Behavioral and hormonal responses in the defensive repertoire during provocation in captive monocled cobra (Naja kaouthia).

The hooding behavior exhibited by cobras is a distinct defensive mechanism against predators, encompassing both visual and auditory displays. This behavior can be triggered by natural predators or humans. Considering that human provocation may potentially stimulate the hypothalamic-pituitary-adrenal (HPA) axis, the present study aimed to determine the pattern of the HPA axis response following human provocation-induced hooding behavior (PV) and provide a detailed analysis of the behavioral PV displays. Our primary hypothesis was that a 5-minute PV could activate the HPA axis to a degree comparable to that in the restraint-induced stress model (RS). The PV, RS-1 (1-minute), and RS-5 (5-minute) restraint models indeed activated the HPA axis. However, the pattern of plasma corticosteroid (CORT), but not arginine vasotocin, in the PV group differed from that in the RS-1 and RS-2 groups. The present study revealed the behavioral components of the PV. The first component appeared to be related to an increase in apparent size that is an intimidation display, while the second hissing and striking component consisted of a bluff charge. Moreover, no correlation was observed between the pattern of plasma CORT and any specific PV display. Finally, the body temperature (Tb) of cobras from RS-5 gradually increased, while the Tb of cobras from PV (5 min) remained unchanged. In conclusion, the activation of the HPA axis emerges as the main physiological response after human provocation. Within 5 min of provocation, the cobras' hooding behavior comprised two display components that were not related to the pattern of plasma CORT.

The modulation of social and non-social behavior by arginine vasotocin in the common waxbill, Estrilda astrild.

The influence of the neuropeptide arginine vasotocin (AVT) has been demonstrated across various species, on an ample range of behaviors, yet the results appear to be highly species-specific. In this study, we aimed to test how AVT influences both social and non-social behaviors in the common waxbill Estrilda astrild, a highly social estrildid finch. Through a within-subject design study, we experimentally manipulated AVT pathways through muscular injections of both an agonist and an antagonist of AVT at different dosages, and performed competition over food tests to assess behavioral changes. Our observations reveal a decrease in birds' movements with both low and high dosages of AVT. Additionally, the higher AVT dosage led to a significant decrease in birds' feeding, aggressive behavior, and allopreening. Conversely, the lower AVT dosage increased the duration of allopreening, which is a proxy for affiliation. The use of Manning Compound, a V1a antagonist, did not produce any changes in behavior, however, the absence of affinity studies for this compound in birds makes it difficult to interpret these results. It is plausible that in common waxbills, AVT V1b or V1a receptors may be involved in regulating movement, feeding, aggressive behavior, and allopreening, rather than V2 AVT receptors.

Arginine Vasotocin Directly Regulates Spermatogenesis in Adult Zebrafish (Danio rerio) Testes.

The neuropeptide vasopressin is known for its regulation of osmotic balance in mammals. Arginine vasotocin (AVT) is a non-mammalian homolog of this neuropeptide that is present in fish. Limited information suggested that vasopressin and its homologs may also influence reproductive function. In the present study, we investigated the direct effect of AVT on spermatogenesis, using zebrafish as a model organism. Results demonstrate that AVT and its receptors (avpr1aa, avpr2aa, avpr1ab, avpr2ab, and avpr2l) are expressed in the zebrafish brain and testes. The direct action of AVT on spermatogenesis was investigated using an ex vivo culture of mature zebrafish testes for 7 days. Using histological, morphometric, and biochemical approaches, we observed direct actions of AVT on zebrafish testicular function. AVT treatment directly increased the number of spermatozoa in an androgen-dependent manner, while reducing mitotic cells and the proliferation activity of type B spermatogonia. The observed stimulatory action of AVT on spermiogenesis was blocked by flutamide, an androgen receptor antagonist. The present results support the novel hypothesis that AVT stimulates short-term androgen-dependent spermiogenesis. However, its prolonged presence may lead to diminished spermatogenesis by reducing the proliferation of spermatogonia B, resulting in a diminished turnover of spermatogonia, spermatids, and spermatozoa. The overall findings offer an insight into the physiological significance of vasopressin and its homologs in vertebrates as a contributing factor in the multifactorial regulation of male reproduction.

