Gonadotropin-releasing hormone signaling in behavioral plasticity

Social regulation of immediate early gene induction in gonadotropin releasing-hormone 1 neurons and singing behavior in canaries (Serinus canaria)

Social cues modulate the neuroendocrine control of reproduction. However, the neural systems involved in the integration of social cues are not well described. Gonadotropin-releasing hormone 1 (GnRH1) cells in the preoptic area (POA) are the final common node that links the brain with peripheral reproductive physiology. These experiments investigated whether induction of the immediate early gene, EGR1, in anatomically localized GnRH1 cell populations in Border canaries is regulated by the social environment. First, we characterized behavioral modifications in singing behavior and found males paired with a female for 2 weeks significantly reduced many aspects of singing behavior. However, paired males had a significantly higher percentage of GnRH1 cells co-labeled with EGR1. The second experiment manipulated the social environment by pairing males and females in mixed sex dyads, same sex dyads or housed birds in isolation. Only when birds are paired in mixed sex dyads was there a significantly greater percentage of GnRH1 cells expressing EGR1 cells. Increased GnRH1-EGR1 co-expression was localized to the rostral POA. These data reveal that discrete GnRH1 cells are involved in the neural integration of specific social cues and support the hypothesis that the POA exhibits functional topography related to courtship and sexual behaviors.

Seasonal variation in gonadal hormones, spatial cognition, and hippocampal attributes: More questions than answers

A large body of research has been dedicated to understanding the factors that modulate spatial cognition and attributes of the hippocampus, a highly plastic brain region that underlies spatial processing abilities. Variation in gonadal hormones impacts spatial memory and hippocampal attributes in vertebrates, although the direction of the effect has not been entirely consistent. To add complexity, individuals in the field must optimize fitness by coordinating activities with the appropriate environmental cues, and many of these behaviors are correlated tightly with seasonal variation in gonadal hormone release. As such, it remains unclear if the relationship among systemic gonadal hormones, spatial cognition, and the hippocampus also exhibits seasonal variation. This review presents an overview of the relationship among gonadal hormones, the hippocampus, and spatial cognition, and how the seasonal release of gonadal hormones correlates with seasonal variation in spatial cognition and hippocampal attributes. Additionally, this review presents other neuroendocrine mechanisms that may be involved in modulating the relationship among seasonality, gonadal hormone release, and the hippocampus and spatial cognition, including seasonal rhythms of steroid hormone binding globulins, neurosteroids, sex steroid hormone receptor expression, and hormone interactions. Here, endocrinology, ecology, and behavioral neuroscience are brought together to present an overview of the research demonstrating the mechanistic effects of systemic gonadal hormones on spatial cognition and the hippocampus, while, at a functional level, superimposing seasonal effects to examine ecologically-relevant circannual changes in gonadal hormones and spatial behaviors.

A 2b-RAD parentage analysis pipeline for complex and mixed DNA samples

Next-generation sequencing technology has revolutionized genotyping in many fields of study, yet parentage analysis often still relies on microsatellite markers that are costly to generate and are currently available only for a limited number of species. 2b-RAD sequencing (2b-RAD) is a DNA sequencing technique developed for ecological population genomics that utilizes type IIB restriction enzymes to generate consistent, uniform fragments across samples. This technology is inexpensive, effective with low DNA inputs, and robust to DNA degradation. Here, we developed a probabilistic genotyping-by-sequencing genetic testing pipeline for parentage analysis by using 2b-RAD for inferring familial relationships from mixed DNA samples and populations. Our approach to partial paternity assignment utilizes a novel weighted outlier paternity index (WOPI) adapted for next-generation sequencing data and an identity-by-state (IBS) matrix-based clustering method for pedigree reconstruction. The combination of these two parentage assignment methods overcomes two major obstacles faced by other genetic testing methods: 1) It allows detection of parentage when closely related or inbred individuals are in the alleged parent population (e.g., in laboratory strains); and 2) it resolves mixed DNA samples. We successfully demonstrate this novel approach by correctly inferring paternity for samples pooled from multiple offspring (i.e., entire clutches) in a highly inbred population of an East African cichlid fish. The unique advantages of 2b-RAD in combination with our bioinformatics pipeline enable straightforward and cost-effective parentage analysis in any species regardless of genomic resources available.

