Changes in plasma levels of gonadotropins and sex steroids in the toad, Bufo japonicus, in association with behavior during the breeding season

Time- and season-dependent changes in the steroidogenic markers in female tree sparrow (Passer montanus)

Seasonal breeders display elevated sex steroid hormone production during reproductive seasons, resulting in significant physiological and structural alterations. One such seasonal breeder adapted to the changing environment is a Tree sparrow (Passer montanus). The study aims to investigate 24-h rhythmicity and annual variations in the expression of steroidogenic gene markers of adult female tree sparrows. Two experiments were conducted; in experiment one, birds (n = 5 birds/time points) were sampled at six time points, i.e., ZT1, ZT5, ZT9, ZT13, ZT17, and ZT21 (ZT = Zeitgeber time, ZT0 = sunrise time) during the reproductive stage; subsequently, hypothalamus and ovary were harvested for gene expression analysis. In experiment two, birds (n = 5/month) were sampled at mid-day every month for a year. Feather molt, follicular diameter, body mass, and bill coloration were recorded. The hypothalamus and ovary were harvested for gene expression studies. Blood plasma cholesterol and progesterone were also measured. The study indicates a larger follicular size during May and June. Whereas, maximum molt was observed during the post-reproductive phase. Cholesterol levels were highest prior breeding phase and higher progesterone levels paralleled larger follicular size. While higher levels of GnIh (gonadotropin-inhibitory hormone) and Dio3 (type 3 deiodinase) were observed during the non-breeding phase, elevated expression of Tshβ (thyroid stimulating hormone subunit beta), Dio2 (type 2 deiodinase), and GnRh (gonadotropin-releasing hormone) was noted during the reproductive period. The study also reveals 24-h rhythmicity in selected steroidogenic markers (StAR, Nr4a1, Er, Scp2, Cyp17a1, Foxl2, Cyp11a1, Hsd11b2, Cyp11b, Cyp19a1, and Vdac1) and seasonal variations directly influence steroidogenesis, which connects with the annual reproductive cycle.

Diversity of Androgens; Comparison of Their Significance and Characteristics in Vertebrate Species

Androgen(s) is one of the sex steroids that are involved in many physiological phenomena of vertebrate species. Although androgens were originally identified as male sex hormones, it is well known now that they are also essential in females. As in the case of other steroid hormones, androgen is produced from cholesterol through serial enzymatic reactions. Although testis is a major tissue to produce androgens in all species, androgens are also produced in ovary and adrenal (interrenal tissue). Testosterone is the most common and famous androgen. It represents a major androgen both in males and females of almost vertebrate species. In addition, testosterone is a precursor for producing significant androgens such as11-ketotestosterone, 5α-dihydrotestosterone, 11-ketodihydrotestosterones and 15α-hydroxytestosterone in a species- or sex-dependent manner for their homeostasis. In this article, we will review the significance and characteristics of these androgens, following a description of the history of testosterone discovery and its synthetic pathways.

Mate calling alters expression of neuropeptide, cocaine- and amphetamine- regulated transcript (CART) in the brain of male frog Microhyla nilphamariensis

Croaking is a unique component of reproductive behaviour in amphibians which plays a key role in intraspecies communication and mate evaluation. While gonadal hormones are known to induce croaking, central regulation of sound production is less studied. Croaking is a dramatic, transient activity that sets apart an animal from non-croaking individuals. Herein, we aim at examining the profile of the neuropeptide cocaine- and amphetamine-regulated transcript (CART) in actively croaking and non-croaking frog Microhyla nilphamariensis. In anurans, this peptide is widely expressed in the areas inclusive of acoustical nuclei as well as areas relevant to reproduction. CART immunoreactivity was far more in the preoptic area (POA), anteroventral tegmentum (AV), ventral hypothalamus (vHy), pineal (P) and pituitary gland of croaking frog compared to non-croaking animals. On similar lines, tissue fragments collected from the mid region of the brain inclusive of POA, vHy, AV, pineal and pituitary gland of croaking frog showed upregulation of CART mRNA. However, CART immunoreactivity in the neuronal perikarya of raphe (Ra) was completely abolished during croaking activity. The data suggest that CART signaling in the brain may be an important player in mediating croaking behaviour in the frog.

Reconsidering reproductive patterns in a model dissociated species, the red-sided garter snake: Sex-specific and seasonal changes in gonadal steroidogenic gene expression

Sex steroid hormones are powerful regulators of reproductive behavior and physiology in vertebrates, and steroidogenesis has distinct sex- and season-specific patterns ultimately dictated by the expression of key enzymes. Most comparative endocrinology studies, however, focus only on circulating levels of sex steroids to determine their temporal association with life-history events in what are termed associated reproductive patterns. The red-sided garter snake (Thamnophis sirtalis parietalis) is a notable exception; this species exhibits maximal sex behavior decoupled from maximal sex steroid production and gametogenesis in what is termed a dissociated reproductive pattern. And while this is true for male red-sided garter snakes and their production of testosterone, females have maximal estradiol production during peak breeding (spring) but only immediately after mating. Here, we demonstrate that expression of ovarian aromatase (conversion of androgens to estrogens) matches the established seasonal hormone pattern in females. Additionally, steroidogenic gene expression in the ovary is broadly reduced if not suppressed compared to the testis throughout the active year. Bizarrely, male red-sided garter snakes demonstrate an unexplained pattern of steroidogenic gene expression in the testis. StAR (import of cholesterol to steroidogenesis) is maximally expressed in spring, yet Hsd17b3 expression (conversion of androstenedione to testosterone) is highest in summer, with the latter matching the established summer peak in male testosterone. The function of elevated StAR in spring is unknown, but our results suggest a decoupling between maximal StAR expression and testosterone biosynthesis (Hsd17b3 expression). We also purport that the reproductive pattern binary should be reassessed given its lack of fit for many vertebrate species that demonstrate seasonal, mixed patterns of (a)synchrony between circulating sex hormones and reproductive behavior.

Social Communication across Reproductive Boundaries: Hormones and the Auditory Periphery of Songbirds and Frogs

Most animals experience reproductive transitions in their lives; for example, reaching reproductive maturity or cycling in and out of breeding condition. Some reproductive transitions are abrupt, while others are more gradual. In most cases, changes in communication between the sexes follow the time course of these reproductive transitions and are typically thought to be coordinated by steroid hormones. We know a great deal about hormonal control of communication behaviors in birds and frogs, as well as the central neural control of these behaviors. There has also been significant interest in the effects of steroid hormones on central nervous system structures that control both the production and reception of communication signals associated with reproductive behaviors. However, peripheral sensory structures have typically received less attention, although there has been growing interest in recent years. It is becoming clear that peripheral sensory systems play an important role in reproductive communication, are plastic across reproductive conditions, and, in some cases, this plasticity may be mediated by steroid hormones. In this article, we discuss recent evidence for the role of peripheral auditory structures in reproductive communication in birds and frogs, the plasticity of the peripheral auditory system, and the role of steroid hormones in mediating the effects of the peripheral auditory system on reproductive communication. We focus on both seasonal and acute reproductive transitions, introduce new data on the role of hormones in modulating seasonal patterns, and make recommendations for future work.

