Administration Of Arginine Vasotocin Research Articles

Intraperitoneal administration of arginine vasotocin (AVT) induces anorexigenic and anxiogenic actions via the brain V1a receptor-signaling pathway in the tiger puffer, Takifugu rubripes

Arginine vasotocin (AVT) is produced mainly in the hypothalamus and as a neurohypophyseal hormone peripherally regulates water-mineral balance in sub-mammals. In addition, AVT-containing neurons innervate several areas of the brain, and AVT also acts centrally as both an anorexigenic and anxiogenic factor in goldfish. However, it is unclear whether these central effects operate in fish in general. In the present study, therefore, we investigated AVT-like immunoreactivity in the brain of the tiger puffer, a cultured fish with a high market value in Japan and also a representative marine teleost species, focusing particularly on whether AVT affects food intake and psychomotor activity. AVT-like immunoreactivity was distributed higher in the ventral region of the telencephalon, the hypothalamus and midbrain. Intraperitoneal (IP) administration of AVT at 100 pmol g−1 body weight (BW) increased the immunoreactivity of phosphorylated ribosomal proteinS6 (RPS6), a neuronal activation marker, in the telencephalon and diencephalon, decreased food consumption and enhanced thigmotaxis. AVT-induced anorexigenic and anxiogenic actions were blocked by IP co-injection of a V1a receptor (V1aR) antagonist, Manning compound (MC) at 300 pmol g−1 BW. These results suggest that AVT acts as an anorexigenic and anxiogenic factor via the V1aR-signaling pathway in the tiger puffer brain.

Administration of Arginine Vasotocin and modified Isotocin improve artificial propagation and post-spawning survival of female yellow catfish

Low rate of spawning and high percentage of death after artificial propagation are frequently observed in catfish, which do harms to the long-term population stability and genetic breeding programs in aquaculture. In this study, yellow catfish (Pelteobagrus fulvidraco), an important freshwater species in China was used as a research model, since the farmed female yellow catfish had poor reproduction performance and a high death rate after treatment with the traditional exogenous hormones, luteinizing hormone releasing hormone analogues2 (LHRH-A2) and human chorionic gonadotropin (HCG). We tried to investigate the roles of the Arginine Vasotocin (AVT)/ Isotocin (IT) neuropeptide family in reproduction and design an optimal strategy for inducing artificial propagation in yellow catfish. Two copies of pro-avt and pro-it were detected in hypothalamus and ovaries of yellow catfish, and their mRNA levels gradually increased during spring-summer season. Furthermore, the transcript levels of pro-avt and pro-it in hypothalamus significantly increased after injection of LHRH-A2 and HCG. Although AVT could not induce germinal vesicle breakdown (GVBD) in female yellow catfish, administration of AVT significantly stimulated premature ovulation in a dose-dependent manner and induced the expression of ovulation-related genes, ptgs2a and acvr1. Furthermore, there is a significant up-regulation of serum prostaglandin E2 (PGE2) and luteinizing hormone (LH) in female fish after AVT treatment, whereas no difference was observed in follicle stimulating hormone (FSH). Since IT of yellow catfish was insoluble in saline, a rigid peptide segment was added at the end of IT (the modified IT was named IT-M), which could greatly improve its solubility and induce ovulation in female yellow catfish. Subsequently, we demonstrated that adding carp pituitary extraction (CPE) to the second injection of traditional methods could efficiently improve the spawned fish, eggs production, fertilization rate, hatching rate and post-spawning survival of female yellow catfish, despite at a relatively high cost in hormones. We further discovered that IT-M + AVT could substitute for HCG + CPE in the second injection and had high efficiency in artificial propagation, reducing the hormone costs to less than one-third. Altogether, we provide an effective and affordable combination of exogenous hormones to improve reproduction performances and post-spawning survival rate in yellow catfish.

