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PubMed1992

Effects of arginine vasotocin, cortisol and adrenergic factors on water balance in the toad Bufo bufo: physiology or pharmacology?

1. The threshold level of exogenous arginine vasotocin (AVT) for increasing the cutaneous water permeability in Bufo bufo was several times higher than has been measured in dehydrated frogs and toads. 2. The beta-agonist isoproterenol was without effect on water balance in hydrated toads but increased the response to large doses of AVT by 25-50%. 3. Implantation of cortisol pellets in water-acclimated toads enhanced the cutaneous water permeability by a factor of 2-3. 4. It is concluded that understanding of water balance in terrestrial anurans may depend upon the unravelling of mechanisms that integrate cutaneous water transport and diuresis.

Adaptation, Physiological↗

PubMed1996

Histological convergent evolution of the accessory submandibular glands in four species of frog-eating bats.

The accessory submandibular glands in four species of bats were examined by electron microscopy. These four species represent two independently evolved lineages. The fringe-lipped bat, Trachops cirrhosis, is a Neotropical phyllostomid species, whereas the false vampire bats of southeast Asia, Megaderma lyra and M. spasma, and the heart-nosed bat, Cardioderma cor, of East Africa are megadermatid species. These glands show extreme deviation from typical salivary gland histology: their secretory endpieces are in the form of follicles and their ducts lack the cytological details that permit identification of diverse duct segments. Despite their unusual histology, the secretory endpieces in M. lyra, M. spasma, and C. cor consist of secretory cells that conform to typical secretory cell morphology. In contrast, secretion by follicular cells in T. cirrhosis involves unusual cytoplasmic bodies, and their mitochondria frequently have intracristal crystalloids. Ducts in all four species consist of simple cuboidal to columnar epithelium without basal striations. Follicles and ducts in all four bats are surrounded by numerous myoepithelial cells and are heavily innervated by hypolemmal nerve terminals. Despite their widely separated geographical ranges, all four bat species consume frogs and other vertebrates. Frogs and toads often possess toxic cutaneous glands that provide a chemical defense against predation. It is postulated that the unusual accessory glands in the four frog-eating species secrete toxin-neutralizing salivary factors. The follicular form of the endpieces permits storage of preformed saliva and their coterie of myoepithelial cells and hypolemmal nerve terminals facilitates the sudden and rapid expulsion of saliva into the oral cavity during the consumption of noxious amphibians.

Animals↗

PubMed1999

Contractile properties of muscles used in sound production and locomotion in two species of gray tree frog.

The sound-producing muscles of frogs and toads are interesting because they have been selected to produce high-power outputs at high frequencies. The two North American species of gray tree frog, Hyla chrysoscelis and Hyla versicolor, are a diploid-tetraploid species pair. They are morphologically identical, but differ in the structure of their advertisement calls. H. chrysoscelis produces very loud pulsed calls by contracting its calling muscles at approximately 40 Hz at 20 degrees C, whereas, H. versicolor operates the homologous muscles at approximately 20 Hz at this temperature. This study examined the matching of the intrinsic contractile properties of the calling muscles to their frequency of use. I measured the isotonic and isometric contractile properties of two calling muscles, the laryngeal dilator, which presumably has a role in modulating call structure, and the external oblique, which is one of the muscles that provides the mechanical power for calling. I also examined the properties of the sartorius as a representative locomotor muscle. The calling muscles differ greatly in twitch kinetics between the two species. The calling muscles of H. chrysoscelis reach peak tension in a twitch after approximately 15 ms, compared with 25 ms for the same muscles in H. versicolor. The muscles also differ significantly in isotonic properties in the direction predicted from their calling frequencies. However, the maximum shortening velocities of the calling muscles of H. versicolor are only slightly lower than those of the comparable muscles of H. chrysoscelis. The calling muscles have similar maximum shortening velocities to the sartorius, but have much flatter force-velocity curves, which may be an adaptation to their role in cyclical power output. I conclude that twitch properties have been modified more by selection than have intrinsic shortening velocities. This difference corresponds to the differing roles of shortening velocity and twitch kinetics in determining power output at differing frequencies.

Animals↗

PubMed1996

The analysis of complex developmental programmes: amphibian metamorphosis.