Behavioural discrimination of male mental gland secretions of the gopher tortoise (Gopherus polyphemus) by both sexes

Chemical communication is important for mate choice, especially at long distances in fragmented populations. The gopher tortoise is a social species that is threatened in the southeast U.S. due to habitat fragmentation and decline. One consequence of habitat loss is reduced mating opportunities, yet chemical signalling in gopher tortoises is relatively under-studied. Here, we investigated chemoreception of tortoise discrimination of chin secretions, or mental gland (MG) secretions. To assess conspecific recognition of male MG secretions, we conducted two paired-choice experiments: one with a neutral odorant control (NC; distilled water) and one with a pungent odorant control (PC; acetone) vs. male MG secretions. Behaviours were defined a priori, and their durations were quantified relative to treatments. Each sex spent significantly more time with MG secretions vs. acetone control during the PC study (p= 0.001). Each sex also sniffed MG swabs more frequently in both studies (PC study: p=0.0003; NC study: p=0.001). A principal components analysis of behavioural durations from the PC study identified one component with a significant treatment effect performed to MG secretions (p=0.0003), including the behaviours sniffing, head bobbing, biting, and eating near a swab. Our study provides the first chemical-behavioural bioassay of MG secretions from male gopher tortoises, suggesting MG secretions may be a source of pheromones.

Effect of nervous stimulation on ovarian steroid secretion in amphibians

In the present study, the effect of nerve stimulation on the secretory activity of the ovary of adult females was analyzed for the first time in amphibians. Results revealed that in Rhinella arenarum the stimulation of nerves that supply the gonad induced an increase in estradiol and progesterone secretion, this response showing differences during the reproductive cycle of the species. During the postreproductive period, an increase in estradiol secretion was observed while, in the reproductive period, progesterone secretion increased. Our results suggest that the sympathetic division of the autonomic nervous system would be responsible for this increase, taking into account that, under our experimental conditions, acetylcholine did not affect the endocrine activity of the gonad, while adrenaline (epinephrine) was effective in inducing steroid secretion an effect that could be due to interaction with β receptors. On the other hand, our data show that the association of adrenaline with follicle-stimulating hormone increased estradiol secretion during the postreproductive period, while the association of catecholamine with LH or hCG increased progesterone secretion during the reproductive period. Our results would suggest that nerve stimulation, mediated by the release of adrenaline, would act synergistically with gonadotrophins to stimulate steroid secretion.

Osmotic 'cost' of reproduction in breeding male toads

Shifts between habitats during reproduction can induce costs that are independent of the reproductive effort and that often apply to both sexes. Such shifts can also illustrate physiological costs complementary to those involving energetic currencies. In this study, we investigated osmotic consequences of reproduction in a context where reproduction induces a shift from terrestrial habitats to freshwater environments. During reproduction, toads migrate to breeding ponds where males remain for several weeks, while females leave shortly after egg-laying. We assessed plasma osmolality of male spined toads during the whole reproductive period (approx. 30 days) in conjunction with markers of individual condition. We found that osmolality decreases during the protracted period of immersion in freshwater during reproduction, presumably through water influx as indicated by body mass changes. Hormonal markers of metabolism and sexual activity were positively correlated with osmolality. Recent research has highlighted hydric 'costs' of reproduction when access to water is limited. Our study adds to this growing field of investigation, yet with an opposite perspective, where water availability linked to reproduction provokes hyperhydration rather than dehydration.

Estradiol and reproduction in the South American toad Rhinella arenarum (Amphibian, Anura)

Rhinella arenarum is a South American toad with wide geographic distribution. Testes of this toad produce high amount of androgens during the non reproductive season and shift steroid synthesis from androgens to 5α-pregnanedione during the breeding. In addition, plasma estradiol (E₂) in males of this species shows seasonal variations but, since testes of R. arenarum do not express aromatase, the source of plasma E₂ remained unknown for several years. However, the Bidder's organ (BO), a structure located at one pole of each testis, is proposed to be the main source of E₂ in male's toads since it expresses several steroidogenic enzymes and is able to produce E₂ from endogenous substrates throughout the year. In addition, there were significant correlations between plasma E₂ and total activity of BO aromatase, and between plasma E₂ and the amount of hormone produced by the BO in vitro. In the toad, apoptosis induced by in vitro treatment with E₂ was mostly detected in spermatocytes during the breeding and in spermatids during the post-reproductive season, suggesting that this steroid has an important role in controlling spermatogenesis. However, in vitro treatment with E₂ had no effect on proliferation. This evidence suggests that the mechanism of action of E₂ on amphibian spermatogenesis is complex and more studies are necessary to fully understand the role of estrogens regulating the balance between cellular proliferation and apoptosis. In addition, in R. arenarum in vitro studies suggested that E₂ has no effect on CypP450c17 protein levels or enzymatic activity, while it reduces 3β-hydroxysteroid dehydrogenase/isomerase (3β-HSD/I) activity during the post reproductive season. As well, E₂ regulates FSHβ mRNA expression all over the year suggesting a down regulation process carried out by this steroid. The effect on LHβ mRNA is dual, since during the reproductive season estradiol increases the expression of LHβ mRNA while in the non-reproductive season it has no effect. In conclusion, the effect of E₂ on gonadotropins and testicular function is complex, not clearly understood and probably varies depending on the species. The aim of the current article is to review evidence on reproductive endocrinology and on the role of estradiol regulating reproduction in amphibians, with emphasis on the South American species Rhinella arenarum.

