Effects of [D-Ala6, Pro9-NEt]-LHRH and catecholaminergic drugs on gonadotropin secretion and ovulation in the Chinese loach (Paramisgurnus dabryanus)

Effects of GnRHa and hCG with or without dopamine receptor antagonists on the spawning efficiency of African catfish (Clarias gariepinus) reared in hatchery conditions

Optimization of artificial reproduction is essential for minimizing genetic diversity, especially when fish are captured from their natural habitats and spawned in controlled conditions. In the present study, there was evaluation of the effects of gonadotropin-releasing hormone analogue (GnRHa) and human chorionic gonadotropin (hCG) with or without dopamine receptor antagonists such as domperidone (DOM) and metoclopramide (MET) on the spawning efficiency of African catfish (Clarias gariepinus) reared in captivity. The control group was intramuscularly (IM) injected with 1 mL of sterile saline solution. The fish specimens of the other six groups were injected IM with GnRHa or hCG, or in combination with either DOM or MET. None of the specimens had ovulations in the control group. There was the longest latency period in specimens treated with only GnRHa or hCG. There were the largest egg mass weight, fecundity, and hatchability (%) in specimens of the GnRHa + MET group. These findings indicate that GnRHa or hCG combined with dopamine receptor antagonists such as DOM and MET resulted in a marked enhancement of ovulation rate and increased the egg mass, fecundity, and hatchability of the treated C. gariepinus, and the values when there was inclusion of the MET treatment exceeded those when there was treatment with DOM.

Ovaprim, a commercial spawning inducer, stimulates gonadotropin subunit gene transcriptional activity: A study correlated with plasma steroid profile, ovulation and fertilization in the catfish Heteropneustes fossilis

The commercial fish spawning inducer Ovaprim (OVP) containing a salmon gonadotropin-releasing hormone analogue and domperidone (a dopamine receptor-2 antagonist) has been widely used as an effective spawning inducer in artificial breeding of fishes. It induces a preovulatory LH surge resulting in final oocyte maturation (FOM) and ovulation through a mechanism involving a steroidogenic shift to secrete a maturation-inducing steroid (MIS). In the present study, a 0.5μL/g body weight dose of OVP each injected at 0h and 24h intraperitoneally into gravid female catfish, Heteropneustes fossilis resulted in periovulatory changes in gonadotropin (GtH) subunit gene expression and steroid hormone levels. The OVP injections induced ovulation time-dependently from 6h onwards with 100% ovulation recorded from 24h to 48h. The fertilization rate was high from 6h to 18h and declined from 24h onwards. The OVP treatment up regulated the expression of GtH subunit genes differentially. The expression of glycoprotein-α (GPα) and luteinizing hormone (LHβ) peaked at 6h and 12h, and declined at 18h and 24h after the first injection. The second OVP injection at 24h elicited only a transient increase in the GPα expression at 6h and a sustained increase in the LHβ expression from 6h to 18h after the second injection, but both transcripts decreased subsequently. The follicle-stimulating hormone (FSHβ) expression responded to the OVP treatment from 12h onwards and maintained a constant level from 18h to 36h after the first injection; the second dose had little effect. Plasma steroids were differentially altered: the levels of estradiol-17β decreased while that of the MIS 17,20β-dihydroxy-4-pregnen-3-one; 17,20β-DP increased, causing the steroidogenic shift preceding FOM and ovulation. The present results indicate that LHβ expression coincides with the ovulation response and the late induction and maintenance of the FSH expression may be related to post-ovulatory events in the ovary.

Tyrosine hydroxylase in the olfactory system, forebrain and pituitary of the Indian major carp, Cirrhinus cirrhosus: organisation and interaction with neuropeptide Y in the preoptic area

Dopamine (DA) inhibits, whereas gonadotrophin-releasing hormone (GnRH) stimulates, luteinisiing (LH) cells in the pituitary of some but not all teleosts. A reduction in the hypophysiotropic dopaminergic tone is necessary for the stimulatory effect of GnRH on LH cells. Neuropeptide Y (NPY) has emerged as one of the potent, endogenous agent that modulates LH secretion directly or indirectly via GnRH. Involvement of NPY in the regulation of hypophysiotropic DA neurones, however, is not known, but there is good evidence suggesting an interaction in the mammalian hypothalamus. DA neurones, identified by tyrosine hydroxylase (TH)-immunoreactivity, were observed widely throughout the brain of the Indian major carp, Cirrhinus cirrhosus. The granule cells and ganglion cells of terminal nerve in the olfactory bulb, and cells in ventral telencephalon and preoptic area (POA) showed conspicuous TH immunoreactivity. In the POA, the nucleus preopticus periventricularis (NPP), divisible into anterior (NPPa) and posterior (NPPp) components, showed prominent TH-immunoreactivity. The majority of TH neurones in NPPa showed axonal extensions to the pituitary and were closely associated with LH cells. The NPPa also appeared to be the site for intense interaction between NPY and DA because it contains a rich network of NPY fibres and few immunoreactive cells. Approximately 89.7 ± 1.5% TH neurones in NPPa were contacted by NPY fibres. Superfused POA slices treated with a NPY Y2 -receptor agonist, NPY 13-36 resulted in a significant (P < 0.001) reduction in TH-immunoreactivity in NPPa. TH neurones in NPPa did not respond to NPY Y1 -receptor agonist, [Leu(31) , Pro(34) ] Neuropeptide Y treatment. We suggest that, by inhibiting DAergic neurones in NPPa via Y2 -receptors, NPY may contribute to the up-regulation of the GnRH-LH cells axis. The microcircuitry of DA and NPY and their interaction in NPPa might be a crucial component in the central regulation of LH secretion in the teleosts.

