Male-specific vasotocin expression in the medaka tuberal hypothalamus: Androgen dependence and probable role in aggression.

Terrestrial vertebrates have a population of androgen-dependent vasotocin (VT)-expressing neurons in the extended amygdala that are more abundant in males and mediate male-typical social behaviors, including aggression. Teleosts lack these neurons but instead have novel male-specific VT-expressing neurons in the tuberal hypothalamus. Here we found in medaka that vt expression in these neurons is dependent on post-pubertal gonadal androgens and that androgens can act on these neurons to directly stimulate vt transcription via the androgen receptor subtype Ara. Furthermore, administration of exogenous VT induced aggression in females and alterations in the androgen milieu led to correlated changes in the levels of tuberal hypothalamic vt expression and aggression in both sexes. However, genetic ablation of vt failed to prevent androgen-induced aggression in females. Collectively, our results demonstrate a marked androgen dependence of male-specific vt expression in the teleost tuberal hypothalamus, although its relevance to male-typical aggression needs to be further validated.

Teleost Nonapeptides, Isotocin and Vasotocin Administration Released the Milt by Abdominal Massage in Male Catfish, Clarias magur.

In the present work the nonapeptides i.e., isotocin and vasotocin alone or in a combination were tested in C. magur to evaluate their effect on stripping by abdominal massage. Also, we used chitosan-carbon nanotube nanocomposites to conjugate the nonapetides isotocin (abbreviated as COOH-SWCNTCSPeP) and isotocin and vasotocin (COOH-SWCNTCSPePs) with the aim of sustaining the effect for a longer duration. The conjugation of nonapeptides with nanocomposites was confirmed by Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). Two experiments were conducted to study the effect of naked (without nanoparticles) and conjugated nonapeptides on the milt release by stripping. Both the experiments consisted of eight treatments which included four naked groups two nanoconjugated groups and two controls. Both naked and nonconjugated formulations were successful in stripping the male catfish. The mRNA expression of selected reproductive genes was analysed to decipher the effect of nanopeptides at the molecular level. Nonapeptide treatment either naked or nanoconjugated, resulted in the upregulation of the transcript level of genes. Histological analysis revealed the concentration of spermatozoa was more in peptide injected groups than in the controls. The synergistic effects of nonapeptides and Ovatide had a positive impact on GSI. Thus, the present formulations were successful in stripping the male catfish to obtain the milt with significant reproductive success. Even though the naked groups perform better but the number of males required to fertilize the eggs in nanoconjuagted groups was smaller making it worth using for the delivery of nonapeptides.

Unraveling vasotocinergic, isotocinergic and stress pathways after food deprivation and high stocking density in the gilthead sea bream.

The influence of chronic stress, induced by food deprivation (FD) and/or high stocking density (HSD), was assessed on stress, vasotocinergic and isotocinergic pathways of the gilthead sea bream (Sparus aurata). Fish were randomly assigned to one of the following treatments: (1) fed at low stocking density (LSD-F; 5kg·m-3); (2) fed at high stocking density (HSD-F, 40kg·m-3); (3) food-deprived at LSD (LSD-FD); and (4) food-deprived at HSD (HSD-FD). After 21days, samples from plasma, liver, hypothalamus, pituitary and head-kidney were collected. Both stressors (FD and HSD) induced a chronic stress situation, as indicated by the elevated cortisol levels, the enhancement in corticotrophin releasing hormone (crh) expression and the down-regulation in corticotrophin releasing hormone binding protein (crhbp) expression. Changes in plasma and liver metabolites confirmed a metabolic adjustment to cope with energy demand imposed by stressors. Changes in avt and it gene expression, as well as in their specific receptors (avtrv1a, avtrv2 and itr) at central (hypothalamus and pituitary) and peripheral (liver and head-kidney) levels, showed that vasotocinergic and isotocinergic pathways are involved in physiological changes induced by FD or HSD, suggesting that different stressors are handled through different stress pathways in S. aurata.

An immunohistochemical study on the distribution of vasotocin neurons in the brain of two weakly electric fish, Gymnotus omarorum and Brachyhypopomus gauderio.

