Prolactin-releasing activity of arginine vasotocin in vitro.

A significant elevation in both luteinizing hormone (LH) and prolactin release was observed in the culture medium of hemipituitaries from castrated estrogen-progesterone (EP) primed female rats incubated for 5 h with arginine vasotocin (AVT) and luteinizing hormone-releasing hormone (LRH) compared to corresponding halves incubated with LRH alone. However, AVT alone did not significantly alter the discharge of LH or prolactin from hemipituitaries of EP-treated rats in vitro. Arginine vasopressin, a natural analogue of AVT, inhibited prolactin release using this same model system. Normal male rat hemipituitaries incubated with AVT released significantly more LH and prolactin into the culture medium than did their corresponding halves. A log-dose response curve indicated that any dose from 100 ng to 10 mug AVT significantly promoted prolactin release. However, the terminal tripeptide of AVT, Pro-Arg-Gly(NH2), failed to modify the discharge of LH or prolactin into the culture medium.     

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.     

Failure to demonstrate self-recognition in gorillas

Two zoo-reared gorillas were each given nearly 400 h of mirror exposure. Extensive mirror gazing and social behaviors were exhibited, the frequency of which decreased gradually over the study period. Neither animal demonstrated the transition from other-directed to self-directed behavior characteristic of both chimpanzees and orangutans, and no evidence of self-recognition was found using the Gallup marking paradigm. These negative findings, after extensive mirror exposure, suggest that the gorilla may be the only great ape which lacks the conceptual ability necessary for self-recognition.     

The cardiac effects of arginine vasotocin in amphibians

1. The cardiac effects of arginine vasotocin (AVT) on isolated atria were examined in three anuran and one urodele species. 2. AVT produced dose-related positive chronotropic and inotropic responses. 3. The responsiveness of the atrial tissue varied among species. 4. Both the basal atrial rate (AR) and tension (T) were attenuated in the presence of phentolamine and propranolol, alpha- and beta-adrenergic antagonists. Isoproterenol, a beta-adrenergic agonist, increased both AR and T, an effect which would be inhibited by propranolol. 5. The effects of AVT on both AR and T were not inhibited by alpha- and beta-adrenergic blockers, nor by verapamil and imidazole with the dosages used in the present study. 6. On the contrary, the effects of AVT on AR, but not T, was enhanced in the presence of both alpha- and beta-adrenergic blockers. 7. The mechanism of action of AVT on the amphibian atrium remains unknown.     

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.     

The role of arginine vasotocin in teleost fish osmoregulation

The AVT system is a key component of the complex mechanism responsible for coordinating the response in teleost fish to hyper-osmotic challenge. The pituitary AVT store falls following transfer to SW from FW and this is accompanied by an increase in circulating AVT levels. This indicates that there has been release of AVT in response to this stimulus and the system is being up-regulated. The effect of an increase in secretion would appear to be predominantly to reduce GFR and urine production as is seen when AVT is injected into FW-adapted fish. This action is consistent with the requirements of hyper-osmotic challenge when water conservation becomes essential.     

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.     

Distribution of arginine vasotocin in the brain of the lizard Anolis carolinensis

Summary The distribution of immunoreactive arginine vasotocin (AVT-ir) was determined in the brain of the lizard Anolis carolinensis. Cells and fibers containing AVT-ir were found in the medial septal region, lamina terminalis, lateral forebrain bundle, preoptic area, supraoptic nucleus, anterior hypothalamus, paraventricular nucleus, periventricular nucleus, arcuate nucleus, and ventromedial nucleus of the thalamus. Occasional AVT-ir cells were found in the interpeduncular nucleus. Fibers containing AVT-ir were found in the cortex, around the olfactory ventricle, in the diagonal band of Broca, amygdala area, dorsal ventricular ridge, striatum, nucleus accumbens, septum, ventromedial hypothalamus, lateral hypothalamus, medial forebrain bundle, median eminence, pars nervosa, nucleus of the solitary tract, locus coeruleus, cerebellar cortex (granular layer), dorsal part of the nucleus of the lateral lemniscus, substantia nigra, and myelencephalon. The intensity of AVT-ir staining was, in general, greater in males than in females. Comparison of AVT-ir distribution in A. carolinensis with those previously published for other reptilian species revealed species-specific differences in distribution of AVT.     

