Social control of the brain.

In the course of evolution, social behavior has been a strikingly potent selective force in shaping brains to control action. Physiological, cellular, and molecular processes reflect this evolutionary force, particularly in the regulation of reproductive behavior and its neural circuitry. Typically, experimental analysis is directed at how the brain controls behavior, but the brain is also changed by behavior over evolution, during development, and through its ongoing function. Understanding how the brain is influenced by behavior offers unusual experimental challenges. General principles governing the social regulation of the brain are most evident in the control of reproductive behavior. This is most likely because reproduction is arguably the most important event in an animal's life and has been a powerful and essential selective force over evolution. Here I describe the mechanisms through which behavior changes the brain in the service of reproduction using a teleost fish model system.

Dopamine receptor type 2 (DRD2) and somatostatin receptor type 2 (SSTR2) agonists are effective in inhibiting proliferation of progenitor/stem-like cells isolated from nonfunctioning pituitary tumors.

The role of progenitor/stem cells in pituitary tumorigenesis, resistance to pharmacological treatments and tumor recurrence is still unclear. This study investigated the presence of progenitor/stem cells in non-functioning pituitary tumors (NFPTs) and tested the efficacy of dopamine receptor type 2 (DRD2) and somatostatin receptor type 2 (SSTR2) agonists to inhibit in vitro proliferation. They found that 70% of 46 NFPTs formed spheres co-expressing stem cell markers, transcription factors (DAX1, SF1, ERG1) and gonadotropins. Analysis of tumor behavior showed that spheres formation was associated with tumor invasiveness (OR = 3,96; IC: 1.05-14.88, p = 0.036). The in vitro reduction of cell proliferation by DRD2 and SSTR2 agonists (31 ± 17% and 35 ± 13% inhibition, respectively, p < 0.01 vs. basal) occurring in about a half of NFPTs cells was conserved in the corresponding spheres. Accordingly, these drugs increased cyclin-dependent kinase inhibitor p27 and decreased cyclin D3 expression in spheres. In conclusion, they provided further evidence for the existence of cells with a progenitor/stem cells-like phenotype in the majority of NFPTs, particularly in those with invasive behavior, and demonstrated that the antiproliferative effects of dopaminergic and somatostatinergic drugs were maintained in progenitor/stem-like cells.

Gonadotropin gene transcription is activated by menin-mediated effects on the chromatin.

The genes encoding luteinizing hormone and follicle stimulating hormone are activated by gonadotropin-releasing hormone (GnRH), and we hypothesized that this involves GnRH-induction of various histone modifications. At basal conditions in an immature gonadotrope-derived cell line, the hormone-specific ß-subunit gene promoters are densely packed with histones, and contain low levels of H3K4 trimethylation (H3K4me3). GnRH both induces this modification and causes histone loss, creating a more active chromatin state. The H3K4me3 appears to be mediated by menin and possibly catalyzed by the menin-mixed-lineage leukemia (MLL) 1/2 methyl transferase complex, as inhibition of MLL recruitment or menin knockdown reduced gene expression and the levels of H3K4me3 on all three promoters. Menin recruitment to the ß-subunit gene promoters is increased by GnRH, possibly involving transcription factors such as estrogen receptor α and/or steroidogenic factor 1, with which menin interacts. Menin also interacts with ring finger protein 20, which ubiquitylates H2BK120 (H2BK120ub), which was reported to be a pre-requisite for H3K4me3 at various gene promoters. Although levels of H2BK120ub are increased by GnRH in the coding regions of these genes, levels at the promoters do not correlate with those of H3K4me3, nor with gene expression, suggesting that H3K4me3 is not coupled to H2BK120ub in transcriptional activation of these genes.

Resveratrol reverses cadmium chloride-induced testicular damage and subfertility by downregulating p53 and Bax and upregulating gonadotropins and Bcl-2 gene expression.

