced sperm motility duration and higher rates of sperm and larvae damage. The sperm volume of the high-temperature group was higher, but their post-injection survival rates were lower. Furthermore, the lowest spawning rate and low egg quality were noted in the high temperature. Cryopreservation using extender E4 (15% DMSO) exhibited superior post-thaw sperm motility and achieved higher fertilization rates. Fertilization rates, embryo development, and larval survival were all highest at the medium temperature. Larvae hatched from fresh sperm at medium temperature exhibited faster growth and fewer deformities. These findings suggest that hormone stimulation coupled with a medium temperature regimen is critical for successful artificial reproduction in goldfish. Cryopreservation with extender E4 holds promise for sperm banking; however, further optimization is necessary to improve fertilization success with thawed sperm. Future research could explore the influence of temperature on sperm physiology and refine cryopreservation protocols to enhance fertilization rates.

A chronic exposure to bisphenol A reduces sperm quality in goldfish associated with increases in kiss2, gpr54, and gnrh3 mRNA and circulatory LH levels at environmentally relevant concentrations

The bisphenol A (BPA)-disrupted reproductive functions have been demonstrated in male animals. In fish, it has been shown that environmentally relevant concentrations of BPA decrease sperm quality associated with inhibition of androgen biosynthesis. However, BPA effects on neuroendocrine regulation of reproduction to affect testicular functions are largely unknown. In the present study, reproductive functions of hypothalamus and pituitary were studied in mature male goldfish exposed to nominal 0.2, 2.0 and 20.0 μg/L BPA. At 90 d of exposure, sperm volume, velocity, and density and motility were decreased in goldfish exposed to 0.2, 2.0, and 20.0 μg/L BPA, respectively (p < 0.05). At 30 d of exposure, there were no significant changes in circulatory LH levels and mRNA transcripts of kiss1, Kiss2, gpr54, and gnrh3. At 90 d of exposure, circulatory LH levels showed trends toward increases in BPA exposed goldfish, which was significant in those exposed to 2.0 μg/L (P < 0.05). At this time, Kiss2, gpr54, and gnrh3 mRNA levels were increased in goldfish exposed to any concentrations of BPA (p < 0.05). This study shows that BPA-diminished sperm quality was accompanied by an increase in circulatory LH levels associated with increases in mRNA transcripts of upstream neuroendocrine regulators of reproduction in goldfish. Further, this is the first study to report circulatory levels of LH in fish exposed to BPA.

Gonadotropin-releasing hormone-independent effects of recombinant vertebrate ancient long opsin in the goldfish Carassius auratus reveal alternative reproduction pathways.

Vertebrate ancient long (VAL)-opsin is a green-sensitive photoreceptor that shows high sequence similarity to vertebrate ancient opsin, which is considered to play a role in sexual maturation via gonadotropin-releasing hormone (GnRH); however, the role of VAL-opsin in vertebrate sexual maturity remains unclear. Therefore, we investigated the possible role of VAL-opsin in reproduction in the goldfish Carassius auratus under a state of GnRH inhibition. Goldfish were injected with recombinant VAL-opsin protein (0.5μg/g body mass) and/or the GnRH antagonist cetrorelix (0.5μg/fish), and changes in the mRNA expression levels of genes associated with goldfish reproduction were measured by quantitative polymerase chain reaction, including those involved in the hypothalamus-pituitary-gonad (HPG) axis, VAL-opsin, GnRH, the gonadotropins (GTHs) luteinizing hormone and follicle-stimulating hormone, and estrogen receptor (ER). Moreover, the fish were irradiated with a green light-emitting diode (520nm) to observe the synergistic effect on the HPG axis with VAL-opsin. Green LED exposure significantly and slightly increased the VAL-opsin and GnRH levels, respectively; however, these effects were blocked in groups injected with cetrorelix at all time points. Cetrorelix significantly decreased the mRNA levels of GTHs and ER, whereas these hormones recovered by co-treatment with VAL-opsin. These results indicate that green LED is an effective light source to promote the expression of sex hormones in fish. Moreover, VAL-opsin not only affects activity of the HPG axis but also appears to act on the pituitary gland directly to stimulate a new sexual maturation pathway that promotes the secretion of GTHs independent of GnRH.