Metamorphosis in frogs and toads is a set of complex developmental programmes controlled by thyroid hormone (TH). The pervasive and dramatic changes that occur as a tadpole turns into a frog have captured the attention of life scientists from many disciplines. For evolutionary biologists, the extent to which related organisms incorporate metamorphosis in their life cycle is of paramount interest. For specialists who study cell death, a burgeoning field of research interest, apoptosis is a major event in metamorphosis. It can be induced in many tissues, even in whole organs, by TH. For endocrinologists, TH-induced metamorphosis is a model for the general problem of the molecular basis of TH action and the interaction of the hypothalamus, the pituitary and the thyroid glands. However, the emphasis in this essay is the use of amphibian metamorphosis to study complex developmental programmes such as vertebrate organogenesis which can be initiated by the simple addition of TH to the tadpole's rearing water.

Animals↗

PubMed1965

EFFECT OF ALKALI METAL CATIONS ON THE POTENTIAL ACROSS TOAD AND BULLFROG URINARY BLADDER.

Isolated urinary bladders of the bullfrog (R. catesbeiana) and the toad (B. marinus) were mounted in an Ussing chamber. Potential differences up to 114 mv were observed in bullfrog bladder when the mucosal surface was bathed in dilute Na(2)SO(4) and the serosal surface in sulfate Ringer's. In experiments with bullfrogs, K was used to replace Na in the mucosal solution and Na was used for K in the serosal solutions. The selectivity was judged in terms of the relative effectiveness of the replacement cation in maintaining the bladder potential. In experiments with toads, K and Rb were equally poor replacements for Na at the mucosal border, while Rb was a good replacement for K at the serosal border. Li in the mucosal solution appeared to depress the potential in part irreversibly. At the serosal border, Li was a partially effective substitute for K, more so than was Na. However, both were poor replacements compared to Rb. The mucosal surface of the urinary bladder of both frog and toad appears to be Na-selective and the serosal surface appears to be K-selective, consistent with the Koefoed-Johnsen-Ussing model for frog skin.

Animals↗

PubMed2006

The tactile-stimulated startle response of tadpoles: acceleration performance and its relationship to the anatomy of wood frog (Rana sylvatica), bullfrog (Rana catesbeiana), and American toad (Bufo americanus) tadpoles.

I described the tactile-stimulated startle response (TSR) of wood frog (Rana sylvatica), bullfrog (Rana catesbeiana), and American toad (Bufo americanus) tadpoles. One purpose was to rank species in terms of maximum acceleration performance. Also, I tested whether anatomical indicators of performance potential were predictive of realized performance. TSRs were elicited in a laboratory setting, filmed at 250 Hz, and digitally analyzed. TSRs began with two, initial body curls during which tadpoles showed a broad spectrum of movement patterns. TSR performance was quantified by maximum linear acceleration and maximum rotational acceleration of the head/body, both of which tended to occur immediately upon initiation of motion (< 0.012 sec into the response). Bullfrog tadpoles had higher maximum acceleration than the other species, but other interspecific differences were not significant. The species' rank order for the anatomical indicator of linear acceleration potential was bullfrog > wood frog > American toad. The species' rank order for the anatomical indicator of rotational acceleration potential was bullfrog > wood frog = American toad. Thus, the anatomical indicators roughly predicted the rank order of interspecific average performance. However, the anatomical indicators did not correlate with individual tadpole performance. Variability in behavioral patterns may obscure the connection between anatomy and performance. This is seen in the current lack of intraspecific correlation between a morphological indicator of acceleration capacity and acceleration performance.

Animals↗

PubMed1999

Allometry in vestibular responses of anurans.

Frogs and toads turn either their heads or bodies opposite to angular accelerations applied around the yaw axis. Thresholds exist for the minimum angular acceleration that induces this vestibulomotor response in individual frogs. These thresholds were recorded for several anuran species that cover a broad range of sizes and life styles. Interspecific variation in the magnitude of the thresholds, which correlated with the ecology and behavior of the species, was documented. Also an allometric relationship was observed between this threshold and body size; the larger the frog, the lower the threshold. In many species, the threshold value for reflexive vestibulomotor responses to angular acceleration was proportional to the -0.4 (+/-0.2) power of body mass. Physical dimensions of the semicircular canals determine, in part, vestibular sensitivity to angular acceleration. Hence changes with growth in the semicircular canals are believed to contribute to the slope of -0.4. The biological significance of this allometry in vestibular responses is discussed and compared to trends in vestibular sensitivity and semicircular canal morphology of other vertebrate classes.