Trans-seasonal activation of the neuroendocrine reproductive axis: Low-temperature winter dormancy modulates gonadotropin-releasing hormone neurons in garter snakes

All animals use external cues from the environment to accurately time life-history events. How the brain decodes environmental stimuli to effect changes in physiology and behavior, however, is poorly understood, particularly with regard to supplementary environmental cues such as temperature. We asked if low-temperature dormancy alters the synthesis and/or release of gonadotropin-releasing hormone (GnRH). We used the well-studied red-sided garter snake (Thamnophis sirtalis) for this study, as low-temperature exposure is both necessary and sufficient to induce reproduction in northern populations of this species. Snakes were collected from the field and hibernated at 4°C or 10°C in complete darkness for up to 16 weeks. In males, increasing duration of low-temperature dormancy significantly increased GnRH-immunoreactive cell number and GnRH soma size (a proxy for relative cell activity) in the forebrain. These changes mirrored those in male reproductive behavior (reported previously) and plasma androgen concentrations. The changes in GnRH cell area observed in males were specific to the neuroendocrine population of cells in the medial preoptic area; soma size in the rostral GnRH cells did not change. Finally, temperature-induced changes in GnRH were sexually dimorphic: neither hibernation temperature nor the duration of winter dormancy significantly modulated GnRH cell number or soma size in females, despite the fact that plasma estradiol and corticosterone increased significantly in response to both. These data demonstrate that the neuroendocrine GnRH system is sensitive to environmental temperature and suggest that GnRH neurons play a conserved but trans-seasonal role in mediating changes in reproductive physiology and behavior in dissociated breeders.

Molecular identification of an androgen receptor and the influence of long-term aggressive interaction on hypothalamic genes expression in black rockfish (Sebastes schlegelii)

This study aims to explore the mechanism on how aggressive interaction alters reproductive physiology by testing whether aggressive interaction can activate the reproductive neuroendocrine function via the hypothalamus-pituitary-gonadal (HPG) axis in black rockfish (Sebastes schlegelii). The expressions of the androgen receptor gene (ar) and gonadotropin-releasing hormone genes (gnrhs), the concentration of plasma androgens, and GSI (the ratio of testes mass to body mass) were compared between the interaction group (dominant males or subordinate males) and the isolation group in male black rockfish after 3 weeks. A full-length cDNA encoding an androgen receptor (AR) of 766 amino acids was isolated. Transcripts encoding this AR were detected at a high relative abundance in the liver, kidney, testis, ovary, muscle, and intestine tissue. Further evaluation of brain genes transcripts abundance revealed that the mRNA levels of gnrh I and ar genes were significantly different between the interaction group and the isolation group in the hypothalamus. However, no significant difference was detected in testosterone, 11-keto-testosterone, and GSI between these two groups. This study indicates that a long-term aggressive interaction affect the expression of hypothalamic gnrh I and ar but may not change the physiological function of the HPG axis in an all-male condition.

Behavioral traits that define social dominance are the same that reduce social influence in a consensus task

The attributes allowing individuals to attain positions of social power and dominance are common across many vertebrate social systems: aggression, intimidation, and coercion. These traits may be associated with influence, but may also be socially aversive, and thereby decrease social influence of dominant individuals. Using a social cichlid fish, we show that dominant males are aggressive, socially central, and influence group movement. Yet, dominant males are poor effectors of consensus in a more sophisticated association task compared with passive, socially peripheral subordinate males. These influential, subordinate males possess behavioral traits opposite of those generally associated with dominance, suggesting that the link between social dominance and social influence is context dependent, and behavioral traits of dominant males impede group consensus formation.

Dominant individuals are often most influential in their social groups, affecting movement, opinion, and performance across species and contexts. Yet, behavioral traits like aggression, intimidation, and coercion, which are associated with and in many cases define dominance, can be socially aversive. The traits that make dominant individuals influential in one context may therefore reduce their influence in other contexts. Here, we examine this association between dominance and influence using the cichlid fish Astatotilapia burtoni, comparing the influence of dominant and subordinate males during normal social interactions and in a more complex group consensus association task. We find that phenotypically dominant males are aggressive, socially central, and that these males have a strong influence over normal group movement, whereas subordinate males are passive, socially peripheral, and have little influence over normal movement. However, subordinate males have the greatest influence in generating group consensus during the association task. Dominant males are spatially distant and have lower signal-to-noise ratios of informative behavior in the association task, potentially interfering with their ability to generate group consensus. In contrast, subordinate males are physically close to other group members, have a high signal-to-noise ratio of informative behavior, and equivalent visual connectedness to their group as dominant males. The behavioral traits that define effective social influence are thus highly context specific and can be dissociated with social dominance. Thus, processes of hierarchical ascension in which the most aggressive, competitive, or coercive individuals rise to positions of dominance may be counterproductive in contexts where group performance is prioritized.