Intracerebroventricular administration of arginine vasotocin (AVT) induces anorexigenesis and anxiety-like behavior in goldfish

Arginine vasotocin (AVT) is known as a neurohypophyseal hormone that regulates water- and mineral-balance in non-mammalian vertebrates. Recent studies revealed that AVT also exerts central effects on behavior. The goldfish has several merits for evaluation of behavioral changes. However, there is few information on the behavioral action of AVT in this species. Here we examined the effects of AVT on food intake and psychomotor activity. AVT was administered intracerebroventricularly at 1, 5 and 10 pmol g−1 body weight (BW). Intracerebroventricular (ICV) administration of AVT at 5 and 10 pmol g−1 BW significantly decreased food intake during 30 min after injection and recovery from anesthesia. The AVT-induced anorexigenic action was attenuated by treatment with the AVT receptor V1aR antagonist Manning compound (MC) at 50 pmol g−1 BW. As the goldfish tends to prefer the lower to the upper area of a tank, we used this preference behavior for assessing psychomotor activity during a 30-min observation period. ICV administration of AVT at 1, 5 and 10 pmol g−1 BW significantly prolonged the time spent in the lower area, but did not affect locomotor activity in the tank at any dose. The action of AVT was similar to that of the central-type benzodiazepine receptor inverse agonist FG-7142 at 10 pmol g−1 BW. AVT-induced anxiety-like behavior was blocked by treatment with MC at 50 pmol g−1 BW. These results indicate that AVT affects food intake and psychophysiological status, and also induces anorexigenic- and anxiogenic-like actions via the V1aR-signaling pathway in the goldfish brain.

Vasotocin increases dominance in the weakly electric fish Brachyhypopomus gauderio

Animals establish social hierarchies through agonistic behavior. The recognition of the own and others social ranks is crucial for animals that live in groups to avoid costly constant conflicts. Weakly electric fish are valuable model systems for the study of agonistic behavior and its neuromodulation, given that they display conspicuous electrocommunication signals that are generated by a very well-known electromotor circuit. Brachyhypopomus gauderio is a gregarious electric fish, presents a polygynous breeding system, morphological and electrophysiological sexual dimorphism during the breeding season, and displays a typical intrasexual reproduction-related aggression. Dominants signal their social status by increasing their electric organ discharge (EOD) rate after an agonistic encounter (electric dominance). Subordinates only occasionally produce transient electric signals (chirps and offs). The hypothalamic neuropeptide arginine-vasotocin (AVT) and its mammalian homologue, arginine- vasopressin (AVP) are key modulators of social behavior across vertebrates. In this study, we focus on the role of AVT on dominance establishment in Brachyhypopomus gauderio by analyzing the effects of pharmacological manipulations of the AVT system in potential dominants. AVT exerts a very specific direct effect restricted only to EOD rate, and is responsible for the electric dominance. Unexpectedly, AVT did not affect the intensity of aggression in either contender. Nor was the time structure affected by AVT administration. We also present two interesting examples of the interplay between contenders by evaluating how AVT modulations, even when directed to one individual, affect the behavior of the dyad as a unit. First, we found that V1a AVT receptor antagonist Manning Compound (MC) induces a reversion in the positive correlation between dominants’ and subordinates’ attack rates, observed in both control and AVT treated dyads, suggesting that an endogenous AVT tone modulates aggressive interactions. Second, we confirmed that AVT administered to dominants induces an increase in the submissive transient electric signals in subordinates.

Effects of peripherally administered urotensin II and arginine vasotocin on the QT interval of the electrocardiogram in trout

