Changes in body fluids of the cocooning fossorial frog Cyclorana australis in a seasonally dry environment

We investigated changes in the lymph (equivalent to plasma) and urine of the cocooning frog Cyclorana australis during the dry season in monsoonal northern Australia. Frogs in moist soil for two days were fully hydrated (lymph 220 mOsm kg(-1), urine 49 mOsm kg(-1)). From five weeks onwards the soil was dry (matric potential <-8000 kPa). Aestivating frogs at three and five months formed cocoons in shallow (<20 cm) burrows and retained bladder fluid (25-80% of standard mass). After three months, urine but not lymph osmolality was elevated. After five months, lymph (314 mOsm kg(-1)) and urine (294 mOsm kg(-1)) osmolality and urea concentrations were elevated. Urea was a major contributing osmolyte in urine and accumulated in lymph after five months. Lymph sodium concentration did not change with time, whereas potassium increased in urine after five months. Active animals had moderate lymph osmolality (252 mOsm kg(-1)), but urea concentrations remained low. Urine was highly variable in active frogs, suggesting that they tolerate variation in hydration state. Despite prolonged periods in dry soil, osmolality increase in C. australis was not severe. Aestivation in a cocoon facilitates survival in shallow burrows, but such a strategy may only be effective in environments with seasonally reliable rainfall.     

Enzyme activity in the aestivating Green-striped burrowing frog (Cyclorana alboguttata)

Green-striped burrowing frogs (Cyclorana alboguttata) can depress their resting metabolism by more than 80% during aestivation. Previous studies have shown that this species is able to withstand long periods of immobilisation during aestivation while apparently maintaining whole muscle mass and contractile performance. The aim of this study was to determine the effect of prolonged aestivation on the levels of metabolic enzymes (CCO, LDH and CS) in functionally distinct skeletal muscles (cruralis, gastrocnemius, sartorius, iliofibularis and rectus abdominus) and liver of C. alboguttata. CS activity was significantly reduced in all tissues except for the cruralis, gastrocnemius and the liver. LDH activity was significantly reduced in the sartorius and rectus abdominus, but remained at control (active) levels in the other tissues. CCO activity was significantly reduced in the gastrocnemius and rectus abdominus, and unchanged in the remaining tissues. Muscle protein was significantly reduced in the sartorius and iliofibularis during aestivation, and unchanged in the remaining muscles. The results suggest that the energy pathways involved in the production and consumption of ATP are remodelled during prolonged aestivation but selective. Remodelling and subsequent down-regulation of metabolic activity seem to target the smaller non-jumping muscles, while the jumping muscles retain enzyme activities at control levels during aestivation. These results suggest a mechanism by which aestivating C. alboguttata are able to maintain metabolic depression while ensuring that the functional capacity of critical muscles is not compromised upon emergence from aestivation.     

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.     

Morphofunctional research on the interrenal gland of the frog Rana temporaria following arginine vasotocin administration

Studies have been made of the effect of injections of hypothalamic nonapeptide neurohormone, arginine vasotocin, on functional condition of the interrenal gland in mature frogs. In unoperated, sham-operated and in animals 10 days after hypophysectomy, single and especially three subsequent injections of arginine vasotocin (5 x 10(-9) M per 1 kg of the body weight) result in evident activation of glandular cells of the interrenal gland which is manifested in the increase of the volume of their nuclei and cytoplasmic area, as well as in the dilatation of the blood vessels. Activation of the interrenal gland in hypophysectomized frogs, which lack endogenous ACTH, indicate the direct para-adenohypophyseal influences of nonapeptide hypothalamic hormones on the activity of glandular cells in the peripheral endocrine glands, in particular, the interrenal gland of the grass frog.     

Diurnal variations in plasma arginine vasotocin (AVT) concentrations in the ovine fetus

Previously we have demonstrated the presence of AVT in the blood of fetal sheep. The source is not clear, but AVT has been identified in fetal pineal and pituitary glands. In view of the circadian secretory pattern of the pineal gland, we questioned whether fetal plasma AVT levels might vary diurnally. Plasma samples from five chronically catheterized ovine maternal ewes and fetal lambs 129-135 days' gestation were obtained at 3-19 hourly intervals for 1-2 days (mean +/- S.E.M. = 35 +/- 6 hours. Plasma AVT levels were determined by radioimmunoassay. Results were analyzed by nonlinear curve fitting procedures to relate hormone levels with time of day. Plasma AVT values for maternal ewes did not vary during the day in response to light/dark periods. The curve for mean fetal plasma AVT plotted against time showed oscillations with a period of about 25 hours (p less than 0.05). Peak fetal AVT levels were observed at 1600 hours and minimal levels at 0400 hours. These results indicate that ovine fetal AVT secretion varies diurnally. The site of AVT secretion may be the pineal gland; however, confirmation of this and identification of the physiological stimuli for secretion of fetal plasma AVT require further information.     