NKB/NK3 system negatively regulates the reproductive axis in sexually immature goldfish (Carassius auratus)

To ascertain the significance of the Neurokinin B/Tachykinin 3 receptor (NKB/NK3) system in goldfish reproduction, two cDNAs encoding tachykinin 3 receptors, namely tacr3a and tacr3b, were cloned. Subsequent studies revealed that the downstream signalling of both Tac3rs can be activated by different NKB peptides, suggesting that the cloned receptors are biologically functional in goldfish. RT-PCR analysis showed that tacr3s are widely expressed in brain regions. During the gonadal development, tacr3a and tacr3b exhibited different expression patterns in the hypothalamus and pituitary. The actions of NKB peptides on reproductive axis was further investigated in vivo. Intraperitoneal injections of NKB peptides significantly reduced the expression of kiss2 and gonadotropin releasing hormone 3 (gnrh3) in the hypothalamus, and the expression of luteinizing hormone beta subunit (lhb) and follicle stimulating hormone beta subunit (fshb) in the pituitary in sexually immature goldfish. Taken together, our findings revealed that NKB/NK3 system plays a negative role in the reproductive axis of immature goldfish.

Toxic effects of bisphenol A on goldfish gonad development and the possible pathway of BPA disturbance in female and male fish reproduction

Bisphenol A (BPA) is an abundant endocrine-disrupting compound that is found in the aquatic environment and has adverse effects on fish reproduction; however, the exact pathway of these impacts is unclear. In this study, the different effects of BPA on ovarian and testis development in goldfish (Carassius auratus) and the different mechanisms underlying these effects were investigated. The gonadosomatic index (GSI) and gonadal histology demonstrated that BPA diminished ovarian maturation in goldfish, which recovered after BPA treatment withdrawal. In males, BPA disrupted testis maturation, but this disruption could not be recovered after BPA treatment withdrawal. The hypothalamic-pituitary-gonad (HPG) axis-related genes sgnrh, fshβ and lhβ were significantly decreased in BPA-treated female fish, while no changes in sex steroid hormone levels and no TUNEL and PCNA staining were found in the ovary, suggesting that BPA may reduce ovarian maturation through the HPG axis. In male fish, TUNEL staining was found in 1 μg L−1 BPA-exposed germ cells and 50 and 500 μg L−1 BPA-exposed Leydig cells. Decreases in 11-KT levels were also found in 50 and 500 μg L−1 BPA-exposed fish, but BPA did not affect genes associated with the HPG axes. This result shows that BPA disrupts testis maturation through apoptosis of germ cells and Leydig cells, thus inducing decreases in 11-KT levels that disrupt spermatogenesis. Collectively, our findings provide insights into the molecular and cellular mechanisms underlying BPA disturbance of goldfish reproduction.

Effects of recombinant vertebrate ancient long opsin on reproduction in goldfish, Carassius auratus: profiling green-wavelength light.

This study was conducted to identify the possible effect of recombinant vertebrate ancient long (VAL) opsin as a non-visual "photoreceptor" in the deep brain of goldfish, Carassius auratus. In addition, we investigated the effects of green-wavelength light on the predictable reproductive function of VAL-opsin as a green-sensitive pigment in the deep brain. To determine this, we quantified changes in gonadotropin hormone (GTH) [GTHα, follicle stimulating hormone (FSH) and luteinizing hormone (LH)] and estrogen receptor (ER; ERα and ERβ) mRNA expression levels associated with goldfish reproduction as well as changes in plasma FSH, LH, and 17β-estradiol (E2) activities after injection of recombinant VAL-opsin protein in two concentrations (0.1 or 0.5μg/g body mass) for 4weeks (injection once weekly) and examined the possible impact of green-wavelength light (500, 520, and 540nm) on the function of VAL-opsin. As a result, all parameters associated with reproduction significantly increased with time and light-emitting diode (LED) exposure. Based on these results, we suggested that VAL-opsin in the deep brain is involved in goldfish maturation, and it is possible that green-wavelength light improves the ability of VAL-opsin to promote maturation by increasing VAL-opsin expression.

