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At least 19 recordsLinked to original sources
PubMed1978

Amphibian embryo protease inhibitor. V. Effect of calcium on the distribution of amphibian trypsin inhibitor during fertilization and subsequent development of Rana pipiens.

In previous publications we have documented the existence in oocytes and embryos of a variety of forms (notably Rana pipiens), massive amounts of a powerful inhibitor of trypsin-like enzymes (ATI). The bulk of the inhibitor in Rana pipiens is localized in yolk platelets. We present evidence here that the distribution of the inhibitor between yolk platelets and cytosol changes and that this change is mediated by variations in the distribution of calcium ions. There is an inverse relationship between ATI and free calcium in the cytosol. Several workers have demonstrated a dramatic rise in free cytosol calcium immediately following fertilization. We confirm this observation, and demonstrate that there is a parallel and equally dramatic decrease in free cytosol ATI during this period. Experiments with purified yolk platelets indicate that calcium effects a release of sequestered inhibitor from these particles. Other experiments indicate that calcium mediates ATI-lippovitellin associations. A calcium mediated flux of ATI from cytosol to yolk is proposed as a device for controlling limited proteolysis in the cytoplasm. We offer this as a model for studying the unmasking of mRNA which follows fertilization.

Animals↗
PubMed1979

Actions of peptides isolated from amphibian skin on amylase release from dispersed pancreatic acini.

In dispersed acini prepared from guinea pig pancreas, peptides isolated from amphibian skin (caerulein, bombesin, litorin, and physalaemin) as well as eledoisin, a peptide isolated from the posterior salivary gland of a Mediterranean octopod, caused a significant increase in amylase release. Each amphibian peptide potentiated the stimulation of amylase release caused by vasoactive intestinal peptide or secretin in that the increase in amylase release caused by an amphibian peptide plus vasoactive intestinal peptide or secretin was significantly greater than the sum of the increase caused by each secretagogue acting alone. Potentiation of amylase secretion did not occur with an amphibian peptide plus cholecystokinin or carbachol.

Amphibians↗
PubMed1978

Actions of peptides isolated from amphibian skin on pancreatic acinar cells.

In dispersed acinar cells prepared from guinea pig pancreas, peptides isolated from amphibian skin (caerulein, bombesin, litorin, and physalaemin) as well as eledoisin, a peptide isolated from the posterior salivary gland of a Mediterranean octopod, increased outflux of 45Ca, release of bound 45Ca, accumulation of cyclic GMP, and release of amylase. In addition, bombesin, litorin, physalaemin, and eledoisin each increased the initial uptake of 45Ca by dispersed acinar cells, whereas C-terminal octapeptide of porcine cholecystokinin (CCK-OP) and carbamylcholine did not increase the initial uptake of 45Ca but, rather, abolished the increase caused by the other agents. None of the actions of these amphibian peptides was altered by concentrations of atropine sufficient to abolish the effects of muscarinic cholinergic agents. None of the amphibian peptides altered cellular cyclic AMP or the increase caused by secretin or porcine vasoactive intestinal peptide (VIP). Acinar cells preincubated with 45Ca plus bombesin showed the same rate of release of 45Ca as did control cells and this rate was not altered by adding bombesin but was increased fivefold by adding CCK-OP. In terms of their chemical structures as well as the potency and efficacy with which they alter acinar cell function, the amphibian peptides plus CCK-OP can be grouped into three pairs: caerulein with CCK-OP, bombesin with litorin, and physalaemin with eledoisin.

Amylases↗
PubMed2026

RePo index: a multidimensional framework to quantify genetic resilience in data-limited amphibian faunas.