Effects of nerve stimulation on amphibian oviductal activity

The present study describes, for the first time in an anuran amphibian, the nerve stimulation effects on the secretory and motor activity of the oviduct of adult females. The results reveal that in Rhinella arenarum oviducts, the epithelial and glandular secretory cells of the mucosa of the pars convoluta respond to nerve stimulation secreting the products synthetized and stored in their cytoplasm. The ultrastructural analysis showed that the cell content released is made up of granular, fibrillar and floccular material, exocytosis being the main secretory mechanism found in epithelial secretory cells, although apocrine and holocrine processes could also be observed. In contrast, in glandular cells only exocytosis processes were found. With respect to the participation of the nervous system in the motility of the duct, observations under our experimental conditions indicated that oviductal nerve stimulation promotes motor activity as manifested by a succession of coordinated contractions and relaxations that generate movements similar to peristaltic waves. These results were observed in oviducts from animals captured during the reproductive and post reproductive periods. However, it is important to note that both the secretory response and duct motility are markedly decreased during the post reproductive period of the species.

Progesterone and prostaglandin F2α induce species-typical female preferences for male sexual displays in Cope's gray treefrog (Hyla chrysoscelis)

Endocrine systems play critical roles in facilitating sexual behavior in seasonally breeding vertebrates. Much of the research exploring this topic has focused on the endocrine correlates of signaling behavior in males and sexual proceptivity in females. What is less understood is how hormones promote the expression of the often complex and highly selective set of stimulus-response behaviors that are observed in naturally breeding animals. In female frogs, phonotaxis is a robust and sensitive bioassay of mate choice and is exhibited by gravid females during the breeding season. In stark contrast, females exhibit low phonotactic responsiveness outside the breeding season, but the administration of hormones can induce sexual proceptivity. Here we test the hypothesis that manipulation of a minimal set of reproductive hormones-progesterone and prostaglandin F2α-are capable of evoking not only proceptive behavior in non-breeding females, but also the patterns of intraspecific selectivity for male sexual displays observed in gravid females tested during the breeding season. Specifically, we investigated whether preferences for faster call rates, longer call durations, and higher call efforts were similar between breeding and hormone-treated females of Cope's gray treefrog (Hyla chrysoscelis). Hormone injections induced patterns of selective phonotaxis in non-breeding females that were remarkably similar to those observed in breeding females. These results suggest that there may be an important contribution of hormonal pleiotropy in regulating this complex, acoustically-guided sexual behavior. Our findings also support the idea that hormonal induction could be used to evaluate hypotheses about selective mate choice, and its underlying mechanisms, using non-breeding females.

A novel method for induction of pairing in Xenopus by addition of steroids into the water

The African clawed frog, Xenopus laevis, is widely used in biological studies. Ovulation of Xenopus is normally induced by the injection of human chorionic gonadotropin (hCG) into the dorsal lymph sac of fully-grown female frogs. Previously, we reported a novel method for inducing Xenopus ovulation by adding a mixture of steroids into the surrounding water. In the present study, we demonstrate how to induce reproductive behavior in male frogs using the same methodology. The types and concentrations of steroids were evaluated, and the efficiency of the selected steroid for the induction of ejaculation was examined. New procedures were also examined for inducing mating by mixing both females and males activated by steroids. In male frogs, testosterone was effective for the induction of physiological changes, accumulation of melanin in the hands and induction of amplexus. Time course experiments revealed that eight hours were sufficient to induce male reproductive behavior and ovulation in females. Finally, we established an efficient means of inducing pairing in frogs that involved pre-treatment of frogs with salt solution followed by testosterone for males and a mixture of estradiol and progesterone for females. Although the numbers of oocytes obtained were relatively fewer than those resulting from hCG injection, the fertilization rate of eggs ovulated using the new treatment method was similar to that with eggs obtained by hCG-injection, and juveniles developed normally. In conclusion, we have developed a novel method to induce pairing in frogs without the need for injections.

Characterization and seasonal changes in LHβ and FSHβ mRNA of Rhinella arenarum (Amphibia, Anura)

In anurans, two types of gonadotropins were described in several species of Ranidae and Pipidae families but only in one of the Bufonidae family. Rhinella arenarum is a bufonid that have the lowest concentration of plasma androgens during the breeding. The objective of this paper was to characterize the cDNA sequence of β subunit of LH and FSH from toad pituitary and study seasonal variation in gonadotropins mRNA using quantitative real-time RT-PCR. The LHβ cDNA is a 636 bp sequence containing an open reading frame (ORF), 45 bp of 5'-untranslated region (UTR) and 174 bp of 3'-UTR. The ORF encodes for a signal peptide of 26 amino acids and a mature protein of 113 amino acids with one N-glycosylation site at the 34th position. The FSHβ cDNA sequence is a 535 bp fragment containing an ORF, 8 bp of 5'-UTR and 152 bp of 3'-UTR. The ORF encodes for a signal peptide of 20 amino acids and a mature protein of 104 amino acids with two N-glycosylation sites at 25th and 42nd positions. Multiple alignments of aminoacid deduced sequences of LHβ and FSHβ (teleosts, amphibians, birds, mammals) showed that all the tetrapods studied conserve 12 cysteins and one (LH) or two (FSH) N-Glycosylation sites. LHβ is closer to teleosts than to mammals and birds while FSHβ is closer to mammals. The analysis of seasonal changes in LHβ and FSHβ mRNA indicates that transcript levels have seasonal variations and that the profile of androgens is opposite to that of the gonadotropins mRNA.

Socially modulated cell proliferation is independent of gonadal steroid hormones in the brain of the adult green treefrog (Hyla cinerea)

Gonadal steroid hormones have been shown to influence adult neurogenesis in addition to their well-defined role in regulating social behavior. Adult neurogenesis consists of several processes including cell proliferation, which can be studied via 5-bromo-2'-deoxyuridine (BrdU) labeling. In a previous study we found that social stimulation altered both cell proliferation and levels of circulating gonadal steroids, leaving the issue of cause/effect unclear. In this study, we sought to determine whether socially modulated BrdU-labeling depends on gonadal hormone changes. We investigated this using a gonadectomy-implant paradigm and by exposing male and female green treefrogs (Hyla cinerea) to their conspecific chorus or control stimuli (i.e. random tones). Our results indicate that socially modulated cell proliferation occurred independently of gonadal hormone levels; furthermore, neither androgens in males nor estrogen in females increased cell proliferation in the preoptic area (POA) and infundibular hypothalamus, brain regions involved in endocrine regulation and acoustic communication. In fact, elevated estrogen levels decreased cell proliferation in those brain regions in the implanted female. In male frogs, evoked calling behavior was positively correlated with BrdU-labeling in the POA; however, statistical analysis showed that this behavior did not mediate socially induced cell proliferation. These results show that the social modulation of cell proliferation can occur without gonadal hormone involvement in either male or female adult anuran amphibians, and confirms that it is independent of a behavioral response in males.

