Articoli di riviste: "Amphibiens – Physiologie"

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Çömden, Esra Akat, Melodi Yenmiş e Berna Çakır. "The Complex Bridge between Aquatic and Terrestrial Life: Skin Changes during Development of Amphibians". Journal of Developmental Biology 11, n. 1 (30 gennaio 2023): 6. http://dx.doi.org/10.3390/jdb11010006.

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Amphibian skin is a particularly complex organ that is primarily responsible for respiration, osmoregulation, thermoregulation, defense, water absorption, and communication. The skin, as well as many other organs in the amphibian body, has undergone the most extensive rearrangement in the adaptation from water to land. Structural and physiological features of skin in amphibians are presented within this review. We aim to procure extensive and updated information on the evolutionary history of amphibians and their transition from water to land—that is, the changes seen in their skin from the larval stages to adulthood from the points of morphology, physiology, and immunology.

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Hernandez-Caballero, Irene, Luz Garcia-Longoria, Ivan Gomez-Mestre e Alfonso Marzal. "The Adaptive Host Manipulation Hypothesis: Parasites Modify the Behaviour, Morphology, and Physiology of Amphibians". Diversity 14, n. 9 (8 settembre 2022): 739. http://dx.doi.org/10.3390/d14090739.

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Parasites have evolved different strategies to increase their transmission from one host to another. The Adaptive Host Manipulation hypothesis states that parasites induce modifications of host phenotypes that could maximise parasite fitness. There are numerous examples of parasite manipulation across a wide range of host and parasite taxa. However, the number of studies exploring the manipulative effects of parasites on amphibians is still scarce. Herein, we extensively review the current knowledge on phenotypic alterations in amphibians following parasite infection. Outcomes from different studies show that parasites may manipulate amphibian behaviours to favour their transmission among conspecifics or to enhance the predation of infected amphibians by a suitable definite host. In addition, parasites also modify the limb morphology and impair locomotor activity of infected toads, frogs, and salamanders, hence facilitating their ingestion by a final host and completing the parasite life cycle. Additionally, parasites may alter host physiology to enhance pathogen proliferation, survival, and transmission. We examined the intrinsic (hosts traits) and extrinsic (natural and anthropogenic events) factors that may determine the outcome of infection, where human-induced changes of environmental conditions are the most harmful stressors that enhance amphibian exposure and susceptibility to parasites.

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Blaustein, Andrew R., Stephanie S. Gervasi, Pieter T. J. Johnson, Jason T. Hoverman, Lisa K. Belden, Paul W. Bradley e Gisselle Y. Xie. "Ecophysiology meets conservation: understanding the role of disease in amphibian population declines". Philosophical Transactions of the Royal Society B: Biological Sciences 367, n. 1596 (19 giugno 2012): 1688–707. http://dx.doi.org/10.1098/rstb.2012.0011.

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Infectious diseases are intimately associated with the dynamics of biodiversity. However, the role that infectious disease plays within ecological communities is complex. The complex effects of infectious disease at the scale of communities and ecosystems are driven by the interaction between host and pathogen. Whether or not a given host–pathogen interaction results in progression from infection to disease is largely dependent on the physiological characteristics of the host within the context of the external environment. Here, we highlight the importance of understanding the outcome of infection and disease in the context of host ecophysiology using amphibians as a model system. Amphibians are ideal for such a discussion because many of their populations are experiencing declines and extinctions, with disease as an important factor implicated in many declines and extinctions. Exposure to pathogens and the host's responses to infection can be influenced by many factors related to physiology such as host life history, immunology, endocrinology, resource acquisition, behaviour and changing climates. In our review, we discuss the relationship between disease and biodiversity. We highlight the dynamics of three amphibian host–pathogen systems that induce different effects on hosts and life stages and illustrate the complexity of amphibian–host–parasite systems. We then review links between environmental stress, endocrine–immune interactions, disease and climate change.

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Glinski, Donna A., S. Thomas Purucker, Robin J. Van Meter, Marsha C. Black e W. Matthew Henderson. "Endogenous and exogenous biomarker analysis in terrestrial phase amphibians (Lithobates sphenocephala) following dermal exposure to pesticide mixtures". Environmental Chemistry 16, n. 1 (2019): 55. http://dx.doi.org/10.1071/en18163.

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Environmental contextMetabolomics can be used to provide a snapshot of an organism’s physiology as the organism is exposed to varying environmental conditions. In this study, laboratory-reared amphibians were exposed to multiple pesticides, analogous to field exposures, resulting in an impact to both pesticide body concentrations and the amphibians’ hepatic metabolome. These data can be used in the environmental and ecological risk assessment of multiple pesticides in non-target species. AbstractPesticide mixtures are frequently co-applied throughout an agricultural growing season to maximise crop yield. Therefore, non-target ecological species (e.g. amphibians) may be exposed to several pesticides at any given time on these agricultural landscapes. The objectives of this study were to quantify body burdens in terrestrial phase amphibians and translate perturbed metabolites to their corresponding biochemical pathways affected by exposure to pesticides as both singlets and in combination. Southern leopard frogs (Lithobates sphenocephala) were exposed either at the maximum or 1/10th maximum application rate to single, double or triple pesticide mixtures of bifenthrin (insecticide), metolachlor (herbicide) and triadimefon (fungicide). Tissue concentrations demonstrated both facilitated and competitive uptake of pesticides when in mixtures. Metabolomic profiling of amphibian livers identified metabolites of interest for both application rates; however, the magnitude of changes varied for the two exposure rates. Exposure to lower concentrations demonstrated downregulation in amino acids, potentially owing to their usage for glutathione metabolism and/or increased energy demands. Amphibians exposed to the maximum application rate resulted in upregulation of amino acids and other key metabolites likely owing to depleted energy resources. Coupling endogenous and exogenous biomarkers of pesticide exposure can be used to form vital links in an ecological risk assessment by relating internal dose to pathophysiological outcomes in non-target species.

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Storey, Kenneth B., e Janet M. Storey. "Molecular Physiology of Freeze Tolerance in Vertebrates". Physiological Reviews 97, n. 2 (aprile 2017): 623–65. http://dx.doi.org/10.1152/physrev.00016.2016.

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Freeze tolerance is an amazing winter survival strategy used by various amphibians and reptiles living in seasonally cold environments. These animals may spend weeks or months with up to ∼65% of their total body water frozen as extracellular ice and no physiological vital signs, and yet after thawing they return to normal life within a few hours. Two main principles of animal freeze tolerance have received much attention: the production of high concentrations of organic osmolytes (glucose, glycerol, urea among amphibians) that protect the intracellular environment, and the control of ice within the body (the first putative ice-binding protein in a frog was recently identified), but many other strategies of biochemical adaptation also contribute to freezing survival. Discussed herein are recent advances in our understanding of amphibian and reptile freeze tolerance with a focus on cell preservation strategies (chaperones, antioxidants, damage defense mechanisms), membrane transporters for water and cryoprotectants, energy metabolism, gene/protein adaptations, and the regulatory control of freeze-responsive hypometabolism at multiple levels (epigenetic regulation of DNA, microRNA action, cell signaling and transcription factor regulation, cell cycle control, and anti-apoptosis). All are providing a much more complete picture of life in the frozen state.

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Frumkes, Thomas E., e Thor Eysteinsson. "The cellular basis for suppressive rod–cone interaction". Visual Neuroscience 1, n. 3 (maggio 1988): 263–73. http://dx.doi.org/10.1017/s0952523800001929.

