Excitatory action of the bird antidiuretic hormone vasotocin on neurons in the subfornical organ

The responsiveness of spontaneously active neurons in the subfornical organ (SFO) of adult ducks to angiotensin II (ANGII) and the bird specific anti-diuretic hormone, arginine vasotocin (AVT), the analog of the mammalian arginine vasopressin (AVP), were investigated in brain slices with extracellular recording technique. 65% (n = 66) of the neurons increased their activity after superfusion with ANGII, the rest were unresponsive. Application of AVT activated 52% (n = 68) of the investigated neurons and like ANGII never caused an inhibition of the spontaneously active SFO neurons. A close correlation exists between the ANGII and AVT sensitivity of duck SFO neurons, because 29 out of 33 neurons were excited by AVT as well as ANGII. The relatively weak antagonistic effect of the V₁-type receptor antagonist Pmp-Tyr (Me)-Arg⁸-vasopressin on the AVT induced excitation suggests a different pharmacology of the bird AVT receptor as compared to the mammalian AVP receptor. The excitatory response of ANGII and AVT on the very same neurons suggest a similar function of both peptides on SFO mediated effects in vivo, such as an increase in water intake. However, peripheral AVT concentrations, unlike ANGII concentrations in the blood are not high enough to activate SFO neurons from the blood side of the blood brain barrier. Therefore AVT is presumably released from synapses of neurons originating within or projecting to the SFO. The identity of the ANGII and AVT reactive neurons suggests that synaptically released AVT should facilitate SFO mediated drinking.Abbreviations _a CSF artificial cerebrospinal fluid - ANGII angiotensin II - AVT arginine vasotocin - AVP arginine vasopressin - ADH antidiuretic hormone - SFO subfornical organ - AVP _4–9 arginine-vasopressin fragment 4–9 - BBB blood-brain barrier     

The involvement of arginine vasotocin in the maturation of the kitten brain

In order to investigate the effects of the nonapeptide hormone arginine vasotocin (AVT) on the maturation of the brain, the following developmental data were tabulated between 5 and 21 days of postnatal life, in kittens, after the daily intraperitoneal administration of 10^?6 mg synthetic AVT: sleep, daily increase of body weight and locomotor, and investigative activities (LIA). Likewise, the day of the eye opening was noted and the brain weight as well as the total lipid levels within the brain in the day of sacrifice (21 days of age) were measured. The daily administration of AVT induced: (1) an increase of the total amount as well as of the intensity of active sleep (AS); (2) a decrease of the LIA; (3) a decrease of the total lipid levels within the brain and (4) a retardation of the eye opening. These effects appeared to be specific because neither arginine vasopressin, nor oxytocin, in the same doses (10^?6 mg), were able to reproduce the effects of AVT. The present results demonstrate that chronic administration of AVT is associated with a retardation of brain maturation. Whether AVT induces this effect by an unique mechanism or there are different mechanisms for the reported developmental data that were affected by AVT, is unknown. However, the present results suggest that the pineal gland, by its effector within the brain, AVT, is involved by an inhibitory pathway in the brain maturation and the hypothesis is advanced that the decrease of AVT content of fetal and neonatal brain could represent a hormonal signal for triggering the beginning of the brain maturation phenomena.     

Arginine vasotocin (AVT) and isotocin (IT) in fish brain: diurnal and seasonal variations

An HPLC assay with solid-phase extraction and fluorescence derivatization was developed for measurement of arginine vasotocin (AVT) and isotocin (IT) in the neural tissues of fish. The efficiency and usefulness of the method have been verified in experiments by examination of peptides concentrations in brains of three fish species. The day-night changes in neuropeptides levels have been studied in brains of adult sea bream (Sparus aurata) and juvenile Atlantic salmon (Salmo salar). Seasonal fluctuations have been investigated in brains of three-spined sticklebacks (Gasterosteus aculeatus). The AVT and IT biosynthesis in brain seems to be controlled independently and probably each neuropeptide plays a different role in a circadian time-keeping system and an endocrine calendar in fish.     

A neurobehavioral model for rapid actions of corticosterone on sensorimotor integration.