Hypothalamic nonapeptides (arginin vasotocin-vasopressin, oxytocin-isotocin) are known to modulate social behaviors across vertebrates. The neuroanatomical conservation of nonapeptide systems enables the use of novel vertebrate model species to identify general strategies of their functional mechanisms. We present a detailed immunohistochemical description of vasotocin (AVT) cell populations and their projections in two species of weakly electric fish with different social structure, Gymnotus omarorum and Brachyhypopomus gauderio. Strong behavioral, pharmacological, and electrophysiological evidence support that AVT modulation of electric behavior differs between the gregarious B. gauderio and the solitary G. omarorum. This functional diversity does not necessarily depend on anatomical differences of AVT neurons. To test this, we focus on interspecific comparisons of the AVT system in basal non-breeding males along the brain. G. omarorum and B. gauderio showed similar AVT somata sizes and comparable distributions of AVT somata and fibers. Interestingly, AVT fibers project to areas related to the control of social behavior and electromotor displays in both species. We found that no gross anatomical differences in the organization of the AVT system account for functional differences between species, which rather shall depend on the pattern of activation of neurons embedded in the same basic anatomical organization of the AVT system.

The effect of starvation and re-feeding on vasotocinergic and isotocinergic pathways in immature gilthead sea bream (Sparus aurata).

This study describes the responses of the vasotocinergic and isotocinergic systems to food deprivation and re-feeding processes in immature gilthead sea bream (Sparus aurata). The animals were subjected to the following experimental treatments: (1) normal feeding (control), (2) food deprivation for 21 days; and (3) re-feeding for 7 days, beginning 14 days after starvation. The animals were sampled at 0, 7, 14 and 21 days from the beginning of the trial. The pituitary and plasma arginine vasotocin (AVT) and isotocin (IT) levels and the hypothalamic pro-vasotocin and pro-isotocin mRNA expression levels were measured. In addition, the mRNA levels of three receptors, avtr v1, avtr v2 and itr, were analyzed in target organs associated with (1) the integration and control of different physiological pathways related to stress and food intake (i.e., the hypothalamus), (2) hormonal release into the bloodstream (i.e., the pituitary), and (3) metabolism and its control (i.e., the liver). The metabolic parameters in the liver were also determined. The hepatosomatic index decreased, and hepatic metabolites were mobilized beginning in the early stages of starvation. Moreover, an over-compensation of these parameters occurred when the fish were re-fed after starvation. In terms of the vasotocinergic and isotocinergic systems, feed restriction induced a clear time-dependent regulation among metabolic organization, stress regulation and orexigenic processes in the mature hormone concentration and pro-peptide and receptor mRNA expression. Our results reveal the important role of the AVT/IT endocrine systems in the orchestration of fish physiology during starvation and re-feeding and indicate their involvement in both central and peripheral organs.

Expression of arginine vasotocin and estrogen receptor alpha (ERα) in the shell gland altered by the specific phase relations of neural oscillations affects the reproductive physiology of Japanese quail.

In order to study the effect of specific phase relation of neural oscillations on reproductive regulation and the response of AVT (the avian homologue of mammalian AVP) the expression of AVT in the shell gland was monitored in sexually immature quail. In this study 3-week-old female Japanese quail were administered with serotonin precursor, 5-hydroxytryptophan followed by the dopamine precursor, l-dihydroxyphenylalanine at interval of 8h and 12h daily over a period of 13days. At thirty two days post treatment, a significant decrease in gonadal activity was seen in 8h quail although 12h quail exhibited an increase as compared to controls. A significant decrease in plasma estradiol level was noted in 8h quail while 12h exhibited no significant difference compared to controls. To address the relative roles of estrogen mediated action we also investigated estrogen receptor alpha (ER-α) expression and localization in the shell gland by visualizing it through confocal immuno-fluorescence microscopy. Results indicate increased expression of immunoreactive (ir)-AVT (myometrium), ir-ER-α (epithelial cells of endometrial region), along with significant increase in hypothalamic, plasma and shell gland AVT and a rapid increase in egg laying thus maintaining full breeding condition in 12h while low expression of ir-AVT and ir-ER-α was observed in 8h quail along with a significant decrease in hypothalamic, plasma and shell gland AVT with the suppression of gonads thereby stopping the egg-laying behaviour was noted. These findings not only suggest the modulation of gonadal development by changing the specific phase relation of neural oscillations but also demonstrate a parallel relation of AVT and gonadal activity in both conditions. It is concluded that the egg laying performance in response to AVT is regulated by the temporal phase relationship of neurotransmitters, and in part, this effect appears to be estrogen dependent.