Female sexual arousal in amphibians

Rather than being a static, species specific trait, reproductive behavior in female amphibians is variable within an individual during the breeding season when females are capable of reproductive activity. Changes in receptivity coincide with changes in circulating estrogen. Estrogen is highest at the point when females are ready to choose a male and lay eggs. At this time female receptivity (her probability of responding to a male vocal signal) is highest and her selectivity among conspecific calls (measured by her probability of responding to a degraded or otherwise usually unattractive male signal) is lowest. These changes occur even though females retain the ability to discriminate different acoustic characteristics of various conspecific calls. After releasing her eggs, female amphibians quickly become less receptive and more choosy in terms of their responses to male sexual advertisement signals. Male vocal signals stimulate both behavior and estrogen changes in amphibian females making mating more probable. The changes in female reproductive behavior are the same as those generally accepted as indicative of a change in female sexual arousal leading to copulation. They are situationally triggered, gated by interactions with males, and decline with the consummation of sexual reproduction with a chosen male. The changes can be triggered by either internal physiological state or by the presence of stimuli presented by males, and the same stimuli change both behavior and physiological (endocrine) state in such a way as to make acceptance of a male more likely. Thus amphibian females demonstrate many of the same general characteristics of changing female sexual state that in mammals indicate sexual arousal.

Sexual hearing: the influence of sex hormones on acoustic communication in frogs

The majority of anuran amphibians (frogs and toads) use acoustic communication to mediate sexual behavior and reproduction. Generally, females find and select their mates using acoustic cues provided by males in the form of conspicuous advertisement calls. In these species, vocal signal production and reception are intimately tied to successful reproduction. Research with anurans has demonstrated that acoustic communication is modulated by reproductive hormones, including gonadal steroids and peptide neuromodulators. Most of these studies have focused on the ways in which hormonal systems influence vocal signal production; however, here we will concentrate on a growing body of literature that examines hormonal modulation of call reception. This literature suggests that reproductive hormones contribute to the coordination of reproductive behaviors between signaler and receiver by modulating sensitivity and spectral filtering of the anuran auditory system. It has become evident that the hormonal systems that influence reproductive behaviors are highly conserved among vertebrate taxa. Thus, studying the endocrine and neuromodulatory bases of acoustic communication in frogs and toads can lead to insights of broader applicability to hormonal modulation of vertebrate sensory physiology and behavior.

Hormonal modulation of phonotaxis and advertisement-call preferences in the gray treefrog (Hyla versicolor)

Hormonal levels fluctuate during the breeding season in many anurans, but the identity of the hormones that modulate breeding behavior and their effects remain unclear. We tested the influence of a combined treatment of progesterone and prostaglandin on phonotaxis, the key proceptive reproductive behavior of female anurans. First, we found that female gray treefrogs (Hyla versicolor) treated with progesterone and prostaglandin exhibited phonotaxis to synthetic male advertisement signals significantly more often than animals treated with ringers vehicle or uninjected controls. Responsive females had greater levels of plasma progesterone and estradiol compared to both control groups, suggesting that these steroids may be promoting phonotaxis. Second, we found that the selectivity of hormonally-induced phonotaxis in H.versicolor was similar to that observed in freshly captured breeding animals. Females made the same choices between acoustic signals after hormone treatments in tests of frequency, call rate and pulse rate, compared to their responses without treatment immediately after collection from the breeding chorus. The preference for a longer call was, however, significantly weaker after hormonal induction of phonotaxis. Hormonally primed females were also less likely to respond in any test and took longer to respond than did freshly collected females. Consequently, our study shows how progesterone-prostaglandin induced phonotaxis in female treefrogs influences both the quality and quantity of phonotaxis, relative to that exhibited by naturally breeding females.

Modulators of Bufo arenarum ovulation

In this study we investigated ovulation in vitro using ovary samples from Bufo arenarum with respect to their response to stimulation with homologous pituitary homogenate (HPH) or with progesterone and prostaglandins (PGF2α and PGE1) as intermediates of pituitary action. Ovary samples were obtained from animals captured during the breeding period. Our results demonstrate that the ovulatory response to all different inducers was dose dependent, the highest percentage of ovulated oocytes being obtained with HPH treatment. An important increase in the ovulatory response was obtained by the association of PGF2α with either HPH or progesterone at suboptimal doses, indicating that this prostaglandin induced a synergistic potentiating effect. Incubation with cyclooxygenase inhibitors (indomethacin or diclofenac sodium) produced a significant decrease in the ovulation induced by HPH, demonstrating that prostaglandins are involved in the action of the pituitary gland in this process. According to our results, PGE1 not only had no participation in the ovulatory process, but also produced an inhibitory effect on ovulation induced by HPH treatment.

Sexual dimorphism of extensor carpi radialis muscle size, isometric force, relaxation rate and stamina during the breeding season of the frog Rana temporaria Linnaeus 1758

Mating success of individual male frogs within explosive breeding species can depend on their ability to compete for a mate and to hold onto that mate during amplexus. Such importance of amplexus has resulted in the evolution of sexual dimorphism in the morphology and contractile characteristics of the anuran forelimb muscles used during amplexus. The aims of our study were to use an explosive breeding frog (Rana temporaria) during the breeding season to compare extensor carpi radialis (ECR) muscle length, mass, isometric activation times, relaxation times, absolute force, relative force (stress) and fatigue between male and female frogs. We found that ECR muscle mass and length were greater (tenfold and 1.4-fold, respectively), absolute tetanic muscle force and relative tetanic force (stress) were greater (16-fold and 2.2-fold, respectively) and relaxation times were slower in males than in females. Male ECR muscles incompletely relaxed during fatigue tests and showed less fatigue than female muscles. These sex differences are likely to be beneficial to the male frogs in allowing them to produce relatively high absolute muscle forces for prolonged periods of time to hold onto their mate during amplexus.

Molecular cloning of estrogen receptor alpha (ERalpha; ESR1) of the Japanese giant salamander, Andrias japonicus

Estrogens are essential for normal reproductive activity in females and males and for ovarian differentiation during a critical developmental stage in many vertebrates. To understand the molecular mechanisms of estrogen action and to evaluate estrogen receptor ligand interactions in the Japanese giant salamander (Andrias japonicus), we isolated cDNA encoding the estrogen receptor (ER) from the liver. A full-length Japanese giant salamander ER cDNA (jgsER) was obtained using 5' and 3' rapid amplification cDNA ends (RACE). The deduced amino acid sequence of the jgsER showed high identity to the Xenopus ERalpha (ESR1) (77.7%). We have applied both the conventional ERE-luciferase reporter assay system and the GAL4-transactivation system to characterize this receptor. In two different transient transfection assay systems using mammalian cells, the jgsER protein displayed estrogen-dependent activation of transcription. The GAL4-transactivation system showed about 10-fold greater activity of the estrogen receptor by hormone when compared to the conventional ERE-luciferase reporter assay system. Tissue distribution of ERalpha mRNA was examined and kidney, ovary and liver exhibited expression. This is the first isolation of an estrogen receptor from a salamander and also is the first functional cDNA obtained from the Japanese giant salamander, an endangered species considered a special natural monument of Japan.