Stress-induced corticosterone (CORT) secretion that causes a rapid blockade of courtship clasping by male roughskin newts (Taricha granulosa) is mediated by a specific neuronal membrane receptor for CORT. Amplectic clasping, which can be triggered by pressure on the ventral body surface and cloaca, is controlled by the influence of medullary neurons on the spinal cord. Using clasping as a simple neurobehavioral model, we have focused our analysis of CORT effects on clasping by examining the steroid's effects on neurophysiological properties of medullary neurons, especially medullary reticulospinal neurons, the principal output cells from the brain to the spinal cord. Systemic CORT caused, within 3 min of injection, diverse reductions in reticulospinal neuron excitability. Another rapid CORT effect on medullary neurons was to depress responsiveness to pressure on the cloaca. Experiments with chronically implanted, freely moving newts revealed that the rapid CORT effects are quite specific to neural processes related to clasping. CORT injections rapidly blocked clasping in response to cloacal stimuli and concurrently depressed neuronal responses to cloacal pressure and firing associated with clasping. Activity of reticulospinal neurons was often associated with nonclasping movements and this activity was rarely altered by CORT. Thus, CORT mainly affected aspects of neuronal function related to clasping. In other neurophysiological experiments, we found that the neuropeptides vasotocin and corticotropin-releasing hormone modified the neural effects of CORT. Prior exposure of medullary neurons to either of these neuropeptides caused systemic CORT administration to rapidly potentiate neuronal responses to cloacal stimuli, indicating that the direction and potency of CORT effects depend critically on the prevailing neuroendocrine state of the brain.     

Arginine vasotocin concentrations in the supraoptic nucleus of the lizard Anolis carolinensis are associated with reproductive state but not oviposition.

Arginine vasotocin (AVT) is a neuropeptide involved in reproductive function in many nonmammalian vertebrates. We determined brain and plasma AVT concentrations during the estrous cycle and oviposition in the lizard Anolis carolinensis. There were no differences in AVT concentrations in the plasma or any brain region during the ovipositional sequence. However, we found that females with an egg in each oviduct and a large pre-ovulatory follicle (diameter > 4.5 mm) in one-ovary had significantly higher AVT concentrations in the supraoptic nucleus (SON) of the hypothalamus than did females with small pre-ovulatory follicles in both ovaries. In a second study, females with an egg in each oviduct and a large pre-ovulatory follicle had significantly greater AVT concentrations in the SON than females with only one oviductal egg and a large pre-ovulatory follicle or females with an egg in each oviduct and a small pre-ovulatory follicle in each ovary. Concentrations of AVT in other brain regions and in the plasma did not differ among these groups. Changes in steroid profiles during estrous and/or direct neural communication between the uterus, ovary, and brain may account for the changes in AVT concentrations seen in the supraoptic nucleus during the estrous cycle of Anolis carolinensis.     

Interactions between vasotocin and other corticotropic factors on the frog adrenal gland

The adrenocortical cells of the amphibian interrenal (adrenal) gland are controlled by multiple factors including neuropeptides and classical neurotransmitters. In particular, it has recently been shown that vasotocin (AVT), the amphibian counterpart of vasopressin, is a potent stimulator of frog corticosteroidogenesis. In the present study, we have investigated the possible interactions between AVT and other regulatory factors on frog interrenal tissue. When AVT (10⁻⁹ M) and serotonin (10⁻⁶ M) were infused together, a strict addition of the individual effects was observed. Similar results were obtained with concomitant infusion of AVT and vasoactive intestinal peptide or AVT and ACTH. In contrast, when AVT (10⁻⁹ M) and acetylcholine (5 × 10⁻⁵ M) were added together, the increase in corticosteroid secretion was less than additive. Dopamine induced a significant reduction of AVT-evoked stimulation of corticosterone production. These results indicate that regulatory peptides or classical neurotransmitters which participate in the control of adrenal steroidogenesis may interact on their target cell to modulate the activity of their congeners.     

New insights into neuropeptide modulation of aggression: field studies of arginine vasotocin in a territorial tropical damselfish

The neuropeptides arginine vasotocin (AVT) and arginine vasopressin are key modulators of affiliation and aggression among non-mammalian and mammalian vertebrates, respectively. Here, we explored AVT's effect on aggression in a wild population of beaugregory damselfish, Stegastes leucostictus, a highly territorial species. Aggression by territorial males towards 'intruders' (bottled fishes) was assessed before and after each male received intramuscular injections of either AVT, Manning compound (an AVT V1a receptor antagonist), isotocin (the teleost homologue of mammalian oxytocin differing from AVT by two amino acids) or saline (vehicle control). Compared to saline controls, AVT and Manning increased and decreased aggression, respectively, while isotocin had no effect. Response selectivity was further established in a dose-response study that revealed an inverted U-shaped function. Compared to saline controls, aggression levels for low and high AVT doses were similar, while medium dose treatments were significantly greater. This type of behavioural response, the first that we know of for a vertebrate neuropeptide, could depend on the binding of AVT to both V1-type and other AVT or non-AVT receptors. The pattern revealed here for damselfish may be symptomatic of species- and context-dependent specificity of AVT's modulation of aggression across teleosts, as is currently proposed for tetrapods.     