Social creatures: Model animal systems for studying the neuroendocrine mechanisms of social behaviour

The interaction of animals with conspecifics, termed social behaviour, has a major impact on the survival of many vertebrate species. Neuropeptide hormones modulate the underlying physiology that governs social interactions, and many findings concerning the neuroendocrine mechanisms of social behaviours have been extrapolated from animal models to humans. Neurones expressing neuropeptides show similar distribution patterns within the hypothalamic nucleus, even when evolutionarily distant species are compared. During evolution, hypothalamic neuropeptides and releasing hormones have retained not only their structures, but also their biological functions, including their effects on behaviour. Here, we review the current understanding of the mechanisms of social behaviours in several classes of animals, such as worms, insects and fish, as well as laboratory, wild and domesticated mammals.

Aging Does Not Affect Beta Modulation during Reaching Movements

During movement, modulation of beta power occurs over the sensorimotor areas, with a decrease just before its start (event-related desynchronization, ERD) and a rebound after its end (event-related synchronization, ERS). We have recently found that the depth of ERD-to-ERS modulation increases during practice in a reaching task and the following day decreases to baseline levels. Importantly, the magnitude of the beta modulation increase during practice is highly correlated with the retention of motor skill tested the following day. Together with other evidence, this suggests that the increase of practice-related modulation depth may be the expression of sensorimotor cortex's plasticity. Here, we determine whether the practice-related increase of beta modulation depth is equally present in a group of younger and a group of older subjects during the performance of a 30-minute block of reaching movements. We focused our analyses on two regions of interest (ROIs): the left sensorimotor and the frontal region. Performance indices were significantly different in the two groups, with the movements of older subjects being slower and less accurate. Importantly, both groups presented a similar increase of the practice-related beta modulation depth in both ROIs in the course of the task. Peak latency analysis revealed a progressive delay of the ERS peak that correlated with the total movement time. Altogether, these findings support the notion that the depth of beta modulation in a reaching movement task does not depend on age and confirm previous findings that only ERS peak latency but not ERS magnitude is related to performance indices.

CREB-B acts as a key mediator of NPF/NO pathway involved in phase-related locomotor plasticity in locusts

Gene expression changes in neural systems are essential for environment-induced behavioral plasticity in animals; however, neuronal signaling pathways mediating the effect of external stimuli on transcriptional changes are largely unknown. Recently, we have demonstrated that the neuropeptide F (NPF)/nitric oxide (NO) signaling pathway plays a regulatory role in phase-related locomotor plasticity in the migratory locust, Locusta migratoria. Here, we report that a conserved transcription factor, cAMP response element-binding protein B (CREB-B), is a key mediator involved in the signaling pathway from NPF2 to NOS in the migratory locust, triggering locomotor activity shift between solitarious and gregarious phases. We find that CREB-B directly activates brain NOS expression by interacting with NOS promoter region. The phosphorylation at serine 110 site of CREB-B dynamically changes in response to population density variation and is negatively controlled by NPF2. The involvement of CREB-B in NPF2-regulated locomotor plasticity is further validated by RNAi experiment and behavioral assay. Furthermore, we reveal that protein kinase A mediates the regulatory effects of NPF2 on CREB-B phosphorylation and NOS transcription. These findings highlight a precise signal cascade underlying environment-induced behavioral plasticity.

The Reversible Sex of Gonochoristic Fish: Insights and Consequences

Fish sex reversal is a means to understand sex determination and differentiation, but it is also used to control sex in aquaculture. This review discusses sex reversal in gonochoristic fish, with the coexistence of genetic and environmental influences. The different periods of fish sensitivity to sex reversal treatments are presented with the mechanisms implicated. The old players of sex differentiation are revisited with transcriptome data and loss of function studies following hormone- or temperature-induced sex reversal. We also discuss whether cortisol is the universal mediator of sex reversal in fish due to its implication in ovarian meiosis and 11KT increase. The large plasticity in fish for sex reversal is also evident in the brain, with a reversibility existing even in adulthood. Studies on epigenetics are presented, since it links the environment, gene expression, and sex reversal, notably the association of DNA methylation in sex reversal. Manipulations with exogenous factors reverse the primary sex in many fish species under controlled conditions, but several questions arise on whether this can occur under wild conditions and what is the ecological significance. Cases of sex reversal in wild fish populations are shown and their fitness and future perspectives are discussed.