Hormonal state influences aspects of female mate choice in the Túngara Frog (Physalaemus pustulosus)

Females alter their mate choices as they transition through different reproductive stages; however, the proximal mechanisms for such behavioral fluctuation are unclear. In many taxa, as females transition through different reproductive stages, there is an associated change in hormone levels; therefore, we examined whether fluctuation in hormone levels serves as a proximal mechanism for within-individual variation in mate choice in female túngara frogs (Physalaemus pustulosus). We manipulated hormone levels of females by administering 0, 10, 100, 500 or 1,000 IU of human chorionic gonadotropin (HCG), which is a ligand for luteinizing hormone (LH) receptors and will therefore cause increased gonadal hormone production. Phonotaxis assays were conducted to measure three aspects of mate choice behavior before and after HCG administration; receptivity (response to a conspecific mate signal), permissiveness (response to a signal that is less attractive than conspecific signals) and discrimination (ability to discern signal differences). The probability of response to a conspecific and an artificial hybrid signal significantly increased at the highest HCG doses. The difference in mean response time between pre- and post-HCG tests was significantly different for both the receptivity and permissiveness tests among the five doses. Increased permissiveness, however, was not due to decreased discrimination because females could discriminate between calls even at the highest HCG doses. These hormonal manipulations caused the same behavioral pattern we reported in females as they transitioned through different reproductive stages (Lynch, K.S., Rand, A.S., Ryan, M.J., Wilczynski, W., 2005. Plasticity in female mate choice associated with changing reproductive states. Anim. Behav. 69, 689-699), suggesting that changes in hormone levels can influence the female's mate choice behavior.

Current research in amphibians: studies integrating endocrinology, behavior, and neurobiology

Amphibian behavioral endocrinology has focused on reproductive social behavior and communication in frogs and newts. Androgens and estrogens are critical for the expression of male and female behavior, respectively, and their effects are relatively clear. Corticosteroids have significant modulatory effects on the behavior of both sexes, as does the peptide neuromodulator arginine vasotocin in males, but their effects and interactions with gonadal steroids are often complex and difficult to understand. Recent work has shown that the gonadal hormones and social behavior are mutually reinforcing: engaging in social interactions increases hormone levels just as increasing hormone levels change behavior. The reciprocal interactions of hormones and behavior, as well as the complex interactions among gonadal steroids, adrenal steroids, and peptide hormones have implications for the maintenance and evolution of natural social behavior, and suggest that a deeper understanding of both endocrine mechanisms and social behavior would arise from field studies or other approaches that combine behavioral endocrinology with behavioral ecology.

Historical perspective: Hormonal regulation of behaviors in amphibians

This review focuses on research into the hormonal control of behaviors in amphibians that was conducted prior to the 21st century. Most advances in this field come from studies of a limited number of species and investigations into the hormonal mechanisms that regulate reproductive behaviors in male frogs and salamanders. From this earlier research, we highlight five main generalizations or conclusions. (1) Based on studies of vocalization behaviors in anurans, testicular androgens induce developmental changes in cartilage and muscles fibers in the larynx and thereby masculinize peripheral structures that influence the properties of advertisement calls by males. (2) Gonadal steroid hormones act to enhance reproductive behaviors in adult amphibians, but causal relationships are not as well established in amphibians as in birds and mammals. Research into the relationships between testicular androgens and male behaviors, mainly using castration/steroid treatment studies, generally supports the conclusion that androgens are necessary but not sufficient to enhance male behaviors. (3) Prolactin acts synergistically with androgens and induces reproductive development, sexual behaviors, and pheromone production. This interaction between prolactin and gonadal steroids helps to explain why androgens alone sometimes fail to stimulate amphibian behaviors. (4) Vasotocin also plays an important role and enhances specific types of behaviors in amphibians (frog calling, receptivity in female frogs, amplectic clasping in newts, and non-clasping courtship behaviors). Gonadal steroids typically act to maintain behavioral responses to vasotocin. Vasotocin modulates behavioral responses, at least in part, by acting within the brain on sensory pathways that detect sexual stimuli and on motor pathways that control behavioral responses. (5) Corticosterone acts as a potent and rapid suppressor of reproductive behaviors during periods of acute stress. These rapid stress-induced changes in behaviors use non-genomic mechanisms and membrane-associated corticosterone receptors.

Gonadal steroids vary with reproductive stage in a tropically breeding female anuran

Tropically breeding anurans that require heavy rainfall in order to reproduce are subject to favorable breeding conditions that are sporadic. Although there is an increased probability of rain during the rainy season, the probability of local rainfall is unpredictable and this may influence female anuran reproductive strategies. The female túngara frog, a neotropical frog that requires standing water to breed, maintains readiness to breed at any time via asynchronous oogenesis. Although females constantly produce and maintain oocytes during the breeding season, this study shows that they have cyclic fluctuations in gonadal hormone levels. Plasma levels of estrogen significantly change during three reproductive stages within a single reproductive cycle (P=0.03), as do plasma levels of progesterone and androgen (P<0.001 and P=0.001, respectively). Furthermore, elevation in plasma estrogen and progesterone concentrations occurs during the same reproductive stage in which it has been reported that females display the maximum frequency of reproductive behaviors, the amplexed stage. Androgen levels, however, are elevated prior to the reproductive stage in which females display maximal reproductive behavior, that is, the unamplexed stage. Our study suggests that the pattern of gonadal hormone fluctuation in a tropically breeding female anuran is similar to the classic paradigm in which there is a temporal relationship between the appearance of reproductive hormones and reproductive behaviors.

Evolutionary insights into the regulation of courtship behavior in male amphibians and reptiles

Comparative studies of species differences and similarities in the regulation of courtship behavior afford an understanding of evolutionary pressures and constraints shaping reproductive processes and the relative contributions of hormonal, genetic, and ecological factors. Here, we review species differences and similarities in the control of courtship and copulatory behaviors in male amphibians and reptiles, focusing on the role of sex steroid hormones, the neurohormone arginine vasotocin (AVT), and catecholamines. We discuss species differences in the sensory modalities used during courtship and in the neural correlates of these differences, as well as the value of particular model systems for neural evolution studies with regard to reproductive processes. For example, in some genera of amphibians (e.g., Ambystoma) and reptiles (e.g., Cnemidophorus), interspecific hybridizations occur, making it possible to compare the ancestral with the descendant species, and these systems provide a window into the process of behavioral and neural evolution as well as the effect of genome size. Though our understanding of the hormonal and neural correlates of mating behavior in a variety of amphibian and reptilian species has advanced substantially, more studies that manipulate hormone or neurotransmitter systems are required to assess the functions of these systems.