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AbstractThe response to spatially focal flicker is enhanced by dim, spatially diffuse, rod-stimulating backgrounds. This effect is called suppressive rod-cone interaction (SRCI) as it reflects a tonic, suppressive influence of dark-adapted rods upon cone pathways which is removed by selective rod-light adaptation. SRCI is observed in amphibian retina with intracellular recordings from most cone-driven cells including the cones themselves, and is most obvious using stimuli flickering at frequencies too rapid for rods to follow. SRCI is blocked by glutamate analogs which selectively block the photic response of horizontal cells (HCs). In the presence of these agents, flicker responses from bipolar cells and cones are enhanced to levels normally seen only with selective rod-light adaptation. In the HCs themselves, SRCI is similarly blocked by lead chloride which blocks rod-, but not cone-related activity.In amphibian and cat HCs and in human observers, SRCI is limited by a space constant of very similar value (between 100 and 150 μm). We suggest that SRCI in all three species is mediated by HCs: in amphibians, SRCI must at least partially reflect rod-modulation of HC feedback onto cones.

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Svinin, Anton O., Igor V. Chikhlyaev, Ivan W. Bashinskiy, Vitaly V. Osipov, Leonid A. Neymark, Alexander Yu Ivanov, Tamara G. Stoyko et al. "Diversity of trematodes from the amphibian anomaly P hotspot: Role of planorbid snails". PLOS ONE 18, n. 3 (29 marzo 2023): e0281740. http://dx.doi.org/10.1371/journal.pone.0281740.

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Trematode infection of the second intermediate hosts can lead to changes in their fitness and, as a result, a change in the invasion rate of animal communities. It is especially pronounced during the invasion of parasite species that reduce activity due to the manipulation of hosts through the changes of their morphology and physiology. One of these cases is an anomaly P syndrome hotspot found in some populations of water frogs and toads in Europe caused by the trematode Strigea robusta metacercariae. The occurrence of pathogen and their participation in ecosystems are intrigues questions in the anomaly P phenomenon, as well as the role of planorbid snails that serve as the first intermediate hosts for many trematode species. Herein, we focused on trematodes spectra from planorbid snails and amphibians from the anomaly P hosts with the aim to undetected interactions between the pathways of parasites. Emerging cercariae of 6802 planorbid snails of dominant species (Planorbarius corneus, Planorbis planorbis, and Anisus spp.) were detected by both morphological and molecular methods in seven waterbodies in Privolzhskaya Lesostep Nature Reserve (Russia). A total of 95 sequences of 18 species were received, and 48 sequences were unique and did not present in any genetic databases. The 18 species of trematodes from snails and 14 species of trematodes from amphibian hosts (Pelophylax ridibundus; Ranidae; Anura) were detected. Three species (Echinostoma nasincovae, Tylodelphys circibuteonis and Australapatemon burti) was new for the trematode fauna of the Middle Volga River region and Russia as a whole. Eleven species of parasitic flatworms have amphibians in their life cycles and nine species used amphibians as metacercariae hosts: Echinostoma nasincovae, E. miyagawai, Echinoparyphium recurvatum, Tylodelphys circibuteonis, Neodiplostomum spathula, Paralepoderma cloacicola, Macrodera longicollis, Strigea robusta, and Strigea strigis. The occurrence of trematode species from planorbid mollusks and frogs were compared.

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Yermolenko, S. V., V. S. Nedzvetsky, V. Y. Gasso, V. A. Spirina, V. B. Petrushevskyi e V. V. Kyrychenko. "Low doses of imidacloprid induce neurotoxic effects in adult marsh frogs: GFAP, NfL, and angiostatin as biomarkers". Regulatory Mechanisms in Biosystems 13, n. 4 (15 novembre 2022): 426–30. http://dx.doi.org/10.15421/022256.

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Imidacloprid is one of the most widely used insecticides in the world. The neurotoxicity of imidacloprid in adult amphibians has not been studied thoroughly. We investigated the expression of glial fibrillary acidic protein (GFAP), neurofilament light chain (NfL) and angiostatin in the amphibian brain to identify valid biomarkers of low dose imidacloprid exposure. For the experiment, 30 individuals of the marsh frog Pelophylax ridibundus were selected. The amphibians were divided into five groups. The duration of the experiment was 7 and 21 days. The exposure concentrations were 10 and 100 µg/L. The results of the study revealed a decrease in the expression of GFAP after 7 days in the exposure groups of 10 and 100 μg/L. An increase in the level of NfL was observed in the group exposed to 10 μg/L after 21 days of the experiment. The angiostatin level was increased after 7 days at 10 µg/L and after 21 days at 100 µg/L. The data obtained indicate that low concentrations of imidacloprid can cause neurotoxic effects in the brain of P. ridibundus. Such effects can have a significant impact on amphibian populations. According to the results of the study of the expression level of GFAP, NfL and angiostatin, it can be stated that imidacloprid has a neurotoxic effect on adult marsh frogs. The studied indicators can be promising biomarkers of environmental pollution by neonicotinoids.

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Turko, Andy J., Giulia S. Rossi e Patricia A. Wright. "More than Breathing Air: Evolutionary Drivers and Physiological Implications of an Amphibious Lifestyle in Fishes". Physiology 36, n. 5 (1 settembre 2021): 307–14. http://dx.doi.org/10.1152/physiol.00012.2021.

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Amphibious and aquatic air-breathing fishes both exchange respiratory gasses with the atmosphere, but these fishes differ in physiology, ecology, and possibly evolutionary origins. We introduce a scoring system to characterize interspecific variation in amphibiousness and use this system to highlight important unanswered questions about the evolutionary physiology of amphibious fishes.

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Gull, Mazhar, Stefan M. Schmitt, Roland E. Kälin e André W. Brändli. "Screening of Chemical Libraries UsingXenopusEmbryos and Tadpoles for Phenotypic Drug Discovery". Cold Spring Harbor Protocols 2023, n. 4 (30 settembre 2022): pdb.prot098269. http://dx.doi.org/10.1101/pdb.prot098269.

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Phenotypic drug discovery assesses the effect of small molecules on the phenotype of cells, tissues, or whole organisms without a priori knowledge of the target or pathway. Using vertebrate embryos instead of cell-based assays has the advantage that the screening of small molecules occurs in the context of the complex biology and physiology of the whole organism. Fish and amphibians are the only classes of vertebrates with free-living larvae amenable to high-throughput drug screening in multiwell dishes. For both animal classes, particularly zebrafish andXenopus, husbandry requirements are straightforward, embryos can be obtained in large numbers, and they develop ex utero so their development can be monitored easily with a dissecting microscope. At 350 million years, the evolutionary distance between amphibians and humans is significantly shorter than that between fish and humans, which is estimated at 450 million years. This increases the likelihood that drugs discovered by screening in amphibian embryos will be active in humans. Here, we describe the basic protocol for the medium- to high-throughput screening of chemical libraries using embryos of the African clawed frogXenopus laevis. Bioactive compounds are identified by observing phenotypic changes in whole embryos and tadpoles. In addition to the discovery of compounds with novel bioactivities, the phenotypic screening protocol also allows for the identification of compounds with in vivo toxicity, eliminating early hits that are poor drug candidates. We also highlight important considerations for designing chemical screens, choosing chemical libraries, and performing secondary screens using whole mount in situ hybridization or immunostaining.

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SÁNCHEZ-CAMACHO, CRISTINA, OSCAR MARÍN e AGUSTÍN GONZÁLEZ. "Distribution and origin of the catecholaminergic innervation in the amphibian mesencephalic tectum". Visual Neuroscience 19, n. 3 (maggio 2002): 321–33. http://dx.doi.org/10.1017/s0952523802192091.

