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PubMed1983

Birefringence signals in mammalian and frog myocardium. E-C coupling implications.

Birefringence signals from mammalian and frog hearts were studied. The period between excitation and the onset of contraction in which optical signals were free of movement artifact was determined by changes in scattered incandescent light and changes in laser diffraction patterns. The birefringence signal preceding contraction was found to behave as a change in retardation and was not contaminated measurably by linear dichroic or isotropic absorption changes. There were two components of the birefringence signal in mammalian heart muscles but only one component in the frog heart. The first component of the birefringence signals in both mammalian and frog hearts had a time course coincident with the action potential upstroke. The second component in mammalian preparations was sensitive to inotropic interventions, such as variation of extracellular Ca2+, stimulation frequency, temperature, and epinephrine, in a manner that correlated with the maximum rate of rise of tension. Caffeine (2-10 mM) not only failed to generate a second component in the frog heart, but also suppressed the second component in the mammalian heart while potentiating twitch tension. The results suggest that the second component of the birefringence signal in the mammalian myocardium is related to Ca2+ release from the sarcoplasmic reticulum.

Action Potentials↗
PubMedDate not supplied

Postfreeze reduction of locomotor endurance in the freeze-tolerant wood frog, Rana sylvatica.

Considerable study has focused on the physiological adaptations for freeze tolerance in the wood frog, Rana sylvatica, a northern species that overwinters within the frost zone, but little attention has been paid to the associated costs to organismal performance. Here we report that freezing causes transient impairment of locomotor endurance and adverse changes in exercise physiology that persist for at least 96 h. Wood frogs frozen at -2 degrees C for 36 h exhibited normal behaviors and hydro-osmotic status and near-normal metabolite (glycogen, glucose, and lactate) levels within 24 h after thawing began. However, when exercised to exhaustion on a treadmill, these frogs showed a 40% reduction in endurance as compared to sham-treated (unfrozen) controls, a reduction that persisted for at least 96 h. Previously frozen frogs exhibited higher rates of lactate accumulation during exercise than controls, suggesting that prior freezing forces greater reliance on the glycolytic pathways of energy production to support exercise. Given that this species breeds in late winter, when subzero temperatures are common, freezing may result in reduced fitness by hampering their ability to reach the pond, avoid predators, and successfully obtain mates.

Acclimatization↗
PubMed2005

Comparative analysis of cutaneous evaporative water loss in frogs demonstrates correlation with ecological habits.

Most frog species show little resistance to evaporative water loss (EWL), but some arboreal species are known to have very high resistances. We measured EWL and cutaneous resistance to evaporation (Rc) in 25 species of frogs from northern Australia, including 17 species in the family Hylidae, six species in the Myobatrachidae, and one each in the Bufonidae and the Microhylidae. These species display a variety of ecological habits, including aquatic, terrestrial, and arboreal specialisations, with the complete range of habits displayed within just the one hylid genus, Litoria. The 25 species measured in this study have resistances that range from Rc=0 to 63.1. These include low values indistinguishable from a free water surface to high values typical of "waterproof" anuran species. There was a strong correlation between ecological habit and Rc, even taking phylogenetic relationships into account; arboreal species had the highest resistance, aquatic species tended to have little or no resistance, and terrestrial species tended to have resistance between those of arboreal and aquatic frogs. For one species, Litoria rubella, we found no significant changes in EWL along a 1,500-km aridity gradient. This study represents the strongest evidence to date of a link between ecological habits and cutaneous resistance to water loss among species of frogs.

Animals↗
PubMed2006

Wiping behavior, skin resistance, and the metabolic response to dehydration in the arboreal frog Phyllomedusa hypochondrialis.