The nonapeptide isotocin in goldfish: Evidence for serotonergic regulation and functional roles in the control of food intake and pituitary hormone release

Nonapeptides are a highly conserved family of peptides synthesized in the neuroendocrine brain and acting on central and peripheral receptors to regulate physiological functions in vertebrates. While the evolution of the two gene families of oxytocin-like and vasopressin-like nonapeptides and their receptors, as well as the neuroanatomy of their independent neuronal circuits have been well-characterized across vertebrate species, comparative studies on the physiological roles across vertebrates are lagging behind. In the current study, we focused on the comparative neuroendocrine functions and regulation of isotocin, the teleost homologue of mammalian oxytocin. Specifically, we address the hypothesis that isotocin exerts opposing effects on food intake and reproduction, which are well-established effects of its homologue oxytocin in mammalian species. Using goldfish, a well-characterized model of neuroendocrine regulation of both food intake and reproduction, we here showed that isotocin acts as an anorexigenic factor while exerting stimulatory effects on pituitary luteinizing hormone and growth hormone release. Given the dual inhibitory and stimulatory roles of serotonin on food intake and pituitary release of reproductive hormone in goldfish, we also investigated the potential crosstalk between both systems using immunohistochemistry and pharmacological approaches. Results provide neuroanatomical and pharmacological evidence for serotonergic regulation of magnocellular isotocinergic neurons in the preoptic area and pituitary. Together, these findings firstly provide the basis to investigate neuroendocrine cross-talk between serotonergic and nonapeptidergic systems in the regulation of both food intake and reproduction in goldfish, and secondly point to a conserved function of oxytocin-like peptides in the differential neuroendocrine control of both physiological processes in vertebrates.

Diel cyclic hypoxia alters plasma lipid dynamics and impairs reproduction in goldfish (Carassius auratus).

Diel cyclic hypoxia occurs with varying frequency and duration in freshwater habitats, yet little is known about its effects on reproduction of freshwater fishes. The present study shows that long-term exposure of goldfish (Carassius auratus) to cyclic hypoxia (0.8±0.2mg/l dissolved oxygen) for 9h or more, per day, altered plasma lipid and sex steroid profiles, which in turn directly or indirectly suppressed ovarian growth and viable spermatozoa production. Hypoxia decreased total cholesterol and high density lipoprotein (HDL p<0.05) and elevated triglycerides (TG; p<0.05) in both sexes. Plasma steroid concentrations particularly of 17α-hydroxyprogesterone (17-HP), estradiol (E2), testosterone (T) in females, and T and 11-ketotestosterone (11-KT) in males were attenuated under diel hypoxic conditions. Intriguingly, both diel and continuous hypoxia elevated plasma E2 and vitellogenin levels in males. However, neither lipid nor steroid profiles recorded any variation in a dose-dependent manner in response to diel hypoxia. The reduced GSI, decreased number of tertiary oocytes, and motile spermatozoa in hypoxic fish clearly indicate suppression of gametogenesis. Thereby, prolonged diel cyclic hypoxia may affect valuable fishery resources and fish population structure by impairing reproductive performances and inducing estrogenic effects in males.