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The mesencephalic tectum plays a prominent role in integrating both visual and multimodal sensory information essential for normal behavior in amphibians. Activity in the mesencephalic tectum is thought to be modulated by the influence of distinct neurochemical inputs, including the catecholaminergic and the cholinergic systems. In the present study, we have investigated the distribution and the origin of the catecholaminergic innervation of the mesencephalic tectum in two amphibian species, the anuran Rana perezi and the urodele Pleurodeles waltl. Immunohistochemistry for dopamine and two enzymes required for the synthesis of catecholamines, tyrosine hydroxylase (TH) and dopamine β-hydroxylase (DBH), revealed a complex pattern of catecholaminergic (CA) innervation in the anuran and urodele mesencephalic tectum. Dopaminergic fibers were primarily present in deep tectal layers, whereas noradrenergic (DBH immunoreactive) fibers predominated in superficial layers. Catecholaminergic cell bodies were never observed within the tectum. To determine the origin of this innervation, applications of retrograde tracers into the optic tectum were combined with immunohistochemistry for TH. Results from these experiments demonstrate that dopaminergic neurons in the suprachiasmatic and juxtacommissural nuclei (in Rana) or in the nucleus pretectalis (in Pleurodeles), together with noradrenergic cells of the locus coeruleus, are the sources of CA input to the amphibian mesencephalic tectum. The present results suggest that similar CA modulatory inputs are present in the mesecencephalic tectum of both anurans and urodeles.

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Greenberg, Dan A., e Wendy J. Palen. "Hydrothermal physiology and climate vulnerability in amphibians". Proceedings of the Royal Society B: Biological Sciences 288, n. 1945 (17 febbraio 2021): 20202273. http://dx.doi.org/10.1098/rspb.2020.2273.

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Concerns over the consequences of global climate change for biodiversity have spurred a renewed interest in organismal thermal physiology. However, temperature is only one of many environmental axes poised to change in the future. In particular, hydrologic regimes are also expected to shift concurrently with temperature in many regions, yet our understanding of how thermal and hydration physiology jointly affect performance and fitness is still limited for most taxonomic groups. Here, we investigated the relationship between functional performance, hydration state and temperature in three ecologically distinct amphibians, and compare how temperature and water loss can concurrently limit activity under current climate conditions. We found that performance was maintained across a broad range of hydration states in all three species, but then declines abruptly after a threshold of 20–30% mass loss. This rapid performance decline was accelerated when individuals were exposed to warmer temperatures. Combining our empirical hydrothermal performance curves with species-specific biophysical models, we estimated that dehydration can increase restrictions on species' activity by up to 60% compared to restriction by temperature alone. These results illustrate the importance of integrating species' hydration physiology into forecasts of climate vulnerability, as omitting this axis may significantly underestimate the effects of future climate change on Earth's biological diversity.

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BAILES, HELENA J., ANN E. O. TREZISE e SHAUN P. COLLIN. "The optics of the growing lungfish eye: Lens shape, focal ratio and pupillary movements inNeoceratodus forsteri(Krefft, 1870)". Visual Neuroscience 24, n. 3 (maggio 2007): 377–87. http://dx.doi.org/10.1017/s0952523807070381.

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Lungfish (order Dipnoi) evolved during the Devonian period and are believed to be the closest living relatives to the land vertebrates. Here we describe the previously unknown morphology of the lungfish eye in order to examine ocular adaptations present in early sarcopterygian fish. Unlike many teleosts, the Australian lungfishNeoceratodus forsteripossesses a mobile pupil with a slow pupillary response similar to amphibians. The structure of the eye changes from juvenile to adult, with both eye and lens becoming more elliptical in shape with growth. This change in structure results in a decrease in focal ratio (the distance from lens center to the retina divided by the lens radius) and increased retinal illumination in adult fish. Despite a degree of lenticular correction for spherical aberration, there is considerable variation across the lens. A re-calculation of spatial resolving power using measured focal ratios from cryosectioning reveals a low ability to discriminate fine detail. The dipnoan eye shares more features with amphibian eyes than with most teleost eyes, which may echo the visual needs of this living fossil.

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Ríos, Eduardo, Jingsong Zhou, Gustavo Brum, Bradley S. Launikonis e Michael D. Stern. "Calcium-dependent Inactivation Terminates Calcium Release in Skeletal Muscle of Amphibians". Journal of General Physiology 131, n. 4 (17 marzo 2008): 335–48. http://dx.doi.org/10.1085/jgp.200709870.

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In skeletal muscle of amphibians, the cell-wide cytosolic release of calcium that enables contraction in response to an action potential appears to be built of Ca2+ sparks. The mechanism that rapidly terminates this release was investigated by studying the termination of Ca2+ release underlying sparks. In groups of thousands of sparks occurring spontaneously in membrane-permeabilized frog muscle cells a complex relationship was found between amplitude a and rise time T, which in sparks corresponds to the active time of the underlying Ca2+ release. This relationship included a range of T where a paradoxically decreased with increasing T. Three different methods were used to estimate Ca2+ release flux in groups of sparks of different T. Using every method, it was found that T and flux were inversely correlated, roughly inversely proportional. A simple model in which release sources were inactivated by cytosolic Ca2+ was able to explain the relationship. The predictive value of the model, evaluated by analyzing the variance of spark amplitude, was found to be high when allowance was made for the out-of-focus error contribution to the total variance. This contribution was estimated using a theory of confocal scanning (Ríos, E., N. Shirokova, W.G. Kirsch, G. Pizarro, M.D. Stern, H. Cheng, and A. González. Biophys. J. 2001. 80:169–183), which was confirmed in the present work by simulated line scanning of simulated sparks. Considering these results and other available evidence it is concluded that Ca2+-dependent inactivation, or CDI, provides the crucial mechanism for termination of sparks and cell-wide Ca2+ release in amphibians. Given the similarities in kinetics of release termination observed in cell-averaged records of amphibian and mammalian muscle, and in spite of differences in activation mechanisms, CDI is likely to play a central role in mammals as well. Trivially, an inverse proportionality between release flux and duration, in sparks or in global release of skeletal muscle, maintains constancy of the amount of released Ca2+.

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BENOIT, EVELYNE. "A Quantitative Description of Nodal Membrane Currents in Myelinated Nerve Fibres of the Lizard Anous Carolinensis". Journal of Experimental Biology 151, n. 1 (1 luglio 1990): 405–22. http://dx.doi.org/10.1242/jeb.151.1.405.

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Experiments were performed on individual nodes of Ranvier from a lizard at 15–16°C, using the method of Nonner (1969). In addition to a leakage current (mean conductance of 19.7 nS), the membrane ionic currents consisted of a Na+ current, completely inhibited by lμmoll−1 external tetrodotoxin, and a K+ current, sensitive to external tetraethylammonium ions and to internal caesium ions. The inactivation time course of the Na+current at 0 mV was well fitted by the sum of two exponential phases, one fast and one slow, with mean time constants of 0.68 and 2.92 ms, respectively. In contrast to observations on amphibian and mammalian preparations, the peak Na+ current showed an almost linear potential dependence at large positive membrane potentials. A mean maximum Na+ conductance of 146.8 nS was calculated. Both the time and potential dependence of the K+ current indicated that it was similar to that found in amphibian nodes of Ranvier. The mean maximum K+ conductance was 51.9 nS. Furthermore, as described in amphibians, three different components of the K+ current (s, f1 and f2) could be separated. We conclude that, under similar experimental conditions, nodal ionic currents are qualitatively and quantitatively similar in lizard and amphibian myelinated nerve fibres, suggesting that the nodal membrane of these two preparations contains similar types of ionic channels. These results strengthen the view that the near absence of nodal K+ channels is a peculiarity of mammalian nerves.

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Stiffler, D. F. "Amphibian calcium metabolism". Journal of Experimental Biology 184, n. 1 (1 novembre 1993): 47–61. http://dx.doi.org/10.1242/jeb.184.1.47.