Several species of arboreal frogs secrete lipids from cutaneous glands and wipe these secretions over the body surfaces to reduce evaporative water losses. Following wiping, frogs become immobile in water-conserving postures, and some have suggested they are torpid. Here we report wiping behaviors and the physiological correlates of immobile postures in the arboreal monkey frog Phyllomedusa hypochondrialis. Skin resistance to water loss was comparatively high, and rates of evaporation were as low as 4% of that from a free water surface. Standard rates of metabolism (SMR) varied from 89 microL O2 h(-1) at 18 degrees C to 316 microL O2 h(-1) at 34 degrees C and were sensitive to both temperature (T) and body mass (W; mL O2 h(-1) = 0.016W0.642 x 10(0.030T)). The mean SMR did not change significantly during four consecutive days of dehydration when animals lost 19%-34% of body mass. Therefore, it appears these frogs do not routinely depress metabolic rates following wiping. However, some individuals that lost higher percentages of body water exhibited trends of decreasing oxygen consumption, suggesting that suppression of metabolic rates might occur at greater levels of body water deficit or perhaps during a slower course of dehydration than imposed by our experiments (e.g., individuals that are secluded during periods of drought).

Animals↗
PubMedDate not supplied

Freezing impairment of male reproductive behaviors of the freeze-tolerant wood frog, Rana sylvatica.

The wood frog (Rana sylvatica), a temperate-zone anuran that overwinters within the frost zone, is adapted to tolerate the freezing and thawing of its tissues. Because the effects of freezing on complex neurobehavioral function are unknown and because R. sylvatica encounters subfreezing temperatures during its late-winter breeding season, we investigated the reproductive behaviors and physiology of male frogs after freezing (minimum body temperature, -2 degrees C) and postthaw recovery (4 degrees C). In tests simulating conditions at the breeding pool, these frogs, which otherwise behaved normally, exhibited reduced mate-searching effort and fewer assaults on mates and did not amplex females until 16-24 h after thawing. Although amplectic ability was ultimately restored in most frogs, they competed poorly for mates against never frozen controls. Further study suggested that the level of behavioral impairment depends on the severity of the freezing exposure. During freezing, tissues accumulated large quantities of the cryoprotectant glucose and desiccated extensively, responses that promote freezing survival. Freezing also caused marked hydroosmotic and metabolic perturbations, which may have impaired neuro-behavioral function, perhaps by interfering with the processing of audio, visual, and tactile stimuli. Individuals that encounter subfreezing temperatures shortly before arriving at the breeding pools may incur reduced reproductive success.

Acclimatization↗
PubMed1984

Probable role of endogenous endotoxins in hepatocytolysis during murine hepatitis caused by frog virus 3.

Three new observations bear out the role of endogenous endotoxins in the pathogenesis of murine hepatitis caused by frog virus 3. First, the LD50 of endotoxin is 20 times lower in mice pretreated for 2.5 hr with a sublethal dose of frog virus 3 than in untreated mice. Animals inoculated with one sublethal dose of lipopolysaccharide 2.5 hr after injection of one sublethal dose of virus die, all having developed extensive hepatocellular necrosis. This hypersensitivity varies according to the intensity of virus-induced destruction of Kupffer cells, which are the intrahepatic target of the virus. Second, mortality is significantly lower and the interval between infection and death longer in axenic mice, which are largely protected from portal endotoxemia. Third, the impairment of some biologic activities of endotoxin (through treatment with polymyxin B or indomethacin, for example) protects mice against hepatic damage and death. Likewise, mice rendered tolerant to endotoxins, and C3H/HeJ mice, which are genetically resistant to endotoxins, survive challenge with frog virus 3 and are refractory with regard to hepatocytolysis . These findings suggest that, in hepatitis caused by frog virus 3, endogenous endotoxins are responsible for extensive hepatocytolysis since virus-induced damage to the hepatic reticuloendothelial system prevents their detoxification.

Animals↗
PubMed1983

The complete nucleotide sequence of the rat 18S ribosomal RNA gene and comparison with the respective yeast and frog genes.