Arginine vasotocin induces sexual behavior of newts by acting on cells in the brain

To investigate whether arginine vasotocin (AVT) acts on target cells in the brain of Taricha granulosa (a urodele amphibian), the behavioral effects of intracerebroventricular (ICV) and intraperitoneal (IP) injections of AVT were compared. Male newts exhibited the greatest sexual activity (amplectic clasping) following an ICV injection of 0.1 μg AVT. Another study showed that nanogram quantities of AVT, administered ICV, stimulated the behavior. An ICV injection of an antagonist to arginine vasopressin, d(CH₂)₅Tyr(Me)AVP, or an anti-AVT immune serum significantly inhibited the sexual behavior. Intracranial implants of 17β-estradiol (E₂) or 5α-dihydrotestosterone (DHT) in castrated males maintained the behavioral response to an injection of AVT. Another study found that an IP injection of DHT or E₂ did not increase the incidence of newt sexual behavior during the 8 hours following the injection.     

Expression of arginine vasotocin receptors in the developing zebrafish CNS

Vasotocin/vasopressin is a neuropeptide that regulates social and reproductive behaviors in a variety of animals including fish. Arginine vasotocin (AVT) is expressed by cells in the ventral hypothalamic and preoptic areas in the diencephalon during embryogenesis in zebrafish suggesting that vasotocin might mediate other functions within the CNS prior to the development of social and reproductive behaviors. In order to examine potential early roles for vasotocin we cloned two zebrafish vasotocin receptors homologous to AVPR_1a. The receptors are expressed primarily in the CNS in similar but generally non-overlapping patterns. Both receptors are expressed in the forebrain, midbrain and hindbrain by larval stage. Of note, AVTR_1a-expressing neurons in the hindbrain appear to be contacted by the axons of preoptic neurons in the forebrain that include avt+ neurons and sensory axons in the lateral longitudinal fasciculus (LLF). Furthermore, AVTR_1a-expressing hindbrain neurons extend axons into the medial longitudinal fasciculus (MLF) that contains axons of many neurons thought to be involved in locomotor responses to sensory stimulation. One hypothesis consistent with this anatomy is that AVT signaling mediates or gates sensory input to motor circuits in the hindbrain and spinal cord.     

Expression of arginine vasotocin receptors in the developing zebrafish CNS

Vasotocin/vasopressin is a neuropeptide that regulates social and reproductive behaviors in a variety of animals including fish. Arginine vasotocin (AVT) is expressed by cells in the ventral hypothalamic and preoptic areas in the diencephalon during embryogenesis in zebrafish suggesting that vasotocin might mediate other functions within the CNS prior to the development of social and reproductive behaviors. In order to examine potential early roles for vasotocin we cloned two zebrafish vasotocin receptors homologous to AVPR_1a. The receptors are expressed primarily in the CNS in similar but generally non-overlapping patterns. Both receptors are expressed in the forebrain, midbrain and hindbrain by larval stage. Of note, AVTR_1a-expressing neurons in the hindbrain appear to be contacted by the axons of preoptic neurons in the forebrain that include avt+ neurons and sensory axons in the lateral longitudinal fasciculus (LLF). Furthermore, AVTR_1a-expressing hindbrain neurons extend axons into the medial longitudinal fasciculus (MLF) that contains axons of many neurons thought to be involved in locomotor responses to sensory stimulation. One hypothesis consistent with this anatomy is that AVT signaling mediates or gates sensory input to motor circuits in the hindbrain and spinal cord.     

Forebrain arginine vasotocin correlates of alternative mating strategies in cricket frogs.