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Calcium is present in amphibian blood at a concentration similar to that in other vertebrates, about 1–2 mmol l-1. The fraction of free calcium in amphibians is lower than that in other tetrapod vertebrates because about 50% of the plasma Ca2+ is bound to plasma proteins and perhaps other molecules. Plasma [Ca2+] varies seasonally, increasing in spring and summer and decreasing in winter. Changes in plasma [Ca2+] also occur during larval development, as the concentration of this ion increases in larval forms as they approach metamorphosis. Calcium is exchanged at a variety of sites in animals. There is evidence for Ca2+ uptake across the skin and gills of larval anurans. It is also transported into the blood from the small intestine (especially the duodenum) and reabsorbed in renal tubules from the glomerular filtrate. The possibility of Ca2+ absorption from urine stored in the urinary bladder has not been confirmed, however. Calcium is stored in bone and in specialized endolymphatic sacs. This Ca2+ can be mobilized when the need arises. There are a number of endocrine and other humoral factors that appear to be involved in amphibian calcium metabolism. These include parathyroid hormone, calcitonin, vitamin D and prolactin.

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Griffioen, John A., Devorah M. Stowe, Macy Trosclair, Larry J. Minter, Chelsey Vanetten e Tara M. Harrison. "Comparison of Dilution on Eastern Box Turtle (Terrapene carolina carolina) and Marine Toad (Rhinella marinus) Blood Parameters as Measured on a Portable Chemistry Analyzer". Veterinary Medicine International 2020 (27 agosto 2020): 1–7. http://dx.doi.org/10.1155/2020/8843058.

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Biochemical testing is an important clinical tool in evaluating the physiology of reptiles and amphibians. Suitable point of care analyzers can allow for rapid delivery of results, but small patient size can inhibit sufficient sample collection. This study evaluated the utility of sample dilution with sterile distilled water as a means of biochemical evaluation when sample volume is limited. Blood was collected from 12 eastern box turtles (Terrapene carolina carolina) and 12 marine toads (Rhinella marinus) and analyzed via i-STAT CHEM8+ cartridges. Two undiluted samples and two samples diluted 1 : 1 with sterile water were evaluated immediately following collection for each animal in the study. Analytes reported in the diluted samples were limited to glucose, ionized calcium, and total carbon dioxide. The expected dilution ratio value of diluted to undiluted samples was 0.5, of which glucose in both turtles and toads was nearest. Dilution ratio values for ionized calcium, however, were higher than expected in both turtles and toads. Sample dilution is not recommended for most analytes included on the CHEM8+ cartridge due to values occurring outside the limits of detection for the analyzer. Glucose and ionized calcium values obtained on diluted samples should be interpreted with caution but may provide clinical utility in reptile and amphibian patients where sample volume is limited.

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Noronha-de-Souza, Carolina R., Kênia C. Bícego, Gustavo Michel, Mogens L. Glass, Luiz G. S. Branco e Luciane H. Gargaglioni. "Locus coeruleus is a central chemoreceptive site in toads". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 291, n. 4 (ottobre 2006): R997—R1006. http://dx.doi.org/10.1152/ajpregu.00090.2006.

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The locus coeruleus (LC) has been suggested as a CO2 chemoreceptor site in mammals. This nucleus is a mesencephalic structure of the amphibian brain and is probably homologous to the LC in mammals. There are no data available for the role of LC in the central chemoreception of amphibians. Thus the present study was designed to investigate whether LC of toads ( Bufo schneideri) is a CO2/H+ chemoreceptor site. Fos immunoreactivity was used to verify whether the nucleus is activated by hypercarbia (5% CO2 in air). In addition, we assessed the role of noradrenergic LC neurons on respiratory and cardiovascular responses to hypercarbia by using 6-hydroxydopamine lesion. To further explore the role of LC in central chemosensitivity, we examined the effects of microinjection of solutions with different pH values (7.2, 7.4, 7.6, 7.8, and 8.0) into the nucleus. Our main findings were that 1) a marked increase in c-fos-positive cells in the LC was induced after 3 h of breathing a hypercarbic gas mixture; 2) chemical lesions in the LC attenuated the increase of the ventilatory response to hypercarbia but did not affect ventilation under resting conditions; and 3) microinjection with acid solutions (pH = 7.2, 7.4, and 7.6) into the LC elicited an increased ventilation, indicating that the LC of toads participates in the central chemoreception.

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Dunand, M., M. L. Aubert, J. P. Kraehenbuhl e B. C. Rossier. "Specific binding sites for ovine prolactin in three amphibian cell lines". American Journal of Physiology-Cell Physiology 248, n. 1 (1 gennaio 1985): C80—C87. http://dx.doi.org/10.1152/ajpcell.1985.248.1.c80.

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Abstract (sommario):

Established cell lines (TB-6c and TB-M) obtained by continuous culture of epithelial cells from toad Bufo marinus urinary bladder, which, in culture, maintained a high degree of functional differentiation, exhibited a significant number of high-affinity (KA = 1-2 X 10(10) M-1) binding sites detected both with radioiodinated (125I) ovine prolactin (oPRL) and human growth hormone (hGH). Binding capacity was higher in the case of TB-6c cells (7,573 +/- 581 sites/cell) than with the TB-M cells (1,160 +/- 87). Similarly, binding sites for oPRL were characterized on Xenopus laevis kidney-derived cell line A6. With oPRL used both as tracer and standard, significant cross-reaction was observed with hGH, less with human or rat prolactin (PRL), and none with human chorionic somatomammotropin, bovine growth hormone, and rat luteinizing hormone or follicle-stimulating hormones. B. marinus pituitary extracts completely displaced the binding of 125I-oPRL to toad bladder binding sites. This finding of specific sites for PRL on amphibian bladder and kidney cells confirms that PRL exerts specific biological actions for the control of electrolyte and water metabolism in the amphibians.

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Wassersug, Richard J., Akemi Izumi-kurotani, Masamichi Yamashita e Tomio Naitoh. "Motion sickness in amphibians". Behavioral and Neural Biology 60, n. 1 (luglio 1993): 42–51. http://dx.doi.org/10.1016/0163-1047(93)90703-k.

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Phillips, John B., Mark E. Deutschlander, Michael J. Freake e S. Chris Borland. "The role of extraocular photoreceptors in newt magnetic compass orientation: parallels between light-dependent magnetoreception and polarized light detection in vertebrates". Journal of Experimental Biology 204, n. 14 (15 luglio 2001): 2543–52. http://dx.doi.org/10.1242/jeb.204.14.2543.

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SUMMARYTheoretical models implicating specialized photoreceptors in the detection of the geomagnetic field have been the impetus for studying the effects of light on magnetic compass orientation. Magnetic orientation in flies, amphibians and birds has been found to be influenced by light, and in all these groups a shift of approximately 90° in the direction of magnetic compass orientation has been observed under certain wavelengths and/or intensities of light. In the eastern red-spotted newt Notophthalmus viridescens, wavelength-dependent effects of light on magnetic compass orientation appear to result from an antagonistic interaction between short-wavelength (≤450nm) and long-wavelength (≥500nm) photoreception mechanisms. We have demonstrated that at least the short-wavelength input to the newt’s magnetic compass is mediated by extraocular photoreceptors located in or near the pineal organ, and here we present new findings that indicate that the putative long-wavelength mechanism is also associated with pineal photoreceptors. Interestingly, the amphibian pineal organ mediates orientation to both the e-vector of plane-polarized light and the magnetic field. Although the wavelength-dependence of the polarized light orientation in amphibians has not been studied, polarization sensitivity in fishes appears to be mediated by two antagonistic photoreception mechanisms that have similar spectral characteristics to those of the newts’ magnetic compass response. These parallels, along with similarities in the types of receptors that are expected to be involved in light-dependent magnetoreception and polarized light detection, suggest that similar photoreception mechanisms may mediate the light-dependent magnetic and polarized light compasses.