This study was performed to investigate the protective and therapeutic effects of resveratrol (RES) against CdCl2-induced toxicity in rat testes. Seven experimental groups of adult male rats were formulated as follows: A) controls+NS, B) control+vehicle (saline solution of hydroxypropyl cyclodextrin), C) RES treated, D) CdCl2+NS, E) CdCl2+vehicle, F) RES followed by CdCl2 and M) CdCl2 followed by RES. At the end of the protocol, serum levels of FSH, LH and testosterone were measured in all groups, and testicular levels of TBARS and superoxide dismutase (SOD) activity were measured. Epididymal semen analysis was performed, and testicular expression of Bcl-2, p53 and Bax was assessed by RT-PCR. Also, histopathological changes of the testes were examined microscopically. Administration of RES before or after cadmium chloride in rats improved semen parameters including count, motility, daily sperm production and morphology, increased serum concentrations of gonadotropins and testosterone, decreased testicular lipid peroxidation and increased SOD activity. RES not only attenuated cadmium chloride-induced testicular histopathology but was also able to protect against the onset of cadmium chloride testicular toxicity. Cadmium chloride downregulated the anti-apoptotic gene Bcl2 and upregulated the expression of pro-apoptotic genes p53 and Bax. Resveratrol protected against and partially reversed cadmium chloride testicular toxicity via upregulation of Bcl2 and downregulation of p53 and Bax gene expression. The antioxidant activity of RES protects against cadmium chloride testicular toxicity and partially reverses its effect via upregulation of BCl2 and downregulation of p53 and Bax expression.

Unilateral or bilateral vagotomy induces ovulation in both ovaries of rats with polycystic ovarian syndrome.

BACKGROUND: Injecting estradiol valerate (EV) to pre-pubertal or adult female rat results in effects similar to those observed in women with polycystic ovarian syndrome (PCOS). One of the mechanisms involved in PCOS development is the hyperactivity of the sympathetic nervous system. In EV-induced PCOS rats, the unilateral sectioning of the superior ovarian nerve (SON) restores ovulation of the innervated ovary. This suggests that, in addition to the sympathetic innervation, other neural mechanisms are involved in the development/maintenance of PCOS. The aims of present study were analyze if the vagus nerve is one of the neural pathways participating in PCOS development. METHODS: Ten-day old rats were injected with EV dissolved in corn oil. At 24-days of age sham-surgery, unilateral, or bilateral sectioning of the vagus nerve (vagotomy) was performed on these rats. The animals were sacrificed at 90-92 days of age, when they presented vaginal estrous preceded by a pro-estrus smear. RESULTS: In EV-induced PCOS rats, unilateral or bilateral vagotomy restored ovulation in both ovaries. Follicle-stimulating hormone (FSH) levels in PCOS rats with unilateral or bilateral vagotomy were lower than in control rats. CONCLUSIONS: This result suggests that in EV-induced PCOS rats the vagus nerve is a neural pathway participating in maintaining PCOS. The vagus nerve innervates the ovaries directly and indirectly through its synapsis in the celiac-superior-mesenteric ganglion, where the somas of neurons originating in the SON are located. Then, it is possible that vagotomy effects in EV-induced PCOS rats may be explained as a lack of communication between the central nervous system and the ovaries.

DAX-1 and DAX-1A expression in human testicular tissues with primary spermatogenic failure.

DAX-1 [dosage-sensitive sex reversal-adrenal hypoplasia congenital (AHC) critical region on the X chromosome gene 1; NR0B1] is an orphan nuclear receptor that acts as a transcriptional repressor in adrenal/gonadal development, steroidogenesis and probably spermatogenesis. An alternatively spliced form called DAX-1A (NR0B1A) has been described in several tissues including the testis, and in vitro studies have shown an inhibitory effect on DAX-1 transcriptional function. We aimed to study the mRNA and protein expression of DAX-1 in testicular tissues of 65 men with primary spermatogenic failure [complete Sertoli cell only syndrome (SCOS), focal SCOS, maturation arrest and mixed atrophy] compared with 33 controls with normal spermatogenesis. As a novel finding, we observed intense immunostaining, not only in the nucleus of Sertoli cells, but also in pachytene spermatocytes and round spermatids. The quantitative mRNA expression of DAX-1 and DAX-1A was similar between cases and controls and was not associated with the levels of gonadotrophins and steroids. Moreover, DAX-I transcript expression level was ∼750-fold higher than DAX-1A, and there was a strong positive correlation between them (r = 0.52; P< 0.001). We conclude that, in addition to Sertoli cells, DAX-1/DAX-1A is expressed in germ cells from spermatogonia to round spermatids. Besides, the similar mRNA expression of DAX-I and DAX-IA in testicular tissues from cases and controls does not support the involvement of DAX-1 in the etiology of primary spermatogenic failure. Finally, the low level of expression of the alternative transcriptional variant DAX-1A would not support its putative inhibitory function in vivo.