Changes in serum sex steroid levels throughout the reproductive cycle of Bufo arenarum females

The changes in the serum levels of the sexual steroids estradiol-17beta (E(2)), testosterone (T), dihydrotestosterone (DHT), and progesterone (P) in Bufo arenarum females were determined by radioimmunoassay (RIA) during 3 consecutive cycles (1999-2001). The serum concentrations of T and DHT, which showed a close parallelism during the annual reproductive cycle, exhibited the highest levels during the preovulatory period, when oogenesis is advanced, while lowest serum levels of these hormones were found during the ovulatory period. The data obtained for E(2) showed a pattern contrary to that determined for androgens. The maximum E(2) concentrations detected in the early postovulatory period might be associated with vitellogenesis and follicular growth. Lowest E(2) concentrations were reached during the period in which B. arenarum undergoes its final hibernation stage. Serum P showed a peak during the preovulatoy period, related to the induction of nuclear maturation in full grown oocytes. A strong decrease in the levels of the circulating hormones was observed after ovariectomy. Our results showed that, out of the four hormones examined, T and DHT were the best indicators of ovarian and oviductal stage, as shown by the strong positive correlation found between androgen levels and organ weight, while E(2) showed a weak negative correlation with ovarian and oviductal weight.

Steroid production in toads

In Bufo arenarum, androgen biosynthesis occurs through a complete 5-ene pathway, including 5-androstane-3beta,17beta-diol as the immediate precursor of testosterone. Besides, steroidogenesis changes during the breeding period, turning from androgens to C(21)-steroids such as 5alpha-pregnan-3alpha,20alpha-diol, 3alpha-hydroxy-5alpha-pregnan-20-one and 5alpha-pregnan-3,20-dione. In B. arenarum, steroid hormones are not involved in hCG-induced spermiation, suggesting that the steroidogenic shift to C(21)-steroids during the breeding be not related to spermiation. The activity of 17-hydroxylase-C(17-20) lyase (CypP450(c17)) decreases during the reproductive season, suggesting that this enzyme would represent a key enzyme in the regulation of seasonal changes. However, the increase in the affinity for pregnenolone of 3beta-hydroxysteroid dehydrogenase (3alphaHSD)/isomerase could also be involved. Moreover, the reduction in CypP450(c17) leading to a reduction in C(19)-steroids, among them dehydroepiandrosterone (DHE), would contribute to the conversion of pregnenolone into progesterone, avoiding the non-competitive inhibition exerted by DHE on this transformation. Additionally, CypP450(c17) possesses a higher affinity for pregnenolone than for progesterone, explaining the predominance of the 5-ene pathway for testosterone biosynthesis. Animals in reproductive condition showed a significant reduction in circulating androgens, enhancing the physiological relevance of all the in vitro results. The in vitro effects of mGnRH and hrFSH on testicular steroidogenesis revealed that both hormones inhibited CypP450(c17) activity. In summary, these results demonstrate that, in B. arenarum, the change in testicular steroidogenesis during the reproductive period could be partially due to an FSH and GnRH-induced decrease in CypP450(c17) activity.

In vitro hCG and human recombinant FSH actions on testicular steroidogenesis in the toad Bufo arenarum

In order to study the regulation of testicular steroidogenesis in the toad Bufo arenarum, the effect of gonadotropins (hCG and hrFSH) on steroidogenic enzymes was determined using an in vitro system. 3beta-Hydroxysteroid dehydrogenase/isomerase activity was not affected by any of the gonadotropins, at any of the concentrations used. In contrast, 5alpha-reductase activity was strongly reduced by both hCG and hrFSH. Human chorionic gonadotropin inhibited the activity of cytochrome P450 17alpha-hydroxylase-C(17-20) lyase (P450(c17)), only at the highest concentration used, while hrFSH strongly reduced P450(c17) activity at all the doses assayed. In conclusion, these data suggest that LH (hCG) and FSH regulate steroidogenic enzymes such as 5alphaRed and P450(c17). The results also suggest that FSH could be involved in the regulation of the change in steroidogenesis undergone by the testis during the breeding season. In turn, the inhibition of P450(c17) activity could result in a reduction of androgen production and an increment of C21 steroids.

Social context influences androgenic effects on calling in the green treefrog (Hyla cinerea)

Courtship behavior in frogs is an ideal model for investigating the relationships among social experience, gonadal steroids, and behavior. Reception of mating calls causes an increase in androgen levels in listening males, and calling, in turn, depends on the presence of androgens. However, previous studies found that androgen replacement does not always restore calling to intact levels, and the relationship between androgens and calling may be context dependent. We examined the influence of androgens on calling behavior in the presence and the absence of social signals in male green treefrogs (Hyla cinerea). We categorized calling during an acoustic stimulus (mating chorus or tones) as evoked and calling in the absence of a stimulus as spontaneous. Intact males received a cholesterol implant, castrated males were castrated and received a cholesterol implant, and T-implanted males were castrated and received a testosterone implant. The androgen levels (mean +/- SE ng/ml of plasma) achieved by the implants were as follows: castrated males, 1.2 +/- 0.2; intact males 21.9 +/- 7.0; T-implanted males, 254.6 +/- 39.5. As in other frogs, calling depends on the presence of androgens, as castration abolished and T replacement maintained calling. However, among intact and T-implanted males, the influence of androgens on calling differed between spontaneous and evoked calling. There was a positive effect of androgen treatment on spontaneous call rate and a positive correlation between spontaneous call rate and androgen levels. The influence of androgen levels on evoked call rate was more complex and interacted with acoustic treatment. Surprisingly, T implants suppressed the chorus-specific increase in calling that is evident in intact males. In addition, in response to the chorus, T-implanted males called less than did intact males, in spite of higher androgen levels. Furthermore, variation in androgens did not explain variation in evoked call rate. These data indicate that androgens influence the motivation to call, but that, when socially stimulated, androgens are necessary but insufficient for calling.