The QT interval of the electrocardiogram (ECG) is a measure of the duration of the ventricular depolarization and repolarization. In fish as in human, the QT interval is positively correlated with the RR interval of the ECG, a measure of the cardiac cycle length. Urotensin II (UII) is a neuropeptide that has been highly conserved from fish to human, and UII and its receptor (UT) are expressed in cardiovascular tissues including the heart. Although UII exerts potent cardiovascular actions, its possible effects on the QT interval have never been investigated. The goal of the present study was to provide insight into the potential effect of UII on the QT interval in an established in vivo trout model. To this end, the effects of UII on dorsal aortic blood pressure (PDA), RR, QT intervals and corrected QT (QTc) for RR interval, were investigated after intra-arterial (IA) injection of 5, 50 and 100pmol UII. The effects of UII were compared to those of two structurally UII-related peptides (URPs), URP1 and URP2, and to those of arginine vasotocin (AVT), homolog of the mammalian arginine vasopressin. IA injection of vehicle or 5pmol UII had no effect on the various parameters. At the 50-pmol dose, UII evoked its usual increase in PDA with a peak value observed 15min after the injection (+22% from baseline, P<0.001). This hypertensive effect of UII was accompanied by a significant increase in the RR interval (+18%, P<0.001), i.e. a bradycardia, and these effects remained constant until the end of the recording. The highest dose of UII evoked similar hypertensive and bradycardic effects. Of interest, the QT interval did not change during the bradycardic action of UII (50 and 100pmol) but the QTc interval significantly decreased. In trout pre-treated with urantide, a peptidic antagonist of UT, the hypertensive and bradycardic actions of 50pmol UII were reduced 3-fold and no change occurred in the QT and QTc intervals. In trout pre-treated with blockers of the autonomic nervous system, the hypertensive effect of UII was maintained but no change appeared in RR, QT and QTc intervals. IA injections of 50pmol URPs were without action on the preceding parameters. IA administration of 50pmol AVT provoked quite similar increase in PDA, and elevation of the RR interval to those evoked by IA injection of UII but, in contrast to UII, AVT injection induced a highly significant and sustained prolongation of the QT interval compared to baseline (+7%, P<0.001) without change in QTc. Our results are indicative of a lack of QT interval change during UII-evoked bradycardia but not after AVT-induced bradycardia and suggest for the first time that some compensatory mechanism specific for the UII peptide is working to stabilize the QT interval. Further research is needed to elucidate the mechanism involved in this action of UII. The potential for UII to prevent detrimental prolongation of cardiac ventricular repolarization might be questioned.

Local vasotocin modulation of the pacemaker nucleus resembles distinct electric behaviors in two species of weakly electric fish

The neural bases of social behavior diversity in vertebrates have evolved in close association with hypothalamic neuropeptides. In particular, arginine-vasotocin (AVT) is a key integrator underlying differences in behavior across vertebrate taxa. Behavioral displays in weakly electric fish are channeled through specific patterns in their electric organ discharges (EODs), whose rate is ultimately controlled by a medullary pacemaker nucleus (PN). We first explored interspecific differences in the role of AVT as modulator of electric behavior in terms of EOD rate between the solitary Gymnotus omarorum and the gregarious Brachyhypopomus gauderio. In both species, AVT IP injection (10μg/gbw) caused a progressive increase of EOD rate of about 30%, which was persistent in B. gauderio, and attenuated after 30min in G. omarorum. Secondly, we demonstrated by in vitro electrophysiological experiments that these behavioral differences can be accounted by dissimilar effects of AVT upon the PN in itself. AVT administration (1μM) to the perfusion bath of brainstem slices containing the PN produced a small and transient increase of PN activity rate in G. omarorum vs the larger and persistent increase previously reported in B. gauderio. We also identified AVT neurons, for the first time in electric fish, using immunohistochemistry techniques and confirmed the presence of hindbrain AVT projections close to the PN that might constitute the anatomical substrate for AVT influences on PN activity. Taken together, our data reinforce the view of the PN as an extremely plastic medullary central pattern generator that not only responds to higher influences to adapt its function to diverse contexts, but also is able to intrinsically shape its response to neuropeptide actions, thus adding a hindbrain target level to the complexity of the global integration of central neuromodulation of electric behavior.

Arginine Vasotocin Treatment Induces a Stress Response and Exerts a Potent Anorexigenic Effect in Rainbow Trout, Oncorhynchus mykiss

The peptide arginine vasotocin (AVT), homologous to mammalian arginine vasopressin, is involved in many aspects of fish physiology, such as osmoregulation, regulation of biological rhythms, reproduction, metabolism or responses to stress, and the modulation of social behaviours. Because a decrease in appetite is a general response to stress in fish and other vertebrates, we investigated the role of AVT as a possible food intake regulator in fish. We used i.c.v. injections for central administration of AVT to rainbow trout (Oncorhynchus mykiss). In a first experiment, we evaluated the temporal response of food intake after AVT treatment. In a second experiment, we investigated the effects of central AVT administration on the response of typical stress markers (plasma cortisol, glucose and lactate), as well as brain serotonergic, noradrenergic and dopaminergic activity. In addition, the mRNA levels of genes involved in food intake regulation [neuropetide Y, pro-opiomelanocortin (POMC), cocaine- and amphetamine-regulated transcript (CART) and corticotrophin-releasing factor (CRF)] and in CRF- (CRF-binding protein) and AVT-signalling (pro-VT and AVT receptor), were also assessed after AVT treatment. Our results showed that AVT is a potent anorexigenic factor in fish. Increases of plasma cortisol and glucose after AVT treatment strongly suggest that AVT administration induced a stress response and that AVT action was mediated by hypothalamic-pituitary-interrenal axis activation, which was also supported by the increase of the serotonergic activity in trout telencephalon and hypothalamus. The increased hypothalamic levels of POMC and CART suggest that these peptides might have a role in the anorexigenic action of AVT, whereas the involvement of CRF signalling is unclear.