The complete nucleotide sequence of the rat 18S ribosomal RNA gene has been determined. A comparison of the rat 18S ribosomal RNA gene sequence with the known sequences of yeast and frog revealed three conserved (stable) regions, two unstable regions, and three large inserts. (A,T) leads to (G,C) changes were more frequent than (G,C) leads to (A,T) changes for three comparisons (yeast leads to frog, frog leads to rat, and yeast leads to rat). GC pairs were inserted preferentially over AT pairs for the same three comparisons. These two factors contribute to the progressively higher GC content of 18S ribosomal RNA of yeast, frog, and rat.

Animals↗
PubMed1992

Effect of electrically induced muscle contractions on posttraumatic edema formation in frog hind limbs.

We tested the hypothesis that repeated muscle contractions induced by high voltage pulsed current (HVPC) would limit volume increases in traumatized frog hind limbs. Twelve frogs were anesthetized, and both hind limbs of each frog were traumatized by impact. Limb volumes were measured via water displacement over a 24-hour period. Four 30-minute treatments of continuous 1-pulse per second HVPC were applied to one limb selected randomly. Stimulation produced muscle contractions that resulted in minimal joint movements. Volume changes from pretrauma limb volumes (in milliliters per kilogram) were analyzed by an analysis of variance for repeated measures. Our hypothesis was rejected (ie, repeated muscle contractions, as induced in this study, did not limit posttraumatic edema formation in frogs). Further investigation of the relative influences of limb position and varying pulse rates, pulse durations, and intensities of HVPC on edema formation may provide valuable insights on effective treatment of edema in humans.

Animals↗
PubMed2005

Subchronic exposure to low concentrations of di-n-butyl phthalate disrupts spermatogenesis in Xenopus laevis frogs.

Due to its widespread use and production, di-n-butyl phthalate (DBP) has become an environmental contaminant. It has been detected in a variety of environmental strata worldwide, including air, water, and soil. Also, monobutyl phthalate, the major metabolite of DBP, has been detected in a variety of human matrices. As a proven endocrine disruptive compound, DBP may contribute to global amphibian declines at much lower concentrations than tested thus far. We evaluated the effects of low concentrations of DBP on spermatogenesis in Xenopus laevis, the African clawed frog. Xenopus tadpoles were exposed to 0, 0.1, 0.5, 1.0, 5.0, or 10.0 ppm DBP, beginning at sexual differentiation (Nieuwkoop and Faber stage 52; 3 weeks of age) and continuing until 100% of controls metamorphosed (stage 66; 8 weeks of age). Upon necropsy at 33 weeks, 4-6% of DBP-treated frogs had only one testis, and 2-4% had retained oviducts. In all DBP treatment groups, seminiferous tubule diameter and the average number of germ cell nests per tubule were lower, and the number of tubules with no germ cells was significantly higher (p < 0.05). The percent of secondary spermatogonial cell nests significantly decreased (p < 0.05) in 1.0, 5.0, and 10.0 ppm groups. Several lesions occurred in DBP-exposed testes including denudation of germ cells, vacuolization of Sertoli cell cytoplasm, thickening of lamina propria of seminiferous tubules, and focal lymphocytic infiltration. Entire sections of testes containing almost exclusively mature spermatozoa were found in 1.0, 5.0, and 10.0 ppm DBP-exposed testes, indicating impairment of spermiation. Testicular hypoplasia and seminiferous tubular dysgenesis were also evident in DBP-treated frogs. Thus, subchronic exposure to low concentrations of DBP impairs spermatogenesis in Xenopus laevis frogs.

Animals↗
PubMed2004

Identification and characterization of evolutionarily conserved pufferfish, zebrafish, and frog orthologs of GASZ.