Discovery of four estrogen receptors and their expression profiles during testis recrudescence in male Spinibarbus denticulatus

Estrogen plays an important role in male reproduction. Most of the actions are mediated by estrogen receptor (ER). To investigate the profile of estrogen affecting male fertility, we firstly cloned four ERs from the male Spinibarbus denticulatus, a local economically important cyprinid fish in China. Phylogenetic tree analysis ranked the four sdERs as two distinct groups of ERalpha and beta, which could be further divided into duplicated isoforms 1 and 2, respectively. High score identities were shared between each of the duplicated isoforms. All of the four sdERs distributed in central nervous system of male fish with a quite broad spectrum. However, distribution diversity became evident between sdERalpha and sdERbeta subtypes in the peripheral tissues. Both of the two isoforms of ERbeta were detected in all seven tissues examined, while expression of sdERalpha1 was mainly limited to liver, kidney, testis and intestine and sdERalpha2 was confined to liver, heart, kidney, testis and gill. During the testis recrudescing stages, serum concentration of luteinizing hormone (LH), testosterone (T) and estradiol-17beta (E(2)) were increasing. T and LH levels in the circulation were high until the later fully recrudesced phase, while serum E(2) level was low all the time. Quantitative real-time RT-PCR analysis determined the most abundance of sdERs in pituitary where the two sdERalpha isoforms positively expressed with testis development, while sdERbeta isoforms expressed with a reverse pattern. sdERalpha1 and sdERbeta1 were the primary forms in testis. sdERalpha1 gradually increased during the recrudescence process while sdERbeta1 firstly decreased during the recrudescing stage and then positively expressed in fully recrudesced stage. Little or no signal was detected in brain. The present work provided evidence of four sdERs in male reproductive system and suggested an important role of sdERalpha1 during testis recrudescence. Pituitary contained duplicates forms of sdERalpha which may play a role in the feedback effects of estrogen on LH secretion.

Amino Acid Neurotransmitters and Dopamine in Brain and Pituitary of the Goldfish: Involvement in the Regulation of Gonadotropin Secretion

An isocratic high-performance liquid chromatographic technique was developed to measure levels of gamma-aminobutyric acid (GABA), glutamate, and taurine in the brain and pituitary of goldfish. Accuracy of this procedure for quantification of these compounds was established by evaluating anesthetic and postmortem effects and by selectively manipulating GABA concentrations by intraperitoneal administration of the glutamic acid decarboxylase (GAD) inhibitor 3-mercaptopropionic acid or the GABA transaminase inhibitor gamma-vinyl GABA. The technique provided a simple, rapid, and reliable method for evaluating the concentrations of these amino acids without the use of complex gradient chromatographic systems. To investigate the relationship between neurotransmitter amino acids and the control of pituitary secretion of gonadotropin, the effects of injection of taurine, GABA, or monosodium glutamate on GABA, glutamate, taurine, and, in some instances, monoamine concentrations in the brain and pituitary were evaluated and related to serum gonadotropin levels. Injection of taurine caused an elevation in serum gonadotropin concentrations. In addition, injection of the taurine precursor hypotaurine but not the taurine catabolite isethionic acid elevated serum gonadotropin levels. Intracerebroventricular injection of either GABA or taurine also elevated serum gonadotropin concentrations. Pretreatment of recrudescent fish with alpha-methyl-p-tyrosine reduced pituitary dopamine concentrations and also potentiated the serum gonadotropin response to taurine. Injection of monosodium glutamate caused an increase of glutamate content in the pituitary at 24 h; this was followed by a decrease at 72 h after administration. Pituitary GABA, taurine, and dopamine concentrations underwent a transient depletion after monosodium glutamate administration, and this was associated with an elevation of serum gonadotropin content.(ABSTRACT TRUNCATED AT 250 WORDS)