Arginine vasotocin induces calling behavior with a female social stimulus and interacts with gonadotropins to affect sexual behaviors in male Xenopus tropicalis.

Arginine vasotocin (AVT) and the mammalian homologue, arginine vasopressin (AVP), modulate vertebrate social behaviors, including vocalizations in male anurans. To study the impact of AVT and social stimuli on calling in male Xenopus tropicalis, we injected males with vehicle, 1 µg, or 10 µg AVT and recorded vocalizations under four social contexts (no stimulus, with male call playback, with a female, and with call playback and a female). More males called when injected with 10 µg AVT. Furthermore, calling males called only when paired with a female. We identified four call types: long fast trill; short fast trill; slow trill; or click. Next, we injected males with vehicle, 10 µg, or 20 µg AVT and recorded vocalizations with or without a female. AVT treatment did not affect calling in this experiment, but we confirmed that more males, regardless of AVT treatment, called when a female was present. Then we evaluated the effect of human chorionic gonadotropin (hCG) on male sexual behavior. 20 IU hCG elevated behavior compared to controls while the 10 IU hCG treatment group was not different from either treatment. Last, we examined the effect of AVT on hCG-induced reproductive behavior. Males were injected with 10 IU hCG or with 10 IU hCG and 20 µg AVT. Males receiving hCG and AVT clasped and called significantly more than males receiving hCG only. Our results suggest that AVT and a female stimulus induce vocalizations in a male pipid anuran, X. tropicalis, and the interaction between gonadotropins and neurohormones influences reproductive behaviors in this anuran amphibian.

Cortisol stimulates arginine vasotocin and isotocin release from the hypothalamo-pituitary complex of round goby (Neogobius melanostomus): Probable mechanisms of action.

There were two aims of this in vitro perfusion study. Firstly, to determine which class of receptors, glucocorticoid (GRs) or mineralocorticoid (MRs), are involved in cortisol regulation of arginine vasotocin (AVT) and isotocin (IT) release from the hypothalamo-pituitary (H-P) complex of round goby (Neogobius melanostomus). Secondly, to determine which pathways, genomic or non-genomic, are involved in the aformentioned process.The H-P explants were perfused with cortisol (1.4 × 10(-) (7) M, 2.8 × 10(-7) M, 0.4 × 10(-6) M); only the highest dose significantly increased a release of both nonapeptides. In the perfusion of H-P explants, we used cortisol (0.4 × 10(-6) M) in combination with GRs antagonist RU486 (0.3 × 10(-6) M) or MRs antagonist C03DA01 (0.36 × 10(-6) M) or transcription inhibitor Actinomycin D (1 × 10(-7) M). All inhibitors were also tested seperately. The contents of AVT and IT in the perfusion media was determined by high-performance liquid chromatography (HPLC) with UV detection. This study suggested that different mechanisms were involved in the regulation of AVT and IT release from H-P complex in round goby. Apparently it was GRs but not MRs that were involved in cortisol regulation of AVT and IT release. In the case of AVT, our data points to both genomic and non-genomic pathways mediating the effect of cortisol; in the case of IT, it is only the non-genomic pathway. This study presents the first feasible mechanisms of cortisol action on AVT and IT release from the H-P complex in round goby.

Cortisol modulates vasotocinergic and isotocinergic pathways in the gilthead sea bream.