Gonadotropin-Inhibitory Hormone, the Piscine Ortholog of LPXRFa, Participates in 17β-Estradiol Feedback in Female Goldfish Reproduction

Gonadotropin-inhibitory hormone (GnIH) plays a critical role in regulating gonadotropin-releasing hormone, gonadotropin hormone, and steroidogenesis in teleosts. In the present study, we sought to determine whether 17β-estradiol (E2) acts directly on GnIH neurons to regulate reproduction in goldfish, a seasonal breeder, and we investigated the role of estrogen receptors (ERs) in mediating this process. We found that GnIH neurons coexpress three types of ERs. Ovariectomy and letrozole implantation into female goldfish at the vitellogenic stage elicited a substantial decrease in the expression of GnIH messenger RNA (mRNA), and E2 supplementation abolished this effect. In primary cultured hypothalamus cells, E2 increased GnIH mRNA levels; surprisingly, selective ERα and ERβ agonists showed opposite effects in regulating GnIH mRNA levels. Using genome walking, we isolated a 2329-bp section of the GnIH promoter sequence, and 7 half-estrogen response elements (EREs) were found in the promoter region. Luciferase assays and electrophoretic mobility shift assay results show that the half-ERE element at -2203 is the key site for competitive binding between ERα and ERβ. Ovariectomy and letrozole implantation into female goldfish in the maturating stage did not change the GnIH mRNA expression levels. Taken together, these findings suggest that E2 binds to multiple types of ERs, which competitively bind to the same half-ERE binding site of the GnIH promoter to achieve both positive and negative feedback in response to estrogen to regulate goldfish reproduction at different stages of ovarian development.

Increased Prostaglandin E_2 Has a Positive Correlation with Plasma Calcium during Goldfish Reproduction

somatic index (r=0.81, p<0.001), plasma Ca and plasma PGE2 levels (r=0.635, p<0.05), and plasma Ca and plasma TRAP activities (r=0.584, p<0.05) from the analysis using samples of both reproductive and non- reproductive stages. Taking these data into consideration, we suggested that PGE2 acts on osteoclasts and increases plasma Ca as a result of osteoclastic bone resorption, and we concluded that PGE2 is an important hormone in Ca metabolism during fish reproduction.

Direct effects of triiodothyronine on production of anterior pituitary hormones and gonadal steroids in goldfish

The present study investigated the effects of triiodothyronine (T3) on pituitary gonadotropin (GTH) subunits, thyroid stimulating hormone (TSH) β subunit, and growth hormone (GH) mRNA levels, as well as gonadal steroid secretion during different stages of reproduction in goldfish. Goldfish pituitary cells cultured with T3 exhibited lower tshβ mRNA levels in all reproductive stages and lower luteinising hormone β (lhβ) mRNA levels in early recrudescence, whereas gh and fshβ mRNA levels were not altered. T3 injections significantly reduced circulating oestrogen (OE2) concentrations in early and mid recrudescent male goldfish, but were without effect on the circulating level of OE2 in female fish. T3 injections also reduced circulating levels of testosterone in both male and female goldfish during the mid stage of gonadal recrudescence. In vitro culture of goldfish ovarian follicles at the late stage of gonadal recrudescence, in the presence of T3, resulted in reduced OE2 secretion; no consistent effect of T3 on testosterone secretion was observed in cultured goldfish ovarian follicles and testis. These findings support the hypothesis that T3 impairs reproduction by inhibiting production of gonadal steroids and pituitary luteinising hormone production in goldfish.

The Application of hCG, CPH and Ovopel in Successful Artificial Reproduction of Goldfish (Carassius auratus auratus) Under Controlled Conditions

Artificial reproduction of fish is one of the main goals of aquaculture production. The aim of this study is to optimize the method of goldfish reproduction under controlled conditions by comparing the effectiveness of carp pituitary homogenate (CPH), Ovopel and human chorionic gonadotropin (hCG), administered as a one-off dose and inducing two spawns in the same fish within a short time period. Goldfish spawners were stimulated with hCG, CPH and Ovopel, and the results were compared to the fish from the control group, comprised of unstimulated fish. In another experiment, spawn were induced twice within an interval of 21 days with the same group of fish. The best results in the first experiment in terms of the percentage of ovulating females and survival to the eyed-egg stage were achieved after administering hCG (100% and 88.7%, respectively). However, the highest fecundity was observed in fish stimulated with Ovopel (89,960 eggs/kg). It was shown in the second experiment that female goldfish produce higher weight of eggs during the first spawning, but the number of eggs/BW ratio was higher during the next reproduction process. Survival, both that of embryos to the eyed-egg stage and that of spawners, is higher during the first reproduction act.