We previously identified Gasz (a germ cell-specific gene encoding a protein containing four ankyrin repeats, a sterile-alpha motif, and a basic leucine zipper) in six mammalian species. Here, we report GASZ orthologs in pufferfish (Fugu rubripes), zebrafish (Danio verio), and frog (Xenopus laevis). Sequences of the three Gasz cDNAs were determined by database mining and 5'- and 3'-rapid amplification of cDNA ends (RACE) followed by sequencing. The three orthologous vertebrate genes encode proteins structurally similar to mammalian GASZ and contain the characteristic four ankyrin repeats (ANKs) and sterile-alpha motif (SAM). Their ANK and SAM domains share 55- 74% and 38-55% amino acid identity with those in human GASZ, respectively. Similar to human and mouse Gasz genes, pufferfish Gasz is composed of 13 exons, spanning approximately 12 kilobases, and flanked by Cftr at its 5'-end and Wnt2 at its 3'-end. Northern and Western blot analyses detect frog Gasz expression only in testis and ovary. In situ hybridization and immunohistochemical analyses show that frog Gasz mRNA and protein expression is confined to pachytene spermatocytes in the testis and to oocytes in the ovary. In frog oocytes, GASZ protein appears to localize to a cytoplasmic structure resembling the Balbiani body, a postulated mRNA transport organizer in the cytoplasm. The high evolutionary conservation and germ cell specificity suggest that GASZ plays an essential role in gametogenesis. The data presented here are important for future studies of the physiological roles of GASZ using fish and amphibians as animal models.

Adaptor Proteins, Signal Transducing↗
PubMed1991

Time-dependent changes in gonadotropin synthesis following gonadectomy in the frog, Rana pipiens.

Anterior pituitary glands from frogs gonadectomized (gonadx) for various periods (0-90 days) were labeled in vitro with 35S-methionine. Shortly (7-10 days) after gonadx, plasma levels and the in vitro basal pituitary secretion of LH and FSH are elevated compared to values in sham-operated frogs. However, LH and FSH become dissociated in long-term (over 40 days) gonadx frogs; FSH remains elevated while LH returns to sham levels. Gth (gonadotropin: LH and FSH) synthesis shows a similar pattern. Gth synthesis becomes elevated after gonadx, but returns to sham levels after 80 days. In short-term (15 days) gonadx females, LH and FSH each comprise approximately the same percentage of counts immunoprecipitated. In contrast, in long-term (90 days) gonadx females, nearly 100% of Gth synthesis can be accounted for solely by FSH; LH synthesis is barely or not detectable. Although the elevated in vitro secretion rate of LH and FSH following gonadx diminishes within 24 h in culture, Gth synthesis remains elevated. This study demonstrates that although the pattern of Gth secretion and synthesis generally parallel each other following gonadx, these two cellular processes can be dissociated from one another. Furthermore, it appears that in frogs, not only the secretion, but also the synthesis, of LH and FSH may be under independent regulation.

Animals↗
PubMed1994

Concentration dependence of lidocaine-induced irreversible conduction loss in frog nerve.

BACKGROUND: Concentration is a causal factor in local anesthetic nerve toxicity. Therefore, it is essential to define a concentration below which injury does not occur. We explored the relation of lidocaine concentration and nonreversible block after drug washout in frog sciatic nerve. METHODS: Frog sciatic nerve was mounted in sucrose-gap or extracellular recording chambers. The observed compound action potential in response to a supramaximal stimulus was used as a measure of nonreversible block after applying lidocaine in a range of concentrations (0.5-200 mM for 15 min) and then washing off (for as long as 180 min). RESULTS: Lidocaine causes a nonreversible block after washout that begins at concentrations as low as 40 mM and increases in a graded fashion with increasing concentrations to complete ablation of the compound action potential at 80 mM (approximately 2%). Extended storage of frogs (5 weeks) at 4 degrees C makes the nerves more resistant to the effects of lidocaine. The presence of nifedipine (10(-5) M), an L-type calcium-channel blocker, makes the nerves more resistant to lidocaine as well. CONCLUSIONS: Lidocaine induces a nonreversible loss of impulse activity in frog nerve in a progressive fashion with increasing drug concentration, beginning at 40 mM (approximately 1.0%). The range of lidocaine that produces such changes in mammalian nerve awaits determination.