Plasma arginine vasotocin and angiotensin II responses to body temperature elevation in the Pekin duck

The relationship between body temperature (T _b) and the plasma concentrations of arginine vasotocin (AVT) and angiotensin II (AII) was examined in conscious, adult Pekin ducks. Exposure of birds to an ambient temperature of 40 °C for 3 h increased T _b by about 1.5 °C and increased breathing rate five-fold. Plasma osmolality was elevated from the normothermic value of 294.9 ± 1.4 mosmol kg⁻¹ by about 8 mosmol kg⁻¹ Circulating AVT levels increased by about 2 pg ml⁻¹ from a basal concentration of 4.98 ± 0.15 pg ml⁻¹, a rise which could be accounted for by the change in osmotic status. Plasma AII concentrations were unchanged from the pre-heat exposure value of 31.8 ± 3.4 pg ml⁻¹. Time control birds, exposed only to an ambient temperature of 22 °C demonstrated no significant changes in any of the measured variables. The results suggest that an increased T _b has no direct effect on the circulating concentrations of AVT or AII in ducks. Accepted: 2 June 1997     

Involvement of arginine vasotocin in reproductive events in the male newt Cynops pyrrhogaster

Effects of arginine vasotocin (AVT) on reproductive events such as courtship behavior, pheromone release, and spermatophore discharge were investigated in the male newt Cynops pyrrhogaster. AVT enhanced the incidence and frequency of androgen-induced courtship behavior. In this case, AVT was likely to act centrally because the behavior was evoked with a much smaller amount of AVT when the hormone was administered intracerebroventricularly than when given intraperitoneally. Involvement of endogenous AVT in spontaneously occurring courtship behavior was also evidenced by the fact that administration of a V1 (vasopressor) receptor antagonist, [d(CH2)5(1), Tyr(Me)2, Arg8-vasopressin] suppressed the expression of the courtship behavior. The water in which AVT-treated males had been kept showed considerable female-attracting activity as compared with the water in which saline-injected males had been kept. Moreover, the content of sodefrin, a female-attracting pheromone in the abdominal gland, was decreased by the intraperitoneal injection of AVT, suggesting that the neurohypophyseal hormone stimulated the release of sodefrin from the abdominal gland into the water. AVT induced contraction of the excised abdominal gland concentration-dependently, and, again, the V1 receptor antagonist suppressed the AVT-induced contraction. Thus, we concluded that AVT induces the pheromone discharge, acting peripherally on a contractile structure of the abdominal gland. AVT was also found to induce spermatophore deposition in the male kept in the absence of the female. Administration of the V1 receptor blocker to the sexually developed males suppressed the spermatophore deposition. All these results indicate the involvement of AVT in reproductive events acting centrally and peripherally.     

Regulation of opioid peptides on the release of arginine vasotocin in the hen

Arginine vasotocin (AVT), an avian neurohypophysial hormone, is released during osmotic stimulation and oviposition. In the present study, the role of opioid peptides on AVT release was studied by examining the effects of an opioid agonist and antagonist on osmotic- and oviposition-induced secretion of AVT. The administration of hypertonic saline (1.5 M NaCl) induced an increase in the plasma levels of AVT. The simultaneous administration of morphine, an opioid receptor agonist, inhibited the osmotically induced increase in plasma levels of AVT in a dose-dependent manner. On the other hand, the co-administration of morphine with naloxone, an opioid receptor antagonist, attenuated the inhibitory effect of morphine. Moreover, injection of naloxone alone enhanced the osmotically induced increase in plasma levels of AVT. However, the administration of morphine did not inhibit the oviposition-induced increase in plasma levels of AVT. These results suggest that osmotic-induced release of AVT may be under opioid regulation, while oviposition-induced release of AVT may be controlled by a different mechanism. J. Exp. Zool. 286:481-486, 2000.     