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.

AVTergic modulation of the agonistic behavior in two species of weakly electric fish with different social strategies

Event Abstract Back to Event AVTergic modulation of the agonistic behavior in two species of weakly electric fish with different social strategies Ana Silva1, 2* and Rossana Perrone1 1 Instituto de Investigaciones Biológicas Clemente Estable, Unidad Bases Neurales de la Conducta, Uruguay 2 Facultad de Ciencias, Laboratorio de Neurociencias, Uruguay Social behaviors in vertebrates are controlled by a complex and conserved brain network. It has been postulated that inter and intraspecific modulations of behavior are correlated with distinctively distributed patterns of this network, which depend on neuroendocrine messengers that integrate extrinsic and intrinsic cues. The hypothalamic neuropeptide arginine-vasotocin (AVT) and its mammalian homologue, vasopressin, are key integrators underlying interspecific, sexual, individual, and social context differences in behavior across vertebrate taxa. Comparative studies of AVT actions between related species with different social structure have been useful for the understanding of brain-behavior relationships. We used two species of weakly electric fish with different social strategies: Gymnotus omarorum, solitary and highly aggressive in intra and intersexual encounters all year round, and Brachyhypopomus gauderio, gregarious and only aggressive in intrasexual encounters during the breeding season. Our previous work showed that AVT produces an increase in the EOD basal rate in B. gauderio but not in G. omarorum, and that AVT is responsible for the nocturnal increase of EOD basal rate observed in the former species during the breeding season. In this study, we explored the effects of IP administration of AVT (1µg/g) and of its antagonist (Manning compound, MC, 2µg/g) in the agonistic behavior of both species. We analyzed dyadic encounters (control, n=10; AVT, n=10; MC, n=6) in independent experiments using experimental protocols in which we could predict the outcome of the conflict: 5-30% size asymmetry in intra and intersexual dyads of non-breeding G. omarorum, same size asymmetry + residency in breeding males of B. gauderio. Thirty minutes prior to the agonistic encounter, we injected AVT (or MC) to the potential winner and saline to the potential loser, and evaluated their effects on conflict resolution, levels of aggression and submission, and dynamics of electric and locomotor displays. AVT and MC administration in B. gauderio had no effect on the agonistic behavior except for their actions on EOD rate: AVT induced and MC blocked the increase of EOD rate observed in winners after conflict resolution. Interestingly, in AVT fights, the intruder significantly increased the emission of electric submission signals (offs) that were only rarely observed in control dyadic encounters. AVT induced no effects on the agonistic behavior of G. omarorum, whereas MC induced a decrease in the aggression levels, in the submission signaling, and prevented the decrease of EOD rate observed in control subordinates after conflict resolution. Taken together, our data indicate that the AVTergic system is involved in the modulation of the agonistic behavior of both species. This modulation shows important interspecific differences that might be crucial in shaping different neural strategies for the control of social behavior. Keywords: Aggression, hypothalamic neuropeptide, Neuromodulation Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Poster Presentation (see alternatives below as well) Topic: Social Behavior Citation: Silva A and Perrone R (2012). AVTergic modulation of the agonistic behavior in two species of weakly electric fish with different social strategies. Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00071 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 13 Mar 2012; Published Online: 07 Jul 2012. * Correspondence: Dr. Ana Silva, Instituto de Investigaciones Biológicas Clemente Estable, Unidad Bases Neurales de la Conducta, Montevideo, 11600, Uruguay, asilva@iibce.edu.uy Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Ana Silva Rossana Perrone Google Ana Silva Rossana Perrone Google Scholar Ana Silva Rossana Perrone PubMed Ana Silva Rossana Perrone Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Renal filtration and reabsorption of GFP in Rana temporaria: Effect of arginine-vasotocin