Investigation of the effects of kisspeptin-10 in methionine-induced lipid peroxidation in testicle tissue of young rats

Disruption of the balance oxidants, antioxidants cause various pathophysiological conditions such as lipid peroxidation, protein degradation, or DNA damage. We have examined possible effects of kisspeptin-10 on the structural damage produced by methionine-induced lipid peroxidation in testicle tissue of young rats. Kisspeptin-10 did not significantly affect spermatogenic cells in seminiferous tubules. Testosterone levels decreased in the methionine group as compared with the control group but without statistical significance. Luteinizing hormone levels decreased in the methionine group as compared with the control group (P < 0.001). Catalase enzyme activity increased in the kisspeptin-10 group (P < 0.01) as compared with the other groups. Catalase mRNA expression was decreased in the methionine group as compared with the kisspeptin group (P < 0.001). Total superoxide dismutase enzyme activity and superoxide dismutase mRNA expression were increased in the kisspeptin group as compared with the methionine group (P < 0.05). In conclusion, kisspeptin treatment may protect the structure of spermatogenic cells against methionine-induced damage.

Behaviors of cavefish offer insight into developmental evolution

Many developmental processes have evolved through natural selection, yet in only a few cases do we understand if and how a change of developmental process produces a benefit. For example, many studies in evolutionary biology have investigated the developmental mechanisms that lead to novel structures in an animal, but only a few have addressed if these structures actually benefit the animal at the behavioral level of prey hunting and mating. As such, this review discusses an animal's behavior as the integrated functional output of its evolved morphological and physiological traits. Specifically, we focus on recent findings about the blind Mexican cavefish, Astyanax mexicanus, for which clear relationships exist between its physical traits and ecosystem. This species includes two morphotypes: an eyed surface dweller versus many conspecific types of blind cave dwellers, some of which evolved independently; all of the blind subtypes derived from eyed surface dwellers. The blind cavefish evolved under clear selection pressures: food is sparse and darkness is perpetual. Simulating the major aspects of a cave ecosystem in the laboratory is relatively easy, so we can use this species to begin resolving the relationships between evolved traits and selection pressures—relationships which are more complex for other animals models. This review discusses the recent advances in cavefish research that have helped us establish some key relationships between morphological evolution and environmental shifts. Mol. Reprod. Dev. 82: 268–280, 2015. © 2015 Wiley Periodicals, Inc.

Characterization of Schizothorax prenanti cgnrhII gene: fasting affects cgnrhII expression

In this study, the role of chicken gonadotropin-releasing hormone II (cgnrhII) in feeding regulation was investigated in Schizothorax prenanti. First, the full-length S. prenanti cgnrhII cDNA consisted of 693 bp with an open reading frame of 261 bp encoding a protein of 86 amino acids. Next, cgnrhII was widely expressed in the central and peripheral tissues. Last, there were significant changes in cgnrhII mRNA expression in the fasted group compared to the fed group in the S. prenanti hypothalamus during 24 h fasting (P < 0.05). Furthermore, the cgnrhII gene expression presented a significant decrease in the fasted group compared with the fed group (P < 0.05) on days 3, 5 and 7, after re-feeding, there was no significant changes in cgnrhII mRNA expression level between refed and fed group on day 9 (P > 0.05). Thus, the results suggest that cGnRH II expression is influenced by fasting and the gene may be involved in feeding regulation in S. prenanti.

GnRH isoforms expression in relation to the gonadal cycle and to dominance rank in the gilthead seabream, Sparus aurata

The manner in which behavior influences the gonadotropin-releasing hormone (GnRH) axis in hermaphroditic fishes is not understood. The Gilthead seabream, Sparus aurata, is a protandrous hermaphrodite with a complex gonadal cycle consisting of a quiescent, pre-spawning, spawning, and post-spawning stage. On two separate experiments, I used real-time quantitative PCR to measure the mRNA expression of three GnRH isoforms in homogenized seabream whole-brain extracts. In the first experiment, I measured the levels of GnRH-1, GnRH-2, and GnRH-3 mRNA throughout the gonad cycle. All three GnRH mRNAs increase around the peak of the spawning season (December). GnRH-3 mRNA expression is also elevated in August, which coincides with the beginning of gonad differentiation. All three GnRH mRNAs have the lowest expression levels in the month of September. There was no difference between males and females in the expression levels of any of the three GnRH mRNA. In the second experiment, I measured individual dominance ranks in six groups of fish, three during quiescence and three during spawning. GnRH-1 mRNA expression was positively correlated with dominance rank only during the quiescent period. The more dominant fish tended to have higher GnRH-1 mRNA expression. The existence of a quiescent-only correlation between GnRH-1 mRNA and dominance rank suggests a mechanism by which activation of gonad maturation could occur first in the most dominant ambisexual fish.