In the present study, we assessed the responses of the vasotocinergic and isotocinergic systems to chronic stress induced by cortisol administration in the gilthead sea bream (Sparus aurata). Pituitary and plasma arginine vasotocin (AVT) and isotocin (IT) levels, as well as hypothalamic pro-vasotocin (pro-VT) and pro-isotocin (pro-IT) mRNA expression levels, were analysed. In addition, the mRNA levels of three receptors, AVTR type V1a2, AVTR type V2 and ITR, were analysed in several target organs associated with the following physiological processes: (i) integration and control (hypothalamus), (ii) metabolism and its control (liver and hypothalamus), (iii) osmoregulation (gills) and (iv) stress response (head kidney). Specimens were injected intraperitoneally with slow-release implants (5 µL g(-1) body mass) containing coconut oil alone (control group) or with cortisol (50 µg g(-1) body mass; cortisol group). Both AVT and IT synthesis and release were correlated with plasma cortisol values, suggesting a potential interaction between both hormonal systems and cortisol administration. Our results suggest that the activation of hepatic metabolism as well as the hypothalamic control of metabolic processes provide the energy necessary to overcome stress, which could be partly mediated by AVTRs and ITR. Upregulation of branchial AVT and IT receptor expression following cortisol treatment suggests an involvement of the vasotocinergic and isotocinergic systems in the regulation of ion channels/transporters during stressful situations. Finally, changes in AVT and IT receptor mRNA expression in the head kidney suggest these nonapeptides participate in feedback mechanisms that regulate the synthesis/release of cortisol. Our results indicate a relationship between cortisol and both the vasotocinergic and isotocinergic systems during simulated chronic stress in S. aurata.

Hypothalamic vasotocin and tyrosine hydroxylase levels following maternal care and selection for low mortality in laying hens.

BACKGROUND: Feather pecking and cannibalism are major concerns in poultry farming, both in terms of animal welfare and farm economics. Genetic selection and introduction of (aspects of) maternal care have been suggested as potential interventions to reduce feather pecking in laying hens. Altered brain development has been proposed to reflect welfare states in animals, and can provide more insight into the underlying processes involved in feather pecking. Both vasotocin (the avian homologue of vasopressin) and dopaminergic neural circuitry have roles in control of social behaviors as well as in the stress response, and may be linked to feather pecking. Thus, the hypothalamus of adult laying hens selected for low early mortality (LML), which show low feather pecking, was examined and compared with a control line of adult laying hens selected for production characteristics only (CL). The effect of foster hen rearing on the two genetic lines and their hypothalamic morphology was also investigated. RESULTS: We demonstrated an increase in the number of neurons positive for the rate-limiting enzyme in dopamine production, tyrosine hydroxylase, in the periventricular area of the hypothalamus in the LML hens compared to CL hens. Hen-reared chicks showed more vasotocin -positive neurons in the medial pre-optic area compared to the hens raised without a hen. No correlations were found between behavior in an open field at 5-6 weeks of age, and the histology of the same hens at adulthood. CONCLUSION: The hypothalamic dopaminergic and vasotinergic systems are altered in hens following genetic selection or maternal care, indicating a potential role for these systems in feather pecking.

The formation and maintenance of social relationships increases nonapeptide mRNA in zebra finches of both sexes.

The nonapeptides oxytocin and vasopressin are believed to be involved in affiliation across species, but converging evidence is lacking. In monogamous zebra finches, oxytocin antagonists decrease pairing. The goal of the present study was to test if this relationship is bidirectional. We predicted that pairing would increase mesotocin (MT) and vasotocin (VT) mRNA (avian homologues of oxytocin and vasopressin) at nonapeptide neurosecretory sites: the paraventrivular nucleus (PVN) of the hypothalamus, which contains both MT and VT, and the bed nucleus of the stria terminalis (BSTm), which contains VT. To test our hypotheses, zebra finches of both sexes paired for 48 hr or 2 weeks in a naturalistic choice paradigm. Birds that did not pair or were not given the opportunity to pair were included as control groups. Pairing increased VT and MT mRNA in the PVN compared to both control groups. In the BSTm, animals paired for 48 hr had more cells expressing VT mRNA than did animals not given the opportunity to pair, and males had higher VT mRNA than did females. In males, singing primarily explained variations in MT mRNA, as well as VT mRNA in both the PVN and BSTm. In females, pairing behaviors explained variations in MT, but did not explain variations in VT in either brain region. Our results provide evidence that the relationship between nonapeptides and pairing are bidirectional and may be sexually differentiated.