Action Potentials↗
PubMed2006

High level of cryptic species diversity revealed by sympatric lineages of Southeast Asian forest frogs.

Amphibians tend to exhibit conservative morphological evolution, and the application of molecular and bioacoustic tools in systematic studies have been effective at revealing morphologically 'cryptic' species within taxa that were previously considered to be a single species. We report molecular genetic findings on two forest-dwelling ranid frogs from localities across Southeast Asia, and show that sympatric evolutionary lineages of morphologically cryptic frogs are a common pattern. These findings imply that species diversity of Southeast Asian frogs remains significantly underestimated, and taken in concert with other molecular investigations, suggest there may not be any geographically widespread, forest-dwelling frog species in the region. Accurate assessments of diversity and distributions are needed to mitigate extinctions of evolutionary lineages in these threatened vertebrates.

Amphibians↗
PubMed1999

Neuromuscular control of prey capture in frogs.

While retaining a feeding apparatus that is surprisingly conservative morphologically, frogs as a group exhibit great variability in the biomechanics of tongue protraction during prey capture, which in turn is related to differences in neuromuscular control. In this paper, I address the following three questions. (1) How do frog tongues differ biomechanically? (2) What anatomical and physiological differences are responsible? (3) How is biomechanics related to mechanisms of neuromuscular control? Frog species use three non-exclusive mechanisms to protract their tongues during feeding: (i) mechanical pulling, in which the tongue shortens as its muscles contract during protraction; (ii) inertial elongation, in which the tongue lengthens under inertial and muscular loading; and (iii) hydrostatic elongation, in which the tongue lengthens under constraints imposed by the constant volume of a muscular hydrostat. Major differences among these functional types include (i) the amount and orientation of collagen fibres associated with the tongue muscles and the mechanical properties that this connective tissue confers to the tongue as a whole; and (ii) the transfer of intertia from the opening jaws to the tongue, which probably involves a catch mechanism that increases the acceleration achieved during mouth opening. The mechanisms of tongue protraction differ in the types of neural mechanisms that are used to control tongue movements, particularly in the relative importance of feed-forward versus feedback control, in requirements for precise interjoint coordination, in the size and number of motor units, and in the afferent pathways that are involved in coordinating tongue and jaw movements. Evolution of biomechanics and neuromuscular control of frog tongues provides an example in which neuromuscular control is finely tuned to the biomechanical constraints and opportunities provided by differences in morphological design among species.

Animals↗
PubMed1990

Half helical turn spacing changes convert a frog into a mouse rDNA promoter: a distant upstream domain determines the helix face of the initiation site.

Transcription of frog rDNA by mouse cell factors is the only documented exception to the observed species selectivity of rRNA gene expression. This heterologous transcription is authentic in that it uses the normal frog upstream and core promoter domains, as well as the normal mouse polymerase I transcription factors, but it initiates at residue -4. We now show that by introducing an insertion or deletion of approximately one-half helical turn anywhere within the 90-bp region between the upstream and core promoter domains, the initiation site moves to residue +1. Promoters bearing spacing changes of approximately one or two full helix turns do not initiate at residue +1, whereas a promoter with a one and one-half-turn helical turn spacing change again supports initiation at residue +1. Thus, the position of the upstream domain of the frog promoter shows a stereo-specific requirement relative to the core promoter domain and dictates the face of the DNA helix on which transcription initiates, 140 bp away. In contrast, relative to the core promoter domain, initiation can occur on either side of the DNA helix. Furthermore, the striking observation that several frog half helical turn spacing change mutants are stronger templates with the mouse factors than the homologous mouse rDNA suggests that the polymerase I transcriptional machinery of even distantly related species is far more similar than generally envisioned.

Animals↗
PubMed2005

How a frog can learn what is where in the dark.

