PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “FROGS AND TOADS”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13Linked to original sources
PubMedDate not supplied

Phylogenetic relationships among anuran trypanosomes as revealed by riboprinting.

Twenty trypanosome isolates from Anura (frogs and toads) assigned to several species were characterized by riboprinting-restriction enzyme digestion of polymerase chain reaction amplified small subunit ribosomal RNA genes. Restriction site polymorphisms allowed distinction of all the recognized species and no intraspecific variation in riboprint patterns was detected. Phylogenetic reconstruction using parsimony and distance estimates based on restriction fragment comigration showed Trypanosoma chattoni to be only distantly related to the other species, while T. ranarum and T. fallisi appear to be sister taxa despite showing non-overlapping host specificities.

Animals↗
PubMed1985

Apical material extracted from amphibian urinary bladder epithelium by enzymes and detergent treatment.

The apical plasma membrane of epithelial cells of frog and toad urinary bladder is subject to large modifications during the induction of water permeability by the antidiuretic hormone. A better characterization of the apical membrane is necessary for a clear understanding of the mechanisms of hormone action. Towards this end, apical material was extracted by enzymatic treatment and by incubation with detergent. Proteolytic enzyme alone had little effect under our conditions. A pretreatment with several glycosidases (alpha-mannosidase or endo-beta-N-acetylglucosaminidase H) increased the hydrolytic action of papain, elastase, proteinase K or Staphylococcus aureus V8 protease and allowed the detection of a major 76 kD in SDS gel electrophoresis. The n-octyl-beta-D-glucopyranoside (0.2%) led to the extraction after 150 mn of 1 to 5 micrograms proteins per cm2 of amphibian urinary bladder apical surface. The extracted proteins migrated as several bands on SDS gels. One of them probably corresponds to the 76 kD fragment obtained after proteolysis. The absence of alteration of the water permeability after extraction and the good preservation of the ultrastructure are evidence for the localisation of the 76 kD at the apical membrane surface. This protein may be the best candidate as antigen to raise antibodies against the apical surface of amphibian urinary bladder epithelial cells.

Animals↗
PubMed1968

Tension due to interaction between the sliding filaments in resting striated muscle. The effect of stimulation.

1. A resting sartorius muscle of the frog or toad possesses a special kind of elasticity which is shown to be due to a component lying between the two sets of filaments. The elastic effect is seen only for very small length changes, up to about 0.2% of the muscle length, and the ;elastic limit' is then reached. If the length change then continues at a constant velocity the tension developed is maintained at a fixed level, producing a sort of frictional resistance. The component responsible is called the ;short-range elastic component', or SREC.2. It is also shown that a small part of the permanent tension of a resting muscle is probably due to ;active' interaction between the filaments. This is called the ;filamentary resting tension', or FRT. For a sarcomere length of 2.0 mu the FRT amounts to about 150 mg in a muscle weighing 100 mg.3. The stiffness of the SREC and the magnitude of the FRT are shown to be related to one another. They are both increased, and may rise to high values, by making the external solution hypertonic.4. The working hypothesis is as follows. In a resting muscle the cross-bridges on the myosin filaments are not entirely inactive, but a very small proportion of them are cross-linked with the actin filaments. The links are very stable and have a long ;life'. The elastic behaviour is due to the flexural rigidity, or spring-like properties of these bridges. The elasticity is ;short-range' because the bridges can be bent, or stretched, only a small way from the steady-state position before the contacts ;slip'. The ;filamentary resting tension' (which is present in the absence of any external length change) is attributed to an ;active process', which operates by imparting ;organized' potential energy to the participating cross-bridges, by potentiating their attachment, against their elastic resistance, to sites on the actin filaments which are displaced towards the Z line.5. It is shown that the ability of the muscle to maintain a ;frictional' resistance to a continuing, slow, length change is suppressed during a maintained tetanic contraction. The process of suppression starts during the period of the latency relaxation.6. It is suggested that the latency relaxation may be due to a reduction of the filamentary resting tension.7. The experiments with the latency relaxation were facilitated by the use of strongly hypertonic solutions. The positive twitch tension is then greatly reduced, or may be practically abolished, while the latency relaxation remains at about its normal size and is extended in duration.