Gonadotropin-releasing hormone plasticity: a comparative perspective

Gonadotropin-releasing hormone 1 (GnRH1) is a key regulator of the reproductive neuroendocrine system in vertebrates. Recent developments have suggested that GnRH1 neurons exhibit far greater plasticity at the cellular and molecular levels than previously thought. Furthermore, there is growing evidence that sub-populations of GnRH1 neurons in the preoptic area are highly responsive to specific environmental and hormonal conditions. In this paper we discuss findings that reveal large variation in GnRH1 mRNA and protein expression that are regulated by social cues, photoperiod, and hormonal feedback. We draw upon studies using histochemistry and immediate early genes (e.g., c-FOS/ZENK) to illustrate that specific groups of GnRH1 neurons are topographically organized. Based on data from diverse vertebrate species, we suggest that GnRH1 expression within individuals is temporally dynamic and this plasticity may be evolutionarily conserved. We suggest that the plasticity observed in other neuropeptide systems (i.e. kisspeptin) may have evolved in a similar manner.

Gonadotropin-releasing hormone 2 suppresses food intake in the zebrafish, Danio rerio

Gonadotropin-releasing hormone (GnRH) is an evolutionarily conserved neuropeptide with 10 amino acid residues, of which several structural variants exist. A molecular form known as GnRH2 ([His(5) Trp(7) Tyr(8)]GnRH, also known as chicken GnRH II) is widely distributed in vertebrates except for rodents, and has recently been implicated in the regulation of feeding behavior in goldfish. However, the influence of GnRH2 on feeding behavior in other fish has not yet been studied. In the present study, therefore, we investigated the role of GnRH2 in the regulation of feeding behavior in a zebrafish model, and examined its involvement in food intake after intracerebroventricular (ICV) administration. ICV injection of GnRH2 at 0.1 and 1 pmol/g body weight (BW) induced a marked decrease of food consumption in a dose-dependent manner during 30 min after feeding. Cumulative food intake was significantly decreased by ICV injection of GnRH2 at 1 pmol/g BW during the 30-min post-treatment observation period. The anorexigenic action of GnRH2 was completely blocked by treatment with the GnRH type I receptor antagonist Antide at 25 pmol/g BW. We also examined the effect of feeding condition on the expression level of the GnRH2 transcript in the hypothalamus. Levels of GnRH2 mRNA obtained from fish that had been provided excess food for 7 days were higher than those in fish that had been fed normally. These results suggest that, in zebrafish, GnRH2 acts as an anorexigenic factor, as is the case in goldfish.

Neural and hormonal mechanisms of reproductive-related arousal in fishes

The major classes of chemicals and brain pathways involved in sexual arousal in mammals are well studied and are thought to be of an ancient, evolutionarily conserved origin. Here we discuss what is known of these neurochemicals and brain circuits in fishes, the oldest and most species-rich group of vertebrates from which tetrapods arose over 350 million years ago. Highlighted are case studies in vocal species where well-delineated sensory and motor pathways underlying reproductive-related behaviors illustrate the diversity and evolution of brain mechanisms driving sexual motivation between (and within) sexes. Also discussed are evolutionary insights from the neurobiology and reproductive behavior of elasmobranch fishes, the most ancient lineage of jawed vertebrates, which are remarkably similar in their reproductive biology to terrestrial mammals.

Gonadotropin-releasing hormone II (GnRH II) mediates the anorexigenic actions of α-melanocyte-stimulating hormone (α-MSH) and corticotropin-releasing hormone (CRH) in goldfish

Intracerebroventricular (ICV) administration of gonadotropin-releasing hormone II (GnRH II), which plays a crucial role in the regulation of reproduction in vertebrates, markedly reduces food intake in goldfish. However, the neurochemical pathways involved in the anorexigenic action of GnRH II and its interaction with other neuropeptides have not yet been identified. Alpha-melanocyte-stimulating hormone (α-MSH), corticotropin-releasing hormone (CRH) and CRH-related peptides play a major role in feeding control as potent anorexigenic neuropeptides in goldfish. However, our previous study has indicated that the GnRH II-induced anorexigenic action is not blocked by treatment with melanocortin 4 receptor (MC4R) and CRH receptor antagonists. Therefore, in the present study, we further examined whether the anorexigenic effects of α-MSH and CRH in goldfish could be mediated through the GnRH receptor neuronal pathway. ICV injection of the MC4R agonist, melanotan II (80 pmol/g body weight; BW), significantly reduced food intake, and its anorexigenic effect was suppressed by ICV pre-administration of the GnRH type I receptor antagonist, antide (100 pmol/gBW). The CRH-induced (50 pmol/gBW) anorexigenic action was also blocked by treatment with antide. ICV injection of CRH (50 pmol/gBW) induced a significant increase of the GnRH II mRNA level in the hypothalamus, while ICV injection of melanotan II (80 pmol/gBW) had no effect on the level of GnRH II mRNA. These results indicate that, in goldfish, the anorexigenic actions of α-MSH and CRH are mediated through the GnRH type I receptor-signaling pathway, and that the GnRH II system regulates feeding behavior.