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22

Pinder, A., e S. Friet. "OXYGEN TRANSPORT IN EGG MASSES OF THE AMPHIBIANS RANA SYLVATICA AND AMBYSTOMA MACULATUM: CONVECTION, DIFFUSION AND OXYGEN PRODUCTION BY ALGAE". Journal of Experimental Biology 197, n. 1 (1 dicembre 1994): 17–30. http://dx.doi.org/10.1242/jeb.197.1.17.

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Many amphibians lay their eggs in gelatinous masses up to 1020 cm in diameter, posing problems for diffusive oxygen delivery. Oxygen may also be provided by water convection between eggs or by oxygen production by endogenous algae. We studied egg masses of two local amphibians, Rana sylvatica and Ambystoma maculatum, to estimate the importance of each of these processes. We injected dye to check for water channels, measured oxygen partial pressures within egg masses to determine the influence of external water convection and lighting, measured oxygen consumption and production in darkness and light and calculated expected gradients through egg masses with a cylindrical, homogeneous egg mass model. Rana sylvatica had relatively loose egg masses with water channels between the eggs; water convection was important for oxygen delivery. Ambystoma maculatum had firm egg masses with no spaces in the jelly between eggs; thus, there was no opportunity for convective oxygen delivery. The egg masses were cohabited by Oophila ambystomatis, a green alga found specifically in association with amphibian egg masses. Oxygen delivery in A. maculatum was by diffusion and by local production by the algal symbiont. Analysis of a cylindrical egg mass model and measurement of oxygen gradients through egg masses indicated that diffusion alone was not adequate to deliver sufficient O2 to the innermost embryos at late developmental stages. In the light, however, egg masses had a net oxygen production and became hyperoxic. Over the course of a day with a 14 h:10 h light:dark cycle, the innermost embryos were alternately exposed to hyperoxia and near anoxia.

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23

Gabor, Caitlin R., Caitlin R. Gabor, Jaime Bosch, Caitlin R. Gabor, Jaime Bosch, Joe N. Fries, Caitlin R. Gabor, Jaime Bosch, Joe N. Fries e Drew R. Davis. "A non-invasive water-borne hormone assay for amphibians". Amphibia-Reptilia 34, n. 2 (2013): 151–62. http://dx.doi.org/10.1163/15685381-00002877.

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Anthropogenic disturbances have been implicated in the rapid decline of amphibians. Disturbances, such as disease and poor water quality, might cause changes in the physiology of amphibians resulting in chronic stress, which can result in decreased growth and development as well as immunosuppression. In amphibians, corticosterone (CORT) is the main hormone released in response to stressors. We took the first steps towards validating a new, non-invasive, technique to assay CORT in amphibians using a water-borne collection method previously used only with fish. In validation of this technique, we found a significant positive correlation between release rates of water-borne CORT and levels of CORT in circulating plasma in adults of the San Marcos salamander, Eurycea nana, and the common midwife toad, Alytes obstetricans. These results indicate that water-borne CORT can be used as a proxy for plasma CORT. Additionally, we examined basic background information on the physiological states of these two species. We found that captive-reared salamanders had significantly lower release rates of CORT than field-collected salamanders. Field-collected salamanders had significantly higher CORT release rates 24 h after capture and transfer to the laboratory. For tadpoles, we found that field-collected tadpoles did not have significantly different CORT release rates than those maintained in the laboratory for four months. Our research indicates that this method of water-borne hormone collection should be viable for many species of amphibians; however, further validation via adrenocorticotropic hormone (ACTH) challenges is required. This method can be a useful tool for assessing the physiological state of laboratory and field populations of amphibians and the effects of urbanization, pesticides and diseases. An important benefit of this method is that it allows for repeated measures of the same individuals and can be less stressful than drawing blood.

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24

Sundqvist, Monika. "Developmental changes of purinergic control of intestinal motor activity during metamorphosis in the African clawed frog, Xenopus laevis". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 292, n. 5 (maggio 2007): R1916—R1925. http://dx.doi.org/10.1152/ajpregu.00785.2006.

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Little is known about the purinergic regulation of intestinal motor activity in amphibians. Purinergic control of intestinal motility is subject to changes during development in mammals. The aim of this study was to investigate purinergic control of intestinal smooth muscle in the amphibian Xenopus laevis and explore possible changes in this system during the developmental phase of metamorphosis. Effects of purinergic compounds on mean force and contraction frequency in intestinal circular muscle strips from prometamorphic, metamorphic, and juvenile animals were investigated. Before metamorphosis, low concentrations of ATP reduced motor activity, whereas the effects were reversed at higher concentrations. ATP-induced relaxation was not inhibited by the P2-receptor antagonist pyridoxalphosphate-6-azophenyl-2′,4′-disulfonic acid (PPADS) but was blocked by the ecto-nucleotidase inhibitor 6- N, N-diethyl-d-β,γ-dibromomethylene ATP ( ARL67256 ), indicating that an ATP-derived metabolite mediated the relaxation response at this stage. Adenosine induced relaxation before, during, and after metamorphosis, which was blocked by the A1-receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX). The stable ATP-analog adenosine 5′-[γ-thio]-triphosphate (ATPγS) and 2-methylthioATP (2-MeSATP) elicited contractions in the circular muscle strips in prometamorphic tadpoles. However, in juvenile froglets, 2-MeSATP caused relaxation, as did ATPγS at low concentrations. The P2Y11/P2X1-receptor antagonist NF157 antagonized the ATPγS-induced relaxation. The P2X-preferring agonist α-β-methyleneadenosine 5′-triphosphate (α-β-MeATP) evoked PPADS-sensitive increases in mean force at all stages investigated. This study demonstrates the existence of an adenosine A1-like receptor mediating relaxation and a P2X-like receptor mediating contraction in the X. laevis gut before, during, and after metamorphosis. Furthermore, the development of a P2Y11-like receptor-mediated relaxation during metamorphosis is shown.

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25

Houck, Lynne D. "Pheromone Communication in Amphibians and Reptiles". Annual Review of Physiology 71, n. 1 (marzo 2009): 161–76. http://dx.doi.org/10.1146/annurev.physiol.010908.163134.

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26

Pearce, J. L., D. Schuurman, K. N. Barber, M. Larrivée, L. A. Venier, J. McKee e D. McKenney. "Pitfall trap designs to maximize invertebrate captures and minimize captures of nontarget vertebrates". Canadian Entomologist 137, n. 2 (aprile 2005): 233–50. http://dx.doi.org/10.4039/n04-029.

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AbstractPitfall traps containing a preservative have become the standard method of sampling for epigeal invertebrates such as carabid beetles and cursorial spiders. However, they often result in high levels of mortality for small mammals and amphibians. We compared the carabid, spider, and vertebrate captures within five pitfall trap types (conventional trap, funnel trap, shallow trap, Nordlander trap, and the ramp trap) to determine the trap type that would reduce vertebrate incidental catch without compromising the capture of invertebrates. We also examined the effect of a mesh screen over pitfall traps on carabid beetle and vertebrate catches. All modifications to the conventional trap design resulted in a reduction in both small mammal and amphibian captures. The shallow pitfall trap and the funnel trap captured a carabid beetle and spider fauna similar to that captured by the conventional trap. The species compositions of the ramp trap and the Nordlander trap were different from those of the other trap types, but these traps were more efficient, capturing more species per individual captured. The ramp trap appeared to be the method of choice for sampling epigeal spiders. Thus, the choice among trap designs for invertebrates depends on the objectives of the study. However, an alternative to the conventional trap design should always be considered to reduce small mammal mortality.