Animals↗
PubMed1978

Calcium transients in isolated amphibian skeletal muscle fibres: detection with aequorin.

1. Single twitch muscle fibres isolated from frogs and toads were microinjected with the Ca2+-sensitive bioluminescent protein aequorin. The fibres contracted normally and emitted flashes of light (aequorin responses) in response to stimulation for many hours thereafter. 2. No luminescence was detected from healthy fibres at rest. 3. The aequorin diffused from the site of injection at a rate consistent with a diffusion coefficient of 5 x 10(-8) cm2/sec. 4. During trains of isometric contractions there was a progressive reduction in both the amplitude and the rate of decline of the aequorin response, an observation consistent with the theory that Ca is redistributed from sites of release to sites of sequestration under such circumstances. 5. In isometric tetani light emission continued to rise long after the plateau of force had been achieved. This and the fact that the amplitude of the tetanic aequorin response increased steeply with increasing stimulus frequency suggest that in tetani the sarcoplasmic [Ca2+] may normally be above the level required to saturate the contractile apparatus. 6. Both in twitches and in tetani the amplitude of the aequorin response increased slightly and then decreased substantially as the fibre was stretched progressively beyond slack length. 7. In potassium contractures the luminescent and mechanical responses first became detectable at about the same [K+], but for equivalent force luminescence was less intense than in twitches. The aequorin response was biphasic in solutions of high [K+]. 8. Exposure of the fibre to Ca2+-free solutions had no influence on either the mechanical or the luminescent responses in twitches. In Ca2+-free solutions tetanic aequorin responses tended not to be maintained as well as normally, suggesting that intracellular Ca stores do become somewhat depleted. 9. In twitches the amplitude of the aequorin response probably reflects the amount of Ca2+ liberated into the cytoplasm rather than a [Ca2+] in equilibrium with the myofilaments. Changes in the rate of decay of the aequorin response may reflect changes in the rate of Ca sequestration by the sarcoplasmic reticulum. 10. In K+-contractures and during the plateaus of tetani the aequorin signal changes slowly enough so that it seems unlikely that substantial gradients of [Ca2+] exist at the sarcomere level. Under such circumstances the amplitude of the aequorin response probably does reflect the [Ca2+] in equilibrium with the myofilaments.

Aequorin↗
PubMed1980

Rheogenic sodium transport in a tight epithelium, the amphibian skin.

1. Intracellular potentials from frog and toad skins were measured to identify rheogenic components of active Na transport across the basolateral membrane. Transcellular current flow and associated R . I-drops were blocked with amiloride or Na-free mucosal solution. 2. The potential difference across the basolateral membrane was found to be hyperpolarized by 18 . 5 +/- 1 . 6 mV above the steady-state value immediately after blockage of apical membrane Na conductance. The hyperpolarization disappeared within 15--25 min. 3. The final steady-state value of 93 . 1 +/- 2 . 5 mV was slightly less than reasonable estimates of the K equilibrium potential. 4. The hyperpolarization could not be observed 3--5 min after addition of ouabain (10(-4) M). 5. Both the magnitude and duration of the hyperpolarization correlate directly with the amount of Na accumulated in the intracellular space. 6. A fraction of the intracellular potential was missing when Na transport was re-established after long term blockage of apical membrane Na entry. It reappeared within 10--20 min. 7. It is suggested that the hyperpolarization is due to rheogenic Na transport across the basolateral membranes. This transport mechanism may contribute some 30--50% of the electrical gradient for passive Na entry across the mucosal membrane. 8. A coupling ratio between pumped fluxes of Na and K of about 2:1 is calculated from the data.