Tests for order restrictions in binary data

In this article, a general procedure is presented for testing for equality of k independent binary response probabilities against any given ordered alternative. The proposed methodology is based on an estimation procedure developed in Hwang and Peddada (1994, Annals of Statistics 22, 67-93) and can be used for a very broad class of order restrictions. The procedure is illustrated through application to two data sets that correspond to three commonly encountered order restrictions: simple tree order, simple order, and down turn order.

Social influences on androgen levels in the southern leopard frog, Rana sphenocephala

Social cues play an important role in modulating neuroendocrine and hormonal states in many vertebrates. Social cues in the form of conspecific advertisement calls have been demonstrated to modulate plasma androgen levels in male Rana sphenocephala, the Southern leopard frog. Male R. sphenocephala were captured and brought to the laboratory for testing. Animals were exposed to one of two acoustical environments: a recording of an active conspecific breeding chorus or a recording of the same chorus in which all the spectral frequencies had been digitally shifted 500 Hz higher. Following 12 nights of exposure to either stimulus, plasma androgen levels were assessed by radioimmunoassay and gonadal morphology was examined to compare group differences. Plasma levels of dihydrotestosterone were significantly higher in males exposed to the conspecific chorus, compared with males exposed to the altered version of the chorus. Gonadal morphology did not differ between the two groups. These results suggest that in addition to environmental cues such as rainfall and other seasonal changes, social cues may also serve as environmental synchronizers among anurans to coordinate reproductive effort.

Substance P downregulates basal and gonadotropin-releasing hormone-induced gonadotropin in vitro secretion by pituitary gland of crested newt, Triturus carnifex

The possible role of Substance P (SP) was studied in the modulation of basal and gonadotopin-releasing hormone (GnRH)-induced gonadotropin secretion in the urodele crested newt, Triturus carnifex. During prereproduction, reproduction (noncourtship and courtship), refractory, recovery and aestivation, male and female pituitaries were incubated with medium-alone, GnRH, SP, GnRH receptor antagonist (antide), and SP receptor antagonist (L-703606). Since antisera raised against gonadotropins are not available for this species, we measured these hormones indirectly through their effects on the secretion of testicular androgens and ovarian progesterone from gonads superfused with the preincubated pituitaries. Pituitaries of both sexes preincubated with medium-alone, GnRH, GnRH plus L-703606, and GnRH plus SP plus L-703606 increased steroid secretion during prereproduction, noncourtship, courtship, and recovery; the increase induced by the pituitaries incubated with medium-alone was lower during prereproduction, noncourtship, and recovery. Pituitaries preincubated with SP, GnRH plus SP, GnRH plus SP plus antide, and SP plus antide did not change basal steroid secretion in any of the reproductive phases considered. Antide, L-703606, GnRH plus antide, GnRH plus SP plus antide plus L-703606, SP plus L-703606, and antide plus L-703606 experimental groups showed the same results as those with medium-alone. These results suggest that SP downregulates gonadotropin release in both Triturus carnifex sexes. In addition, an antagonist role, through receptor-independent mechanisms, exists between GnRH (upregulation) and SP (downregulation) in the modulation of pituitary.

Ontogenetic profile of FSH and LH in Rana esculenta

Circulating levels and pituitary content of FSH and LH were determined by specific radioimmunoassays in Rana esculenta starting a few days after hatching until the completion of metamorphosis. Both gonadotropins were found in the pituitary as well as in the blood plasma at all stages of development examined here. The plasma concentrations of FSH and LH were more or less uniform during pre- and prometamorphosis, but increased significantly at the onset of metamorphic climax. The plasma levels of FSH and LH remained high at the completion of metamorphosis. The pituitary content of FSH and LH was low in early premetamorphosis. It increased slightly through prometamorphosis and metamorphic climax, following which a highly significant increase occurred. Whereas plasma concentrations of FSH and LH were essentially similar within a single stage of development, the pituitary FSH content was severalfold higher than pituitary LH. The significance of these results is discussed in relation to the functional maturation of the brain-pituitary-gonadal axis in the frog.

Hormonal and cellular brain mechanisms regulating the amplexus of male and female water frog (Rana esculenta)

The role of nitric oxide (NO) synthase, prostaglandin E2-9-ketoreductase, and aromatase brain activities in regulating frog amplexus was assessed in the water frog (Rana esculenta). Plasma concentrations of testosterone were higher, and concentrations of 17beta-oestradiol lower, in amplexing males than in unamplexing males; while concentrations of testosterone and PGE2 were lower, and those of 17beta-oestradiol and PGF2alpha higher, in amplexing females compared to unamplexing females. Hormone release rescued from frog brains in vitro mirrored plasma hormone measures. Brain aromatase activity was lower in amplexing males; NO synthase was lower and PGE2-9-ketoreductase and aromatase were higher in amplexing females. In male brains, PGE2-9-ketoreductase inhibitor decreased PGF2alpha release and increased that of PGE2; aromatase inhibitor decreased 17beta-oestradiol and increased testosterone release. In female brains, NO donor and PGE2-9-ketoreductase inhibitor increased testosterone and PGE2 release and decreased that of 17beta-oestradiol and PGF2alpha; NO synthase inhibitor decreased testosterone release and PGE2 and increased 17beta-oestradiol and PGF2alpha release; PGF2alpha decreased testosterone release and increased 17beta-oestradiol release; aromatase inhibitor decreased 17beta-oestradiol release and increased testosterone release. In female brains, NO donor and PGE2-9-ketoreductase inhibitor decreased PGE2-9-ketoreductase and aromatase activities; PGF2alpha increased aromatase activity; NO synthase inhibitor increased PGE2-9-ketoreductase and aromatase activity. The data suggest that, in amplexing female brains, external and/or internal stimuli inhibit NO synthase, decreasing NO and activating PGE2-9-ketoreductase; in turn, PGF2alpha increases aromatase activity and 17beta-oestradiol release; while, in amplexing male brains, stimuli inhibit aromatase activity, thereby increasing testosterone production.

