Seasonal changes in the activity of rhodanese in frog (Rana temporaria) liver.

1. The investigators studied annual changes in rhodanese activity in mitochondria and cytosol of frog liver cells (Rana temporaria) and found that the value of the enzyme-specific activity was higher in mitochondria than in cytosol, showing significant seasonal fluctuations. 2. The character of changes in the rhodanese activity in mitochondria, regardless of the sex of the studied animal, was demonstrated to be dependent upon the seasonal changes in frog thyroid gland function. 3. In the supernatant fraction of R. temporaria liver homogenate, seasonal changes of rhodanese specific activity seemed to be related to changes in hepatic function.     

NAG infection of grass frog (Rana temporaria) tadpoles]

Rana temporaria tadpoles (2250) were contaminated with three types of NAG vibrio cultures. Clinical, bacteriological and morphological examinations showed the larvae to be suffering from an acute infection during the first 2 days after the contamination. Then the vibrios persisted in the tadpole organism for a long time and were excreted in the feces.     

The skin sensitivity of the frog Rana temporaria to chlorides]

Analysis of total impulse reactions evoked in skin branches of the spinal nerves by application of 0.1-1.0 mol/l solutions of KCl, NaCl, NH4Cl, and CaCl2 to the skin in the grass frog showed that the reaction of the peripheral nervous elements depends not only on the concentration of a test-solution, but on the nature of the cation as well. The problem of specificity of acidic and saline sensitivity of the skin in amphibians is discussed.     

Immunoreactive Tamm-Horsfall protein in the kidney and skin of the frog Rana temporaria

Summary Tamm-Horsfall protein (THP) is the main protein in normal human urine, and is found in the thick limb of the Loop of Henle in human kidney, and in other mammalian species. The skin of the frog, Rana temporaria, has similar physiological properties to this mammalian kidney tissue. In the present study, an immunohistological method involving an antibody to human THP was used to investigate the distribution of this distinctive protein in frog kidney and skin, and to compare its distribution with that found in the kidney tubules of rat and rabbit. THP-positive material was detected in the distal renal tubules and nephric duct of frogs, and was also located in the superificial epidermis of skin. It is suggested that its presence in amphibian skin is consistent with the hypothesis that THP is an important component of tissues that absorb sodium and chloride ions, but remain impermeable to water.     

Tooth replacement in the frog Rana temporaria

The development and replacement of teeth in the frog Rana temporaria is analyzed by dividing the life cycle of the tooth into a number of stages. These stages are identified by the examination of alizarin whole mounts. The dentition in this species is fairly complete and the percentage of functional loci is approximately 74. The teeth in alternate loci are usually at about the same stage in development. The low percentage of non-functional loci is accounted for by the retention of functional teeth over a large fraction of the total life cycle time and the relatively rapid ankylosis of replacement teeth. It is suggested that tooth replacement is essentially a process which involves teeth in alternate loci and that the replacement waves (which connect alternate loci) run parallel to the longitudinal axis of the jaw and are of infinite length. This basic pattern is obscured by many breaks which occur in the replacement waves. The presence of such breaks may be accounted for by variations in the time intervals between the successive stimuli which initiate the Zahnreihen, or simply by the acceleration or deceleration of the development of teeth in one or more loci.     

Ba2+-Induced conductance fluctuations of spontaneously fluctuating K+ channels in the apical membrane of frog skin (Rana temporaria)