Neuroendocrinology of Reproduction and Social Behaviors in Reptiles: Advances Made in the Last Decade.

Among amniotes, reptiles are ectothermic and are clearly distinguished from mammals and birds. Reptiles show great diversity not only in species numbers, but also in ecological and physiological features. Although their physiological diversity is an interesting research topic, less effort has been made compared to that for mammals and birds, in part due to lack of established experimental models and techniques. However, progress, especially in the field of neuroendocrinology, has been steadily made. With this process, basic data on selected reptilian species have been collected. This review article presents the progress made in the last decade, which includes 1) behavioral regulation by sex steroid hormones, 2) regulation of seasonal reproduction by melatonin and GnRH, and 3) regulation of social interaction by arginine vasotocin. Through these research topics, we provide insights into the physiology of reptiles and the latest findings in the field of amniote neuroendocrinology.

Early starvation in European seabass (Dicentrarchus labrax) larvae has no drastic effect on hepatic intermediary metabolism in juveniles.

The present study aims to investigate nutritional programming through early starvation in the European seabass (Dicentrarchus labrax). European seabass larvae were fasted at three different developmental periods for three durations from 60 to 65 dph (F1), 81 to 87 dph (F2), and 123 to 133 dph (F3). Immediate effects were investigated by studying gene expression of npy (neuropeptide Y) and avt (Arginine vasotocin) in the head, while potential long-term effects (i.e., programming) were evaluated on intermediary metabolism later in life (in juveniles). Our findings indicate a direct effect regarding gene expression in the head only for F1, with higher avt mRNA level in fasted larved compared to controls. The early starvation periods had no long-term effect on growth performance (body weight and body length). Regarding intermediary metabolism, we analyzed related key plasma metabolites which reflect the intermediary metabolism: no differences for glucose, triglycerides, and free fatty acids in the plasma were observed in juveniles irrespective of the three early starvation stimuli. As programming is mainly linked to molecular mechanisms, we then studied hepatic mRNA levels for 23 key actors of glucose, lipid, amino acid, and energy metabolism. For many of the metabolic genes, there was no impact of early starvation in juveniles, except for three genes involved in glucose metabolism (glut2-glucose transporter and pk-pyruvate kinase) and lipid metabolism (acly-ATP citrate lyase) which were higher in F2 compared to control. Together, these results highlight that starvation between 81 to 87 dph may have more long-term impact, suggesting the existence of a developmental window for programming by starvation. In conclusion, European seabass appeared to be resilient to early starvation during larvae stages without drastic impacts on intermediary metabolism later in life.

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.

A journey from speech to dance through the field of oxytocin.

In this article, I am going through my scientific and personal journey using my work on oxytocin as a compass. I recount how my scientific questions were shaped over the years, and how I studied them through the lens of different fields ranging from linguistics and neuroscience to comparative and population genomics in a wide range of vertebrate species. I explain how my evolutionary findings and proposal for a universal gene nomenclature in the oxytocin-vasotocin ligand and receptor families have impacted relevant fields, and how my studies in the oxytocin and vasotocin system in songbirds, humans and non-human primates have led me to now be testing intranasal oxytocin as a candidate treatment for speech deficits. I also discuss my projects on the neurobiology of dance and where oxytocin fits in the picture of studying speech and dance in parallel. Lastly, I briefly communicate the challenges I have been facing as a woman and an international scholar in science and academia, and my personal ways to overcome them.

Urban and rural male song sparrows (Melospiza melodia) differ in territorial aggression and activation of vasotocin neurons in response to song challenge.