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27

Taylor, Edwin W., David Jordan e John H. Coote. "Central Control of the Cardiovascular and Respiratory Systems and Their Interactions in Vertebrates". Physiological Reviews 79, n. 3 (1 luglio 1999): 855–916. http://dx.doi.org/10.1152/physrev.1999.79.3.855.

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This review explores the fundamental neuranatomical and functional bases for integration of the respiratory and cardiovascular systems in vertebrates and traces their evolution through the vertebrate groups, from primarily water-breathing fish and larval amphibians to facultative air-breathers such as lungfish and some adult amphibians and finally obligate air-breathers among the reptiles, birds, and mammals. A comparative account of respiratory rhythm generation leads to consideration of the changing roles in cardiorespiratory integration for central and peripheral chemoreceptors and mechanoreceptors and their central projections. We review evidence of a developing role in the control of cardiorespiratory interactions for the partial relocation from the dorsal motor nucleus of the vagus into the nucleus ambiguus of vagal preganglionic neurons, and in particular those innervating the heart, and for the existence of a functional topography of specific groups of sympathetic preganglionic neurons in the spinal cord. Finally, we consider the mechanisms generating temporal modulation of heart rate, vasomotor tone, and control of the airways in mammals; cardiorespiratory synchrony in fish; and integration of the cardiorespiratory system during intermittent breathing in amphibians, reptiles, and diving birds. Concluding comments suggest areas for further productive research.

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28

BARNI, SERGIO, VITTORIO BERTONE, ANNA CLETA CROCE, GIOVANNI BOTTIROLI, FRANCO BERNINI e GIUSEPPE GERZELI. "Increase in liver pigmentation during natural hibernation in some amphibians". Journal of Anatomy 195, n. 1 (luglio 1999): 19–25. http://dx.doi.org/10.1017/s0021878299004999.

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The amount/distribution of liver melanin in 3 amphibian species (Rana esculenta, Triturus a. apuanus, Triturus carnifex) was studied during 2 periods of the annual cycle (summer activity–winter hibernation) by light and electron microscopy, image analysis and microspectrofluorometry. The increase in liver pigmentation (melanin content) during winter appeared to be correlated with morphological and functional modifications in the hepatocytes, which at this period were characterised by a decrease in metabolic activity. These findings were interpreted according to the functional role (e.g. phagocytosis, cytotoxic substance inactivation) played by the pigment cell component in the general physiology of the heterothermic vertebrate liver and, in particular, in relation to a compensatory engagement of these cells against hepatocellular hypoactivity during the winter period.

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29

Carvajalino-Fernández, Juan Manuel, Maria Argenis Bonilla Gomez, Liliana Giraldo-Gutierréz e Carlos Arturo Navas. "Freeze tolerance in neotropical frogs: an intrageneric comparison using Pristimantis species of high elevation and medium elevation". Journal of Tropical Ecology 37, n. 3 (maggio 2021): 118–25. http://dx.doi.org/10.1017/s026646742100016x.

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AbstractParamos are high-elevation tropical Andean ecosystems above the tree line that display variable temperature and frequent freezing spells. Because a significant anuran community lives in this environment, physiological protection against freezing must characterise individuals in this community. Antifreeze protection has been studied in amphibians from other communities, and it is likely that Paramo anurans rely on the same underlying molecules that convey such protection to Nearctic species. However, given the pervasive presence of freezing spells in the Paramos year-round, the processes of activating protection mechanisms may differ from that of seasonal counterparts. Accordingly, this study investigated cryoprotection strategies in high-elevation tropical frogs, using as a model the terrestrial and nocturnal genus Pristimantis, specifically P. bogotensis, P. elegans and P. nervicus from Paramos, and the warm ecosystem counterparts P. insignitus, P. megalops and P. sanctaemartae. We focused on freeze tolerance and its relationship with glucose accumulation and ice formation. Under field conditions, the highest elevation P. nervicus exhibited higher glucose concentration at dawn compared to noon (1.7 ± 0.6 mmol/L versus 3.5 ± 1.32 mmol/L). Under experimental thermal freeze exposure for 2 hours between −2 and −4 ºC, the glucose concentration of the three Paramo species increased but physiological diversity was evident (P. nervicus 126%; P. bogotensis 100%; and P. elegans 55%). During this test, body ice formation was assessed calorimetrically. The species with the highest body ice formation was P. bogotensis (17% ± 5.37; maximum value: 63%; n = 8), followed by P. nervicus (5% ± 3.27; maximum value: 11%; n = 5) and P. elegans (0.34% ± 0.09; maximum value: 1%; n = 4). The study shows physiological diversity both within a genus and across the amphibian community around the freezing contour. Overall, Paramo species differ in freezing physiology from their low-elevation counterparts. Thus, climate shifts increasing freezing spells may affect the structure of communities in this zone.

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30

Kettlun, Claudia, Adom González, Eduardo Ríos e Michael Fill. "Unitary Ca2+ Current through Mammalian Cardiac and Amphibian Skeletal Muscle Ryanodine Receptor Channels under Near-physiological Ionic Conditions". Journal of General Physiology 122, n. 4 (15 settembre 2003): 407–17. http://dx.doi.org/10.1085/jgp.200308843.

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Ryanodine receptor (RyR) channels from mammalian cardiac and amphibian skeletal muscle were incorporated into planar lipid bilayers. Unitary Ca2+ currents in the SR lumen-to-cytosol direction were recorded at 0 mV in the presence of caffeine (to minimize gating fluctuations). Currents measured with 20 mM lumenal Ca2+ as exclusive charge carrier were 4.00 and 4.07 pA, respectively, and not significantly different. Currents recorded at 1–30 mM lumenal Ca2+ concentrations were attenuated by physiological [K+] (150 mM) and [Mg2+] (1 mM), in the same proportion (∼55%) in mammalian and amphibian channels. Two amplitudes, differing by ∼35%, were found in amphibian channel studies, probably corresponding to α and β RyR isoforms. In physiological [Mg2+], [K+], and lumenal [Ca2+] (1 mM), the Ca2+ current was just less than 0.5 pA. Comparison of this value with the Ca2+ flux underlying Ca2+ sparks suggests that sparks in mammalian cardiac and amphibian skeletal muscles are generated by opening of multiple RyR channels. Further, symmetric high concentrations of Mg2+ substantially reduced the current carried by 10 mM Ca2+ (∼40% at 10 mM Mg2+), suggesting that high Mg2+ may make sparks smaller by both inhibiting RyR gating and reducing unitary current.

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31

Kikuyama, Sakaé, Kazutoshi Yamamoto, Takeo Iwata e Fumiyo Toyoda. "Peptide and protein pheromones in amphibians". Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology 132, n. 1 (maggio 2002): 69–74. http://dx.doi.org/10.1016/s1096-4959(01)00534-6.

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32

Fritsche, R., e A. Jacobsson. "Ontogeny of cardiovascular regulation in amphibians". Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 124 (agosto 1999): S31. http://dx.doi.org/10.1016/s1095-6433(99)90120-4.

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33

Gargaglioni, Luciane H., e William K. Milsom. "Control of breathing in anuran amphibians". Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 147, n. 3 (luglio 2007): 665–84. http://dx.doi.org/10.1016/j.cbpa.2006.06.040.

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34

Gargaglioni, L. H. "24.2. Control of Breathing in Amphibians". Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 148 (agosto 2007): S109. http://dx.doi.org/10.1016/j.cbpa.2007.06.285.

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35

Huang, Min Yi, Ren Yan Duan e Xiao Li Ji. "Amphibian as a Model to Study Environmental Problem". Applied Mechanics and Materials 71-78 (luglio 2011): 3179–82. http://dx.doi.org/10.4028/www.scientific.net/amm.71-78.3179.