Variations in the expression of vasotocin and isotocin receptor genes in the gilthead sea bream Sparus aurata during different osmotic challenges.

The dynamic changes in mRNA expression levels for vasotocin (AVT) and isotocin (IT) receptor gene levels were assessed in a time-course response study in immature male specimens of the gilthead sea bream (Sparus aurata) submitted to hyper- (55‰ salinity) and hypo-osmotic (5‰ salinity) challenges. Two different cDNAs for the AVT receptor and one for the IT receptor (V1a2-type and V2-type AVTR, and ITR, respectively) were cloned by screening an S. aurata brain cDNA library. Genes for these receptors were expressed differentially and is nearly ubiquitously in 26 of the examined tissues. In the gills, both environmental salinity challenges up-regulated AVTR V1a2-type gene expression concomitantly with mRNA expression protein activity of Na(+), K(+)-ATPase gene expression and protein, whereas the AVTR V2-type and cystic fibrosis transmembrane conductance regulator (CFTR) mRNA levels were associated with mRNAs environmental salinity, indicating a possible connection between AVTRs and these transporters. In kidney, AVTR V1a2-type gene expression peaked rapidly and lasted only a short time (12-24h) in response to both osmotic challenges. In contrast, AVTR V2-type mRNA levels were enhanced in specimens exposed to hyperosmotic conditions, whereas they decreased under hypoosmotic environments, suggesting an antidiuretic role related to the vasoconstriction function. In the hypothalamus, only the expression of the AVTR V2-type gene was enhanced at 7 and 14 days under both experimental conditions. In the liver, both AVTRs had increased mRNA levels, with the upregulation of their AVTR V2-type gene increasing faster than the V1a2-type. The ITR gene was not sensitive to variations of external salinity in any of the analyzed tissues. Our results demonstrate the involvement of the vasotocinergic, but not the isotocinergic, pathway as well as the hypothalamic function, in the adjustments of both osmoregulatory and metabolic processes after osmotic challenges.

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 (0.2µg) and high (1µg) 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 3weeks 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.

Arginine vasotocin and androgen pathways are associated with mating system variation in North American cichlid fishes.

Neuroendocrine pathways that regulate social behavior are remarkably conserved across divergent taxa. The neuropeptides arginine vasotocin/vasopressin (AVT/AVP) and their receptor V1a mediate aggression, space use, and mating behavior in male vertebrates. The hormone prolactin (PRL) also regulates social behavior across species, most notably paternal behavior. Both hormone systems may be involved in the evolution of monogamous mating systems. We compared AVT, AVT receptor V1a2, PRL, and PRL receptor PRLR1 gene expression in the brains as well as circulating androgen concentrations of free-living reproductively active males of two closely related North American cichlid species, the monogamous Herichthys cyanoguttatus and the polygynous Herichthys minckleyi. We found that H. cyanoguttatus males bond with a single female and together they cooperatively defend a small territory in which they reproduce. In H. minckleyi, a small number of large males defend large territories in which they mate with several females. Levels of V1a2 mRNA were higher in the hypothalamus of H. minckleyi, and PRLR1 expression was higher in the hypothalamus and telencephalon of H. minckleyi. 11-ketotestosterone levels were higher in H. minckleyi, while testosterone levels were higher in H. cyanoguttatus. Our results indicate that a highly active AVT/V1a2 circuit(s) in the brain is associated with space use and social dominance and that pair bonding is mediated either by a different, less active AVT/V1a2 circuit or by another neuroendocrine system.

Evolution of the reproductive endocrine system in chordates.