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.     

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.     

Sex and seasonal co-variation of arginine vasotocin (AVT) and gonadotropin-releasing hormone (GnRH) neurons in the brain of the halfspotted goby

Gonadotropin-releasing hormone (GnRH) and arginine vasotocin (AVT) are critical regulators of reproductive behaviors that exhibit tremendous plasticity, but co-variation in discrete GnRH and AVT neuron populations among sex and season are only partially described in fishes. We used immunocytochemistry to examine sexual and temporal variations in neuron number and size in three GnRH and AVT cell groups in relation to reproductive activities in the halfspotted goby (Asterropteryx semipunctata). GnRH-immunoreactive (-ir) somata occur in the terminal nerve, preoptic area, and midbrain tegmentum, and AVT-ir somata within parvocellular, magnocellular, and gigantocellular regions of the preoptic area. Sex differences were found among all GnRH and AVT cell groups, but were time-period dependent. Seasonal variations also occurred in all GnRH and AVT cell groups, with coincident elevations most prominent in females during the peak- and non-spawning periods. Sex and temporal variability in neuropeptide-containing neurons are correlated with the goby's seasonally-transient reproductive physiology, social interactions, territoriality and parental care. Morphological examination of GnRH and AVT neuron subgroups within a single time period provides detailed information on their activities among sexes, whereas seasonal comparisons provide a fine temporal sequence to interpret the proximate control of reproduction and the evolution of social behavior.     

Sensory modulation and behavioral choice during feeding in the Australian frog, Cyclorana novaehollandiae

This study investigates how visual and tactile sensory information, as well as biomechanical effects due to differences in physical characteristics of the prey, influence feeding behavior in the frog Cyclorana novaehollandiae. Video motion analysis was used to quantify movement patterns produced when feeding on five prey types (termites, waxworms, crickets, mice and earthworms). Twelve kinematic variables differed significantly among prey types, and twelve variables were correlated with prey characteristics (including mass, length, height and velocity of movement). Results indicate that C.␣novaehollandiae uses a different strategy to capture each prey type. Visual assessment of prey characteristics appeared to be more important in modulating feeding behavior than tactile cues or biomechanical effects. We propose a hierarchical hypothesis of behavioral choice, in which decisions are based primarily on visual analysis of prey characteristics. In this model, the frogs first choose between jaw prehension and tongue prehension based on prey size. If they have chosen jaw prehension, they next choose between upward or downward head rotation based on length and height of the prey. If they have chosen tongue prehension, they next choose between behavior for fast and slow prey. Final decisions may be the result of behavioral fine tuning based on tactile feedback. Accepted: 5 August 1996     

Dietary intake effects on arginine vasotocin and aldosterone in cloacal fluid of whitebellied sunbirds (Nectarinia talatala)

The main objective of this study was to determine whether or not the renal outputs of the osmoregulatory hormones arginine vasotocin (AVT) and aldosterone (ALDO) reflect the osmotic status of whitebellied sunbirds (Nectarinia talatala). The birds were fed a range of sucrose concentrations (from 0.07 to 2.5 mol/l, with osmolalities of 70 to approximately 5,800 mosM/kg), and adjusted their intakes so that they drank large volumes of dilute diets and small volumes of concentrated diets. Renal fluid outputs were appropriately regulated so that large volumes of cloacal fluid (CF) were voided on the dilute diets and small volumes on the concentrated diets. Accordingly, plasma AVT concentrations increased with increasing sugar concentration; however, AVT outputs in CF did not change in a similar manner, rather they decreased as dietary concentration increased. It was not possible to measure plasma ALDO concentrations in the small sunbirds because of insufficient blood samples available; however, ALDO outputs in CF did vary with the sucrose diets and renal function, being highest on the most concentrated diet. In addition ALDO output in CF fell markedly when sodium was added to the 0.5 mol/l sucrose diet. We conclude that in sunbirds fed increasingly concentrated sucrose solutions, changes in CF outputs of ALDO, but not AVT, appear to reflect the water flux and hydration state of these birds.     