Animals↗
PubMed1991

Spike discharge properties that are related to the characteristic frequency of single units in the frog auditory nerve.

Single units from the auditory nerve of frogs and toads have their receptor cells located in two separate sensory organs that provide disjoint frequency ranges. The amphibian papilla (ap) provides units with characteristic frequency (CF) in the low- and mid-frequency regions and the basilar papilla (bp) provides units with high CF. There are gross differences in both the mechanical design and innervation patterns of the two organs, so that one might expect discharge properties for units with different CF to differ in many respects. However, there have been few reports of response attributes that correlate strongly with CF for units in the mid- and high-CF regions. Measurements of automated tuning curves from 250 units in Rana pipiens show that W10 dB, the bandwidth of the tuning curve measured 10 dB above CF threshold, is consistently larger for high-CF units than for low- and mid-frequency units. When units are classified into three groups by an objective statistical method using only CF and W10 dB measurements, the groups appear to correspond reasonably well with the low-, mid-, and high-frequency categories identified in many other studies.

Acoustics↗
PubMed1977

Isometric tension and instantaneous stiffness in amphibian skeletal muscle exposed to solutions of increased tonicity.

The instantaneous elasticity and maximum isometric tetanic tension of isolated frog and toad sartorii have been measured in hypertonic Ringer solution. Although the mechanical response of contraction muscle continued to decrease as the tonicity of the bathing solution was increased to 1.26 X R, 1.52 X R, and 2.04 X R, a similar change in the instantaneous stiffness could not be shown. This finding was not expected on the basis of our current model of the cross-bridge mechanism which predicts that the instantaneous stiffness is a measure of the total number of tension-generating cross-bridges formed in a stimulated muscle. The compatability of our findings with an electrostatic theory of the cross-bridge mechanism proposed by Iwazumi (1970) is discussed.

Animals↗
PubMed1977

Prolonged potentials in gastrointestinal muscles induced by calcium chelation.

When stomach muscles of skate, toad, or frog or intestinal muscle of cat are treated with Ca-free physiological solutions containing 2-5 mM EGTA or EDTA, spontaneous spikes and slow waves disappear reversibly. With continued treatment, depolarization of 25-30 mV from resting potentials of -65 mV occurs and rhythmic prolonged potentials of several seconds duration appear. They show rapid depolarization to near zero and rapid repolarization and they may continue for several hours. The prolonged potentials disappear when Na is replaced by Li, Tris, or choline. They are insensitive to TTX. The EGTA-induced waves are abolished by Mn, Co, La, verapamil, and D 600. After 10-15 min in 5 mM EGTA, voltage-current and abolition of anomalous rectification. It is concluded that when bound Ca is removed by a chelator, nonspecific reduction in resistance occurs and Na ions may enter rhythmically through channels normally used by Ca.

Animals↗
PubMed1975

Theory of current source-density analysis and determination of conductivity tensor for anuran cerebellum.

The theoretical basis of current source-density (CSD) analysis in the central nervous system is described. Equations relating CSD, the current flow vector, and the extracellular field potential are given. It is shown that the CSD provides superior resolution of neuronal events when compared to conventional field-potential analysis. Expressions for the CSD in rectangular Cartesian coordinates are derived, including the general case of anisotropic, inhomogeneous conductive tissue, and a coordinate system rotated with respect to the principal axes (APPENDIX). The minimum number of spatial dimensions for accurate CSD analysis is discussed. The conductivity tensor was experimentally measured in frog and toad cerebella. All three principal components of the tensor were evaluated and their spatial gradients determined to be negligible. It was also shown that the conductivity was independent of potential. Thus the anuran cerebellum is anisotropic, homogeneous, and ohmic. On the basis of these results the appropriate mathematical expression for the CSD was selected.

Animals↗
PubMed2000

Immunocytochemical localization of gonadotropin-releasing hormones in the brain of a viviparous caecilian amphibian, Typhlonectes natans (Amphibia: Gymnophiona).