The cephalochordate, amphioxus, is phylogenetically placed at the most primitive position in the chordate clade. Despite many studies on the endocrine system of amphioxus, definitive evidence has not been reported for the presence an endocrine system comparable to the pituitary-gonadal axis, which is important in the regulation of reproduction in vertebrates. Recent genome analyses in the amphioxus, Branchiostoma floridae, showed that it does not have any pituitary hormone genes except the thyrostimulin gene. Thyrostimulin is a heterodimeric glycoprotein hormone consisting of α and ß subunits, and is present in various organs of vertebrates. Analyses of a phylogenetic tree and a synteny suggest that amphioxus' thyrostimulin is an ancestral type of the glycoprotein hormones in chordates. In addition, genes for sex steroidogenic enzymes belonging to the CYP family were found in the genome sequences. The conversion pathway of sex steroids from cholesterol to estrogen, androgen, and major sex steroids was also identified in the gonads of amphioxus in vitro. Furthermore, we demonstrated the expression of genes encoding thyrostimulin and sex steroidogenic enzymes by an in situ hybridization technique. Here, we discuss the evolution of hormones and reproductive functions in the neuroendocrine control system of chordates.

From vasotocin to stress and cognition.

Sex and stress hormones coordinate experience and behaviour with physiological regulations. In the brain the sex hormones act to promote the repertoire of affiliative and reproductive behaviours. Stress hormones target in particular brain circuits underlying emotional arousal and cognition. To exert these actions the hormones operate in concert with neuropeptide secreting systems. Here I will discuss three examples of hormone action on brain and behaviour. First in the song bird manipulation of brain vasotocin promotes acquisition of a stable stereotyped song pattern. Second in mammal's central glucocorticoid feedback action, initiated and enhanced by vasopressin, is mediated by two types of nuclear receptors that operate in complementary fashion to maintain homeostasis and health. One receptor system, the mineralocorticoid receptors, activates the switch from spatial to habit learning under stressful conditions, while the stress-induced behavioural response is stored in the memory via activation of the glucocorticoid receptors. Third, genetic predisposition and early life experience program neuropeptide and glucocorticoid systems for life with the goal to match with expected future demands. Hence, a mismatch between the early imprinted response modes with later life conditions enhances vulnerability to disease. These three topics have in common that they illustrate how hormones govern plasticity of neural stress circuitry underlying complex behavioural tasks, how upon dysregulation psychiatric disorders may develop for which the individual is predisposed and how such hormone action may promote resilience still present in the diseased brain.

Dopaminergic regulation of mate competition aggression and aromatase-Fos colocalization in vasotocin neurons.

Recent experiments demonstrate that aggressive competition for potential mates involves different neural mechanisms than does territorial, resident-intruder aggression. However, despite the obvious importance of mate competition aggression, we know little about its regulation. Immediate early gene experiments show that in contrast to territorial aggression, mate competition in finches is accompanied by the activation of neural populations associated with affiliation and motivation, including vasotocin (VT) neurons in the medial bed nucleus of the stria terminalis (BSTm) and midbrain dopamine (DA) neurons that project to the BSTm. Although VT is known to facilitate mate competition aggression, the role of DA has not previously been examined. We now show that in male zebra finches (Taeniopygia guttata), mate competition aggression is inhibited by the D(2) agonist quinpirole, though not the D(1) agonist SKF-38393 or the D(4) agonist PD168077. The D(3) agonist 7-OH-DPAT also inhibited aggression, but only following high dose treatment that may affect aggression via nonspecific binding to D(2) receptors. Central VT infusion failed to restore D(2) agonist-inhibited aggression in a subsequent experiment, demonstrating that D(2) does not suppress aggression by inhibiting VT release from BSTm neurons. In a final experiment, we detected D(2) agonist-induced increases in immunofluorescent colocalization of the product of the immediate early gene c-fos and the steroid-converting enzyme aromatase (ARO) within VT neurons of the BSTm. Thus, although VT and DA appear to influence mate competition aggression independently, BSTm VT neurons are clearly influenced by the activation of D(2) receptors, which may modify future behaviors.

Comparison of arginine vasotocin immunoreactivity differences in dominant and subordinate green anole lizards.