This study explores the resilience of Chilean amphibians to environmental disturbances through an integrative approach that combines ecological, demographic, bibliometric, and molecular information. A total of 58 species distributed across 14 genera and 9 families were evaluated via the resilience potential (RePo) index, which incorporates eleven criteria grouped into five dimensions: distribution, population trends, emerging diseases, evolutionary history, and genetic records. The results revealed high ecological vulnerability: 83% of the species were classified as non resilient (45% with no resilience and 38% with low resilience), and none reached the high-resilience category. At the family level, Telmatobiidae presented the lowest resilience values, whereas Leptodactylidae presented the highest. At the genus level, Insuetophrynus was identified as the most vulnerable taxon, with no molecular records and an extremely restricted distribution. In contrast, species such as Rhinella spinulosa and Pleurodema thaul presented moderate resilience, suggesting greater adaptive potential and relevance for functional studies. From a bibliometric perspective, a bias toward classical research topics (distribution, physiology, and taxonomy) was detected, with limited representation of integrative approaches such as genetic conservation or climate change. The conceptual modularity in the literature was low (Q = 0.1328), indicating weak thematic differentiation and little integration of omics tools. Most species lack transcriptomic and genomic data, severely limiting the assessment of their adaptive mechanisms. In this context, the RePo index has emerged as an integrative tool useful for operationalizing concepts such as evolutionarily significant units (ESUs) and management units (MUs), which are essential for evidence-based conservation. Finally, this study highlights the need to incorporate high-throughput sequencing (HTS) technologies and to participate in international initiatives, such as the Amphibian Genomics Consortium, as a strategic path forward for advancing adaptive conservation of Chilean amphibians.

Animals↗
PubMed1978

The effects of alpha and beta adrenergic agents on spleen cell antigen binding in four amphibian species.

Adults of two urodele amphibian species (Triturus cristatus carnifex and Cynops hongkongensis) and two anuran species (Rana temporaria and Xenopus laevis laevis) were immunized with a 25% suspension of sheep or horse erythrocytes. After eight or 14 days, splenic lymphocytes were removed, and their specific red cell-binding capacities tested by immunocytoadherence. Antigen-binding cells were classified as high-dose nonsecretory (S-) or secretory (S+), according to whether they bound a single layer or several layers or erythrocytes. The stimulation of both alpha and beta adrenoreceptors reduced the numbers of S+ rosettes formed by Triturus and Cynops lymphocytes, whereas a beta agonist increased and an alpha agonist decreased S+ rosette formation by Rana and Xenopus splenic lymphocytes. These effects were blocked by alpha and beta adrenoreceptor antagonists. Low-dose immunization of Xenopus with a 0.0025% suspension of sheep erythrocytes gave a minimal number of S+ rosettes two and eight days after immunization, and beta adrenoreceptor stimulation had no effect on antigen binding. These results are discussed in terms of the distribution of alpha and beta adrenoreceptors in amphibians and possible relationships between S+ and high-dose S- antigen-binding cells, and support the view that functional lymphocyte heterogeneity exists in these lower vertebrates.

Amphibians↗
PubMedDate not supplied

New and uncommon indole- and imidazole-alkylamines in skins of amphibians from Australia and Papua New Guinea.

Extracts of the skin of some amphibians from Australia and Papua New Guinea contained, in addition to the usual 5-hydroxyindolealkylamines and histamine: a. two new, hitherto unknown indolealkylamines, i.e. O-sulphate of bufotenidine and 2-(3-indolyl) ethyltrimethylammonium, a quaternary ammonium base of tryptamine. The rare O-sulphate of bufotenine was also present, the occurrence of which had previously been demonstrated only in the skin of some South American toads; b. a series of uncommon imidazolealkylamines, such as N'-acetylhistamine, N'-methylhistamine, N',N'-dimethylhistamine, spinaceamine and 6-methylspinaceamine. It appears evident that amphibian skin continues to be an exceptionally rich source of aromatic amines.

Amines↗
PubMed1979

Local analysis or the composition of amphibian and shark teeth using laser probe mass spectrometry.