Localization of arginine vasotocin (AVT) mRNA in extrasomal compartments of magnocellular neurons in the chicken hypothalamo-neurohypophysial system

In the chicken, arginine vasotocin (AVT) is produced in and secreted by magnocellular neurons in the supraoptic (SON) and paraventricular (PVN) nuclei. To test the hypothesis of axonally transported AVT mRNA, the localization of AVT mRNA within extrasomal, axonal/dendritic compartments in the chicken hypothalamo-neurohypophysial system (HNS) were examined using AVT specific in situ hybridization histochemistry (ISHH) and RT-PCR. Many perikarya in the PVN and external--but none in the ventral subgroup of the SON show ISHH signals clearly extended into one or two processes, some with branching collaterals, traceable over a distance of more than 100 microns. Furthermore by using RT-PCR, AVT mRNA was detected in the median eminence and neurohypophysis representing the distal parts of the HNS, mainly consisting of axons and/or axon terminals. These observations of axonal mRNA offer new insights to the organization and function of the avian HNS.     

Renal function and plasma arginine vasotocin during water deprivation in an Australian parrot,the galah (Cacatua roseicapilla)

Summary Renal function was measured in an Australian parrot, the galah (Cacatua roseicapilla), which is distributed across the most arid regions of the continent. Renal function was assessed by the constant infusion technique in hydrated galahs, and in both hydrated and dehydrated birds by means of osmotic minipumps. The glomerular filtration rate (GFR) of the galah is similar to calculated values for a bird of its size. However, effective renal plasma flow tended to be low and therefore filtration fraction was high. Water deprivation for a period of 5 days caused a decrease in body weight and an increase in plasma osmolality and haematocrit. The GFR declined steadily such that weight-specific GFR on the fifth day of water deprivation was 68% of control values. The water deprivation produced a 2.6-fold elevation of plasma arginine vasotocin (AVT) levels, with an overall sensitivity of release of AVT of 0.16±0.02 pg·ml^-1 per mOsm·kg^-1. The galah possesses renal mechanisms which enable it to conserve significant amounts of water during times of water stress.Abbreviations AVT arginine vasotocin - EDTA ethylene diamine tetra-acetate - GFR glomerular filtration rate - P _AVT plasma arginine vasotocin - PAH para-amino hippuric acid - SNGFR single nephron glomerular filtration rate     

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.     

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.     

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.     

High density and food deprivation affect arginine vasotocin, isotocin and melatonin in gilthead sea bream (Sparus auratus)

Arginine vasotocin (AVT) and isotocin (IT) levels in plasma and pituitary, and melatonin (MEL) levels in plasma were determined in gilthead sea bream (Sparus auratus) subjected to two different types of stress: i) high density (HD) and ii) food deprivation (NF: non-fed). Fishes were randomly assigned to one of 4 treatments that lasted for 14 days: 1) fed fish under normal low density (ND, 4 kg m(-3)); 2) non-fed (NF) fish under ND; 3) fed fish under high density (HD, 70 kg m(-3)); and 4) non-fed fish under HD. Ten fish from each tank were anaesthetized, weighed and plasma and pituitary samples were taken. Plasma and pituitary AVT and IT content were determined by HPLC, while plasma MEL was assayed by RIA. Plasma AVT and IT values were enhanced in all fish kept at high density. The response of AVT was much stronger than that of IT. The highest pituitary AVT and IT levels were shown in NF fish kept at normal density. The significantly higher plasma MEL levels were measured in fed fish kept at HD. These results suggest a role of AVT, IT and MEL in response of sea bream to a common stress factor, high density. Although food deprivation does not influence AVT and IT plasma levels, it seems to affect hypothalamic synthesis of nonapeptides. Further studies are required to elucidate the complex role of AVT, IT and MEL in the sea bream's response to different stress stimuli.     

Relationships between renal hemodynamics and plasma levels of arginine vasotocin and mesotocin during hemorrhage in the domestic fowl (Gallus domesticus)

1. Renal tissue blood flow (renal perfusion) and plasma levels of arginine vasotocin (AVT) and mesotocin (MT) were measured in anesthetized chickens before and during hemorrhage. 2. Renal perfusion did not decrease (P less than 0.05) until nearly 50% of the blood volume had been removed. The decrease in renal perfusion was not related to arterial blood pressure but was concomitant with an increase (P less than 0.05) in plasma AVT levels. 3. Renal perfusion during hemorrhage was positively correlated with plasma MT levels by the regression equation: renal perfusion = 0.091 (MT)-1.1459 which was highly significant (P less than 0.001, r2 = 0.95). 4. The results of this study suggest that MT as well as AVT may participate in regulating blood flow in the avian kidney.     

Failure to demonstrate antigonadotrophic activities of arginine vasotocin in the mouse.

Arginine vasotocin (AVT) has previously been proposed to be a pineal hormone which reduces reproductive competency in mammals. The effects of AVT on the growth of immature reproductive organs of the mouse have been studied using blind study techniques. Evidence is presented which fails to support the proposed role of AVT as a mammalian antigonadotrophin.