Acceleration↗

PubMed1982

Sexual dimorphism in succinic dehydrogenase staining of toad pretrigeminal nucleus.

The anuran (toad and frog) pretrigeminal nucleus is probably involved in the production of vocalizations, including the male mating call. This nucleus is especially obvious when stained by the succinic dehydrogenase method. In the American toad, a striking sexual dimorphism is shown by such staining. The male nucleus contains numerous, large cells that stain intensely. Such cells are smaller and infrequent in females.

Animals↗

PubMed1992

Wasting disease associated with cutaneous and renal nematodes, in commercially obtained Xenopus laevis.

Xenopus laevis, the South African clawed frog or toad, is a member of the family Pipidae. Now in high demand for research purposes, they are available commercially. Its reported lifespan is up to fifteen years. Investigators and caretakers are frustrated when commercially obtained, young frogs (four years or younger), not subjected to any studies, "waste" and die. The wasting syndrome is characterized by anorexia, color change, and "flaky skin." Often the first sign of this syndrome is the presence of large fragments of "flakes" of desquamated epithelium in the water. At necropsy, these frogs are thin and have rough skin instead of smooth slimy skin. Histologic examination reveals tortuous intraepithelial cavities or tunnels that contain nematodes, and associated mild to moderate granulomatous inflammation. Nematodes are also found in the kidneys of some of these frogs, usually in Bowman's space, wrapped around the glomerulus. The cutaneous capillarid nematode is identified as Pseudocapillaroides xenopi. Successful treatment with ivermectin and thiabendizole has been reported. The renal glomerular nematode has not been identified.

Animals↗

PubMed1991

Polymorphism in purified guanylate cyclase from vertebrate rod photoreceptors.

Guanylate cyclase from rod photoreceptors of amphibian (toad, Bufo marinus, and frog, Rana catesbeiana) and bovine retinas was solubilized and purified by a single chromatography step on a GTP-agarose column. Silver staining of purified amphibian enzymes in SDS/polyacrylamide gels disclosed a doublet band (110 and 115 kDa), while the bovine enzyme appeared as a singlet band (110 kDa). The identification of these guanylate cyclases was confirmed using three chromatography systems with the purified enzymes. Specific binding to Con A-Sepharose suggested that rod guanylate cyclase is a glycoprotein. Two-dimensional gel electrophoresis of purified toad, frog, and bovine enzymes resolved two, three, and five variants, respectively, that differed in isoelectric point. Two variants of toad guanylate cyclase showed differences in various characterizations. These data suggest multiple mechanisms for regulation of guanylate cyclase activity in vertebrate rod photoreceptors.

Animals↗

PubMed2005

Elevated corticosterone levels elicit non-calling mating tactics in male toads independently of changes in circulating androgens.

Competition among males for a limited number of females may result in the expression of condition-dependent alternative mating tactics. In such cases, decision rules mediating mating tactic expression are likely to be influenced by a male's external as well as internal environment. For example, experimental studies with anuran amphibians (frogs and toads) indicate that changes in the social-acoustic environment alter the probability that an individual adopts a calling versus non-calling "satellite" mating tactic. However, there is considerable variation in the behavioral responses of individuals in such studies, suggesting that physiological differences among individuals play an important role in tactic expression. For instance, recent models predict that natural elevation in adrenal glucocorticoids during vocal production alters androgen production and/or neural activity to mediate transitions between reproductive tactic expression in anuran amphibians. Using corticosteroid injections, we show that elevation in circulating corticosterone levels significantly increase the probability that free-ranging male Great Plains toads (Bufo cognatus) and Woodhouse's toads (B. woodhousii) adopt a non-calling satellite tactic. Corticosterone-induced behavioral transitions occurred rapidly (<1 h) and independently of fluctuations in circulating androgen levels, suggesting a direct effect of glucocorticoids on brain centers controlling vocal production. We discuss our findings in the context of behavioral studies that alter the social-acoustic environment to examine its influence on tactic expression.

Androgens↗

PubMed1991

Two types of fast K+ channels in rat myelinated nerve fibres and their sensitivity to dendrotoxin.