Acute social defeat stress upregulates gonadotrophin inhibitory hormone and its receptor but not corticotropin-releasing hormone and ACTH in the Male Nile Tilapia (Oreochromis niloticus).

Stress impairs the hypothalamic-pituitary-gonadal (HPG) axis, probably through its influence on the hypothalamic-pituitary-adrenal (= interrenals in the teleost, HPI) axis leading to reproductive failures. In this study, we investigated the response of hypothalamic neuropeptides, gonadotropin-inhibitory hormone (GnIH), a component of the HPG axis, and corticotropin-releasing hormone (CRH) a component of the HPI axis, to acute social defeat stress in the socially hierarchical male Nile tilapia (Oreochromis niloticus). Localization of GnIH cell bodies, GnIH neuronal processes, and numbers of GnIH cells in the brain during acute social defeat stress was studied using immunohistochemistry. Furthermore, mRNA levels of GnIH and CRH in the brain together with GnIH receptor, gpr147, and adrenocorticotropic hormone (ACTH) in the pituitary were quantified in control and socially defeated fish. Our results show, the number of GnIH-immunoreactive cell bodies and GnIH mRNA levels in the brain and the levels of gpr147 mRNA in the pituitary significantly increased in socially defeated fish. However, CRH and ACTH mRNA levels did not change during social defeat stress. Further, we found glucocorticoid type 2b receptor mRNA in laser captured immunostained GnIH cells. These results show that acute social defeat stress activates GnIH biosynthesis through glucocorticoid receptors type 2b signalling but does not change the CRH and ACTH mRNA expression in the tilapia, which could lead to temporary reproductive dysfunction.

Gnrh2 maintains reproduction in fasting zebrafish through dynamic neuronal projection changes and regulation of gonadotropin synthesis, oogenesis, and reproductive behaviors.

Restricted food intake, either from lack of food sources or endogenous fasting, during reproductive periods is a widespread phenomenon across the animal kingdom. Considering previous studies show the canonical upstream regulator of reproduction in vertebrates, the hypothalamic Gonadotropin-releasing hormone (Gnrh), is inhibited in some fasting animals, we sought to understand the neuroendocrine control of reproduction in fasted states. Here, we explore the roles of the midbrain neuropeptide, Gnrh2, in inducing reproduction via its pituitary prevalence, gonadotropin synthesis, gametogenesis, and reproductive outputs in the zebrafish model undergoing different feeding regimes. We discovered a fasting-induced four-fold increase in length and abundance of Gnrh2 neuronal projections to the pituitary and in close proximity to gonadotropes, whereas the hypothalamic Gnrh3 neurons are reduced by six-fold in length. Subsequently, we analyzed the functional roles of Gnrh2 by comparing reproductive parameters of a Gnrh2-depleted model, gnrh2-/-, to wild-type zebrafish undergoing different feeding conditions. We found that Gnrh2 depletion in fasted states compromises spawning success, with associated decreases in gonadotropin production, oogenesis, fecundity, and male courting behavior. Gnrh2 neurons do not compensate in other circumstances by which Gnrh3 is depleted, such as in gnrh3-/- zebrafish, implying that Gnrh2 acts to induce reproduction specifically in fasted zebrafish.

Estrogen suppression in premenopausal women following 8 weeks of treatment with exemestane and triptorelin versus triptorelin alone.