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In order to obtain a better insight of the possible threat of environmental factor to wildlife, especially to amphibians, we studied influences of dicofol on heart rate inR. nigromaculataby applying biological signal recording and monitoring system.R. nigromaculatawas injected in ventral lymph follicle in different doses of dicofol solution, and then observed the changes of heart rate after 7 days. The results showed that with the concentration of dicofol solution increasing, the heart rate, systolic tension and diastolic tension changed. The aim of this research is to discuss the cause of dicofol on the physiology in frogs. It can be concluded that dicofol affects the electronic activity of the frog’s heart.

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36

Theiss, Klaus, H. Peter Richter, Adolf Dörge e Bernd Lindemann. "Vacuolation of Isolated Amphibian Urocytes". Cellular Physiology and Biochemistry 2, n. 5 (1992): 253–63. http://dx.doi.org/10.1159/000154647.

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37

Gnionsahe, A., M. Claire, N. Koechlin, J. P. Bonvalet e N. Farman. "Aldosterone binding sites along nephron of Xenopus and rabbit". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 257, n. 1 (1 luglio 1989): R87—R95. http://dx.doi.org/10.1152/ajpregu.1989.257.1.r87.

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Distal segment of several amphibians exhibits aldosterone-modulated ion transport properties. On the other hand, A6 cells, derived from Xenopus laevis (XL) kidney, are aldosterone sensitive. We examined the distribution of aldosterone binding sites in isolated tubules of XL compared with rabbit. After incubation with 2 nM [3H]aldosterone, microdissected tubular segments from proximal (PT), distal straight segment (DST), and flask cell collecting (CT) tubules from XL and from rabbit cortical thick ascending limb (CTAL), connecting (CNT), and collecting (CCD) tubules were processed for dry film autoradiography. In XL, specific nuclear labeling of type I (mineralocorticoid) sites was restricted to DST. Labeling of type II (glucocorticoid) sites was present all along the tubule. No specific cytoplasmic labeling was observed, except for type II sites in PT. In the rabbit, aldosterone binds to both type I and type II sites in the three tubular segments studied. In these segments, the binding was about fourfold higher than in DST of XL. These results bring direct evidence in designating the distal tubule of amphibians as a target epithelium for aldosterone. In addition, they suggest that A6 cell line may derive from DST of the Xenopus nephron.

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38

Woodley, Sarah K. "Pheromonal communication in amphibians". Journal of Comparative Physiology A 196, n. 10 (5 giugno 2010): 713–27. http://dx.doi.org/10.1007/s00359-010-0540-6.

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39

Smotherman, M. S., e P. M. Narins. "Hair cells, hearing and hopping: a field guide to hair cell physiology in the frog". Journal of Experimental Biology 203, n. 15 (1 agosto 2000): 2237–46. http://dx.doi.org/10.1242/jeb.203.15.2237.

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Abstract (sommario):

For more than four decades, hearing in frogs has been an important source of information for those interested in auditory neuroscience, neuroethology and the evolution of hearing. Individual features of the frog auditory system can be found represented in one or many of the other vertebrate classes, but collectively the frog inner ear represents a cornucopia of evolutionary experiments in acoustic signal processing. The mechano-sensitive hair cell, as the focal point of transduction, figures critically in the encoding of acoustic information in the afferent auditory nerve. In this review, we provide a short description of how auditory signals are encoded by the specialized anatomy and physiology of the frog inner ear and examine the role of hair cell physiology and its influence on the encoding of sound in the frog auditory nerve. We hope to demonstrate that acoustic signal processing in frogs may offer insights into the evolution and biology of hearing not only in amphibians but also in reptiles, birds and mammals, including man.

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40

Gaudino, G., A. Fasolo, G. Merlo, L. H. Lazarus, T. Renda, L. D'Este e F. Vandesande. "Active peptides from amphibian skin are also amphibian neuropeptides". Peptides 6 (gennaio 1985): 209–13. http://dx.doi.org/10.1016/0196-9781(85)90376-6.

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41

Bögi, Christian, Gregor Levy, Ilka Lutz e Werner Kloas. "Functional genomics and sexual differentiation in amphibians". Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology 133, n. 4 (dicembre 2002): 559–70. http://dx.doi.org/10.1016/s1096-4959(02)00162-8.

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42

Theiss, Klaus, Pedro Mestres-Ventura, H. Peter Richter e Bernd Lindemann. "Membrane Redistribution in Isolated Amphibian Urocytes". Cellular Physiology and Biochemistry 2, n. 5 (1992): 236–52. http://dx.doi.org/10.1159/000154645.

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43

Kondrashev, S. L. "Neuroethology and color vision in amphibians". Behavioral and Brain Sciences 10, n. 3 (settembre 1987): 385. http://dx.doi.org/10.1017/s0140525x0002330x.

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44

Hillman, Stanley S., Andrew Zygmunt e Mark Baustian. "Transcapillary Fluid Forces during Dehydration in Two Amphibians". Physiological Zoology 60, n. 3 (maggio 1987): 339–45. http://dx.doi.org/10.1086/physzool.60.3.30162287.

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45

Oishi, Tadashi, Kiyoko Nagai, Yumiko Harada, Mayumi Naruse, Masumi Ohtani, Emi Kawano e Satoshi Tamotsu. "Circadian Rhythms in Amphibians and Reptiles: Ecological Implications". Biological Rhythm Research 35, n. 1-2 (febbraio 2004): 105–20. http://dx.doi.org/10.1080/09291010412331313278.

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46

WOOD, CHRIS M., R. S. MUNGER e D. P. TOEWS. "Ammonia, Urea and H+ Distribution and the Evolution of Ureotelism in Amphibians". Journal of Experimental Biology 144, n. 1 (1 luglio 1989): 215–33. http://dx.doi.org/10.1242/jeb.144.1.215.

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Abstract (sommario):

In theory, the distribution of ammonia across cell membranes (Tammi/Tamme) between intracellular and extracellular fluids (ICF and ECF) may be determined by the transmembrane pH gradient (as in mammals), the transmembrane potential (as in teleost fish), or both, depending on the relative permeability of the membranes to NH3 and NH4+ (pNH3/pNH4+). The resting distributions of H+ (via [14C]DMO), ammonia and urea between plasma and skeletal muscle, and the relative excretion rates of ammonia-N and urea-N, were measured in five amphibian species (Bufo marinus, Ambystoma tigrinum, Rana catesbeiana, Necturus maculosus and Xenopus laevis). Although ureai/ureae ratios were uniformly close to 1.0, Tammi/Tamme. ratios correlated directly with the degree of ammoniotelism in each species, ranging from 9.1 (Bufo, 10% ammoniotelic) to 16.7 (Xenopus, 79% ammoniotelic). These values are intermediate between ratios of about 30 (low pNH3/pNH4+) in ammoniotelic teleost fish and about 3 (high pNH3/pNH4+) in ureotelic mammals. The results indicate that amphibians represent a transitional stage in which ammonia distribution is influenced by both the pHi-pHe gradient and the membrane potential, and that a reduction in cell membrane permeability to NH4+ (i.e. increased pNH3/pNH4+) was associated with the evolution of ureotelism. Hyperosmotic saline exposure increased urea excretion 10-fold in Xenopus, while ammonia excretion remained unchanged. Tammi/Tamme fell, but this response was attributable to an abolition of the pHi-pHe gradient, rather than a physiological change in the cell membrane pNH3/pNH4+.

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47

Gargaglioni, Luciane H., Janice T. Meier, Luiz G. S. Branco e William K. Milsom. "Role of midbrain in the control of breathing in anuran amphibians". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 293, n. 1 (luglio 2007): R447—R457. http://dx.doi.org/10.1152/ajpregu.00793.2006.