The molecular forms and brain distribution of gonadotropin-releasing hormone (GnRH) have been well studied in the amphibian orders Urodela (salamanders and newts) and Anura (frogs and toads). In the order Gymnophiona (caecilians), however, few species have been investigated. Antibodies against different molecular forms of GnRH were used to immunohistochemically localize the GnRH-containing neurons in the brain of the caecilian, Typhlonectes natans which differs from most other amphibians in that it is viviparous. An antibody selective for mammalian GnRH recognized cell bodies predominantly in the septo-preoptic area but only with occasional cell bodies in the lateral hypothalamus and ventral thalamic eminence. Thick, prominent fibers in the septal region and fibers within the terminal nerve were also labeled. An antibody selective for chicken-II GnRH labeled a population of cell bodies in the dorsal hypothalamus, ventral thalamus and midbrain tegmentum. Thin fibers projected laterally from these cells. An antibody specific for salmon GnRH did not label cell bodies but did show intense terminal field immunoreactivity. The brain of this caecilian, therefore, contains three antigenically distinct forms of GnRH. The mammalian and chicken-II GnRH peptides have been shown in other amphibians but the distribution of cells and fibers was unique in this caecilian.

Amphibians↗
PubMed1980

Comparative aspects of luteinizing hormone-releasing hormone structure and function in vertebrate phylogeny.

Immunoreactive LHRH was detected in hypothalamic and extrahypothalamic brain extracts of the rat, bird (pigeon and chicken), reptile (tortoise and lizard), amphibian (frog and toad), teleost (cichid), and elasmobranch (dogfish) and in the whole brain of the cyclostome (bagfish). The concentration of hypothalamic immunoreactive LHRH was more than 5-fold greater than that of the extrahypothalamic brain. Mammalian and amphibian hypothalamic immunoreactive LHRH yielded displacement curves parallel to those of synthetic LHRH in assays employing four antisera which recognize different regions of the decapeptide, thus suggesting a similarity in the structure of their LHRH. Hypothalamic immunoreactive LHRH from the bird, reptile, teleost, and elasmobranch differed from the mammalian and amphibian peptide in yielding displacement curves nonparallel to those of synthetic LHRH with three different antisera (1076, 743, and 744) which bind between Trp3 and Pro9 of LHRH. The differenece in structure appears to be near Leu7. With antiserum 422 which binds the NH2- and CO2H- termini of LHRH, bird, reptile, and teleost hypothalamic extracts yielded displacement curves parallel to that of synthetic LHRH. Bird, reptile, and teleost hypothalamic extracts showed displacement curves parallel to each other in all assays. In studies on the relative quantitation of LHRH, all four antisera gave similar values of immunoreactive LHRH concentration in mammalian hypothalamic extracts and in amphibian hypothalamic extracts. By contrast, assay of bird, reptile, teleost, and elasmobranch hypothalamic extracts with antiserum 422 gave much higher values than did the other antisera, suggesting that the LHRH peptide is structurally different from mammalian and amphibian LHRH in the region of Leu7 but similar at the NH2- and CO2H-termini. These conclusions are supported by studies on the biological activity of hypothalamic LHRH from the different species using dispersed ovine anterior pituitary cells in culture. The LH release responses to equivalent amounts of immunoreactive LHRH (as measured by antiserum 422 which binds a region of LHRH essential for biological activity) from the various species were similar, indicating that the biologically active region of the molecule has been conserved in evolution. Structural differences in vertebrate hypothalamic immunoreactive LHRH were confirmed by cation exchange and high pressure liquid chromatography. Our findings of differences and similarities in vertebrate LHRH support a contemporary phylogenetic scheme.

Amphibians↗
PubMed1983

Post-contractile phosphocreatine splitting in muscle as revealed by time-resolved 31P nuclear magnetic resonance.

