Male Courtship Pheromones Induce Cloacal Gaping in Female Newts (Salamandridae)

Pheromones are an important component of sexual communication in courting salamanders, but the number of species in which their use has been demonstrated with behavioral evidence remains limited. Here we developed a behavioral assay for demonstrating courtship pheromone use in the aquatically courting Iberian ribbed newt Pleurodeles waltl. By performing an in-depth study of the courtship behavior, we show that females invariably open their cloaca (cloacal gaping) before engaging in pinwheel behavior, the circling movement that is the prelude to spermatophore uptake. In contrast, cloacal gaping was not observed in failed courtships, where females escaped or displayed thanatosis. Since gaping mainly occurred during male amplexus and cloacal imposition, which is the obvious period of pheromone transfer, we next investigated whether male courtship water (i.e., water holding courtship pheromones) alone was able to induce this reaction in females. These tests showed that courtship water induced cloacal gaping significantly more than water, even in the absence of a male. Cloacal gaping thus provides a simple and robust test for demonstrating courtship pheromone use in the Iberian ribbed newt. Since opening the cloaca is an essential prerequisite for spermatophore pick-up in all internally fertilizing salamanders, we hypothesize that variations on this assay will also be useful in several other species.     

An acute stressor alters steroid hormone levels and activity but not sexual behavior in male and female Ocoee salamanders (Desmognathus ocoee)

Stressors that are chronic have clear suppressive effects on reproductive behaviors in both males and females. Stressors that are acute have effects on reproductive behavior that are less clear. We measured the effects of an acute bout of handling in laboratory-housed male and female Ocoee salamanders (Desmognathus ocoee), a species with a prolonged mating season. Handling resulted in decreased locomotory activity and elevated plasma corticosterone, a hallmark of the vertebrate stress response. Handling also decreased plasma testosterone in males and elevated plasma estradiol in females. Despite the handling-induced changes in hormone levels, handling had minimal impact on courtship and mating. Other species in which reproduction is insensitive to acute stressors may live in extreme environments with limited reproductive opportunities, whereas Ocoee salamanders live in a relatively temperate environment with multiple reproductive opportunities. Together, these data indicate that an allostatic response to a stressor can alter locomotory activity and elevate corticosterone without suppressing nonessential behaviors like courtship and mating in a species in which reproductive opportunities can occur over a period of multiple months. The lack of reproductive suppression in Ocoee salamanders might be due to the low energetic cost of courtship and mating in this species combined with potentially elevated energetic stores, highlighting the importance of considering energy budgets when making predictions about behavioral effects of acute stressors.     

Conspecific and heterospecific pheromone effects on female receptivity

Courtship pheromones play an important role in salamander reproductive behaviour. In salamanders of the family Plethodontidae, males deliver specialized pheromones to females during courtship interactions. These courtship pheromones increase female receptivity and may be involved in mate discrimination. In order to test hypotheses related to mate discrimination, we staged courtship encounters between male-female Plethodon shermani pairs in which the female received pheromones obtained from either conspecific (P. shermani) or heterospecific (P. yonahlossee orP. montanus ) males. Both conspecific and heterospecific pheromones increased female receptivity. Moreover, pheromones from both heterospecific species were as effective as the conspecific pheromone in increasing female receptivity inP. shermani females. Our results suggest that the courtship pheromone signal and function may be conserved across related species, with mate discrimination occurring before pheromone delivery. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.     

Endogenous glucocorticoids play a positive regulatory role in the anti-keyhole limpet hemocyanin in vivo antibody response

Glucocorticoids (GCs) are commonly reported to be immunosuppressive. Studies that support this involve the administration of synthetic GCs such as dexamethasone at high pharmacological doses and using in vitro assay systems that may have limited relevance to the role of GCs during normal in vivo immune responses. Therefore, the following experiments tested the conclusion that GCs are generally immunosuppressive. Adult male Sprague Dawley rats received adrenalectomy (ADX) or sham surgery. ADX rats were given either basal corticosterone (CORT) replacement in their drinking water (25 microg/ml) or no CORT. Rats were immunized with keyhole limpet hemocyanin (KLH), and blood samples were taken. ADX rats with no CORT replacement had reduced anti-KLH IgM and IgG responses compared with sham-operated controls. ADX rats that received basal CORT replacement had partially restored anti-KLH IgM, but still had suppressed anti-KLH IgG. Administration of GC receptor type I (RU28318) and type II (RU40555) receptor antagonists also reduced the anti-KLH IgM and IgG responses. ADX rats that received both basal CORT replacement and low dose injections of CORT on days 5 and 7 after KLH had anti-KLH IgG levels equal to those of sham-operated controls. Finally, the GC elevation 4-7 days after immunization may play a role in stimulating the IgM to IgG2a switch. GC receptor blockade reduced the anti-KLH IgG2a and splenic IFN-gamma, but not the anti-KLH IgG1, response. Given that IFN-gamma is an important regulator of the IgM to IgG2a switch, it is possible that the small rise in GC found 4-7 days after KLH facilitates IgG2a isotype switching.     

