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PubMed2004

Vasculature of the parotoid glands of four species of toads (bufonidae: bufo).

The parotoid glands of toads (Bufonidae) consist of large aggregations of granular glands located between the otic region of the skull and the scapular region. To determine the circulatory pattern of these glands, we perfused the vascular systems of Bufo alvarius, B. marinus, B. terrestris, and B. valliceps with either India ink or Microfil, a fine latex. The perfused glands were studied by gross dissection, microscopic examination, and histology. The vascular patterns of the parotoid glands were compared to the arrangement of vessels in the dorsal skin of Rana sphenocephala (Ranidae), a frog that lacks parotoid glands. The parotoid glands of the four species of toads are supplied with blood by the lateral and dorsal cutaneous arteries and are drained by one or more branches of the internal jugular vein. The dorsal cutaneous artery supplies most of the blood to the parotoid glands in B. terrestris and B. valliceps. In B. alvarius and B. marinus, both the lateral and dorsal cutaneous arteries serve major roles in the blood supply of the glands. These patterns of blood flow have not been described previously for parotoid glands and conflict with earlier accounts for B. alvarius and B. marinus. The arteries and veins associated with the parotoid glands of toads are present in R. sphenocephala, but are arranged differently. In R. sphenocephala, the lateral cutaneous artery supplies the dorsal and lateral skin posterior to the shoulder region, whereas the dorsal cutaneous artery supplies the skin of the shoulder region. In toads, both the lateral and dorsal cutaneous arteries supply the skin of the shoulder region and ramify into subcutaneous capillaries that surround the secretory units of the parotoid glands. Extensive vasculature presumably is important for delivering cholesterol and other precursor molecules to the parotoid glands, where those compounds are converted into toxins.

Animals↗
PubMed1975

The excretion of hydrogen ion by the isolated amphibian skin: effects of antidiuretic hormone and amiloride.

H+ extrusion by the isolated skins of two amphibia, Rana ridibunda and Bufo bufo, was studied in order to test for the presence of exchange mechanisms of the type Na+/H+ and Cl-/HCO3-, which have been described in several epithelial structures. The preparations were mounted in chambers of the Ussing type, so that the short-circuit current could be used as a function of Na+ transport and the pH-stat techinique was utilize to determine the rates of H+ extrusion under different experimental conditions. The conditions were either the withdrawal of the ions intervening the mentioned exchanges (Cl- or Na+), or the addition of drugs with well-known effects on Na+ up-take and transport (antidiuretic hormone and amiloride). In the frog skin, H+ excretion was detected in solutions containing either Cl- or SO4-2-, with identical rates. Again, Na+ substitution by Mg-2+ had no effect on H+ excretion rates, neither did the suppression of Na+ influx by amiloride or its stimulation by antidiuretic hormone. These experiments were repeated with similar results in gland-free preparations of the epidermis of frog skin separated from the corion by the action of collagenase. Experiments in toad skin that H+ excretion could not be detected whan Cl- was present in the outer medium, but became apparent if an impermant anion, SO4-2-, was used. This observation is compatible with the existence of an exchange mechanism of the type Cl-/HCO3-. Secondly, in these preparations H+ extrusion increased after stimulation with antidiuretic hormone and decreased when amiloride was used or when Na+ was substituted by Mg+, suggesting that a least a fraction of the total H+ efflux is linked to Na+ influx. In the isolated frog skin this mechanism does not seem to be operative.

Amiloride↗
PubMed1978

Lack of effect of blood-volume expansion on short-circuit current across an isolated toad skin incorporated in the circulation of a rat.

1. Evidence for the existence of 'natriuretic hormone' resides, in part, in the demonstration that blood volume expansion in the dog is followed by a transient fall in short-circuit current (SCC) across a frog skin incorporated within its circulation. 2. We have attempted to confirm this effect in the rat, with a toad skin (Xenopus laevis) incorporated within the circulation. The skins, bathed in whole rat blood, displayed low SCC; skins bathed in 'mammalian' Ringer solution displayed equally low SCC, but responded normally to pitressin or amiloride. 3. When volume expansion was induced in ten rats by infusion of equilibrated whole blood (28 ml/kg body weight) there was a brisk rise in systemic blood pressure, diuresis, natriuresis and kaliuresis. 4. This blood-volume expansion was without detectable effect on the SCC across the skins incorporated within the rats' circulations.