We have designed and constructed a 25 mm diameter chamber in order to study the phosphorus nuclear magnetic resonance (31P NMR) spectra from a considerable mass of toad and frog muscles (16 sartorii weighing 5-10 g) which were maintained in a well-oxygenated condition at 4 degrees C. We have thus been able to measure the biochemical changes that accompany contraction and recovery with improved time-resolution. Using this apparatus it is shown that splitting of phosphocreatine (PCr) continues for a few minutes after relaxation. Subsequently the PCr is rebuilt by oxidative processes in the familiar way, with a time-constant congruent to 10 min. By studying tetanic contractions of various durations we have shown that the time-course of the post-contractile PCr splitting is similar to that of the heat production that cannot yet be accounted for by known chemical changes. Myosin and actomyosin ATPase reactions most likely underlie the post-contractile ATP utilization. The results suggest that the post-contractile ATP utilization is responsible for the unexplained enthalpy mentioned above.

Animals↗
PubMed1990

Occurrence of tetrathyridia of Mesocestoides sp. (Cestoidea: Cyclophyllidea) in North American anurans (Amphibia).

A new host and geographic locality record is reported for tetrathyridia of Mesocestoides sp. in two species of ranid frogs (Rana berlandieri and R. pipiens) from Texas and New York, respectively. Tetrathyridia were found encapsulated in liver and mesenteries of the hosts. Morphological examination and experimental inoculation of these tetrathyridia into mice demonstrated the absence of capacity for asexual proliferation. Overall prevalence of infection was low in anurans from Arkansas, Texas and New York, but intensities can be generally high. In addition, a summary of frogs and toads from North America reported as hosts of tetrathyridia of Mesocestoides sp. is presented.

Animals↗
PubMed1993

Mucor amphibiorum infection in platypus (Ornithorhynchus anatinus) from Tasmania.

Mucor amphibiorum, a fungus previously isolated from frogs and toads, is reported from free-living platypus, Ornithorhynchus anatinus, from rivers in northern Tasmania. This fungus is responsible for the severe ulcerative skin condition originally described by Munday and Peel (1983). Mucor amphibiorum was isolated from dermal lesions on four separate occasions. The gross and histopathological appearance of the fungal lesions were similar to the earlier description. In vivo this fungus develops as spherical forms containing a number of daughter spherules; no mycelia are seen in tissue sections. By contrast, the in vitro growth consists of aerial aseptate mycelia and sporangia, features typical of the genus Mucor. This is the first report of this organism causing a fatal disease in a mammal. Susceptibility to infection may be due to the platypus having a body temperature of 32 C while the maximum temperature for growth of M. amphibiorum is 36 C.

Animals↗
PubMedDate not supplied

[The effect of the composition of the medium on the concentration of free calcium ions in the cells of the follicular wall in the common frog and in the clawed toad].

The concentration of intracellular free calcium ions in the follicle wall cells and in the follicle cells of Rana temporaria in Ringer solution is 150 +/- 10 and in the follicle wall cells of Xenopus laevis, 220 +/- 10 nM. In a chloride-free saline, its concentration in the same cells is 2.5-3 times that in Ringer solution. Voltage-dependent Ca(2+)-channel blockers diltiazem and verapamil (100 microM) reduce the level of intracellular free calcium ions in R. temporaria follicle wall cells cultivated in a chloride-free saline to 170 +/- 20 nM, which practically does not differ from the level in Ringer solution. Inhibitors (100 microM) decrease the rate of "spontaneous" maturation of R. temporaria follicle-enclosed oocytes both in chloride-free and Ringer solutions. It was concluded that an increased level of intracellular free calcium ions in the follicle cells, among other factors, may determine the stimulating effect of the medium (Ringer or chloride-free solution) on "spontaneous" maturation of follicle-enclosed amphibian oocytes. Voltage-dependent calcium channels appear to be involved in Ca2+ influx into the cells.

Animals↗