In cricket frogs, Acris crepitans, sexually active males can switch between calling and noncalling (satellite) mating strategies and injections of the neuropeptide arginine vasotocin (AVT) stimulate calling behavior. We report here that this behavioral variation of animals under field conditions is associated with variations in AVT-immunoreactive (AVT-ir) staining in distinct brain nuclei. In both calling and satellite males, one AVT-ir brain region was found in a continuous string of cells between the medial amygdala and the nucleus accumbens (ACC). Satellite males possessed significantly more AVT-ir staining in the brain (cells and fibers) than calling males at the level of the ACC, although not in the medial amygdala. This difference in AVT-ir staining in the ACC can, in part, be explained by differences in the density of staining within the cells and in cell size. In addition, satellite males had significantly higher AVT-ir staining in the fibers medial to the ACC than calling males. Because other studies have demonstrated that AVT stimulates calling behavior, a plausible hypothesis is that calling males are releasing more AVT from neurons in the ACC, depleting reserves within the cells, and that the released AVT elicits calling behavior. AVT immunoreactivity levels are also higher in the ACC in both calling and satellite males than in female cricket frogs, which do not call. Satellite males may therefore have AVT reserves that might allow them to call depending on the social conditions.     

Effect of vasotocin on locomotor activity in bullfrogs varies with developmental stage and sex

Although neurohypophysial peptides are present in many regions of the developing and adult bullfrog (Rana catesbeiana) brain, the function of these peptides remains unclear. To investigate possible behavioral actions, we examined locomotor activity following peptide injection in bullfrogs at various developmental stages. An intraperitoneal (ip) injection of arginine vasotocin (AVT) in tadpoles (stages V, X, or XVII) produced an immediate and dose-dependent inhibition of locomotor activity. On the other hand, AVT stimulated activity when administered ip to juvenile or adult female bullfrogs, but did not influence activity in juvenile or adult males. The minimum effective dose of AVT, when injected directly into the brain of tadpoles, was 100-fold less than that observed when injected ip, suggesting a central nervous system site of action for this peptide. A vasopressin receptor antagonist (d(CH2)5[Tyr(Me)2]AVP administered ip or icv) significantly increased locomotor activity in tadpoles, compared to controls. Oxytocin, vasopressin, and AVP4-9 inhibited activity in tadpoles while mesotocin, des Gly(NH2)AVP, and pressinoic acid had no significant effect. Injection of PGF2 alpha also significantly decreased activity levels in tadpoles. However, pretreatment of tadpoles with indomethacin, a prostaglandin synthesis inhibitor, did not prevent the behavioral effects of AVT, suggesting that prostaglandin synthesis is not required for this response. In summary, AVT influenced locomotor activity in bullfrog tadpoles and female frogs. This effect shifted during development from an inhibitory action in tadpoles to a stimulatory effect in metamorphosed female frogs. The effect of AVT on juvenile and adult frog locomotion was sexually dimorphic, as this peptide altered female behavior but not male behavior.     

Arginine vasotocin regulation of interspecific cooperative behaviour in a cleaner fish

In an interspecific cooperative context, individuals must be prepared to tolerate close interactive proximity to other species but also need to be able to respond to relevant social stimuli in the most appropriate manner. The neuropeptides vasopressin and oxytocin and their non-mammalian homologues have been implicated in the evolution of sociality and in the regulation of social behaviour across vertebrates. However, little is known about the underlying physiological mechanisms of interspecific cooperative interactions. In interspecific cleaning mutualisms, interactions functionally resemble most intraspecific social interactions. Here we provide the first empirical evidence that arginine vasotocin (AVT), a non-mammalian homologue of arginine vasopressin (AVP), plays a critical role as moderator of interspecific behaviour in the best studied and ubiquitous marine cleaning mutualism involving the Indo-Pacific bluestreak cleaner wrasse Labroides dimidiatus. Exogenous administration of AVT caused a substantial decrease of most interspecific cleaning activities, without similarly affecting the expression of conspecific directed behaviour, which suggests a differential effect of AVT on cleaning behaviour and not a general effect on social behaviour. Furthermore, the AVP-V1a receptor antagonist (manning compound) induced a higher likelihood for cleaners to engage in cleaning interactions and also to increase their levels of dishonesty towards clients. The present findings extend the knowledge of neuropeptide effects on social interactions beyond the study of their influence on conspecific social behaviour. Our evidence demonstrates that AVT pathways might play a pivotal role in the regulation of interspecific cooperative behaviour and conspecific social behaviour among stabilized pairs of cleaner fish. Moreover, our results suggest that the role of AVT as a neurochemical regulator of social behaviour may have been co-opted in the evolution of cooperative behaviour in an interspecific context, a hypothesis that is amenable to further testing on the potential direct central mechanism involved.     