Failure to demonstrate serotonergic neurons in the myenteric plexus of the rat

Summary Several recent studies suggested that serotonergic neuron-like elements are present in the guinea pig ileum. The present paper reports an extensive study of the digestive tract of the rat with the use of a histofluorescence technique. Administration of the serotonin precursor, tryptophan, associated with a monoamine oxidase inhibitor, did not allow histochemical demonstration of rapidly fading, yellow fluorescent, 6-hydroxydopamine-resistant neurons; conversely such neurons were readily detected in the brain. It is concluded that serotonergic neuron-like elements cannot be detected histochemically in the rat myenteric plexus area after chemical sympathectomy.     

Isolation and structure elucidation of bovine pineal arginine vasopressin: arginine vasotocin not identified

A large number of reports have demonstrated the presence of neurohypophysial hormone-like peptides in mammalian pineal glands and an antigonadotropic function has been ascribed to pineal arginine vasotocin (AVT). We have undertaken large scale purification of bovine pineal neurohypophysial hormone-like substances which demonstrate mouse mammary milk-ejection activity (ME-activity) in vitro. Peptides with ME-activity were extracted from more than 5 kg of bovine pineal glands. ME-activity containing peptides were found in both high (Mr approximately 10,000-15,000) and low (Mr approximately 500-1000) Mr species from Sephadex G-25 chromatography of 0.2 N acetic acid extracts. After ultrafiltration in 5% formic acid, the neurohypophysial hormone-like peptides were localized to an ultrafiltration Mr 500-1000 retentate. A homogeneous peptide, which shared an identical retention time (RT) and amino acid sequence with synthetic 8-arginine vasopressin (AVP), was isolated by serial semipreparative high performance liquid chromatography. On the other hand, the non-mammalian nonapeptide AVT was not identified.     

Brain arginine vasotocin concentrations related to sexual behaviors and hydromineral balance in an amphibian

Arginine vasotocin (AVT), a potent stimulator of sexual behaviors and regulator of hydromineral balance in male rough-skinned newts (Taricha granulosa), was measured in 11 brain areas using microdissection and radioimmunoassay procedures. A 60-min test for sexual behaviors was used to segregate males into two groups: sexually responsive (initiated amplectic clasping behaviors) and sexually unresponsive (exhibited no sexual behaviors). Compared to sexually unresponsive males, sexually responsive males had significantly higher concentrations of immunoreactive (ir) AVT in the dorsal preoptic area, optic tectum, ventral infundibular nucleus, and cerebrospinal fluid. These results provide evidence for a behavioral action of endogenous AVT in T. granulosa. In another study, irAVT was measured in normal males (control newts maintained in water) and males that were dehydrated for 6 hr. Compared to normal males, dehydrated males had significantly lower concentrations of irAVT in the ventral preoptic area, but not in the other 10 areas of the brain. That different brain areas are associated with sexual behaviors and hydromineral balance suggests that there are some neuroanatomical separations between the behavioral and hydromineral aspects of the vasotocinergic system in this amphibian.     

Duration of androgen treatment modifies behavioral response to arginine vasotocin in Taricha granulosa

Five and eighteen days after surgery, injection of arginine 8-vasotocin (AVT) stimulated clasping behavior in castrated controls (unimplanted or cholesterol-implanted) but not in androgen-implanted, castrated newts (Taricha granulosa). Conversely, AVT injected 33 days after castration increased the incidence of courtship behavior of androgen-implanted males, but not of unimplanted castrates. Plasma androgen concentration of androgen-implanted castrates (as determined by radioimmunoassay) was maintained at a level typical of intact males at the peak of the breeding season. Because the AVT-androgen interaction could occur at the level of the pituitary gland, castrated, androgen-implanted newts were hypophysectomized and injected with AVT. Hypophysectomy did not abolish the behavioral response to AVT.     

Failure to demonstrate natriuretic activity in the posterior pituitary after immunoneutralization of the vasopressin content.

The attempt to demonstrate the presence of a natriuretic substance in the posterior pituitary after immunoneutralization of the AVP content failed. Rats infused i.v. AVP-immunoneutralized posterior pituitary extract did not respond by natriuresis to a saline infusion, in contrast to those infused untreated posterior pituitary extract. Thus, vasopressin seems to be the natriuretic substance in the posterior pituitary extract.