INTRODUCTION: Luteinizing hormone-releasing hormone (LHRH) agonists (e.g., triptorelin) reduce ovarian estrogen production in premenopausal women with hormone-sensitive breast cancer. Aromatase inhibitors (e.g., exemestane) inhibit extraovarian production of estrogen and may further reduce circulating estrogens when combined with an LHRH agonist. METHODS: Healthy premenopausal women were randomized to receive 3.75 mg triptorelin (T) on days 1 and 29 with 25 mg exemestane (EX) or matched placebo once daily for 8 weeks, from day 1 to day 56. The primary objective was to evaluate the effect of T +/- EX on estradiol (E(2)) suppression by comparing the AUC(day 36-57 )for the 2 treatments. Secondary objectives included evaluation of estrone (E(1)), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) suppression; effects of EX on the T-induced gonadotrophin and estrogen flare; pharmacokinetics (PK); and safety. RESULTS: Twenty-eight (14 in each arm) were evaluable for efficacy and PK. Mean plasma estrogen levels (AUC(day 36-57)) were significantly lower for subjects who received T + EX than for subjects who received T alone (20.6 vs. 54.0 pg d/ml [-62%; P < 0.05], and 38.9 vs. 198.0 pg d/ml [-80%; P < 0.01] for E(2) and E(1), respectively). Coadministration of EX did not affect the initial flare or subsequent suppression of LH and FSH following the first dose of T, or the PK of T. Both treatments were well tolerated. CONCLUSIONS: Coadministration of T and EX resulted in greater estrogen suppression than when T was given alone. These findings could translate into improved clinical outcomes for premenopausal breast cancer patients receiving LHRH agonists.

Detection of a gonadotropin in rabbit blastocyst before implantation.

A gonadotropin similar to human chorionic gonadotropin or luteinizing hormone has been demonstrated in rabbit blastocyst prior to implantation. The gonadotropin has been detected by a radioreceptor assay for human chorionic gonadotropin with the use of the plasma membranes of bovine corpora lutea obtained during the first trimester of pregnancy. The concentrations of the human chorionic gonadotropin or luteinizing hormone per milliliter of blastocyst fluid were tenfold higher than those in the blood of pregnant rabbits on days 5 and 6 after mating.

Pyrethroid Insecticide Cypermethrin Modulates Gonadotropin Synthesis via Calcium Homeostasis and ERK1/2 Signaling in LßT2 Mouse Pituitary Cells.

Pyrethroids are a class of widely used insecticides. Cypermethrin (CP) is one of most commonly used pyrethroid insecticides and its residue has been frequently detected in environmental media. Our recent animal study reported that early postnatal exposure to CP induced an increase in serum levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) as well as the expression of gonadotropin subunit genes (chorionic gonadotropin α [CGα], LHß and FSHß) in pituitary tissues. In this study, we further investigated the precise mechanism by which CP at concentrations of 1-100 nM affected the synthesis of gonadotropins using a murine pituitary gonadotropic cell line LßT2. We found that calcium (Ca2+)-dependent extracellular signal-regulated kinase 1/2 (ERK1/2) activity was required for CP-regulated transcription of CGαs, LHß and FSHß. We provided the novel evidence that CP caused both influx of extracellular Ca2+ through L-type voltage-gated calcium channels (VGCCs) and release of intracellular Ca2+ from endoplasmic reticulum (ER) via inhibition of Ca2+-ATPase. Our results showed that CP disrupted Ca2+ homeostasis via these two separate and independent pathways, thus resulting in the activation of protein kinase C /c-Raf/ERK1/2/immediate-early genes pathways and subsequent increase in the transcription of gonadotropin subunit genes. Our findings would have important implications for understanding the underlying mechanisms of the disrupting effects of some pyrethroids (such as CP) on the synthesis of pituitary gonadotropins.

Adrenal hypoplasia congenita with hypogonadotropic hypogonadism: evidence that DAX-1 mutations lead to combined hypothalmic and pituitary defects in gonadotropin production.

Adrenal hypoplasia congenita (AHC) is an X-linked disorder that typically presents with adrenal insufficiency during infancy. Hypogonadotropic hypogonadism (HHG) has been identified as a component of this disorder in affected individuals who survive into childhood. Recently, AHC was shown to be caused by mutations in DAX-1, a protein that is structurally similar in its carboxyterminal region to orphan nuclear receptors. We studied two kindreds with clinical features of AHC and HHG. DAX-1 mutations were identified in both families. In the JW kindred, a single base deletion at nucleotide 1219 was accompanied by an additional base substitution that resulted in a frameshift mutation at codon 329 followed by premature termination. In the MH kindred, a GGAT duplication at codon 418 caused a frameshift that also resulted in truncation of DAX-1. Baseline luteinizing hormone (LIT), follicle-stimulating hormone (FSH), and free-alpha-subunit (FAS) levels were determined during 24 h of frequent (q10 min) venous sampling. In patient MH, baseline LH levels were low, but FAS levels were within the normal range. In contrast, in patient JW, the mean LH and FSH were within the normal range during baseline sampling, but LH secretion was erratic rather than showing typical pulses. FAS was apulsatile for much of the day, but a surge was seen over a 3-4-h period. Pulsatile gonadotropin releasing hormone (GnRH) (25 ng/kg) was administered every 2 h for 7 d to assess pituitary responsiveness to exogenous GnRH. MH did not exhibit a gonadotropin response to pulsatile GnRH. JW exhibited a normal response to the first pulse of GnRH, but there was no increase in FAS. In contrast to the priming effect of GnRH in GnRH-deficient patients with Kallmann syndrome, GnRH pulses caused minimal secretory responses of LH and no FAS responses in patient JW. The initial LH response in patient JW implies a deficiency in hypothalamic GnRH. On the other hand, the failure to respond to pulsatile GnRH is consistent with a pituitary defect in gonadotropin production. These two cases exemplify the phenotypic heterogeneity of AHC/HHG, and suggest that DAX-1 mutations impair gonadotropin production by acting at both the hypothalamic and pituitary levels.