Galanin immunoreactivity increased in chicken supraoptic neurons after activation of the vasotocin system at oviposition

The avian arginine vasotocin (AVT) synthesized in the hypothalamic magnocellular neurons and released from the posterior pituitary is known to be involved in the regulation of uterine contractions for oviposition in chickens. However, regulation of AVT synthesis and release within the magnocellular hypothalamus has not been elucidated. Galanin, the oviposition inducing factor in the oviduct of the hen, has been demonstrated to have sexually dimorphic stimulatory action in oxytocin- and vasopressin neurons in the mammalian hypothalamus. In this study, galanin and AVT immunoreactivity was investigated around the time of oviposition in the supraoptic nucleus (SON) to determine if galanin modulates AVT synthesis and/or release. Within SON neurons increased AVT immunoreactivity before oviposition and the decreased AVT immunoreactivity after oviposition implied function-related peptide release. The significantly increased number of galanin neurons co-localizing with AVT immediately after oviposition suggests that galanin is involved in the negative feedback to limit AVT release in the SON. Thus, these data support the idea that AVT in the SON is involved in central regulation of oviposition and that AVT release could be modulated by the neuropeptide galanin.     

Development of vasotocin pathways in the bullfrog brain

The brain of adult bullfrogs (Rana catesbeiana) contains six populations of cells which are immunoreactive for the neurohypophysial peptide arginine vasotocin (AVT). It is unknown when some of these cell populations first appear during development and when the sexual differences in AVT distribution first become apparent. We therefore used immunocytochemistry to examine development of AVT pathways in developing bullfrog tadpoles and in newly metamorphosed froglets of both sexes. AVT-immunoreactive (AVT-ir) cells were already present in the three diencephalic areas (magnocellular preoptic nucleus, suprachiasmatic nucleus and hypothalamus) at stage III (Taylor and Kollros stages), the earliest stage examined. Cell size in the magnocellular nucleus was not bimodally distributed in either tadpoles or froglets. AVT-ir cells in the telencephalic septal nucleus and amygdala did not appear until stage VI. There was no sexual difference in the density of AVT-ir cells or fibers in the amygdala of tadpoles or froglets. Finally, cells in the hindbrain pretrigeminal nucleus appeared much later-after stage XX. Thus, different populations of neurons begin to express AVT at unique times during development. The sexual dimorphism in AVT content observed in the amygdala of adult bullfrogs must appear during juvenile development or at adulthood.     

Galanin immunoreactivity increased in chicken supraoptic neurons after activation of the vasotocin system at oviposition.

The avian arginine vasotocin (AVT) synthesized in the hypothalamic magnocellular neurons and released from the posterior pituitary is known to be involved in the regulation of uterine contractions for oviposition in chickens. However, regulation of AVT synthesis and release within the magnocellular hypothalamus has not been elucidated. Galanin, the oviposition inducing factor in the oviduct of the hen, has been demonstrated to have sexually dimorphic stimulatory action in oxytocin- and vasopressin neurons in the mammalian hypothalamus. In this study, galanin and AVT immunoreactivity was investigated around the time of oviposition in the supraoptic nucleus (SON) to determine if galanin modulates AVT synthesis and/or release. Within SON neurons increased AVT immunoreactivity before oviposition and the decreased AVT immunoreactivity after oviposition implied function-related peptide release. The significantly increased number of galanin neurons co-localizing with AVT immediately after oviposition suggests that galanin is involved in the negative feedback to limit AVT release in the SON. Thus, these data support the idea that AVT in the SON is involved in central regulation of oviposition and that AVT release could be modulated by the neuropeptide galanin.     

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.     

Antipyretic effect of arginine vasotocin in toads

Arginine vasotocin (AVT) is a nonmammalian analog of the mammalian hormone arginine vasopressin (AVP). These peptides are known for their antidiuretic and pressor effects. More recently, AVP has been recognized as an important antipyretic molecule in mammals. However, no information exists about the role of AVT in febrile ectotherms. We tested the hypothesis that AVT is an antipyretic molecule in the toad Bufo paracnemis. Toads equipped with a temperature probe were placed in a thermal gradient, and preferred body temperature was recorded continuously. A behavioral fever was observed after lipopolysaccharide (LPS) was injected systemically (200 microg/kg). Systemically injected AVT (300 pmol/kg) alone caused no significant change in body temperature, but abolished LPS-induced fever. Moreover, a smaller dose of AVT (10 pmol/kg), which did not affect LPS-induced fever when injected peripherally, abolished fever when injected intracerebroventricularly. We therefore conclude that AVT plays an antipyretic role in the central nervous system, by means of behavior, in an ectotherm, a fact consistent with the notion that AVT/AVP elicits antipyresis by reducing the thermoregulatory set point.