Pheromonal inhibition of male courtship behaviour in the brown tree snake, Boiga irregularis: a mechanism for the rejection of potential mates

Pheromones play a central role in coordinating the events leading up to copulation in snakes. We report here a novel pheromone system in the brown tree snake in which females release a pheromone that inhibits male courtship behaviour. In a previous study, we made observations of female brown tree snakes releasing cloacal secretions (CS) during courtship that appeared to cause courting males to cease courtship. All snakes have glands that release CS through ducts located along the cloacal orifice. Although CS have been studied for many years, their function in the mediation of snake behaviour has not been experimentally well determined. We examined the role of CS in the reproductive behaviour of male and female brown tree snakes. We conducted four experiments to test the effect of both male and female CS on brown tree snake behaviour under two behavioural contexts, courtship and male-male ritualized combat. Within each experiment, we compared the effects of CS to a control. Female CS caused a decrease in the time that males spent courting females and a decrease in the intensity of courtship compared with the control treatment. Male CS did not, however, affect the time that males spent displaying courtship or the intensity of that courtship. Neither male nor female CS had significant effects on male ritualized combat behaviour, including time that males spent in combat or the intensity of combat behaviours displayed. Furthermore, neither female nor male CS had an effect on female courtship versus controls. The inhibition of brown tree snake reproductive behaviours is specific to female CS inhibiting male courtship behaviour. This pheromone acts in concert with the female sex pheromone to regulate the events leading to copulation.Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Consumption of a high-fat diet rapidly exacerbates the development of fatty liver disease that occurs with chronically elevated glucocorticoids

Chronically elevated glucocorticoids (GCs) and a high-fat diet (HFD) independently induce insulin resistance, abdominal obesity, and nonalcoholic fatty liver disease (NAFLD). GCs have been linked to increased food intake, particularly energy-dense "comfort" foods. Thus we examined the synergistic actions of GCs and HFD on hepatic disease development in a new rodent model of chronically elevated GCs. Six-week-old male Sprague-Dawley rats received exogenous GCs, via subcutaneous implantation of four 100-mg corticosterone (Cort) pellets, to elevate basal GC levels for 16 days (n = 8-10 per group). Another subset of animals received wax pellets (placebo) to serve as controls. Animals from each group were randomly assigned to receive a 60% HFD or a standard high-carbohydrate (13% fat and 60% carbohydrate) diet. Cort + HFD resulted in central obesity, despite a relative weight loss, a 4-fold increase in hepatic lipid content, hepatic fibrosis, and a 2.8-fold increase in plasma alanine aminotransferase levels compared with placebo + chow controls. Hepatic injury developed independent of inflammation, as plasma haptoglobin levels were reduced with Cort treatment. Insulin resistance and hepatic steatosis occurred with Cort alone; these outcomes were further exacerbated by the HFD in the presence of elevated Cort. In addition to fatty liver, the Cort + HFD group also developed severe insulin resistance, hyperinsulinemia, hyperglycemia, and hypertriglyceridemia, which were not evident with HFD or Cort alone. Thus a HFD dramatically exacerbates the development of NAFLD and characteristics of the metabolic syndrome in conditions of chronically elevated Cort.     