When living in urban habitats, 'urban adapter' species often show greater aggression toward conspecifics, yet we do not understand the mechanisms underlying this behavioral shift. The neuroendocrine system regulates socio-sexual behaviors including aggression and thus could mediate behavioral responses to urbanization. Indeed, urban male song sparrows (Melospiza melodia), which are more territorially aggressive, also have greater abundance of the neuropeptide arginine vasotocin (AVT) in nodes of the brain social behavior network. Higher abundance of AVT could reflect long-term synthesis that underlies baseline territoriality or short-term changes that regulate aggression in response to social challenge. To begin to resolve the timeframe over which the AVT system contributes to habitat differences in aggression we used immediate early gene co-expression as a measure of the activation of AVT neurons. We compared Fos induction in AVT-immunoreactive neurons of the bed nucleus of the stria terminalis (BSTm) and paraventricular nucleus of the hypothalamus (PVN) between urban and rural male song sparrows in response to a short (< 5 min.) or long (> 30 min.) song playback to simulate territorial intrusion by another male. We found that urban males had a higher proportion of Fos-positive AVT neurons in both brain regions compared to rural males, regardless of the duration of song playback. Our results suggest that AVT neurons remain activated in urban males, independently of the duration of social challenge. These findings that Fos induction in AVT neurons differs between rural and urban male song sparrows further implicate this system in regulating behavioral responses to urbanization.

Vasotocin expression is associated with social preference development of the medaka fish.

The neurohypophysial peptide arginine vasotocin (VT) and its mammalian ortholog, arginine vasopressin, function in physiological and behavioral events. These functions have been identified in neuroendocrinological studies using adult animals; however, there is little information on whether VT is associated with social behavior development in fish. Here, we examined social preference in medaka fish of various ages and investigated how VT expression changes during development. The 1-, 2-, 4-, and 8-week post-hatching (wph) larvae, juveniles, and 5-month-old adults were individually introduced to the grouped fish of each age group, and the social preference index (SPI) was compared among ages based on the time spent in the interaction zone near the grouped fish in a test tank. The SPI was significantly higher in the 4-wph larvae, 8-wph juveniles, and adult fish than in the 1- and 2-wph larvae. VT expression increased with age from 1 to 4 wph. Similarly, the expression was high in 4-wph, 8-wph, and adult fish. Furthermore, it was also found that the SPI and the VT expression decreased in the socially isolated larva during the 4 weeks after hatching compared to the levels in the grouped 4-wph larvae. These findings suggest that social preference develops with age and that conspecifics are necessary for social development in medaka larvae. Furthermore, our results suggest that VT is associated with the development of social preferences in medaka.

Characterization of an Aplysia vasotocin signaling system and actions of posttranslational modifications and individual residues of the ligand on receptor activity.

The vasopressin/oxytocin signaling system is present in both protostomes and deuterostomes and plays various physiological roles. Although there were reports for both vasopressin-like peptides and receptors in mollusc Lymnaea and Octopus, no precursor or receptors have been described in mollusc Aplysia. Here, through bioinformatics, molecular and cellular biology, we identified both the precursor and two receptors for Aplysia vasopressin-like peptide, which we named Aplysia vasotocin (apVT). The precursor provides evidence for the exact sequence of apVT, which is identical to conopressin G from cone snail venom, and contains 9 amino acids, with two cysteines at position 1 and 6, similar to nearly all vasopressin-like peptides. Through inositol monophosphate (IP1) accumulation assay, we demonstrated that two of the three putative receptors we cloned from Aplysia cDNA are true receptors for apVT. We named the two receptors as apVTR1 and apVTR2. We then determined the roles of post-translational modifications (PTMs) of apVT, i.e., the disulfide bond between two cysteines and the C-terminal amidation on receptor activity. Both the disulfide bond and amidation were critical for the activation of the two receptors. Cross-activity with conopressin S, annetocin from an annelid, and vertebrate oxytocin showed that although all three ligands can activate both receptors, the potency of these peptides differed depending on their residue variations from apVT. We, therefore, tested the roles of each residue through alanine substitution and found that each substitution could reduce the potency of the peptide analog, and substitution of the residues within the disulfide bond tended to have a larger impact on receptor activity than the substitution of those outside the bond. Moreover, the two receptors had different sensitivities to the PTMs and single residue substitutions. Thus, we have characterized the Aplysia vasotocin signaling system and showed how the PTMs and individual residues in the ligand contributed to receptor activity.