The neuroendocrine action potential. Winner of the 2008 Frank Beach Award in Behavioral Neuroendocrinology

Animals are remarkably well equipped to respond to changes in their environment across different time scales and levels of biological organization. Here, I introduce a novel perspective that incorporates the three main processes the nervous system uses to integrate and process information: electrophysiological, genomic, and neuroendocrine action potentials. After discussing several examples of neuroendocrine action potentials, I lay out the commonalities of these temporally organized responses and how they might be interrelated with electrophysiological activity and genomic responses. This framework provides a novel outlook on longstanding questions in behavioral neuroendocrinology and suggests exciting new avenues for further research that will integrate across disciplines and levels of biological organization.

Evidence for two distinct KiSS genes in non-placental vertebrates that encode kisspeptins with different gonadotropin-releasing activities in fish and mammals

Kisspeptins, the products of KiSS-1 gene, have recently emerged as fundamental regulators of reproductive function in different mammalian and, presumably, non-mammalian species. To date, a single form of KiSS-1 has been described in mammals, and recently, in several fish species and Xenopus. We report herein the cloning and characterization of two distinct KiSS-like genes, namely, KiSS-1 and KiSS-2, in the teleost sea bass. While KiSS-1 encodes a peptide identical to rodent kisspeptin-10, the predicted KiSS-2 decapeptide diverges at 4 amino acids (FNFNPFGLRF). Genome database searches showed that both genes are present in non-placental vertebrate genomes. Indeed, phylogenetic and genome mapping analyses suggest that KiSS-1 and KiSS-2 are paralogous genes that originated by duplication of an ancestral gene, although KiSS-2 is lost in placental mammals. KiSS-1 and KiSS-2 mRNAs are present in brain and gonads of sea bass, medaka and zebrafish. Comparative functional studies demonstrated that KiSS-2 decapeptide was significantly more potent than KiSS-1 peptide in inducing LH and FSH secretion in sea bass. In contrast, KiSS-2 decapeptide only weakly elicited LH secretion in rats, whereas KiSS-1 peptide was maximally effective. Our data are the first to provide conclusive evidence for the existence of a second KiSS gene, KiSS-2, in non-placental vertebrates, whose product is likely to play a dominant stimulatory role in the regulation of the gonadotropic axis at least in teleosts.

Signaling by G-protein-coupled receptor (GPCR): studies on the GnRH receptor

Gonadotropin-releasing hormone (GnRH) is the first key hormone of reproduction. GnRH analogs are extensively used in in vitro fertilization, and treatment of sex hormone-dependent cancers, due to their ability to bring about 'chemical castration'. The interaction of GnRH with its cognate type I receptor (GnRHR) in pituitary gonadotropes results in the activation of Gq/G(11), phospholipase Cbeta (PLCbetaI), PLA(2), and PLD. Sequential activation of the phospholipases generates the second messengers inositol 1, 4, 5-trisphosphate (IP(3)), diacylglycerol (DAG), and arachidonic acid (AA), which are required for Ca(2+) mobilization, the activation of various protein kinase C isoforms (PKCs), and the production of prostaglandin (PG) and other metabolites of AA, respectively. PKC isoforms are the major mediators of the downstream activation of a number of mitogen-activated protein kinase (MAPK) cascades by GnRH, namely: extracellular signal-regulated kinase (ERK), jun-N-terminal kinase (JNK), and p38MAPK. The activated MAPKs phosphorylate both cytosolic and nuclear proteins to initiate the transcriptional activation of the gonadotropin subunit genes and the GnRHR. While Ca(2+) mobilization has been found to initiate rapid gonadotropin secretion, Ca(2+), together with various PKC isoforms, MAPKs and AA metabolites also serve as key nodes, in the GnRH-stimulated signaling network that enables the gonadotropes to decode GnRH pulse frequencies and translating that into differential gonadotropin synthesis and release. Even though pulsatility of GnRH is recognized as a major determinant for differential gonadotropin subunit gene expression and gonadotropin secretion very little is yet known about the signaling circuits governing GnRH action at the 'Systems Biology' level. Direct apoptotic and metastatic effects of GnRH analogs in gonadal steroid-dependent cancers expressing the GnRHR also seem to be mediated by the activation of the PKC/MAPK pathways. However, the mechanisms dictating life (pituitary) vs. death (cancer) decisions made by the same GnRHR remain elusive. Understanding these molecular mechanisms triggered by the GnRHR through biochemical and 'Systems Biology' approaches would provide the basis for the construction of the dynamic connectivity maps, which operate in the various cell types (endocrine, cancer, and immune system) targeted by GnRH. The connectivity maps will open a new vista for exploring the direct effects of GnRH analogs in tumors and the design of novel combined therapies for fertility control, reproductive disorders and cancers.