In the intention of confirming and extending previous studies on the ultrastructure of the teeth of the lower vertebrates, we have performed analyses of the amounts of various chemical elements present in the teeth of two amphibians and a shark. For this purpose we employed a laser probe mass spectrometer, with which we were able to measure profiles of the variation of amount of the different elements with depth at the different points chosen for analysis. The results are expressed as relative abundances using phosphorus as reference. Differences in the relative amounts of many elements can be observed at different sample points on a tooth, and, for a given sample point, at different depths. These differences certainly reflect ultrastructural features, although some of these may not yet have been described. Fluorine has been found to be much abundant in the teeth of a shark than in those of amphibians.

Amphibians↗
PubMed1979

Insulin effects on protein synthesis and secretion in primary cultures of amphibian hepatocytes.

The objective of the present study was to determine the effects of insulin on amphibian hepatocytes in primary culture. Hepatocytes were isolated from adult bullfrogs by collagenase perfusion and maintained as monolayers in serum-free medium. Cells cultured in the continuous presence of insulin exhibited a relatively constant rate of protein secretion over the first four to five days, whereas controls showed an almost three-fold decrease over the same time period. The decline in secreted proteins was equally represented in most exported proteins, except that serum albumin secretion showed twice as much of a decrease relative to the other proteins. The maintenance of protein secretion by insulin was the result of its effect on protein synthesis. The rate of protein synthesis was measured by the incorporation of (3H)-leucine into protein using culture medium containing 0.5 mM leucine, a condition where the specific radioactivity of leucyl-tRNA was shown to be equal to that of (3H)-leucine in the medium. Cultures maintained with insulin for 60 hours synthesized protein at two to three times the rate found in non-insulin treated controls whose rate of protein synthesis was first detectably decreased after nine hours of culture in the insulin-free medium. Sedimentation profiles of polyribosomes from hepatocytes maintained for 60 hours without insulin showed proportionately fewer ribosomes in large polysomes and more in monosomes and free ribosomal subunits than ribosomes from cells cultured with insulin. This result suggests that the decrease in protein synthesis found in the absence of insulin is due to a defect in initiation. Insulin does not exert its effect by regulating cellular levels of ATP; no change in ATP content was found in cells maintained with or without insulin. The results show that insulin maintains high levels of protein synthesis and secretion in amphibian hepatocytes. The hepatocytes in monlayer culture provide a system to study the molecular mechanisms involved in the translational control of protein synthesis by insulin.

Albumins↗
PubMed1977

Immuno-cytochemical demonstration, in the external region of the amphibian median eminence, of separate vasotocinergic and mesotocinergic nerve fibres.

By means of single and double immuno-enzyme cytochemical staining techniques, it was shown that the external region of the amphibian median eminence contains separate vasotocinergic and mesotocinergic nerve fibres. Moreover, it was demonstrated that the vasotocinergic fibres also contain neurophysin. In animals in which the hypothalamic magnocellular neurosecretory preoptic nuclei had been completely removed, the immuno-reactive vasotocinergic and mesotocinergic fibres of the median eminence had disappeared. From this result, it is concluded that, at least the great majority of the vasotocinergic and mesotocinergic fibres of the external region of the amphibian median eminence are processes of neurosecretory perikarya located in the hypothalamic magnocellular preoptic nuclei. On the other hand, our results do not exclude the possibility that a minority of these neurosecretory fibres originate from small immuno-reactive perikarya which were found in the tuber cinereum. The observation that both kinds of processes accumulate around blood capillaries of the hypophysial portal system strongly suggests that they play a role in the control of the activity of the pars distalis of the hypophysis.

Animals↗
PubMed1977

[Control of pituitary secretion of melanotropin in an anuran amphibian by thyrotropin releasing factor (TRH). Study in vitro].

Intermediate lobes from Rana esculenta pituitary glands were continuously superfused for 7 hrs at 28 degrees C with amphibian culture medium. alpha-MSH release was measured by use of a sensitive double antibody radio-immunoassay system. alpha-MSH secretion was inhibited by low temperatures. A large increase in alpha-MSH release was observed when Thyrotropin Releasing Hormone (TRH) at doses ranging from 10(-9) to 10(-7) molar was added to the superfusion medium. Since large amounts of TRH are to be found in the hypothalamus of amphibians but have no effect over pituitary TSH secretion, the action of TRH over alpha-MSH release may have a physiological significance.