The renal tubular uptake of green fluorescent protein (GFP) in frog Rana temporaria was studied by laser confocal microscopy. The specific green fluorescence was revealed in the proximal tubule cells 30 min after intravenous GFP injection. The GFP fluorescence was distributed predominantly in the apical part of the cytoplasm in the form of the intensively fluorescing vesicles. The GFP injections increased dose-dependently the GFP tubular uptake. This was confirmed by the quantitative assessment of intensity of the specific fluorescence, its relative vesicular density, and by correlation analysis. Preliminary administration of arginine vasotocin into the dorsal lymphatic sac decreased significantly the GFP absorption. The effect of arginine vasotocin was inhibited by pretreatment a vasopressin V1-receptor antagonist. These results suggest that a decrease in the GFP absorption is due to a fall of the AVT-dependent glomerular filtration rate and consequently a decrease in the filtered GFP amount. The effect of arginine vasotocin on the GFP absorption seems to be mediated via the V1-like receptors of preglomerular blood vessels.

Molecular neuroendocrine events during stress in poultry

Magnocellular neurons in the hypothalamic paraventricular nucleus containing arginine vasotocin (AVT) project to the posterior pituitary and release the peptide peripherally to target tissues. Parvocellular neurons contain either corticotropin-releasing hormone (CRH), AVT, or both neuropeptides and project to the median eminence. Corticotropin-releasing hormone and AVT are then transported to the anterior pituitary where they bind to CRH1 or vasotocin VT2 receptors, many found co-localized on the same pituitary cell type, the corticotrope. Central administration of CRH compared with AVT is more effective in releasing the stress hormone corticosterone, whereas peripheral administration of AVT is more efficacious. Simultaneous, peripheral administration of CRH and AVT also resulted in a synergistic release of corticosterone. Cell culture studies demonstrated a synergistic release of the second messenger, cyclic adenosine monophosphate, when both CRH and AVT were added to cells transfected with CRH and VT2 receptors, providing a possible explanation for the enhanced release of corticosterone following combined peripheral administration of the 2 peptides. A social stress model, mature male-male interaction, demonstrated activation of neurons in the paraventricular nucleus and suggested that the posterior pituitary as well as the anterior pituitary are involved in a social stress response.

Sex differences in plasma corticosterone release in undisturbed chickens ( Gallus gallus) in response to arginine vasotocin and corticotropin releasing hormone

In birds, two neuropeptides, corticotropin releasing hormone (CRH) and arginine vasotocin (AVT), are major regulators of the hypothalamo-pituitary-adrenal axis (HPA) during the stress response. In birds, however, the relative efficacy of CRH and AVT to stimulate the HPA axis in males and females remains unknown. The purpose of this study was to determine the time course of CORT release following central CRH and AVT administration to male and female chickens. Chickens were fitted with a stainless steel cannula surgically implanted in the lateral ventricle and a catheter chronically inserted in the jugular vein. Birds were housed individually in cages behind a one-way glass partition and unnecessary noise was avoided during the sampling period. Each bird received a single 5.0 μl intracerebroventricular (ICV) injection of either saline (SAL), AVT (10 and 100 pmol), or CRH (10 and 100 pmol). Blood was sampled remotely every 15 min for 2 h and plasma CORT was determined by radioimmunoassay. There was a significant increase in plasma CORT concentration in males injected with 100 pmol AVT beginning at 15 min post-injection through 2 h compared with SAL injected birds. In males, injection of 100 pmol CRH was significantly more effective in releasing CORT compared to an equal molar concentration of AVT or SAL. In females, ICV injection of 100 pmol AVT induced moderate increase in CORT levels. In contrast, 100 pmol CRH significantly increased plasma CORT compared to SAL injected controls but the CORT response was nearly 50% less than that obtained in males.

Effects of arginine vasotocin, isotocin and melatonin on blood pressure in the conscious atlantic cod (Gadus morhua): hormonal interactions?