During the night 180 lateral-line organs allow the clawed frog Xenopus to localize prey by detecting water waves emanating from insects floundering on the water surface. Not only can the frog localize prey but it can also determine its character. This suggests waveform reconstruction, and a key question is how the frog can establish the appropriate neuronal hardware. Detecting time differences arising from the input on the skin is a key to neuronal information processing, and spike-timing-dependent synaptic plasticity (STDP) therefore seems to be the natural tool. We show how supervised STDP allows a frog to learn what is where in the dark. Learning can also be derived from a minimization principle.

Animals↗
PubMed1984

Cytoplasmic microtubules of normal and tumor cells of the leopard frog. Temperature effects.

The cytoplasmic microtubule complex (CMTC) was examined in monolayer cultures of normal tadpole mesonephros, primary renal adenocarcinoma, and an established cell line derived from a pronephric renal adenocarcinoma (PNKT-4B) of the leopard frog, Rana pipiens. Immunocytochemistry revealed typical arrays of microtubules extending from the cytocentrum to the cell periphery in all three cell types when cultured at 28 degrees C; similar results were obtained at 20 degrees C. However, the CMTC was disorganized in both tumor types, in contrast to the retention of a typical CMTC in normal tissue cultured at 7 degrees C. The response of PNKT-4B cells differed from that of normal tadpole mesonephros when treated with the microtubule inhibitor drug nocodazole. At 28 degrees C, PNKT-4B and tadpole mesonephros cells lost their CMTC with nocodazole treatment, and both were able to reconstitute CMTC when nocodazole was removed. Similarly, both lost CMTC organization with nocodazole and culture at 70 degrees C. However, while normal cells could effect a recovery at 7 degrees C after the removal of nocodazole, PONKT-4B cells were unable to restructure CMTC under the same conditions. Metastasis in the frog renal adenocarcinoma is temperature-dependent, with an elevated prevalence of metastasis in tumor-bearing frogs maintained at 28 degrees C. Few metastatic colonies are detected in tumor-bearing frogs maintained at a low temperature (7 degrees C). Other studies have indicated that microtubules, which are essential for cell motility, play an important role in the invasion by tumor cells of normal tissue fragments in vitro. The effects of temperature on metastasis of the Lucke renal adenocarcinoma are consistent with temperature-mediated changes in tumor-cell CMTC.

Adenocarcinoma↗
PubMed2004

Proposal to transfer 'Aegyptianella ranarum', an intracellular bacterium of frog red blood cells, to the family Flavobacteriaceae as 'Candidatus Hemobacterium ranarum' comb. nov.

'Aegyptianella ranarum' (order Rickettsiales), an ultrastructurally defined small, Gram-negative rod, is known to replicate in the red blood cells of frogs. Heretofore, this bacterium has not been characterized genetically. We cloned and sequenced the 16S rRNA (1310 bp) and gyrB (718 bp) genes of 'A. ranarum' from a Canadian frog blood specimen. In situ hybridization (with an 'A. ranarum' 16S rRNA gene polymerase chain reaction product as probe) and electron microscopy confirmed that 'A. ranarum' forms cytoplasmic inclusions in frog erythrocytes. blast comparisons with GenBank 16S rRNA and gyrB sequences showed that both 'A. ranarum' genes were most similar (91% and 67% identity) to those of Chryseobacterium meningosepticum, a bacterium in the family Flavobacteriaceae. In contrast, 'A. ranarum' 16S rRNA shared only 61% identity with Aegyptianella pullorum. Phylogenetic analyses of these genes using phylip supported 'A. ranarum' as a member of Flavobacteriaceae, but suggested that its cladistic sibling may be Bergeyella zoohelcum or Weeksella virosa, rather than C. meningosepticum. We propose to classify 'Aegyptianella ranarum' as 'Candidatus Hemobacterium ranarum' in the family Flavobacteriaceae. Our results provide a starting point for studies of related intraerythrocytic bacterial infections in frogs.

Anaplasmataceae↗