The neuropeptide arginine vasotocin (AVT) and its mammalian homologue arginine vasopressin (AVP) are believed to be involved in many social behaviors including territorial aggression. Testosterone (T) is also important for controlling territorial aggression, and it is believed to be involved in modulating AVT/AVP levels in the brain. In this study, male Anolis carolinensis were paired (n=11 pairs) in a neutral cage and were allowed to establish a dominant-subordinate relationship for 10 days (experimental groups) or housed in a neutral cage with or without a female (control groups; each n=4). On 10th day animals were sacrificed and their brain sections were processed for AVT immunohistochemistry and their serum was analyzed for testosterone levels. AVT immunoreactive (AVT-ir) cell numbers were counted in the anterior hypothalamus (AH), paraventricular nucleus (PN), posterior hypothalamus (PH), preoptic area (POA), and supra optic nuclei (SON). 2-way randomized block design was conducted to assess AVT-ir cell number differences between dominant and subordinate animals and Pearson's correlations were used to determine if a relationship existed between T levels and AVT-ir cell numbers. Dominant animals had more AVT-ir cells in the POA compared to subordinate animals, and subordinate animals had fewer AVT-ir cells in the POA compared to males housed either singly or with a female. There were no differences in AVT-ir cell numbers between dominant and subordinate animals in other areas. T levels were not correlated with the AVT-ir cell numbers in any area. Thus dominant animals have increased AVT-ir cell numbers compared to subordinate animals in a brain region known to be important in male sexual behavior. However, this difference is not related to differences in T.

Conserved sensory-neurosecretory cell types in annelid and fish forebrain: insights into hypothalamus evolution.

Neurosecretory control centers form part of the forebrain in many animal phyla, including vertebrates, insects, and annelids. The evolutionary origin of these centers is largely unknown. To identify conserved, and thus phylogenetically ancient, components of neurosecretory brain centers, we characterize and compare neurons that express the prohormone vasotocin (vasopressin/oxytocin)-neurophysin in the developing forebrain of the annelid Platynereis dumerilii and of the zebrafish. These neurons express the same tissue-restricted microRNA, miR-7, and conserved, cell-type-specific combinations of transcription factors (nk2.1, rx, and otp) that specify their identity, as evidenced by the specific requirement of zebrafish rx3 for vasotocin-neurophysin expression. MiR-7 also labels another shared population of neurons containing RFamides. Since the vasotocinergic and RFamidergic neurons appear to be directly sensory in annelid and fish, we propose that cell types with dual sensory-neurosecretory properties were the starting point for the evolution of neurosecretory brain centers in Bilateria.

Effects of early embryonic exposure to genistein on male copulatory behavior and vasotocin system of Japanese quail.

Genistein is a phytoestrogen, particularly abundant in soybeans that can bind estrogen receptors and sex hormone binding proteins, exerting both estrogenic and antiestrogenic activity. In this study we used the Japanese quail embryo as a test end-point to investigate the effects of early embryonic exposure to genistein on male copulatory behavior and on vasotocin parvocellular system. Both differentiate by the organizational effects of estradiol during development and may therefore represent an optimal model to study the effects of xenoestrogens. We injected two doses of genistein (100 and 1000 microg) into the yolk of 3-day-old Japanese quail eggs. Other eggs were treated with either 25 microg of estradiol benzoate or sesame oil as positive and negative controls. At the age of 6 weeks, behavioral tests revealed a significant decrease of all aspects of copulatory behavior (in comparison to the control group) in estradiol-treated birds. In contrast, genistein-treated animals demonstrated various degrees of decrease in the mean frequencies of some aspects of the sexual behavior. The computerized analysis of vasotocin innervation in medial preoptic, stria terminalis and lateral septum nuclei revealed a statistically significant decreased immunoreactivity in treated animals compared to control ones. These results demonstrate that genistein, similarly to estradiol, has an organizational effect on quail parvocellular vasotocin system and on copulatory behavior. In conclusion, present results confirm, in this avian model, that embryonic exposure to phytoestrogens may have life-long effects on sexual differentiation of brain structures and behaviors.