A presumptive role for GABA in the stimulatory effects of Des-Gly10, [D-Ala6]-LHRH-ethylamide and pimozide on the gonadotropin release in carp

To investigate the effect of endogenous gamma-aminobutyric acid (GABA) on the blood maturating gonadotropin (GtH) levels, or to study its interaction with pimozide (dopamine antagonist) and a luteinizing hormone-releasing hormone analog (LHRH-a), sexually mature male and female carps were treated with drugs that may either inhibit GABA biosynthesis or GABA degradation. In females the irreversible inhibitor of GABA-transaminase, gamma-vinyl GABA (GVG), which was to increase the endogenous GABA-ergic tone, had no influence on GtH release. On the other hand, the increased GtH response to the combination of pimozide (PIM) and LHRH-a was clearly enhanced by the administration of 3-mercaptopropionic acid (MPA), an inhibitor of the rate limiting enzyme of GABA-biosynthesis. In males the GABA-ergic compound, valproic acid (DPA) decreased LHRH-a stimulated GtH levels. In male carps that received PIM to diminish the dopaminergic inhibition of GtH release, the spermiating response to LHRH-a was increased by administration of MPA. These data suggest that GABA interacts with the action of dopamine and the gonadotropin releasing hormone (GnRH) on the release of GtH.

Dopamine inhibits gonadotropin secretion in the Chinese loach (Paramisgurnus dabryanus)

The effects of dopamine on gonadotropin (GtH) secretion in sexually mature Chinese loach were investigated. Spontaneous secretion of GtH was inhibited within 1 h following an intramuscular injection of dopamine (100 μg/g body wt). Similarly, dopamine (50 and 100 μg/g body wt) caused a significant reduction in serum GtH in fish with elevated GtH levels as a result of pretreatment with gonadotropin-releasing hormone (GnRH) analogs either alone or in combination with the dopamine receptor antagonist domperidone. In summary, the present study provides direct evidence that dopamine functions as a gonadotropin-release inhibitory factor in the Chinese loach by blocking spontaneous and GnRH-stimulated GtH release.

Control of gonadotropin release in the Atlantic croaker (Micropogonias undulatus): evidence for lack of dopaminergic inhibition

Gonadotropin (GTH) secretion is known to be under inhibitory dopaminergic control in several species of fish. To investigate whether this is also the case in the Atlantic croaker (Micropogonias undulatus), juvenile and adult croaker were treated with a gonadotropin-releasing hormone analog (des-Gly10D-Ala6Pro9 n ethylamide luteinizing hormone-releasing hormone (LHRHa), 1-100 ng/g body wt) in combination with various dopaminergic drugs (1-20 mg/kg body wt). None of the dopamine antagonists tested, metoclopramide, pimozide, haloperidol, and domperidone, were able to increase plasma GTH levels above those induced by treatment with LHRHa alone and in some cases the gonadotropin response to LHRHa was reduced. The dopamine agonists bromocriptine and apomorphine either had no effect on the normal response to LHRHa or increased it. None of the drugs tested had any detectable effect on GTH levels in the absence of LHRHa. These results provide evidence for a lack of dopaminergic inhibition in the control of GTH secretion in the Atlantic croaker.

Effects of [D-Arg6, Trp7, Leu8, Pro9NEt]-luteinizing hormone-releasing hormone (sGnRH-A) and [D-Ala6, Pro9NEt]-luteinizing hormone-releasing hormone (LHRH-A), in combination with pimozide or domperidone, on gonadotropin release and ovulation in the Chinese loach and common carp

The effects of LHRH-A and sGnRH-A alone and in combination with the dopamine receptor antagonists pimozide (PIM) and domperidone (DOM) on stimulation of gonadotropin (GtH) secretion and ovulation in Chinese loach (Paramisgurnus dabryanus) and common carp (Cyprinus carpio) were studied. When tested in the absence of a dopamine receptor antagonist, sGnRH-A was about 10-fold more potent than LHRH-A in stimulating GtH secretion in loach, whereas these peptides were of similar effectiveness in common carp. Both peptides were effective alone in inducing ovulation in loach, but were ineffective in common carp. PIM and DOM stimulate a small but significant increase in serum GtH, and greatly potentiate the effects of LHRH-A and sGnRH-A on GtH secretion and ovulation in both species. DOM was of equal or somewhat greater potency than PIM in potentiating the action of releasing hormone agonists in loach; however, DOM had markedly greater effectiveness in common carp. sGnRH-A in the presence of DOM was more effective than LHRH-A in stimulating GtH secretion and ovulation in common carp. The present studies suggest that there are marked differences in the relative contribution of GnRH and dopamine in the control of GtH secretion in loach and common carp, and indicate in particular that the more intense dopaminergic inhibitory control of GtH release in common carp modifies the responsiveness of the pituitary to GnRH peptides.