The effects of exogenous arginine vasotocin (AVT), isotocin (IT) and melatonin on the blood pressure of conscious Atlantic cod (Gadus morhua) were examined. Ventral aortic blood pressure (PVA) was recorded from a cannula inserted into the afferent branchial artery of the third gill arch. Dorsal aortic blood pressure (PDA) was recorded via a cannula implanted into the efferent branchial artery in the same gill arch. Each fish received two doses (10 and 50 ng kg-1) of AVT, IT and melatonin. AVT was also administered in combination with melatonin. Injection of 10 ng kg-1 AVT produced significant hypertension, especially in animals injected during the daytime. In contrast, the same dose of IT induced no significant change in either PVA or PDA. Administration of 10 ng kg-1 melatonin at night caused a long-lasting decrease in both parameters. Melatonin also inhibited the increase in blood pressure elicited by AVT. These results indicate that AVT, but not IT, is vasopressor in the cod. The effects of combined administration of melatonin and AVT show the antihypertensive action of melatonin in AVT-induced hypertension.

Effects of exogenous arginine vasotocin on circulating levels of thyroid hormones and melatonin in the pigeon, Columbia livia

The effects of intravenous injections of two different preparations of synthetic arginine vasotocin (AVT), deamino-dicarba-arginine vasotocin and arginine vasotocin diacetate tetrahydrate on serum levels of thyroxine (T 4), triiodothyronine (T 3) and melatonin were studied in the resting pigeon. Although variations depending on factors such as the type of AVT preparation and the dose used and also the duration of treatment were apparent, both preparations of AVT produced an increase in serum levels of T 4 and a decrease in that of T 3. The T 3: T 4 ratio was also significantly lower in response to AVT administration. However, no statistically significant changes in serum levels of melatonin were discernible with the administration of either of the two AVT preparations, even though melatonin levels in most AVT-treated groups showed a trend ( P > 0.05) to be higher than that in the controls. The rise in T 4 levels is indicative of increased release of T 4 and/or the inhibition of its conversion to the active hormone, T 3. The drop in T 3 may account for the AVT-induced reduction in the metabolic rate of the pigeon observed in an earlier study. The absence of a significant increase in melatonin indicates that AVT could not produce such a change in the daytime in resting pigeons, in contrast to that in flown homing pigeons, suggesting that the modulating effect of AVT on melatonin levels is dependent on the physiological state of the animal.

Neurophysiological effects of vasotocin and corticosterone on medullary neurons: implications for hormonal control of amphibian courtship behavior.

Research on a wide variety of vertebrates, from fish to mammals, reveals that corticosteroid hormones and vasotocin-like neuropeptides can potently modulate reproductive behaviors. But, it is not clear how the behavioral effects of these chemical messengers relate to functional properties of behavior-controlling neurons. This problem was investigated in the roughskin newt, Taricha granulosa, an amphibian in which the administration of arginine vasotocin (AVT) facilitates and corticosterone (CORT) inhibits courtship clasping of females by males. In waking, immobilized male newts, neurophysiological effects of AVT and CORT were studied in neurons in the rostral medulla due to the probable role of these neurons in the control of clasping. Topical medullary application of a clasp-facilitating dose of AVT produced a rapid increase in neuronal responsiveness to pressure on the cloaca, a trigger stimulus for clasping responses. Neuronal responses to noncloacal somatic stimuli and to moving visual stimuli were also enhanced. Systemic CORT administration, which has previously been shown to depress newt medullary neuronal sensory responsiveness, reversed the action of AVT such that the peptide depressed sensory responsiveness when applied 30 min after CORT. When AVT application preceded CORT injection by 10-17 min, however, the usual suppressive CORT effect was reversed and this treatment resulted in a rapidly appearing potentiation of neuronal activity and enhanced somatic sensory responsiveness. If the interval between AVT and CORT was increased to 30 min, the steroid caused a rapid depression of firing and a diminished somatic sensory responsiveness in most neurons, similar to what occurs in newts treated with CORT alone.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of arginine vasotocin and prostaglandin F 2α on oviposition and luteolysis in the common snapping turtle Chelydra serpentina