Chronic Glucocorticoid Exposure-Induced Epididymal Adiposity Is Associated with Mitochondrial Dysfunction in White Adipose Tissue of Male C57BL/6J Mice

Prolonged and excessive glucocorticoids (GC) exposure resulted from Cushing''s syndrome or GC therapy develops central obesity. Moreover, mitochondria are crucial in adipose energy homeostasis. Thus, we tested the hypothesis that mitochondrial dysfunction may contribute to chronic GC exposure-induced epididymal adiposity in the present study. A total of thirty-six 5-week-old male C57BL/6J mice (∼20 g) were administrated with 100 µg/ml corticosterone (CORT) or vehicle through drinking water for 4 weeks. Chronic CORT exposure mildly decreased body weight without altering food and water intake in mice. The epididymal fat accumulation was increased, but adipocyte size was decreased by CORT. CORT also increased plasma CORT, insulin, leptin, and fibroblast growth factor 21 concentrations as measured by RIA or ELISA. Interestingly, CORT increased plasma levels of triacylglycerols and nonesterified fatty acids, and up-regulated the expression of both lipolytic and lipogenic genes as determined by real-time RT-PCR. Furthermore, CORT impaired mitochondrial biogenesis and oxidative function in epididymal WAT. The reactive oxygen species production was increased and the activities of anti-oxidative enzymes were reduced by CORT treatment as well. Taken together, these findings reveal that chronic CORT administration-induced epididymal adiposity is, at least in part, associated with mitochondrial dysfunction in mouse epididymal white adipose tissue.     

Courtship in the Zig-Zag Salamander (Plethodon dorsalis): Insights into a Transition in Pheromone-Delivery Behavior

Courtship in plethodontid salamanders includes the delivery of male courtship pheromones by two distinct modes. Within the eastern Plethodon clade of the tribe Plethodontini, members of the Plethodon cinereus species group use an ancestral ‘vaccination’ mode of delivery, while members of the P. glutinosus group use an olfactory delivery mode. In order to shed light on this transition in delivery mode, I observed courtship behavior in P. dorsalis, a species that is phylogenetically intermediate to the P. cinereus and P. glutinosus groups. My observations indicate that P. dorsalis also is intermediate to the P. cinereus and P. glutinosus species groups in terms of courtship behavior. The context of delivery of male courtship pheromones in P. dorsalis is similar to that of the P. cinereus species group; however, the mode of pheromone delivery in P. dorsalis is olfactory. Thus, a transition in the context of pheromone delivery underlies the more obvious change in pheromone delivery mode. I discuss these findings in terms of the evolution of courtship pheromone delivery across the eastern Plethodon clade. I also report the first observations of ‘premature’ spermatophore deposition by male plethodontids.     

In vivo activity of 11β-hydroxysteroid dehydrogenase type 1 in man: effects of prednisolone and chenodesoxycholic acid

The 11β-hydroxysteroid dehydrogenases (11β-HSDs) play a pivotal role in glucocorticoid (GC) action. 11β-HSD1 is a predominant reductase, activating GCs from inert metabolites, whereas 11β-HSD2 is a potent dehydrogenase inactivating GCs. Knowing the metabolic effects of GCs, a selective inhibition of 11β-HSD1 represents a potential target for therapy of impaired glucose tolerance, insulin insensitivity and central obesity. In vitro, 11β-HSD1 is selectively inhibited by chenodesoxycholic acid (CDCA) and upregulated under GC exposure. Therefore, we aimed to investigate the effects of CDCA and prednisolone on hepatic 11β-HSD1 activity in vivo by measuring 11-reduction of orally given cortisone (E) acetate to cortisol (F). CDCA or placebo was given to 5 male healthy volunteers within a randomised cross-over trial before and after oral administration of 12.5 mg E acetate at 8:00 h. For measurement of in vivo effects of GCs on 11β-HSD1 activity, hepatic reduction of 25 mg E acetate before and after treatment with prednisolone (30 mg for 6 days) was determined in 7 healthy males. Serum GC levels were determined using a fully automated liquid chromatographic system. CDCA had no effect on the activity of 11β-HSD1 in vivo. Prednisolone therapy leads to a marked rise in serum F concentrations and an elevated F/E serum ratio. This proves GC-induced activation of hepatic 11β-HSD1, which could not be extinguished by a parallel increase of IGF-1 under prednisolone. CDCA does not affect in vivo activity of 11β-HSD1 when given in therapeutic dosages. During GC treatment, increased hepatic activation of E to F may aggravate metabolic side effects of GCs such as seen in the metabolic syndrome.     