Fish and chips: functional genomics of social plasticity in an African cichlid fish

Behavior and physiology are regulated by both environment and social context. A central goal in the study of the social control of behavior is to determine the underlying physiological, cellular and molecular mechanisms in the brain. The African cichlid fish Astatotilapia burtoni has long been used as a model system to study how social interactions regulate neural and behavioral plasticity. In this species, males are either socially dominant and reproductively active or subordinate and reproductively suppressed. This phenotypic difference is reversible. Using an integrative approach that combines quantitative behavioral measurements, functional genomics and bioinformatic analyses, we examine neural gene expression in dominant and subordinate males as well as in brooding females. We confirm the role of numerous candidate genes that are part of neuroendocrine pathways and show that specific co-regulated gene sets (modules), as well as specific functional gene ontology categories, are significantly associated with either dominance or reproductive state. Finally, even though the dominant and subordinate phenotypes are robustly defined, we find a surprisingly high degree of individual variation in the transcript levels of the very genes that are differentially regulated between these phenotypes. The results of the present study demonstrate the molecular complexity in the brain underlying social behavior, identify novel targets for future studies, validate many candidate genes and exploit individual variation in order to gain biological insights.

Inhibitory effect of chicken gonadotropin-releasing hormone II on food intake in the goldfish, Carassius auratus

Gonadotropin-releasing hormone (GnRH) is an evolutionarily conserved neuropeptide with 10 amino acid residues, which possesses some structural variants. A molecular form known as chicken GnRH II ([His(5) Trp(7) Tyr(8)] GnRH, cGnRH II) is widely distributed in vertebrates, and has recently been implicated in the regulation of sexual behavior and food intake in an insectivore, the musk shrew. However, the influence of cGnRH II on feeding behavior has not yet been studied in model animals such as rodents and teleost fish. In this study, therefore, we investigated the role of cGnRH II in the regulation of feeding behavior in the goldfish, and examined its involvement in food intake after intracerebroventricular (ICV) administration. ICV-injected cGnRH II at graded doses, from 0.1 to 10 pmol/g body weight (BW), induced a decrease of food consumption in a dose-dependent manner during 60 min after treatment. Cumulative food intake was significantly decreased by ICV injection of cGnRH II at doses of 1 and 10 pmol/g BW during the 60-min post-treatment observation period. ICV injection of salmon GnRH ([Trp(7) Leu(8)] GnRH, sGnRH) at doses of 0.1-10 pmol/g BW did not affect food intake. The anorexigenic action of cGnRH II was completely blocked by treatment with the GnRH type I receptor antagonist, Antide. However, the anorexigenic action of cGnRH II was not inhibited by treatment with the corticotropin-releasing hormone (CRH) 1/2 receptor antagonist, *-helical CRH((9-41)), and the melanocortin 4 receptor antagonist, HS024. These results suggest that, in the goldfish, cGnRH II, but not sGnRH, acts as an anorexigenic factor, as is the case in the musk shrew, and that the anorexigenic action of cGnRH II is independent of CRH- and melanocortin-signaling pathways.