Animals↗
PubMed1979

Fate maps and cell differentiation in the amphibian embryo--an experimental study.

The aim of this paper is to test two different fate maps for the amphibian blastula with respect to their predictions concerning the process of cell differentiation. The first of these fate maps is the one proposed by Vogt, according to which all three germ layers can be projected on to the surface of the embryo. The second is a revision which claims that only endoderm and ectoderm are located in the surface, while the mesoderm is represented by free cells in the interior of the embryo. The testing has been performed by observing the differentiation of small explants of cells taken from various regions of the embryo. It was found that the spontaneous cell differentiation comprises three patterns: undifferentiated cells (free interior cells and circumpolar endodermal cells), fibroblast-like cells (the remaining endodermal cells) and epidermis (ectodermal cells). Further differentiation occurs only through induction, exerted either by the fibroblast-like endodermal cells or by heparan sulphate. When induced, the equatorial ectodermal cells give rise to swollen, hyaline cells (chordocytes), while the remaining ectodermal cells form a sequence of cell differentiation patterns, mesenchyme cells, nerve cells, melanophores and xanthophores. The free interior cells differentiate into striated muscle cells and elongated collagen-producing fibroblasts. Our results thus confirm the revised fate map, and they also give an insight into the mechanisms of the initial cell differentiations in the amphibian embryo.

Ambystoma↗
PubMed1976

Oildroplets in the eyes of adult anuran amphibians: a comparative survey.

Oildroplets in the eyes of terrestrial vertebrates are spherical cellular organelles that stain for lipids, have no discernible internal structure, and often contain carotenoids and possibly other chemicals. A survey of 97 species of anuran amphibians (frogs and toads) revealed that all species of 16 families surveyed possessed yellow oildroplets of varying size in the cells of the pigment epithelium, except for three species that appear to have secondarily lost them during evolution. Furthermore, 25 species of six families also possess colorless oildroplets at the distal end of the inner segments of single cones and principal cones of the double-cone system; two species of the Ranidae appear to have secondarily lost such retinal oildroplets. Every species possesses epithelial or retinal oildroplets or both. Lastly, small oildroplet-like inclusions were discovered in the red blood cells of two species. All of Walls' ('42) summary generalizations about anuran oildroplets are incorrect: oildroplets are not restricted to the Ranidae, are not yellow when found in the cones, and do not correlate with photoactic behavior in 87 species. Evidence is reviewed suggesting that the primary function of anuran oildroplets is chemical storage, perhaps related to the visual pigment cycle. Oildroplets in the cones may additionally act as filters of ultraviolet radiation.

Amphibians↗
PubMed1977

A diffusion model for mesoderm induction in amphibian embryos.

In this paper we try to answer the question whether diffusion is a possible mechanism to explain mesoderm induction in Amphibians. First the embryological data are discussed and a hypothesis for mesoderm formation is set forth. The blastula being essentially a hollow sphere, we assume that the induction mechanism in an embryo at the blastula stage can be simulated by diffusion-reaction processes on spherical surfaces. A model is constructed for the simple case when the source is held constant with respect to time, the decay proportional to the concentration and the diffusion coefficient a constant. From simulation we find a (best) value for the decay constant to be 6 x 10(-5)/sec and for the diffusion constant to be 0.24 x 10(-6) cm2/sec. The relation between the parameters is derived from an analytic solution for the diffusion process on a spherical surface with a continuously producing point source and the concentration proportional to the decay. The form and regulative properties of the steady concentration gradient are discussed.

Amphibians↗
PubMed1979

Cation permeation of the amphibian motor end-plate.