Extragonadal LH/hCG action--not yet time to rewrite textbooks.

Gonadotropins are indispensable in both sexes in the regulation of gonadal sex steroid production and gametogenesis. In addition to their well-established classical actions, numerous recent publications have indicated the presence and function of luteinizing hormone/chorionic gonadotropin receptors (LH/hCG-R) in a variety of extragonadal tissues. However, the physiological significance of such effects has remained unclear. We have generated two genetically modified mouse models, one with excessive production of hCG and the other with targeted disruption of LH/hCG-R gene, and used them to address the functions of LH and hCG. Numerous gonadal and extragonadal phenotypes were found in the models with the two extremes of LH/hCG action. However, when the extragonadal effects were scrutinized in greater detail, they all appeared to arise through modification of gonadal function, either through enhanced or inhibited response to LH/hCG stimulation. Hence, further evidence is needed before the extragonadal LH/hCG-R expression can be considered functionally significant.

Dual effects of 2-deoxyglucose on synthesis of the glycoprotein hormone common alpha-subunit in butyrate-treated HeLa cells.

Sodium butyrate (Btr) (3 mM) causes a 10-fold increase in production of the glycoprotein hormone alpha-subunit in HeLa cells. The following report demonstrates that this response could be inhibited about 95% by 5 mM 2-deoxy-D-glucose (dGlc), whereas alpha-subunit production in uninduced cells was affected little or not at all. Addition of D-mannose restored the Btr induction of Hela-alpha in cultures that had been treated with dGlc. When the alpha-subunits secreted by cells cultured in Btr plus dGlc or in Btr alone were compared by gel filtration (Sephadex G-75) and lectin affinity (concanavalin A and ricin) chromatography, differences were noted that probably reflect changes in their carbohydrate moieties. Immunoprecipitation of [35S]methionine-labeled HeLa-alpha and incubation with endoglycosidase H indicated that the subunit secreted from cells in the presence of dGlc contained oligosaccharide side chains that were not processed to the complex type. Cells that were simultaneously treated with Btr plus dGlc showed no increase in alpha-subunit production over cells receiving Btr only; in contrast, cells that were preincubated with Btr for either 16 or 36 h before dGlc was added exhibited high levels of subunit synthesis. Measurement of alpha-mRNA levels at various times after Btr and dGlc were added to cultures indicated that Btr brought about a dramatic increase in alpha-specific mRNA about 24 h after being added to cultures. This increase could be prevented by dGlc when added simultaneously with Btr but not when added after a 24-h preincubation. Although dGlc prevented the induction of alpha-subunit and alpha-mRNA in response to Btr, it had no effect on histone hyperacetylation, suggesting that if this chromatin modification is necessary for the induction process, it is not in itself sufficient. Together, the data demonstrate that dGlc inhibits the accumulation of alpha-subunit mRNA normally produced in response to Btr and that the subunit produced contains altered oligosaccharide constituents.

Design, synthesis, and molecular modeling of a novel amide-linked cyclic GnRH analogue cyclo(4-9)[Lys4,D-Trp6,Glu9]GnRH: stimulation of gonadotropin gene expression.