Animals↗
PubMedDate not supplied

Large retinal ganglion cells that form independent, regular mosaics in the bufonoid frogs Bufo marinus and Litoria moorei.

Population-based methods were used to study labeled retinal ganglion cells from the cane toad Bufo marinus and the treefrog Litoria moorei, two visually competent bufonoid neobatrachians with contrasting habitats. In both, cells with large somata and thick dendrites formed distinct types with independent mosaics. The alpha(a), alpha(ab), and alpha(c) mosaics of Bufo in all major respects resembled those of ranids, studied previously, and could be provisionally matched to the same functional classes. As in other frogs, some alpha(a) cells were displaced and many alpha-cells of all types were asymmetric, but within each type all variants belonged to one mosaic. Nearest-neighbor analyses and spatial correlograms confirmed that all three mosaics were regular and independent. In Litoria, monostratified alpha(a) cells were not found. Instead, two bistratified types were present, distinguished individually by soma size and dendritic caliber and collectively by membership of independent mosaics: the larger (approximately 0.8% of all ganglion cells) was termed alpha1(ab) and the smaller (approximately 2.2%) alpha2ab. An alpha(c) cell type was also present, although too inconstantly labeled for mosaic analysis. Nearest-neighbor analyses and spatial correlograms confirmed that the two alpha(ab) mosaics were regular and independent. Densities, proportions, soma sizes, and mosaic statistics are tabulated for each species. The emergence of a consensus pattern of alpha-cell types in fishes and frogs, from which this treefrog partly diverges, offers new possibilities for studying correlations between function, phylogeny, ecology, and neuronal form.

Animals↗
PubMed1977

Tazonomy of Toxoplasma.

After reviewing reports of the hosts, structure and life cycle of Toxoplasma, the genus is placed in the apicomplexan family Eimeriidae and the folllowing 7 species are recognized: Toxoplasma gondii (Nicolle & Manceaux) (type species) from about 200 species of mammals and birds, with oocysts in felids; Toxoplasma alencari (Da Costa & Pereira) from the frog Leptodactylus ocellatus; Toxoplasma brumpti Coutelen from the iguana Iguana tuberculata; Toxoplasma colubri Tibaldi from the snakes Coluber melanoleucus and Coluber viridiflavus; Toxoplasma hammondi (Frenkel & Dubey) (a new combination for Hammondia hammondi) from the house mouse with oocysts in the domestic cat; Toxoplasma ranae Levine & Nye from the leopard frog Rana Pipiens; and Toxoplasma serpai Scorza, Dagert & Iturriza Arocha from the toad Bufo marinus.

Animals↗
PubMed1988

Temperature-dependence of rod photoresponses from the aspartate-treated retina of the frog (Rana temporaria).

The effects of temperature changes on rod photoresponses were studied by recording the aspartate-isolated mass receptor potential in the dark-adapted retina of the frog Rana temporaria. The amplitude of saturating responses, indicating the magnitude of the dark current, increased linearly with temperature in the measured range 6-26 degrees C, extrapolating to zero dark current at 0 degrees C. Sensitivity was maximal around 18 degrees C but the decrease towards lower temperatures was shallow. The results show that rod phototransduction in the frog Rana temporaria is adapted to lower temperatures than in the tropical toad Bufo marinus. Responses to dim flashes were, approximately up to peak, well fitted by the same 'independent activation' model with four delay stages as have been found to best describe current responses from single toad rods. The kinetics (reciprocal time-to-peak) showed Arrhenius-type temperature-dependence with apparent activation energy 12.4 kcal mol-1 and Q10 = 2.1.

Adaptation, Physiological↗
PubMed1972

Melanophore stimulating hormone: release inhibition by ring structures of neurohypophysial hormones.

Tocinamide and tocinoic acid, ring structures of oxytocin, are potent inhibitors of the release of melanophore stimulating hormone from the rat and hamster pituitary in vitro. Tocinamide is effective at concentrations as low as 10-(14)M on the mammalian pituitary. These peptides do not affect release of the hormone on the frog (Rana pipiens) pars intermedia, but they do inhibit release in the bullfrog (Rana catesbeiana) and the toad (Bufo marinus). The specificity of the peptides on inhibition of the hormone is demonstrated by the fact that oxytocin, lysine vasopressin, and pressinoic acid and pressinamide (ring structures of the vasopressins) do not show such inhibitory activity. Hypothalamic extracts of either the frog (Rana pipiens) or the rat inhibit release of the hormone from pituitaries of either species. The inhibitory effects of tocinamide and tocinoic acid, like that of hypothalamic extracts, are reversible.