How inversion variants can shape neural circuitry: Insights from the three-morph mating tactics of ruffs.

Behavior polymorphisms underlying alternative mating tactics can evolve due to genetic inversions, especially when inversions capture sets of genes involved in hormonal regulation. In the three-morph system of the ruff (Calidris pugnax), two alternative morphs (Satellites and Faeders) with distinct behaviors and low circulating testosterone are genetically determined by an inverted region on an autosomal chromosome. Here, we discuss recent findings on the ruff and present novel insights into how an inversion that poses drastic constraints on testosterone production might lead to morph-specific differences in brain areas that regulate social behavior. A gene responsible for converting testosterone to androstenedione (HSD17B2) is located inside the inverted region and is a promising candidate. We identify a single missense mutation in the HSD17B2 gene of inverted alleles that is responsible for a 350-500% increase in testosterone to androstenedione conversion, when mutated in the human HSD17B2 protein. We discuss new evidence of morph differences in neural HSD17B2 expression in embryos and circulating androgens in sexually-immature juveniles. We suggest processes that shape morph differences in behavior likely begin early in ontogeny. We propose that the organization of behaviorally relevant neuron cell types that are canonically sexually dimorphic, such as subpopulations of aromatase and vasotocin neurons, should be particularly affected due to the life-long condition of low circulating testosterone in inversion morphs. We further emphasize how HSD17B2 catalytic activity extends beyond androgens, and includes estradiol oxidation into estrone and progesterone synthesis. Lastly, we underscore dimerization of HSD17B2 as an additional layer of complexity that merits consideration.

Reproductive roles of the vasopressin/oxytocin neuropeptide family in teleost fishes.

The vertebrate nonapeptide families arginine vasopressin (AVP) and oxytocin (OXT) are considered to have evolved from a single vasopressin-like peptide present in invertebrates and termed arginine vasotocin in early vertebrate evolution. Unprecedented genome sequence availability has more recently allowed new insight into the evolution of nonapeptides and especially their receptor families in the context of whole genome duplications. In bony fish, nonapeptide homologues of AVP termed arginine vasotocin (Avp) and an OXT family peptide (Oxt) originally termed isotocin have been characterized. While reproductive roles of both nonapeptide families have historically been studied in several vertebrates, their roles in teleost reproduction remain much less understood. Taking advantage of novel genome resources and associated technological advances such as genetic modifications in fish models, we here critically review the current state of knowledge regarding the roles of nonapeptide systems in teleost reproduction. We further discuss sources of plasticity of the conserved nonapeptide systems in the context of diverse reproductive phenotypes observed in teleost fishes. Given the dual roles of preoptic area (POA) synthesized Avp and Oxt as neuromodulators and endocrine/paracrine factors, we focus on known roles of both peptides on reproductive behaviour and the regulation of the hypothalamic-pituitary-gonadal axis. Emphasis is placed on the identification of a gonadal nonapeptide system that plays critical roles in both steroidogenesis and gamete maturation. We conclude by highlighting key research gaps including a call for translational studies linking new mechanistic understanding of nonapeptide regulated physiology in the context of aquaculture, conservation biology and ecotoxicology.

Identification of neurohypophysial hormones and the role of VT in the parturition of pregnant seahorses (Hippocampus erectus).

Neurohypophysial hormones regulate the reproductive behavior of teleosts; however, their role in the gestation and parturition of ovoviviparous fishes with male pregnancy (syngnathids) remains to be demonstrated. In the present study, the complementary DNA (cDNA) sequences of arginine vasotocin (VT) and isotocin (IT) from the lined seahorse (Hippocampus erectus) were cloned and identified. We observed that the mature core peptides of seahorse VT and IT were conserved among teleosts. In the phylogenic tree, seahorse VT and IT were clustered independently with teleost VT and IT. The tissue distribution patterns of VT and IT were similar, and both were highly expressed in the brain, gills, and gonads. Interestingly, they were also expressed to some extent in the brood pouch. In situ hybridization revealed that VT and IT messenger RNA (mRNA) signals in the brain were mainly located in the preoptic area region of the hypothalamus. Intraperitoneal administration of the VT core peptide to pregnant seahorses induced premature parturition, stimulated gonadotropin release, increased serum estrogen levels, and decreased prolactin secretion. Moreover, VT injection upregulated the mRNA expression of the membrane estrogen receptor in the brood pouch. In summary, neurohypophysial hormones promote premature parturition by regulating estrogen synthesis through the hypothalamus-pituitary-gonad axis.