Thyroid hormone and reproduction in goldfish

Event Abstract Back to Event Thyroid hormone and reproduction in goldfish Hamid R. Habibi1, 2*, Erik R. Nelson1, 2 and Euan R O. Allan1, 2 1 University of Calgary, Department of Biological Sciences, Canada 2 Duke University Medical Center, Pharmacology and Cancer Biology, United States As in many vertebrates, fish reproduction is regulated by environmental cues such as photoperiod and temperature. During reproductive season a significant amount of metabolic energy is diverted to development of ovary and testis through precise regulation of brain-pituitary-peripheral axis by a number of key hormones, including pituitary gonadotropins and gonadal steroids. Since thyroid hormones are important regulator of metabolism and development in vertebrates, we investigated the possibility that thyroid hormones may mediate a change from gonadotropic to somatotropic state. Multiple experiments were performed across the four reproductive seasons to test the effects of triiodothyronine (T3) on estrogen and androgen receptors in the liver, testis and ovary as well as secretion of gonadal steroids and expression of pituitary glycoprotein hormone subunits (TSHβ, LHβ & FSHβ) and aromatase. Previous studies suggested that thyroid hormones influence reproduction in vertebrates, but little information is available on the mechanisms. In the present study, we test the hypothesis that thyroid hormones regulate pituitary hormone and gonadal steroid production in fish. The results demonstrate that thyroid hormone, (T3) regulates estrogen level as well as estrogen receptor subtypes (ER alpha, beta-1 and beta-II) in the testis and ovary of goldfish. We also observed that T3 influence pituitary gonadotropin and gonadal aromatase gene expression in goldfish. Collectively, it appears that T3 acts to diminish gonadotropic response by influencing hormone production as well as decreasing sensitivity to estrogen by down-regulating the estrogen receptor subtypes. We propose that thyroid hormones play a role in switching energy expenditure from reproductive to growth in goldfish. Funded by NSERC grants to HRH. Keywords: comparative endocrinology Conference: 25th Conference of the European Comparative Endocrinologists, Pécs, Hungary, 31 Aug - 4 Sep, 2010. Presentation Type: Conference Presentation Topic: Comparative endocrinology Citation: Habibi HR, Nelson ER and Allan EO (2010). Thyroid hormone and reproduction in goldfish. Front. Endocrinol. Conference Abstract: 25th Conference of the European Comparative Endocrinologists. doi: 10.3389/conf.fendo.2010.01.00006 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 Aug 2010; Published Online: 29 Aug 2010. * Correspondence: Dr. Hamid R Habibi, University of Calgary, Department of Biological Sciences, Calgary, Canada, habibi@ucalgary.ca Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Hamid R Habibi Erik R Nelson Euan R O Allan Google Hamid R Habibi Erik R Nelson Euan R O Allan Google Scholar Hamid R Habibi Erik R Nelson Euan R O Allan PubMed Hamid R Habibi Erik R Nelson Euan R O Allan Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Interactions between gonadotropin-releasing hormone (GnRH) and orexin in the regulation of feeding and reproduction in goldfish ( Carassius auratus)