Animals↗
PubMed1994

The gonadotropin-releasing hormone (GnRH) neuron system of the clawed toad Xenopus laevis.

The GnRH immunoreactive (GnRH-ir) neuronal system of the Clawed toad Xenopus laevis was studied and compared with the GnRH-ir system of the frog Rana esculenta. Polyclonal antibodies against mammalian (mGnRH) and chicken type-II GnRH (cGnRH-II), and monoclonal antibodies against mGnRH were used in the study. In the Xenopus laevis, most of the immunopositive neuronal cell bodies were located in telencephalic (35-50 per cent) and diencephalic areas (50-65 per cent). About 15-20 per cent of the GnRH perikarya appeared in mesencephalic tegmental regions. Besides the larger GnRH fiber tracts present also in mammals, the toad has rich mGnRH immunopositive axon population in the mesencephalon and in the upper part of the medulla. A similar distribution of the GnRH-ir neuronal elements exists in Rana esculenta, but the number of stained cells and fibers was less. Specificity of the staining of cGnRH-IIir structures located in the lower brainstem could not be proved and therefore the study is only restricted to the findings with mGnRH-antibodies.

Animals↗
PubMed1998

Antimicrobial peptides of the brevinin-2 family isolated from gastric tissue of the frog, Rana esculenta.

Four structurally related peptides with potent growth-inhibitory activity towards Escherichia coli were isolated from an extract of the stomach of the European green frog Rana esculenta, and were identified as members of the brevinin-2 family. Two peptides, termed brevinin-2Eg (GIMDTLKNLA10 KTAGKGALQS20 LLNHASCK LS30GQC) and brevinin-2Eh (GIMDTLKNLA10 KTAGKGALQS20 LLNHASCKL S30 KQC) have not been described previously. One peptide is identical to brevinin-2Ec, previously isolated from R. esculenta skin secretions, and one peptide is identical to brevinin-2Ef whose structure has been deduced from a cloned cDNA prepared from a R. esculenta skin cDNA library. The data demonstrate that certain peptides of the brevinin-2 family, like the magainins in the toad, Xenopus laevis, may play an important role in protecting the gastrointestinal tract of Ranid frogs against microbial invasion.

Amino Acid Sequence↗
PubMed1998

Effects of boron and nitrate on hatching success of amphibian eggs.

As part of a land-application wastewater disposal system in central Pennsylvania, vernal ponds are commonly exposed to wastewater effluent containing high levels of boron and nitrate. We examined the individual effects of these compounds on the eggs of amphibians breeding in these ponds. Wood frog (Rana sylvatica), Jefferson salamander (Ambystoma jeffersonianum), spotted salamander (A. maculatum), and American toad (Bufo americanus) eggs were exposed to boron (0, 50, and 100 mg L-1) and nitrate (0, 10, 25, and 40 mg L-1) under laboratory conditions. There was no difference in the hatching success or proportion of deformed larvae among the four nitrate levels in any of the species. High boron concentrations reduced the hatching success of B. americanus and produced more deformed offspring in R. sylvatica, A. jeffersonianum, and A. maculatum. Deformed R. sylvatica and A. jeffersonianum hatchlings displayed a "curling defect" in which the larvae had a crescent body shape and expressed difficulty in swimming. A. maculatum larvae from high boron treatments displayed a different abnormality, possibly because of longer times to hatching, characterized by a swelling of the thoracic region and altered gill morphology. Although the concentrations of boron and nitrate tested were within the range measured in wastewater effluent, maximum levels of boron and nitrate in breeding ponds were only 1.5 mg L-1 and 26.7 mg L-1 respectively, likely due to rainwater dilution and biological and chemical processes reducing the levels of these compounds in vernal ponds. Nonetheless, these studies are the first to examine the effects of boron and nitrate on amphibian egg hatching success, and to demonstrate that elevated boron concentrations can detrimentally affect the development of amphibian embryos.

Amphibians↗
PubMed2002

Antimicrobial peptide defenses against pathogens associated with global amphibian declines.