Oxytocin and vasotocin receptor variation and the evolution of human prosociality.

Modern human lifestyle strongly depends on complex social traits like empathy, tolerance and cooperation. These diverse facets of social cognition have been associated with variation in the oxytocin receptor (OTR) and its sister genes, the vasotocin/vasopressin receptors (VTR1A/AVPR1A and AVPR1B/VTR1B). Here, we compared the available genomic sequences of these receptors between modern humans, archaic humans, and 12 non-human primate species, and identified sites that show heterozygous variation in modern humans and archaic humans distinct from variation in other primates, and for which we could find association studies with clinical implications. On these sites, we performed a range of analyses (variant clustering, pathogenicity prediction, regulation, linkage disequilibrium frequency), and reviewed the literature on selection data in different modern-human populations. We found five sites with modern human specific variation, where the modern human allele is the major allele in the global population (OTR: rs1042778, rs237885, rs6770632; VTR1A: rs10877969; VTR1B: rs33985287). Among them, variation in the OTR-rs6770632 site was predicted to be the most functional. Two alleles (OTR: rs59190448 and rs237888) present only in modern humans and archaic humans were putatively under positive selection in modern humans, with rs237888 predicted to be a highly functional site. Three sites showed convergent evolution between modern humans and bonobos (OTR: rs2228485 and rs237897; VTR1A: rs1042615), with OTR-rs2228485 ranking highly in terms of functionality and reported to be under balancing selection in modern humans (Schaschl, 2015) [1]. Our findings have implications for understanding hominid prosociality, as well as the similarities between modern human and bonobo social behavior.

Neuroendocrine Regulation of Plasma Cortisol Levels During Smoltification and Seawater Acclimation of Atlantic Salmon.

Diadromous fishes undergo dramatic changes in osmoregulatory capacity in preparation for migration between freshwater and seawater. One of the primary hormones involved in coordinating these changes is the glucocorticoid hormone, cortisol. In Atlantic salmon (Salmo salar), cortisol levels increase during the spring smoltification period prior to seawater migration; however, the neuroendocrine factors responsible for regulating the hypothalamic-pituitary-interrenal (HPI) axis and plasma cortisol levels during smoltification remain unclear. Therefore, we evaluated seasonal changes in circulating levels of cortisol and its primary secretagogue-adrenocorticotropic hormone (ACTH)-as well as transcript abundance of the major regulators of HPI axis activity in the preoptic area, hypothalamus, and pituitary between migratory smolts and pre-migratory parr. Smolts exhibited higher plasma cortisol levels compared to parr across all timepoints but circulating ACTH levels were only elevated in May. Transcript abundance of preoptic area corticotropin-releasing factor b1 and arginine vasotocin were ~2-fold higher in smolts compared to parr in February through May. Smolts also had ~7-fold greater hypothalamic transcript abundance of urotensin 1 (uts-1a) compared to parr in May through July. When transferred to seawater during peak smolting in May smolts rapidly upregulated hypothalamic uts-1a transcript levels within 24 h, while parr only transiently upregulated uts-1a 96 h post-transfer. In situ hybridization revealed that uts-1a is highly abundant in the lateral tuberal nucleus (NLT) of the hypothalamus, consistent with a role in regulating the HPI axis. Overall, our results highlight the complex, multifactorial regulation of cortisol and provide novel insight into the neuroendocrine mechanisms controlling osmoregulation in teleosts.

Maternal exposure to bisphenol S induces neuropeptide signaling dysfunction and oxidative stress in the brain, and abnormal social behaviors in zebrafish (Danio rerio) offspring.