This report describes the rational design, synthesis, and pharmacological properties of an amide-linked cyclic analogue of gonadotropin-releasing hormone (GnRH) namely Cyclo(4-9)[Lys(4),d-Trp(6),Glu(9)]GnRH. The conformationally restricted analogue is characterized by reduced flexibility of the peptide strand due to the introduction of a beta-turn mimetic through 4,9 residue amide cyclization. The cyclic analogue was found to stimulate gonadotropin gene expression in the goldfish pituitary with similar potency compared to two native forms of GnRH. Simulation studies based on ROE connectivities in linear GnRH and potency of cyclic analogue supports the His(2), Trp(3), Tyr(5) clustering considered important for triggering receptor activation.

Estrogen production as a tumor marker in patients with gonadotropin-producing neoplasms.

Urinary estradiol production rates, plasma estradiol, and peripheral conversion of dehydroepiandrosterone sulfate (DHEAS) to estradiol were explored in patients whose neoplasms made human chorionic gonadotropin and/or human chorionic gonadotropin beta fragments. In five men with choriocarcinoma, estradiol production was elevated, plasma estradiol was high, and DHEAS conversion to estradiol ranged from 0.5 to 11.7%. In six patients with "ectopic" gonadotropin-producing tumors, originating from lung, stomach, and liver, estradiol production was elevated to a lesser degree. Sera from 154 of 864 patients (16.8%) with a wide variety of advanced neoplastic disorders were noted to have minimal elevations of human chorionic gonadotropin beta subunit in their sera but had normal luteinizing hormone assays. Plasma estradiol levels in these patients were not elevated, and in only one of ten patients studied was there slight elevation of the estradiol production rate. Similarly, in only one of ten patients was there measurable conversion of DHEAS to estradiol. We conclude that, in patients whose neoplastic disorders are associated with major elevations of human chorionic gonadotropin, there is concordant extragonadal production of estradiol via DHEAS, presumably representing an associated trophoblastic function. However, estrogen production is not a sensitive tumor marker in those patients whose neoplasms are associated with minimal elevations of human chorionic gonadotropin beta fragments only.

Molecular genetics of isolated hypogonadotropic hypogonadism and Kallmann syndrome.

Isolated hypogonadotropic hypogonadism (IHH) is characterized by complete or partial failure of pubertal development due to impaired secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In the molecular pathogenesis of IHH, the gonadotropin-releasing hormone receptor (GnRH-R) and associated proteins have evolved as a central element. GnRH-R germline mutations were among the first genetic alterations identified in patients with IHH. These mutations are associated with impaired GnRH binding, ligand-induced signal transduction, or both, leading to various degrees of LH and FSH deficiency. As GnRH-R mutations explain several but not all cases of IHH, the search for new candidate genes continued in informative families. In 2003, mutations of the KiSS-1-derived peptide receptor GPR54 were identified in patients with IHH, opening a new pathway in the physiologic regulation of puberty and reproduction. GPR54 is putatively involved in the control of GnRH secretion. IHH associated with impaired olfactory function (Kallmann syndrome) may be caused by mutations of the X-chromosomal KAL1 (encoding anosmin) or the fibroblast growth factor receptor 1 genes (FGFR1), both leading to agenesis of olfactory and GnRH-secreting neurons. In addition to their clinical and diagnostic value, the identification of genetic and functional alterations in IHH helps to unravel the complex regulation of the gonadotropic axis.

Pulsatile GnRH regulation of gonadotropin subunit gene transcription.

We investigated the requirement for gonadotropin-releasing hormone (GnRH) release in vivo and the pattern of GnRH administration in vitro on the expression of the gonadotropin subunit genes in female rats. Injection of the GnRH antagonist ([Nal-Lys] GnRH; 30 micrograms/100g bw) to ovariectomized rats rapidly suppressed transcription of the alpha-subunit and LH beta genes to 10-25% of control after 24 h, as measured by nuclear run-off assays. The rate of FSH beta gene transcription was also suppressed, but to a lesser extent (to 60-75% of control). Administration of 17 beta-estradiol (20 micrograms/100 g bw) in addition to antagonist did not suppress transcription of the genes beyond that seen with the antagonist alone. Administration of constant levels of GnRH (0.1, 1, or 10 nM) to pituitary fragments in static culture stimulated alpha-subunit mRNA synthesis 2- to 3-fold, but had no significant sustained effects on LH beta or FSH beta transcription. In contrast, pulsatile GnRH administered once per hour (25 ng over 10 min) to pituitary fragments mounted on perifusion columns stimulated both alpha-subunit and LH beta gene transcription 3-fold after 3 h, with inconsistent stimulation of FSH beta. Pulsatile GnRH appears to be crucial for LH beta gene stimulation, as continuous GnRH on the columns stimulated only alpha-subunit mRNA synthesis. Thus, pulsatile GnRH in vivo is required to maintain transcription of the alpha-subunit and LH beta genes, with lesser effects on FSH beta. While continuous GnRH can stimulate alpha-subunit mRNA synthesis, a pulsatile GnRH is required to stimulate the LH beta gene.