Global declines of amphibian populations are a source of great concern. Several pathogens that can infect the skin have been implicated in the declines. The pathogen most frequently associated with recent die-offs is a chytrid fungus, Batrachochytrium dendrobatidis. A second fungus, Basidiobolus ranarum, was isolated from declining populations of Wyoming toads. A third pathogen, Aeromonas hydrophila, is an opportunistic bacterium found in healthy frogs, but capable of inducing disease. Among the immune defense mechanisms used by amphibians is the production of antimicrobial peptides in granular glands in the skin. These packets of natural antibiotics can be emptied onto the skin when the amphibian is injured. To determine whether antimicrobial skin peptides defend against these amphibian pathogens, six peptides (magainin I, magainin II, PGLa, CPF, ranalexin, and dermaseptin), from three species, and representing three structurally different families of peptides, were tested in growth inhibition assays. We show here that the peptides can kill or inhibit growth of both fungi but not Aeromonas. Although each peptide varied in its effectiveness, at least one from each species was effective against both fungi at a concentration of about 10-20 microM. This is the first direct evidence that antimicrobial peptides in the skin can operate as a first line of defense against the organisms associated with global amphibian declines. It suggests that this innate defense mechanism may play a role in preventing or limiting infection by these organisms.

Aeromonas hydrophila↗
PubMed1967

Partition of sodium fluxes in isolated toad oocytes.

1. The rate constant for Na efflux from the oocyte calculated from (d/dt) (ln [Na(*)](i)]) is only approximately 52% of that calculated from (d/dt)[(ln(d[Na(*)](i))dt)]. The difference may be interpreted by supposing that 48% of the internal Na of the oocyte is either bound to proteins or sequestered in cell organelles.2. The mean rate constant for Na efflux was 6.4 x 10(-3) min(-1) corresponding to an apparent Na efflux rate of 13.3 p-mole/cm(2).sec. When this is corrected for the increase in surface area produced by microvilli the true efflux rate is 1.1-1.3 p-mole/cm(2).sec.3. The action of ouabain (1-5 muM) appears to involve two different effects: (a) there is 48-65% inhibition of the membrane Na pump, and (b) there is a release of some of the sequestered Na in the cell.4. Removal of external K causes a 40% reduction in Na efflux although this value may be an underestimation owing to the presence of K which has leaked from the cell and may be retained near the cell surface.5. Raising the external K concentration to 15 mM reduces the inhibitory effect of ouabain by approximately a half.6. It was concluded that the Na pump in the toad oocyte may have a slightly lower level of activity than that in frog muscle, but that its general properties are similar to those in frog muscle and some other animal cells.

Animals↗
PubMed2003

The effects of ultraviolet-B radiation on the toxicity of fire-fighting chemicals.

The interactive effects of ultraviolet (UV) and fire-retardant chemicals were evaluated by exposing rainbow trout (Oncorhyncus mykiss) juveniles and tadpoles of southern leopard frogs (Rana sphenocephala) to six fire-retardant formulations with and without sodium ferrocyanide (yellow prussiate of soda [YPS]) and to YPS alone under three simulated UV light treatments. Yellow prussiate of soda is used as a corrosion inhibitor in some of the fire-retardant chemical formulations. The underwater UV intensities measured were about 2 to 10% of surface irradiance measured in various aquatic habitats and were within tolerance limits for the species tested. Mortality of trout and tadpoles exposed to Fire-Trol GTS-R, Fire-Trol 300-F, Fire-Trol LCA-R, and Fire-Trol LCA-F was significantly increased in the presence of UV radiation when YPS was present in the formulation. The boreal toad (Bufo boreas), listed as endangered by the state of Colorado (USA), and southern leopard frog were similar in their sensitivity to these chemicals. Photoenhancement of fire-retardant chemicals can occur in a range of aquatic habitats and may be of concern even when optical clarity of water is low; however, other habitat characteristics can also reduce fire retardant toxicity.

Ammonia↗
PubMed1983

Inhibition of gastric acid secretion in the gastric brooding frog, Rheobatrachus silus.

The female gastric brooding frog Rheobatrachus silus broods its young in its stomach. A substance that inhibits gastric acid secretion in a toad stomach preparation in vitro appears to be secreted by the developing young. This substance has been identified as prostaglandin E2. Rheobatrachus silus may thus have developed a mechanism whereby prostaglandin secreted by the larvae inhibits acid secretion in the stomach of the female until the larvae have completed development and emerged as juvenile frogs by way of the female's mouth.

Animals↗