Embryonic exposure to corticosterone modifies aggressive behavior through alterations of the hypothalamic pituitary adrenal axis and the serotonergic system in the chicken

Exposure to excess glucocorticoids (GCs) during embryonic development influences offspring phenotypes and behaviors and induces epigenetic modifications of the genes in the hypothalamic–pituitary–adrenal (HPA) axis and in the serotonergic system in mammals. Whether prenatal corticosterone (CORT) exposure causes similar effects in avian species is less clear. In this study, we injected low (0.2 μg) and high (1 μg) doses of CORT into developing embryos on day 11 of incubation (E11) and tested the changes in aggressive behavior and hypothalamic gene expression on posthatch chickens of different ages. In ovo administration of high dose CORT significantly suppressed the growth rate from 3 weeks of age and increased the frequency of aggressive behaviors, and the dosage was associated with elevated plasma CORT concentrations and significantly downregulated hypothalamic expression of arginine vasotocin (AVT) and corticotropin-releasing hormone (CRH). The hypothalamic content of glucocorticoid receptor (GR) protein was significantly decreased in the high dose group (p < 0.05), whereas no changes were observed for GR mRNA. High dose CORT exposure significantly increased platelet serotonin (5-HT) uptake, decreased whole blood 5-HT concentration (p < 0.05), downregulated hypothalamic tryptophan hydroxylase 1 (TPH1) mRNA and upregulated 5-HT receptor 1A (5-HTR1A) and monoamine oxidase A (MAO-A) mRNA, but not monoamine oxidase B (MAO-B). High dose CORT also significantly increased DNA methylation of the hypothalamic GR and CRH gene promoters (p < 0.05). Our findings suggest that embryonic exposure to CORT programs aggressive behavior in the chicken through alterations of the HPA axis and the serotonergic system, which may involve modifications in DNA methylation.     

Integrative Studies of Amphibians: From Molecules to Mating

SYNOPSIS. Studies of reproductive behavior in amphibians havebeen especially successful in synthesizing data produced frommolecular and physiological research with evolutionary parameters,such as measures of reproductive success. In particular, tworelatively new areas of amphibian research are highly amenableto synthetic studies. One area is the nature of chemical communicationby pheromone delivery in terrestrial salamanders. Male courtshippheromones, for example, are delivered to the female duringmating. These pheromones typically are received by the accessoryolfactory system and act (presumably via the hypothalamus) toincrease female receptivity. At an evolutionary level, pheromonedelivery can increase male courtship success and thus the likelihoodthat a given male will sire offspring. Variation in pheromonecomposition and effectiveness will permit us to trace the evolutionof the male pheromone on a phylogeny of related populationsand species. At a proximal level, salamander courtship pheromonesare being chemically analyzed in order to identify specificprotein components that affect female receptivity. It also willbe possible to determine whether chemical variation among malesis related to behavioral effectiveness. Thus, courtship pheromonedelivery is a behavior that has invited scrutiny from a combinationof evolutionary and mechanistic perspectives. The second researcharea that is gaining from a synthetic approach is the investigationof relationships between hormonal mechanisms and reproductivebehavior in field populations of anurans and salamanders. Amphibiansare an understudied group, and the area of hormone-behaviorrelationships is inspired by testable hypotheses based on studiesof other terrestrial vertebrates. The ability to correlate physiologicalmeasures with estimates of reproductive success identifies areasof amphibian research that will profit from continued attention.     

Sex,social status and physiological stress in primates: the importance of social and glucocorticoid dynamics

Social status has been associated with health consequences, although the mechanisms by which status affects health are relatively unknown. At the physiological level, many studies have investigated the potential relationship between social behaviour/rank and physiological stress, with a particular focus on glucocorticoid (GC) production. GCs are of interest because of their experimentally established influence on health-related processes such as metabolism and immune function. Studies in a variety of species, in both naturalistic and laboratory settings, have led to complex outcomes. This paper reviews findings from primates and rodents and proposes a psychologically and physiologically relevant framework in which to study the relationship between social status and GC function. We (i) compare status-specific GC production between male and female primates, (ii) review the functional significance of different temporal patterns of GC production, (iii) propose ways to assess these temporal dynamics, and (iv) present novel hypotheses about the relationship between social status and GC temporal dynamics, and potential fitness and health implications. To understand whether GC production mediates social status-related fitness disparities, we must consider social contest conditions and the temporal dynamics of GC production. This framework will provide greater insights into the relationship between social status, physiological stress and health.     