GPR54 and rGnRH I gene expression during the onset of puberty in Nile tilapia

The Kiss1/GPR54 system has recently been shown to play a key role in the onset of puberty in mammals. Growing evidence suggests that this system is also conserved across vertebrates although very few studies so far have been performed in lower vertebrates. The aims of this study were firstly in the teleost Nile tilapia to screen tissues for GPR54 expression levels, secondly to measure the expression patterns of GPR54 and GnRH I receptor (rGnRH I) in whole brains during the onset of puberty and finally to determine the effects of continuous illumination (LL) on receptor expression levels. Results confirmed that GPR54 was predominantly expressed in the brain and pituitary of adult tilapia. Furthermore, a significant increase of GPR54 gene expression was found in tilapia brains at 11 weeks post hatch (wph) followed by rGnRH I at 13 wph just prior to the histological observation of vitellogenic oocytes and active spermatogenesis in ova and testes at 17 wph. These results suggest a correlation between the increase of GPR54 expression in the brain and the onset of puberty. Finally, a significant effect of LL was observed on GPR54 expression levels which were characterized by a delayed surge with significantly lower levels than those of control fish. The current study not only suggests a link between the Kiss1/GPR54 system and the onset of puberty in a tropical batch spawning teleost that would be a highly conserved feature across vertebrates but also that the transcriptional mechanisms regulating GPR54 expression could be directly or indirectly influenced by light.

Annotation of expressed sequence tags for the East African cichlid fish Astatotilapia burtoni and evolutionary analyses of cichlid ORFs

Background

The cichlid fishes in general, and the exceptionally diverse East African haplochromine cichlids in particular, are famous examples of adaptive radiation and explosive speciation. Here we report the collection and annotation of more than 12,000 expressed sequence tags (ESTs) generated from three different cDNA libraries obtained from the East African haplochromine cichlid species Astatotilapia burtoni and Metriaclima zebra.

Results

We first annotated more than 12,000 newly generated cichlid ESTs using the Gene Ontology classification system. For evolutionary analyses, we combined these ESTs with all available sequence data for haplochromine cichlids, which resulted in a total of more than 45,000 ESTs. The ESTs represent a broad range of molecular functions and biological processes. We compared the haplochromine ESTs to sequence data from those available for other fish model systems such as pufferfish (Takifugu rubripes and Tetraodon nigroviridis), trout, and zebrafish. We characterized genes that show a faster or slower rate of base substitutions in haplochromine cichlids compared to other fish species, as this is indicative of a relaxed or reinforced selection regime. Four of these genes showed the signature of positive selection as revealed by calculating K_a/K_s ratios.

Conclusion

About 22% of the surveyed ESTs were found to have cichlid specific rate differences suggesting that these genes might play a role in lineage specific characteristics of cichlids. We also conclude that the four genes with a K_a/K_s ratio greater than one appear as good candidate genes for further work on the genetic basis of evolutionary success of haplochromine cichlid fishes.

LHRH-(1-5): a bioactive peptide regulating reproduction

Luteinizing hormone-releasing hormone-I (LHRH-I) was isolated from the mammalian hypothalamus and shown to be the primary regulator of reproduction through its initiation of pituitary gonadotropin release. Subsequently, it has also been shown to have non-pituitary actions. Although the regulation of LHRH-I synthesis and release has been extensively studied, there is additional evidence to suggest that processing of the peptide represents another layer of regulation. The focus of this review will be on evidence for the action of LHRH-(1-5), the pentapeptide metabolite of LHRH-I, in regulating LHRH-I synthesis, secretion and reproductive behavior. The involvement of LHRH-(1-5) in the control of aspects of reproduction might represent yet another level of regulatory complexity through neuropeptide processing.

Sex and seasonal co-variation of arginine vasotocin (AVT) and gonadotropin-releasing hormone (GnRH) neurons in the brain of the halfspotted goby

Gonadotropin-releasing hormone (GnRH) and arginine vasotocin (AVT) are critical regulators of reproductive behaviors that exhibit tremendous plasticity, but co-variation in discrete GnRH and AVT neuron populations among sex and season are only partially described in fishes. We used immunocytochemistry to examine sexual and temporal variations in neuron number and size in three GnRH and AVT cell groups in relation to reproductive activities in the halfspotted goby (Asterropteryx semipunctata). GnRH-immunoreactive (-ir) somata occur in the terminal nerve, preoptic area, and midbrain tegmentum, and AVT-ir somata within parvocellular, magnocellular, and gigantocellular regions of the preoptic area. Sex differences were found among all GnRH and AVT cell groups, but were time-period dependent. Seasonal variations also occurred in all GnRH and AVT cell groups, with coincident elevations most prominent in females during the peak- and non-spawning periods. Sex and temporal variability in neuropeptide-containing neurons are correlated with the goby's seasonally-transient reproductive physiology, social interactions, territoriality and parental care. Morphological examination of GnRH and AVT neuron subgroups within a single time period provides detailed information on their activities among sexes, whereas seasonal comparisons provide a fine temporal sequence to interpret the proximate control of reproduction and the evolution of social behavior.