The effect of dendrotoxin (DTX), a component of the venom of the Eastern green mamba snake, Dendroaspis angusticeps, on K+ currents in rat myelinated nerve fibres was studied in voltage clamp experiments, immunocytochemistry and binding experiments. The analysis of K+ tail currents in 160 mM KCl solution revealed that K+ channels with slow gating kinetics predominate in the intact node of Ranvier. These slow K+ channels were not blocked by DTX. Intact nerve fibres additionally showed fast K+ tail currents of small amplitude which could be blocked by DTX. After enzymatic demyelination with pronase, fast K+ currents of large amplitude appeared. Analysis of the non-monotonous voltage dependence of the fast K+ conductance and the partial pharmacological block by DTX suggest the presence of two subtypes of fast K+ channels in rat nerve fibres similar to the Kf1 and Kf2 channels previously described in the frog and toad node of Ranvier. The DTX concentration required for 50% inhibition (IC50) for the Kf1 component was 8 nM. The IC50 of the blocked Kf2 component was the same as that for Kf1, but the Kf2 component was only partially blocked (about 50%). In contrast to frog nerve, these two fast K+ channel subtypes are located predominantly in the paranodal region. Immunocytochemical staining experiments with DTX using the peroxidase-antiperoxidase technique confirmed the electrophysiological data. In intact nodes, either no staining or only slight staining in some fibres was found. After demyelination, extensive staining of paranodal and internodal regions occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1981

Potassium channels in the nodal membrane of rat myelinated fibres.

Following some preliminary reports, mammalian fibres from rabbit and rat have recently been successfully studied in detail by means of the voltage clamp. The early transient or sodium conductance system was found to be similar to that in frog and squid axons. However, the delayed conductance or potassium currents were found to be negligible. Only after chemical and osmotic manipulations, which were said to expose channels buried under the myelin, did Chiu and Ritchie find delayed currents in rabbit fibres. If confirmed, this would mean that the membrane conductance system of mammalian fibres is so different from that of invertebrate and amphibian axon models as to make the data base gathered from amphibian myelinated fibres (frog and toad) and invertebrate giant axons (squid and myxicola) irrelevant to human nd other mammalian fibres. However, we show here that it is possible to find in the normal nodal membrane of rat myelinated fibres potassium currents that flow through channels which are similar in many respects to those found in the frog node of squid axons.

Animals↗

PubMed1990

Studies of epithelial electrolyte transport by marker ions.

The paper reviews several recent studies in which marker ions, such as Rb and Br, were used to identify ion transport pathways and membrane properties in epithelia. In the frog skin epithelium, using Rb as a substitute for K, Cl transport mechanisms across the basolateral membranes of principal cells were studied. The data suggest that intracellular Cl is maintained above electrochemical equilibrium by an Na-K-2Cl cotransport system which, under non-stimulated conditions, is normally quiescent. In toad and frog skins, the route of transepithelial Cl movement was investigated. A subpopulation of mitochondria-rich cells demonstrated a ready exchange of Br with the apical and basal bathing media, consistent with the view that these cells constitute a transcellular anion shunt. Moreover, voltage-activation resulted in an increased Br uptake from the apical bath. Nevertheless, because of the very small number of these cells, it may be questioned whether the mitochondria-rich cell constitutes the only shuntpathway for Cl. In other studies, Rb uptake was employed to measure the Na/K-pump activity. In principal cells of the frog skin epithelium, amiloride inhibited Rb uptake and lowered Na concentration, supporting the view that this cell type is engaged in amiloride-sensitive Na transport. In contrast, no significant changes in the Rb, Na, and Cl concentration of mitochondria-rich cells were detectable. Studies with Rb as marker ion in the rabbit urinary bladder revealed that the epithelium behaves like a functional syncytium with regard to transepithelial ion transport.

Amiloride↗

PubMed2000

The genetics of amphibian declines: population substructure and molecular differentiation in the yosemite toad, Bufo canorus (Anura, bufonidae) based on single-strand conformation polymorphism analysis (SSCP) and mitochondrial DNA sequence data.