The administration of arginine vasotocin (AVT) to gravid snapping turtles with steroidogenically active corpora lutea and high plasma progesterone concentration (1480 ± 155 pg/ml) did not trigger oviposition, whereas 12 days after ovulation when luteolysis occurred and plasma progesterone concentration was low (570 ± 78 pg/ml), treatment with AVT caused oviposition. Controls with high plasma progesterone concentration (1605 ± 185 pg/ml) oviposited 15–23 days after ovulation when plasma progesterone concentration dropped to 201 ± 35 pg/ml. Deluteinization-induced oviposition was initiated 15 hr after surgery and was completed by 30 hr. Oviposition of complete clutches occurred and was correlated with a significant drop in plasma progesterone. Sham-operated turtles did not exhibit oviposition and no significant change in progesterone concentration was observed. A single injection of prostaglandin F 2α (PGF) in recently ovulated turtles induced early luteolysis and a significant decrease in plasma progesterone concentration after 24–30 hr. A single administration of PGF caused the disappearance of steroidogenic features such as the smooth endoplasmic reticulum and mitochondria with tubular cristae 48 hr later. Also PGF triggered the invasion of a hyaline-like material from the luteal theca into the luteal cell mass which eventually induced luteolysis. The role of AVT, PGF, and progesterone in relation to egg retention and oviposition is discussed.

Intranasal vasotocin decreases cerebrospinal fluid 5-HIAA levels in man

A single dose (10 ng/kg) of the nonapeptide arginine vasotocin (AVT) administered intranasally to healthy young men, significantly decreased 5-HIAA levels in the lumbar cerebrospinal fluid (CSF) 8 hr after its administration. So far, this represents the smallest amount of an active substance able to alter CSF 5-HIAA levels in man. It is suggested that the decrease of CSF 5-HIAA levels after AVT administration reflects an AVT-induced reduction of the brain 5-HT turnover.

Effects of prolactin, adrenocorticotrophin, neurohypophysial peptides, cortisol, and androgens on some osmoregulatory parameters of the hypophysectomized catfish, Heteropneustes fossilis (Bloch)

Daily injections of ovine prolactin (PRL), cortisol acetate (FA), arginine vasotocin (AVT), and adrenocorticotrophic hormone (ACTH), at doses ranging from 0.1 to 500 mU/g, 0.2 to 25 μg/g, 0.01 to 0.02 μg/g, and 5 to 10 mU/g respectively, for 5 days elevated plasma osmolarity and plasma sodium levels in the 3-day hypophysectomized catfish, Heteropneustes fossilis maintained in tap water. PRL enhanced urine production and decreased urine osmolarity and sodium concentration. Administration of FA and AVT increased urine output as well as urine osmolarity and sodium concentration, thereby resulting in severe natriuresis. Simultaneous administration of PRL and FA to hypophysectomized catfish restored plasma osmolarity and sodium concentration to normal levels even in the presence of increased urinary salt loss. However, if the fishes were maintained in deionized water, administration of PRL and FA had no effect on plasma osmolarity or plasma sodium levels suggesting that these hormones increase plasma osmotic pressure by stimulating active uptake of salts from the external medium. Neither PRL nor AVT evoked any increase in plasma cortisol level indicating that their effects on catfish osmoregulation are not mediated through cortisol production. Isotocin, testosterone, and Δ 4-androstenedione had no effect on any of the plasmatic or urinary parameters. It is concluded that prolactin, cortisol, and AVT are the principal hormones for osmoionic homeostasis in this catfish and that they act through independent mechanisms.

A GABAergic habenulo-raphe pathway mediates both serotoninergic and hypnogenic effects of vasotocin in cats

Extremely small amounts (10 −4 pg) of the pineal nonapeptide arginine vasotocin (AVT), injected into the pineal recess of freely moving cats, decreased the levels of 5-hydroxyindole acetic acid (5-HIAA) in the raphe dorsalis nucleus and induced slow wave sleep. In cats with lesions in the lateral habenula, 10 −4 pg AVT injected into the pineal recess, failed to decrease raphe dorsalis 5-HIAA levels and to induce slow wave sleep. The GABA antagonist picrotoxin (1 ng) injected into the pineal recess 15 min before the administration of AVT (10 −4 pg), completely prevented AVT from decreasing raphe dorsalis 5-HIAA levels and from inducing slow wave sleep. A highly significant correlation could be established between the decrease of raphe dorsalis 5-HIAA levels and the induction of slow wave sleep. No changes in raphe dorsalis 5-HIAA levels could be detected in cats injected with 10 −4 pg AVT into the lateral or into the fourth ventricle. Neither arginine vasopressin nor oxytocin (10 −4 pg) injected into the pineal recess, could alter raphe dorsalis 5-HIAA levels. It is concluded that AVT induces slow-wave sleep in cats by activating an inhibitory GABAergic lateral habenula-raphe dorsalis pathway.

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.