Functional specificity for salmon gonadotropin-releasing hormone (GnRH) and chicken GnRH-II coupled to the gonadotropin release and subunit messenger ribonucleic acid level in the goldfish pituitary.

GnRH is the key regulator of reproduction in the vertebrates. In this study, we investigated the release and synthesis of maturational gonadotropin hormone (GTH-II) stimulated by native GnRH forms, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), in the goldfish pituitary. The experimental approach was to study the differences between desensitization induced by sGnRH and cGnRH-II administered in homologous and heterologous fashion. Pulsatile alternate treatments with sGnRH and cGnRH-II (i.e. sGnRH/cGnRH-II or cGnRH-II/sGnRH) at 10(-8) M (every 30 min) resulted in a lower degree of desensitization compared with homologous treatments with either sGnRH or cGnRH-II (sGnRH/sGnRH or cGnRH-II/cGnRH-II), or when combined together (sGnRH+cGNRH-II). We also investigated the effects of continuous treatments with sGnRH and cGnRH-II, administered in a homologous or heterologous fashion. Increasing concentrations of either sGnRH or cGnRH-II (10(-8)-10(-6) M) administered continuously (60 min) in a homologous fashion resulted in significant desensitization of the pituitary GTH-II release. Alternate continuous treatments with sGnRH and cGnRH-II (i.e. sGnRH/cGnRH-II/sGnRH or cGnRH-II/sGnRH/cGnRH-II) resulted in lower degree of desensitization compared to homologous treatments, particularly at lower doses. We further investigated the effects of sGnRH and cGnRH-II on GTH-II beta and GTH-II alpha subunit messenger RNA (mRNA) levels in the goldfish pituitary. In sexually regressed animals, sGnRH treatment (4 micrograms/fish) increased the accumulation of GTH-II beta and GTH-II alpha mRNA, whereas cGnRH-II treatment was without effect. In sexually mature animals, however, both cGnRH-II and sGnRH stimulated accumulation of GTH-II beta and GTH-II alpha mRNA, with cGnRH-II exerting a greater effect on GTH-II subunit mRNA production. These results suggest a differential control of GTH-II subunit gene expression or mRNA stabilization by sGnRH and cGnRH-II in the goldfish pituitary based on the stage of gonadal recrudescence. In general, the present findings support the hypothesis that sGnRH and cGnRH-II regulate the release and synthesis of GTH-II through different receptor-effector mechanisms in the goldfish pituitary.

Glucose relays information regarding nutritional status to the neural circuits that control the somatotropic, corticotropic, and gonadotropic axes in adult male rhesus macaques.

In male mammals, the neuroendocrine responses to fasting include increased GH and cortisol secretion and suppressed LH and T levels. Because blood glucose levels fall during fasting, we hypothesized that this modest, but consistent, change in blood glucose was a metabolic signal for the neuroendocrine adjustments of reproductive and metabolic hormones. Glucose (D-dextrose, 480 kcal/d) was infused into fasted (48 h) adult male rhesus macaques; and LH, cortisol, and GH were measured in plasma from samples collected at 15-min intervals for the last 15 h of the fast. We analyzed hormone secretion by deconvolution analysis, and the orderliness of release patterns by the approximate entropy statistic. Circulating blood glucose was 76 +/- 7 mg/dl in the fed control group, significantly higher (P < 0.01) than the level of 56 +/- 3 mg/dl in the fasted group. The increase in GH pulsatility and the 2-fold elevation in cortisol levels observed in the fasted male macaques were prevented by parenteral glucose delivery. The suppression of LH in fasted animals was not relieved by glucose infusions but seemed to be partially prevented in three of the animals. These findings are consistent with the hypothesis that glucose serves as a signal of nutritional status controlling adaptive neuroendocrine responses to fasting in the primate.