We present a comprehensive survey of genetic variation across the range of the narrowly distributed endemic Yosemite toad Bufo canorus, a declining amphibian restricted to the Sierra Nevada of California. Based on 322 bp of mitochondrial cytochrome b sequence data, we found limited support for the monophyly of B. canorus and its closely related congener B. exsul to the exclusion of the widespread western toad B. boreas. However, B. exsul was always phylogenetically nested within B. canorus, suggesting that the latter may not be monophyletic. SSCP (single-strand conformation polymorphism) analysis of 372 individual B. canorus from 28 localities in Yosemite and Kings Canyon National Parks revealed no shared haplotypes among these two regions and lead us to interpret these two parks as distinct management units for B. canorus. Within Yosemite, we found significant genetic substructure both at the level of major drainages and among breeding ponds. Kings Canyon samples show a different pattern, with substantial variation among breeding sites, but no substructure among drainages. Across the range of B. canorus as well as among Yosemite ponds, we found an isolation-by-distance pattern suggestive of a stepping stone model of migration. However, in Kings Canyon we found no hint of such a pattern, suggesting that movement patterns of toads may be quite different in these nearby parklands. Our data imply that management for B. canorus should focus at the individual pond level, and effective management may necessitate reintroductions if local extirpations occur. A brief review of other pond-breeding anurans suggests that highly structured populations are often the case, and thus that our results for B. canorus may be general for other species of frogs and toads.

Animals↗

PubMed1980

Tadpole of the clawed frog, Xenopus laevis, as an experimental intermediate host of Angiostrongylus cantonensis.

Frogs and toads, as paratenic hosts, are known to be sources of human angiostrongyliasis. The present investigation was carried out to examine the role of the tadpole as an experimental intermediate host. First-, second-, and third-stage larvae were found in tadpoles of Xenopus laevis from the 1st, 14th, and 18th days, respectively, after exposure to the first-stage larva of Angiostrongylus cantonensis. Third-stage larvae collected from a frog which had metamorphosed from an exposed tadpole reached maturity and oviposited in an albino rat. This is the first demonstration that a vertebrate, the tadpole of X. laevis, can serve as an experimental intermediate host of A. cantonensis.

Animals↗

PubMed1988

Insulin and phorbol ester stimulate conductive Na+ transport through a common pathway.

Insulin stimulates Na+ transport across frog skin, toad urinary bladder, and the distal renal nephron. This stimulation reflects an increase in apical membrane Na+ permeability and a stimulation of the basolateral membrane Na,K-exchange pump. Considerable indirect evidence has suggested that the apical natriferic effect of insulin is mediated by activation of protein kinase C. However, no direct information has been available documenting that insulin and protein kinase C indeed share a common pathway in stimulating Na+ transport across frog skin. In the present work, we have studied the interaction of insulin and phorbol 12-myristate 13-acetate (PMA), a documented activator of protein kinase C. Preincubation of skins with 1,2-dioctanoylglycerol, another activator of protein kinase C, increases baseline Na+ transport and reduces the subsequent natriferic response to PMA. Preincubation with PMA markedly reduces the subsequent natriferic action of insulin. This effect does not appear to primarily reflect PMA-induced internalization of insulin receptors. The insulin receptors are localized on the basolateral surface of frog skin, but the application of PMA to this surface is much less effective than mucosal treatment in reducing the response to insulin. Preincubation with D-sphingosine, an inhibitor of protein kinase C, also reduces the natriferic action of insulin. The current results provide documentation that insulin and protein kinase C share a common pathway in stimulating Na+ transport across frog skin. The data are consistent with the concept that the natriferic effect of insulin on frog skin is, at least in part, mediated by activation of protein kinase C.

Animals↗

PubMed2002

A forerunner of septohippocampal cholinergic system is present in amphibians.

The medial pallium of anuran amphibians (frogs and toads) has been considered homologue to the mammalian hippocampus. While physiological and behavioral studies have strengthened this homology, basic anatomical features of the hippocampus were not observed in amphibians. The septohippocampal cholinergic pathway is among the most prominent afferent connection of the hippocampus and is involved in learning and memory processes. In the present study, double labeling techniques revealed that up to 18% of the retrograde labeled cells in the medial septal nucleus and nucleus of the diagonal band of the frog were cholinergic. This pathway can be considered as a forerunner of the septohippocampal pathway of mammals and might represent the anatomical substrate for learning processes in which the medial pallium is involved in amphibians.

Acetylcholine↗