Recent studies show that bisphenol S (BPS) induces multiple adverse effects in exposed organisms; however, the maternal effects of BPS exposure remain poorly understood. Here, we expose adult female zebrafish to environmentally relevant concentrations of BPS (0, 1, 10, 30 µg/L) and 1 µg/L of 17-ß-estradiol (E2) as a positive control for 60 days. Females were then paired with BPS-unexposed males and their offspring were raised in control water for 6 months. Maternal exposure to BPS was found to alter social behavior and anxiety response in a dose-specific manner in male offspring. Group preferences and social cohesion were significantly reduced by maternal exposure to 1 and 10 µg/L BPS, respectively. Additionally, maternal exposure to 1 and 30 µg/L BPS and E2 decreased offspring stress responses during the novel tank test. The impaired social behavior was associated with elevated arginine-vasotocin (AVT) level as well as with the altered expression of genes involved in AVT signaling pathway (AVT, avpr1aa) and enzymatic antioxidant genes (cat and Mn-sod) in the brain. Collectively, these results suggest that maternal exposure to environmentally relevant concentrations of BPS alters social behavior in zebrafish offspring, which is likely mediated by oxidative stress and disruption of neuropeptide signaling pathways in the brain.

Signaler's Vasotocin Alters the Relationship between the Responder's Forebrain Catecholamines and Communication Behavior in Lizards (Anolis carolinensis).

Dynamic fluctuations in the distribution of catecholamines across the brain modulate the responsiveness of vertebrates to social stimuli. Previous work demonstrates that green anoles (Anolis carolinensis) increase chemosensory behavior in response to males treated with exogenous arginine vasotocin (AVT), but the neurochemical mechanisms underlying this behavioral shift remains unclear. Since central catecholamine systems, including dopamine, rapidly activate in response to social stimuli, we tested whether exogenous AVT in signalers (stimulus animals) impacts catecholamine concentrations in the forebrain (where olfactory and visual information are integrated and processed) of untreated lizard responders. We also tested whether AVT influences the relationship between forebrain catecholamine concentrations and communication behavior in untreated receivers. We measured global catecholamine (dopamine = DA, epinephrine = Epi, and norepinephrine = NE) concentrations in the forebrain of untreated responders using high-performance liquid chromatography-mass spectrometry following either a 30-min social interaction with a stimulus male or a period of social isolation. Stimulus males were injected with exogenous AVT or vehicle saline (SAL). We found that global DA, but not Epi or NE, concentrations were elevated in lizards responding to SAL-males relative to isolated lizards. Lizards interacting with AVT-males had DA, Epi and NE concentrations that were not significantly different from SAL or isolated groups. For behavior, we found a significant effect of social treatment (AVT vs. SAL) on the relationships between (1) DA concentrations and the motivation to perform a chemical display (latency to tongue flick) and (2) Epi concentrations and time spent displaying mostly green body coloration. We also found a significant negative correlation between DA concentrations and the latency to perform a visual display but found no effect of social treatment on this relationship. These data suggest that catecholamine concentrations in the forebrain of untreated responders are associated with chemical and visual communication in lizards and that signaler AVT alters this relationship for some, but not all, aspects of social communication.

Air sac and gill vasotocin receptor gene expression in the air-breathing catfish Heteropneustes fossilis exposed to water and air deprivation conditions.