Links between energy homeostasis and reproduction have been demonstrated in vertebrates. As a general rule, abundant food resources favor reproduction whereas low food availability induces an inhibition of reproductive processes. In both mammals and fish, gonadotropin-releasing hormone (GnRH) and orexin (OX) are hypothalamic neuropeptides that play critical roles in the regulation of sexual behavior and appetite, respectively. In order to assess possible interactions between orexin and GnRH in the control of feeding and reproduction in goldfish, we examined the effects of chicken GnRH (cGnRH-II) intracerebroventricular (ICV) injection on feeding behavior and OX brain mRNA expression as well as the effects of orexin ICV injections on spawning behavior and cGnRH-II brain mRNA expression. Treatment with cGnRH-II at doses that stimulate spawning (0.5 ng/g or 1 ng/g) resulted in a decrease in both food intake and hypothalamic orexin mRNA expression. Treatment with orexin A at doses that stimulate feeding (10 ng/g) induced an inhibition of spawning behavior and a decrease in cGnRH-II expression in the hypothalamus and optic tectum-thalamus. Our results suggest that the anorexigenic actions of cGnRH-II in goldfish might be in part mediated by OX and that orexin inhibits reproductive behavior in part via the inhibition of the GnRH system. Our data suggest the existence of a coordinated control of feeding and reproduction by the orexin and GnRH systems in goldfish.

Homologous regulation of estrogen receptor subtypes in goldfish (Carassius auratus)

While considerable information is available on the physiological effects of estrogen, much less is known about the regulation of estrogen receptor (ER) subtypes, particularly in non-mammalian vertebrates. Using goldfish as primary experimental model, we investigated sex- and tissue-specific homologous regulation of ER subtypes (ERalpha, ERbetaI, and ERbetaII) by estradiol in vivo, in the liver and gonads. Treatment with estradiol, significantly upregulated transcript levels for all three types of ERs (ERalpha, ERbetaI, and ERbetaII) in the goldfish ovary and testis. In the goldfish liver, treatment with estradiol significantly increased ERalpha, ERbetaI transcript levels without affecting ERbetaII. In all cases increased ER transcript level was correlated with increased ER protein level determined by Western blot analysis, although we are not able to distinguish between ER subtypes. The results provide strong support for the hypothesis that homologous regulation of ERs is tissue- and gender-specific, and may be a mechanism for estrogen-mediated regulation of reproduction in goldfish.

Male goldfish reproductive behaviour and physiology are severely affected by exogenous exposure to 17β-estradiol

Mature male goldfish were exposed to different concentrations of the natural hormone 17β-estradiol (E 2). Two methods of exposure were employed, via ingestion at 0, 1, 10 and 100 μg/g food and via the water at 0, 1 and 10 μg/l. The fish were exposed for 24–28 days during the spawning period. The males were then paired with an artificially induced, spawning female and their sexual behaviour was observed during a 15 min period. The physiological status of the fish was also examined with respect to GSI, presence of milt and spawning tubercles and the blood plasma concentration of E 2. Despite the relatively short exposure period, exposure to physiological levels of E 2 was shown to severely affect the male goldfish reproductive behaviour and physiology. In conclusion, the results from this study and the ability to interpret the effects on this well-studied species, show that the effects of E 2, and possibly other estrogenic EDCs, have severe effects at several vital levels of male goldfish reproduction. The results also suggests that the hormone E 2 can act as an endocrine disrupting chemical (EDC) in the environment.