Measurements of acetylcholine-induced single-channel conductance and null potentials at the amphibian motor end-plate in solutions containing Na, K, Li and Cs ions (Gage & Van Helden, 1979; J. Physiol. (London) (in press) were analyzed in terms of three models. Two of these models, the "neutral" site channel model and the "charged" site channel model were developed to cater for three cations. Both were shown to be able to explain the dependence of single-channel conductance on membrane potential and gave the following sequences of equilibrium constants and mobilities. KLi/KNa/KK/KCs = 7:1.1:1:0.9 and UCs/UK/UNa/ULi = 1.4:1:0.58:0.13 at 8 degrees C. Similar sequences were obtained at 20 degrees C. Although the neutral model fitted the data for relative conductances in Li-, Cs- and Na-solutions slightly better than the charged model, experiments done in normal [NaCl] and [NaCl]/2 solutions could only be fitted by the neutral model. In contrast, the third model, the Constant Field Equation, was unable to fit the conductance data in any of the above situations. The data available suggests that permeation is through "long" neutral channels, lined with high field-strength negative polar groups and including one or possibly more high resistance barriers for anions.

Amphibians↗
PubMed1975

The formation of synapses in amphibian striated muscle during development.

1. A study has been made of the formation of synapses in developing reinnervated and cross-reinnervated amphibian twitch muscles which receive either a focal (iliofibularis) or a distributed (sartorius) innervation from 'en plaque' nerve terminals using histological, ultrastructural and electrophysiological techniques. 2. During the development of the tadpole through metamorphosis to the adult frog, the sartorius myofibres increased in length at about twice the rate of the iliofibularis myofibres, due to a fast rate of growth at their insertions on to the pelvic tendon. 3. The short iliofibularis and sartorius myofibres of young tadpoles (800 mum long) possessed only a single synapse and the iliofibularis myofibres did not receive any further innervation during development. However the sartorius myofibres received further transient innervation on the new muscle laid down during development at the fast growing pelvic insertion, until the distance between the original synapse formed on the myofibres and the synapse at the pelvic end of the muscle was about 12 mm. 4. During development synapses possessed either skewed, multimodal, or unimodal m.e.p.p. amplitude-frequency distributions; the intervals between m.e.p.p.s. were not distributed randomly according to a Poisson process, as m.e.p.p.s. of similar amplitudes tended to be separated by very short intervals; the unit-size e.p.p. had a similar amplitude-frequency distribution as the m.e.p.p.s. if these had a unimodal distribution. 5. Reinnervation or cross-reinnervation of the sartorius and the iliofibularis muscles in adults or at a late stage of development simply reconstituted the normal focal and distributed innervation patterns of the muscles, as found in the control muscles of the contralateral and unoperated legs. 6. These observations on synapse formation in amphibia are consistent with the hypothesis that during development the axon making the initial synaptic contact on the muscle cells induces a property over a length of muscle membrane adjacent to this site which makes it refractory to synapse formation; thus during reinnervation or cross-reinnervation of adult muscles this refractory property constrains synapse formation to these sites.

Amphibians↗
PubMed1975

Induction of neural differentiation in cultures of amphibian undetermined presumptive epidermis by cyclic AMP derivatives.

Induction of neural differentiation in cultures of undetermined presumptive epidermis from three amphibian species was achieved by the addition of 1 millimolar dibutyryl adenosine 3',5'-monophosphate, 8-bromadenosine 3',5'-monophosphate, or adenosine C',E'-monophosphate together with theophylline. Adenosine 5'-monophosphate, adenosine 2',3'-monophosphate, dibutyryl guanosine 3',5'-monophosphate, and butyrate at 1 millimolar are ineffective. These results suggest that the action of the primary inductor or inductors may be mediated via adenosine 3',5'-monophosphate.

Amphibians↗
PubMed1979

Voltage dependence of junctional conductance in early amphibian embryos.

Isolated pairs of blastomeres from early amphibian embryos (Ambystoma, Rana, Xenopus) are electrontonically coupled. Junctional conductance and permeability to the dye Lucifer Yellow are markeldy and reversibly decreased by moderate transjunctional polarization in either direction. The relationship between junctional conductance and transjunctional voltage is sufficiently steep that a physiological role in regulation of intercellular communication is plausible.

Ambystoma↗