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Abstract (sommario):

The present study was designed to explore systematically the midbrain of unanesthetized, decerebrate anuran amphibians (bullfrogs), using chemical and electrical stimulation and midbrain transections to identify sites capable of exciting and inhibiting breathing. Ventilation was measured as fictive motor output from the mandibular branch of the trigeminal nerve and the laryngeal branch of the vagus nerve. The results of our transection studies suggest that, under resting conditions, the net effect of inputs from sites within the rostral half of the midbrain is to increase fictive breathing frequency, whereas inputs from sites within the caudal half of the midbrain have no net effect on fictive breathing frequency but appear to act on the medullary central rhythm generator to produce episodic breathing. The results of our stimulation experiments indicate that the principal sites in the midbrain that are capable of exciting or inhibiting the fictive frequency of lung ventilation, and potentially clustering breaths into episodes, appear to be those primarily involved in visual and auditory integration, motor functions, and attentional state.

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48

GLEESON, TODD T. "Patterns of Metabolic Recovery from Exercise in Amphibians and Reptiles". Journal of Experimental Biology 160, n. 1 (1 ottobre 1991): 187–207. http://dx.doi.org/10.1242/jeb.160.1.187.

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Abstract (sommario):

The physiological responses of amphibians and reptiles undergoing vigorous exercise are qualitatively similar to those of other vertebrates. Oxygen consumption increases rapidly to rates that are three- to 10-fold the rates at rest. The aerobic response to graded exercise in locomoting reptiles and amphibians is for the most part linear. Oxygen transport by the cardiovascular system during exercise is accomplished by factorial increases in heart rate and oxygen extraction from arterial blood in a fashion similar to that in mammals. Increments in stroke volume during exercise are small or in some cases negative. The influence of temperature or of intracardiac shunting on the cardiovascular function of active amphibians and reptiles is poorly understood. These aerobic responses to exercise are accompanied by robust anaerobic contributions to energy metabolism, resulting in significant lactate accumulation and glycogen depletion. The rate of lactate accumulation during exercise is generally greater in reptiles than in amphibians, but in all cases is so rapid that the only significant substrate source to support anaerobic energy production is muscle glycogen. Vigorous behavior in these animals is therefore limited to some degree by the maintenance and replenishment of muscle glycogen stores. Whereas data from rats and dogs suggest that most lactate is oxidized to CO2 following exercise, amphibians and reptiles appear to use lactate as a substrate for immediate muscle glycogen replenishment. Data from a variety of amphibians and lizards demonstrate that lactate removal following activity and glycogen replenishment are stoichiometrically and temporally related. Studies employing isotopically labelled compounds in intact frogs and lizards indicate that most lactate is resynthesized to glycogen during recovery. In vivo studies suggest skeletal muscle as the site for glycogenesis from lactate, and in vitro studies from many laboratories demonstrate a gluconeogenic capacity in skeletal muscle of lizards, frogs and salamanders. The liver appears to play no significant role in recovery metabolism in any of these classes. Data from lizard muscle suggest that oxidative fiber types have the most significant gluconeogenic capacity, and that the process may be stimulated by the hormonal milieu that exists following exercise. Whereas the recovery metabolism of many mammals seems to facilitate the rapid return of acid-base balance via lactate oxidation, the strategy of lactate removal employed by amphibians and reptiles provides for a mechanism of immediate muscle glycogen replenishment and consequently a reestablished capacity for subsequent activity.

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49

Fishman, A. P., R. G. DeLaney e P. Laurent. "Circulatory adaptation to bimodal respiration in the dipnoan lungfish". Journal of Applied Physiology 59, n. 2 (1 agosto 1985): 285–94. http://dx.doi.org/10.1152/jappl.1985.59.2.285.

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In the dipnoan lungfish, Protopterus aethiopicus, P. annectens, and Lepidosiren paradoxa, the ductus is a short powerful muscular vascular trunk forming a channel for communication between the systemic and pulmonary circulations. In structure, the dipnoan ductus is very similar to the ductus arteriosus (Botalli) in the mammal. Innervation is abundant, consisting of myelinated and nonmyelinated nerve fibers issuing, at least in part, from the vagus. Neurons are present in the adventitia, and numerous nerve profiles, filled with small agranular vesicles, are closely associated with the myocytes, suggesting strong cholinergic control. Perfusion of the ductus in vitro using hypoxic saline causes it to dilate; conversely it is constricted by alpha-agonists. Dopamine and prostaglandin E2 are potent dilators, whereas the beta-agonist, isoproterenol, and acetylcholine are less powerful. A vasomotor segment has been identified on the pulmonary artery (PAVS) close to its junction with the ductus. Its location and structure are similar to the corresponding segment in amphibians and reptiles. It is innervated by endings filled with small clear vesicles. Granular vesicle cells are also present within the adventitia. The PAVS is constricted by acetylcholine. As in amphibians, alpha-agonists and hypoxic saline are without vasomotor effects. Based on the anatomic and physiological observations, a concept of cyclic perfusion of the gas exchangers in Dipnoi is proposed. During the alternation between air breathing (emersion) and apneic phases (immersion), the pattern of the circulation in the lungfish oscillates between that of a tetrapod and a fish.

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Stinner, J. N., L. K. Hartzler, M. R. Grguric e D. L. Newlon. "A protein titration hypothesis for the temperature-dependence of tissue CO2 content in reptiles and amphibians." Journal of Experimental Biology 201, n. 3 (1 febbraio 1998): 415–24. http://dx.doi.org/10.1242/jeb.201.3.415.

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Whole-body CO2 stores are known to increase with cooling in reptiles and amphibians (-[CO2]/T ). The aim of this study was to determine the mechanism(s) producing this inverse relationship. The [CO2]/T coefficients were determined for eight reptilian and one amphibian species and were found to differ by a factor of approximately 10, from -0.21 mmol kg-1 °C-1 in the Mediterranean spur-thighed tortoise Testudo graeca to -0.02 mmol kg-1 °C-1 in the bullfrog Rana catesbeiana. The [CO2]/T coefficients were correlated with values in the literature for in vivo plasma pH/T coefficients ([CO2]/T=-0.188.24pH/T; r2=0.87). Plasma electrolyte concentrations (Na+, K+, Ca2+, Mg2+, Cl-, inorganic phosphate, SO42- and lactate), [protein], [CO2], PCO2 and pH were measured in chronically cannulated resting black racer snakes Coluber constrictor. When the temperature was reduced from 30 to 10 °C, pH increased slightly (by -0.0028 pH units °C-1), PCO2 decreased by 7 mmHg, [CO2] increased by 3.2 mmol l-1 and [HPO42-+H2PO4-] increased by 0.7 mmol l-1. Concentrations of protein and of the remaining electrolytes were not significantly different (P>0.05) at 30 and 10 °C. Net plasma protein charge, calculated from the principle of electroneutrality (the sum of the cations in mequiv = the sum of anions in mequiv), was -0.48 mequiv g-1 protein at 30 °C and -0.38 mequiv g-1 protein at 10 °C. This 21 % decrease was attributed to the increases in [CO2] (i.e. carbonic acid) and inorganic phosphate concentration. Between 30 and 10 °C, skeletal muscle pH and [CO2] in C. constrictor increased (by -0.009 units °C-1 and -0.125 mmol kg-1 °C-1, respectively), [Na+] and [Cl-] each decreased by approximately 12 mequiv l-1, and [K+] and the percentage of water did not change significantly. It is concluded that the increase in whole-body CO2 stores with cooling in reptiles and amphibians results from the passive effects of temperature changes upon the ionization constants of proteins and the active adjustment of PCO2 (ventilatory regulation), so that -pK is greater than -pH. Active transmembrane ion-exchange processes do not appear to be involved.

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