Activin and its receptors in the goldfish

Activin (βAβA, βAβB and βBβB) is a dimeric protein that belongs to the transforming growth factor-β (TGF-β) superfamily of growth factors and is involved in the regulation of many physiological and developmental processes. Recently, we have demonstrated that porcine activin stimulated goldfish gonadotropin-II (GTH-II) and growth hormone (GH) secretion from dispersed pituitary cells in static culture and pituitary fragments in perifusion. The action of activin in the goldfish is unique in that it has an acute stimulatory effect on the secretion of GTH-II and GH, whereas in mammals activin usually exhibits long-term stimulatory actions on FSH secretion. The action mechanism of activin is different from that of gonadotropin-releasing hormone (GnRH). Using domain-specific antibodies against mammalian activin subunits, we subsequently demonstrated the existence of immunoreactive activin subunits (βA and βB) in the goldfish ovary, testis, pituitary and brain, suggesting endocrine, paracrine and autocrine roles for activin in the regulation of goldfish reproduction. Both activin βA and βB subunits have been cloned from goldfish genome by polymerase chain reaction (PCR). Using the PCR fragments as probes, we have cloned a full length cDNA coding for activin βB subunit from the goldfish ovary. Both activin βA and βB subunits show high homology to those of other vertebrates with the βB subunit much more conserved (93 and 98% identity with human and zebrafish βB subunit, respectively). The identity of the cloned βB subunit was further confirmed by expression in the Chinese hamster ovary (CHO) cells and detection of the specific activity of activin in the culture medium. The messenger RNA of activin βB subunit is expressed in a variety of goldfish tissues including ovary, testis, brain, pituitary, kidney and liver, suggesting a wide range of physiological roles for activin in the goldfish. We have also cloned a full length cDNA coding for the activin Type IIB receptor from the goldfish ovary, suggesting that activin may have paracrine or autocrine actions on the ovarian functions. The identity of the cloned receptor was confirmed by specific binding of125 I-activin on COS-1 cells transfected with the cloned Type IIB receptor.

In-vivo evaluation of dopamine receptor-mediated inhibition of gonadotrophin secretion from the pituitary gland of the goldfish, Carassius auratus.

Dopamine acts directly on the pituitary to modulate gonadotrophin (GtH) secretion in goldfish (Carassius auratus). In the light of this important role for dopamine in the regulation of goldfish reproduction, this investigation was designed to evaluate the receptor specificity of this dopamine inhibition and to describe the use of domperidone, a specific dopamine D2-receptor antagonist, in the manipulation of pituitary function in goldfish. To investigate the specificity of dopamine inhibition of GtH secretion, selected dopamine receptor antagonists were injected i.p. to block dopamine receptors thereby increasing GtH secretion as reflected by increased serum concentrations of GtH. Serum GtH levels were significantly increased by the active stereoisomer (-)-sulpiride in a dose-related fashion; (+)-sulpiride had no effect. Comparison of dopamine antagonists at low doses indicated that only domperidone and pimozide caused significant increases in serum concentrations of GtH. Dopamine antagonists potentiated the action of a gonadotrophin-releasing hormone analogue (GnRH-A) with an order of potency of domperidone = pimozide greater than metoclopramide = fluphenazine. [3H]Domperidone, injected i.p. with unlabelled domperidone, entered the blood and achieved maximum concentrations 12 h after injection, but did not accumulate in the brain in appreciable amounts. Gonadal 3H radioactivity was usually equal to or in excess of blood radioactivity, while [3H]domperidone was highly concentrated in the pituitary in a time-dependent fashion, with maximal accumulation occurring 24 h after injection. The time-course of pituitary accumulation of [3H]domperidone correlated well with the temporal increase in serum GtH levels in response to i.p. injected domperidone or domperidone plus an analogue of LHRH. Domperidone increased serum concentrations of GtH in a dose-related fashion; an analogue of salmon GnRH (sGnRH-A) increased the sensitivity and magnitude of the serum GtH response to domperidone. Serum concentrations of GtH were increased by sGnRH-A in a dose-related fashion; a low dose of domperidone substantially increased the sensitivity of the serum GtH response to sGnRH-A. These results indicate that dopamine inhibits GtH secretion from the goldfish pituitary by acting through a specific mechanism mediated by a dopamine D2 receptor. Domperidone increased serum concentrations of GtH, potentiated the action of gonadotrophin-releasing hormones and did not pass into the brain after i.p. injection into goldfish. The data also suggest that dopamine and GnRH, although acting through different receptors, influence the effect of each other on GtH release.

Repressive Factors Controlling Reproduction in Goldfish

Repressive Factors Controlling Reproduction in Goldfish