Heteropneustes fossilis is a facultative air-breathing freshwater catfish and inhabits ponds, ditches, swamps, marshes and rivers that dry up in summers. It possesses a pair of unique tubular accessory respiratory organ (air sac), which is a modification of the gill chamber and enables it to live in water-air transition zones. In the catfish, three vasotocin (Vt) receptor gene paralogs viz., v1a1, v1a2 and v2a were identified for Vt actions. In the present study, the receptor gene transcripts were localized in the gill and air sac by in situ hybridization, and their expression levels in relation to water and air deprivation conditions were investigated by quantitative RT-PCR. The catfish were exposed to 1 h and 2 h in gonad inactive (resting) and gonad active (prespawning) phases. The gene paralogs showed overlapping distribution in the respiratory epithelium of primary and secondary lamellae of gills and reduced lamellae of the air sacs. In water deprivation (forced aerial mode of respiration) experiment, v2a expression showed a high fold increase in the air sac, which was unchanged or inhibited in the gill. Both v1a1 and v1a2 expression was significantly upregulated in the air sac but showed varied responses in the gill. The gill v1a1 expression was unchanged in the resting phase and modestly upregulated in the prespawning phase. The gill v1a2 expression was modestly upregulated at 1 h in both phases but unchanged at 2 h. In the air deprivation experiment (forced aquatic respiration), the v2a expression in the air sac was inhibited except for a mild stimulation at 1 h in the prespawning phase. In the gill, the v2a expression was stimulated with a steep upregulation at 2 h in the prespawning phase. Both v1a1 and v1a2 expression was significantly high in the gill but only modestly increased or unchanged in the air sac. The expression patterns point to a functional distinction; the V2 type receptor expression was higher in the air sac during forced aerial respiration, and the V1 type receptor expression was highly prominent in the gill during forced aquatic respiration. Water and air deprivation treatments caused a significant increase in plasma cortisol level, and the stimulation was higher in the water deprivation fish in the resting phase but equally prominent in the water and air deprivation groups in the prespawning phase. The results indicate that the changes in the expression patterns of Vt receptor genes may be a sequel to stress (hypoxic, metabolic and osmotic), and both Vt and cortisol may interact to counter the stress responses. This study shows that Vt has a new role in the control of air sac functions.

Neuropeptidergic control of neurosteroids biosynthesis.

Neurosteroids are steroids synthesized within the central nervous system either from cholesterol or by metabolic reactions of circulating steroid hormone precursors. It has been suggested that neurosteroids exert pleiotropic activities within the central nervous system, such as organization and activation of the central nervous system and behavioral regulation. It is also increasingly becoming clear that neuropeptides exert pleiotropic activities within the central nervous system, such as modulation of neuronal functions and regulation of behavior, besides traditional neuroendocrinological functions. It was hypothesized that some of the physiological functions of neuropeptides acting within the central nervous system may be through the regulation of neurosteroids biosynthesis. Various neuropeptides reviewed in this study possibly regulate neurosteroids biosynthesis by controlling the activities of enzymes that catalyze the production of neurosteroids. It is now required to thoroughly investigate the neuropeptidergic control mechanisms of neurosteroids biosynthesis to characterize the physiological significance of this new neuroendocrinological phenomenon.

Aggressive but not reproductive boldness in male green anole lizards correlates with baseline vasopressin activity.

Across species, individuals within a population differ in their level of boldness in social encounters with conspecifics. This boldness phenotype is often stable across both time and social context (e.g., reproductive versus agonistic encounters). Various neural and hormonal mechanisms have been suggested as underlying these stable phenotypic differences, which are often also described as syndromes, personalities, and coping styles. Most studies examining the neuroendocrine mechanisms associated with boldness examine subjects after they have engaged in a social interaction, whereas baseline neural activity that may predispose behavioral variation is understudied. The present study tests the hypotheses that physical characteristics, steroid hormone levels, and baseline variation in Ile3-vasopressin (VP, a.k.a., Arg8-vasotocin) signaling predispose boldness during social encounters. Boldness in agonistic and reproductive contexts was extensively quantified in male green anole lizards (Anolis carolinensis), an established research organism for social behavior research that provides a crucial comparison group to investigations of birds and mammals. We found high stability of boldness across time, and between agonistic and reproductive contexts. Next, immunofluorescence was used to colocalize VP neurons with phosphorylated ribosomal protein S6 (pS6), a proxy marker of neural activity. Vasopressin-pS6 colocalization within the paraventricular and supraoptic nuclei of the hypothalamus was inversely correlated with boldness of aggressive behaviors, but not of reproductive behaviors. Our findings suggest that baseline vasopressin release, rather than solely context-dependent release, plays a role in predisposing individuals toward stable levels of displayed aggression toward conspecifics by inhibiting behavioral output in these contexts.