Timing of glucocorticoid administration determines severity of lipid metabolism and behavioral effects in rats

Glucocorticoids (GCs) are a group of steroid hormones secreted by the adrenal glands in circadian cycles, and the dysregulation of GC signaling has been suggested to cause metabolic syndrome. Even though prolonged GC exposure is associated with serious side effects such as metabolic syndrome and central nervous system disorders, the use of GCs in anti-inflammatory and immunosuppressive therapies has been continuously rising. Meanwhile, the exact mechanisms by which GCs can influence the lipid metabolism as well as behavior and how they are affected by time remain unknown. In this study, the effects of two different long-term GC dosing regimens on lipid metabolism and behavior were investigated. Male Wistar rats received daily administrations of the GC dexamethasone sodium phosphate (DEX, 0.5 mg/kg body weight) at either ZT0 (Dex0) or ZT12 (Dex12). After 6 weeks of treatment, DEX-treated rats, especially those treated at ZT0, had higher hepatic lipid accumulation and serum triglyceride levels and less locomotor activity than did control rats. In addition, serum levels of corticosterone, 5-hydroxy tryptamine and norepinephrine were decreased in the Dex0 group but not in the Dex12 group compared to the control group. Furthermore, quantitative real-time polymerase chain reaction analysis indicated that the chronic administration of GCs at ZT0 upregulated genes related to glycolysis and lipid synthesis and downregulated genes related to fatty acid β-oxidation in the liver more remarkably than administration at ZT12. Both DEX-treated groups displayed severely altered expression patterns of the core clock genes Bmal1 and Per2 in the liver and in fat. In addition, the expression of glutamate aspartate transporter, glial fibrillary acidic protein and glutamate transporter-1, astrocyte-related genes important for maintaining nervous system functions, was drastically decreased in the hippocampus of DEX-treated rats, especially when DEX was given at ZT0. In conclusion, our findings confirm that the severity of side effects, indicated by altered lipid metabolism and behavioral activity, depends on the timing of GC administration and is associated with the degree of glucocorticoid receptor dysfunction after dosing at disparate time points.     

Adiponutrin: A multimeric plasma protein

The interest in adiponutrin stems from adiponutrin variant I148M, which is strongly associated to non-alcoholic fatty liver disease. Adiponutrin has to date been considered to be solely an intracellular protein, with a role in lipid metabolism in liver and adipose tissue. However, a physiologically relevant role for adiponutrin has not been found. The aim of this study was to investigate the presence of adiponutrin in human plasma, a new facet of adiponutrin research. We demonstrate that adiponutrin is present in plasma as disulfide-bond dependent multimers, estimated to circulate at a concentration of 1.25–4 nM. Experiments reveal that adiponutrin is released from HepG2 cells in the presence of oleate. The presence of adiponutrin in plasma makes it accessible for clinical investigations and use as a potential biomarker for metabolic disease.     

Endocrine regulation of reproductive behavior in the newt Cynops pyrrhogaster

Hormonal control of the expression of courtship behavior and of secretion of the female-attracting pheromone sodefrin by the male red-bellied newt, Cynops pyrrhogaster, together with the hormonal influence on the responsiveness to the pheromone in the female, is reviewed.Expression of the initial stage of the courtship behavior, i.e., tail vibration by the male in front of the female, is dependent on prolactin (PRL) and androgen. During the courtship, sodefrin seems to be released from the cloaca through the ducts of the abdominal gland. Both content of immunoreactive sodefrin and preprosodefrin mRNA levels in the abdominal gland are elevated by a combination of PRL and androgen, indicating that the pheromone synthesis is stimulated by these two hormones. On the other hand, the discharge of sodefrin is accelerated by AVT, its action being mediated by V1 receptor. In female newts, responsiveness of the vomeronasal epithelium to the pheromone is elevated by a combination of PRL and estrogen. Thus, it can be concluded that PRL, AVT, and sex steroids are key hormones for the reproductive performance in the red-bellied newt. In this article, the significance of the structure of the pheromone molecule as a peptide is also discussed in terms of its species-specificity and its effectiveness in an aquatic environment.     

果蝇求偶行为的影响因素及其分子基础

果蝇Drosophila melanogaster Meigen是进行行为遗传学研究的极好材料。果蝇的雄性求偶行为已经被作为行为遗传学研究的模式。文章简要介绍近年来在遗传和分子水平上对果蝇性信息素和求偶行为的研究进展,尤其是突变体在果蝇行为遗传学研究中的应用。通过对果蝇求偶行为的分析,分别介绍果蝇的性信息素及视觉、听觉、嗅觉和味觉相关基因在果蝇求偶和交配行为过程中的作用。