In vitro nitric oxide effects on basal and gonadotropin-releasing hormone-induced gonadotropin secretion by pituitary gland of male crested newt (Triturus carnifex) during the annual reproductive cycle

The objective of this study was to test the possible nitric oxide (NO) involvement in pituitary gonadotropin secretion in the male crested newt, Triturus carnifex. Pituitaries were incubated in vitro with medium alone, GnRH, NO donor (NOd, sodium nitroprusside), NO synthase inhibitor (NOSi, Nomega-nitro-L-arginine methyl ester), cGMP analogue (cGMPa, 8-bromo-cGMP), soluble guanylate cyclase inhibitor (sGCi, cystamine), GnRH plus NOSi, GnRH plus sGCi, and NOd plus sGCi during the annual reproductive cycle: pre-reproduction, reproduction (noncourtship and courtship), and the refractory, recovery, and estivation periods. To determine pituitary gonadotropin secretion indirectly, newt testes were superfused in vitro with preincubated pituitaries, and androgen release was determined. NO synthase (NOS) activity and cGMP levels were assessed in the preincubated pituitaries. Medium alone- and GnRH-preincubated pituitary increased androgen secretion during pre-reproduction, noncourtship, courtship, and recovery; the GnRH-induced increase was higher than the medium alone-induced increase during pre-reproduction, noncourtship, and recovery. NOd and cGMPa increased androgens in all reproductive phases considered except courtship; the NOd- and cGMP-induced increase was higher than the medium alone-induced increase during pre-reproduction, noncourtship, and recovery. NOS activity was highest during courtship and lowest during the refractory and estivation periods. GnRH increased NOS activity during pre-reproduction, noncourtship, and recovery. Cyclic GMP levels were highest during courtship and lowest during the refractory period and estivation. GnRH increased cGMP levels during pre-reproduction, noncourtship, and recovery, while NOd did so during all reproductive phases considered. These results suggest that basal and GnRH-induced gonadotropin secretion are up-regulated by NO in the pituitary gland of the male Triturus carnifex.

Seasonal fluctuations in pituitary gland and plasma levels of gonadotropic hormones in Rana

Changes in plasma and pituitary levels of two gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), in male and female Korean frogs (Rana dybowskii and Rana nigromaculata) were examined. Plasma levels of LH and FSH were measured by radioimmunoassay using antibodies raised against bullfrog LH and FSH. In male and female R. dybowskii, plasma concentrations of LH were low in early hibernation (October-January) and increased to high levels by late hibernation, when breeding occurs (late February-early March). Plasma FSH levels were also higher in the breeding period than during hibernation in male and female animals, but absolute levels of FSH were much lower than those of LH. In females, pituitary LH levels were higher in early hibernation, whereas pituitary FSH in females and pituitary LH and FSH in males changed little during hibernation. Plasma LH levels of frogs having uterine eggs or in amplexus were much higher (> 25 ng/ml) than those of frogs with unovulated follicles (December) (< 8 ng/ml) or frogs that had already spawned (< 11 ng/ml). In R. nigromaculata, plasma LH and FSH levels of females collected during hibernation (October-May) were relatively low; however, following hibernation, plasma LH and FSH levels were markedly elevated for a short period. Thus, these animals exhibit a clear gonadotropin surge prior to ovulation and spawning. Soon after spawning, however, gonadotropin levels dropped to basal levels. Following spawning in females, levels of FSH increased steadily and rapid follicle growth occurred until August. By September, FSH had dropped to basal levels. In males, a sharp elevation of LH and FSH levels occurred during the short breeding period followed by a second increase in August, when early stages of spermatogenesis were evident.

Orientation of the toad, Bufo japonicus, toward the breeding pond

A variety of orientation cues has been suggested for the migration to the breeding site in adult amphibians. We categorized the cues into the following 3 groups: 1) cues from the breeding pond such as male calling and pond odors, 2) celestial cues such as the sun light and the magnetic field of the earth and 3) cues from the area or route of the migration which compose a local map such as a visual and olfactory maps. To determine which of these is used by the toad, Bufo japonicus, we designed and conducted a displacement experiment in which migrating toads from one direction were transported to the ground in the opposite side of the pond. The displaced toads were completely disoriented and moved to random directions. We conclude that the toad uses a local map to orient to the breeding pond and cues from celestial bodies and the pond are not used. We also found that adult toads tracked the same route on both trips from and to the pond. This suggests that the local map was memorized by newly metamorphosed toads at their first terrestrial trip from the pond. The next step of our study was to determine what sense is used to receive the cue. We found blind toads, whose upper and lower eye-lids were stitched together, could reach the pond at a similar rate with the sham-operated and intact toads. However, anosmic toads, whose olfactory mucosa were damaged by the treatment with a 5% silver nitrate solution, rarely reached the pond.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro induction of vitellogenin synthesis in Rana esculenta: role of the pituitary

Vitellogenin (VTG), a complex protein, is a precursor of yolk protein (lipovitellin and phosvitin) in all oviparous vertebrates studied to date. In amphibians, as in other oviparous vertebrates, VTG synthesis is hormonally dependent; estradiol-17 beta (E2) is especially important, although in vivo in the frog Rana esculenta the pituitary may be involved in hepatic VTG synthesis and secretion. The present in vitro experiments carried out during the main phases of the annual reproductive cycle of this frog showed that homologous pituitary homogenate (HPH), as well as E2, stimulated VTG synthesis in male and female livers, although their patterns of VTG secretion showed some differences with respect to the induction time and the rate of VTG secretion. The hepatic response to HPH occurred after a longer time than that of E2 VTG induction, and no cooperation between HPH and E2 was found in the VTG synthesizing response. It should be emphasized that during the refractory period (July), hepatic VTG synthesis in males and females could only be induced by HPH. These data demonstrate, for the first time, a direct action of HPH on VTG synthesis in male and female frog livers in all the periods tested; hepatic responsiveness to HPH and E2 varies with season and sex.

Amplexus induces surge of luteinizing hormone in male toads, Bufo japonicus

At mating time in the wild, male toads (Bufo japonicus) exhibit a surge in circulating luteinizing hormone (LH) that is thought to result in spermiation. Experiments were performed to identify proximate control of this gonadotropin surge. Male toads migrating to a breeding pond were captured and put in plastic containers either with equal numbers of females or without females. All the males placed with the females clasped them in amplexus that lasted for about 12 hr. During this period, plasma LH and follicle-stimulating hormone levels increased progressively to about 25 and 2 times the initial levels, respectively, and then returned to the initial levels. No significant increases in plasma gonadotropin levels were observed in the males kept without females. These results suggest that the amplexus directly induced the LH surge, but do not preclude control by pheromonal or visual stimuli. To isolate effects of these factors, solitary male toads were kept with dummies of the female. The dummy was a block of "konnyaku," Japanese food whose component is mannan extracted from the root of a plant. Konnyaku is highly elastic, white in color, and virtually odorless. Thus, these dummies felt, but did not look or smell, realistic. All the males clasped their dummy and formed amplexus for 12 hr or more; an LH surge indistinguishable from that with the females was observed. It is concluded that the amplexus itself is the stimulus that induces the LH surge, and subsequent spermiation, in male toads. A strongly male-biased sex ratio, combined with a need to time spermiation precisely with actual mating, may have resulted in the evolution of this neuroendocrine reflex in male Bufo.