Summary We studied the influence of mucosal Ba²⁺ ions on the recently described (Zeiske & Van Driessche, 1979a, J. Membrane Biol. 47:77) transepithelial, mucosa towards serosa directed K⁺ transport in the skin ofRana temporaria. The transport parametersG (conductance), PD (potential difference),I _sc (short-circuit current, K⁺ current), as well as the noise ofI _sc were recorded. Addition of millimolar concentrations of Ba²⁺ to the mucosal K⁺-containing solution resulted in a sudden but quickly reversible drop inI _sc.G andI _sc decreased continuously with increasing Ba²⁺ concentration, (Ba²⁺) _o . The apparent Michaelis constant of the inhibition by Ba²⁺ lies within the range 40–80 m. The apical membrane seems to remain permselective for K⁺ up to 500 m (Ba²⁺) _o . Higher (Ba²⁺) _o , however, appears to induce a shunt (PD falls,G increases). This finding made an accurate determination of the nature of the inhibition difficult but our results tend to suggest a K⁺-channel block by K⁺–Ba²⁺ competition. In the presence of Ba²⁺, the power spectrum of the K⁺ current shows a second Lorentzian component in the low-frequency range, in addition to the high-frequency Lorentzian caused by spontaneous K⁺-channel fluctuations (Van Driessche & Zeiske, 1980). Both Lorentzian components are only present with mucosal K⁺ and can be depressed by addition of Cs⁺ ions, thus indicating that Ba²⁺ ions induce K⁺-channel fluctuations. The dependence of the parameters of the induced Lorentzian on (Ba²⁺) _o , shows a rise in the plateau values to a maximum around 60 m (Ba²⁺) _o , followed by a sharp and progressive decrease to very low values. The corner frequency which reflects the rate of the Ba²⁺-induced fluctuations, however, increases quasi-linearly up to 1mm (Ba²⁺) _o with a tendency to saturate at higher (Ba²⁺) _o . Based on a three-state model for the K⁺ channel (having one open state, one closed by the spontaneous fluctuation and one blocked by Ba²⁺) computer calculations compared favorably with our results. The effect of Ba²⁺ could be explained by assuming reversible binding at the outer side of the apical K⁺ channel, thereby blocking the open channel in competition with K⁺. The association-dissociation of Ba²⁺ at its receptor site is thought to cause a chopping of the K⁺ current, resulting in modulated current fluctuations.     

Sex reversal and primary sex ratios in the common frog (Rana temporaria)

Sex reversal has been suggested to have profound implications for the evolution of sex chromosomes and population dynamics in ectotherms. Occasional sex reversal of genetic males has been hypothesized to prevent the evolutionary decay of nonrecombining Y chromosomes caused by the accumulation of deleterious mutations. At the same time, sex reversals can have a negative effect on population growth rate. Here, we studied phenotypic and genotypic sex in the common frog (Rana temporaria) in a subarctic environment, where strongly female‐biased sex ratios have raised the possibility of frequent sex reversals. We developed two novel sex‐linked microsatellite markers for the species and used them with a third, existing marker and a Bayesian modelling approach to study the occurrence of sex reversal and to determine primary sex ratios in egg clutches. Our results show that a significant proportion (0.09, 95% credible interval: 0.04–0.18) of adults that were genetically female expressed the male phenotype, but there was no evidence of sex reversal of genetic males that is required for counteracting the degeneration of Y chromosome. The primary sex ratios were mostly equal, but three clutches consisted only of genetic females and three others had a significant female bias. Reproduction of the sex‐reversed genetic females appears to create all‐female clutches potentially skewing the population level adult sex‐ratio consistent with field observations. However, based on a simulation model, such a bias is expected to be small and transient and thus does not fully explain the observed female‐bias in the field.     

MHC zygosity in the frog,Rana temporaria

The major histocompatibility complex (MHC) zygosity of the field-collected frogs, Rana temporaria, was detected by progeny testing. Groups of sibling tadpoles were grafted with intrafamilial tail-tip allografts and the ratio of rapidly rejected allografts to slowly rejected ones was estimated. Twenty-five percent of parental frogs appeared to be MHC homozygotes. Thus, MHC homozygosity in natural frog populations seems to be considerably higher than in wild mouse populations.     

Genome size variation in the common frog Rana temporaria

Genome size variation in the common frog (Rana temporaria) was investigated with flow cytometry in three latitudinally separated populations in Sweden to see whether it could provide a useful tool for sex-identification in this species. Depending on the sex and population, per cell DNA content (2C value) varied from 8.823 to 11.266 pg with a mean (+/- SE) 2C value of 9.961+/-0.083 pg. Analysis of variance revealed significant differences in genome size among populations and between sexes. Females had ca 3% larger genomes (x=10.133+/-0.068 pg) than males (x=9.832+/-0.068 pg) in all of the populations (sex x population interaction: P>0.10). Individuals from the southern-most population had significantly (x=9.330+/-0.081 pg) smaller genomes than those from the more northern populations (x=10.032+/-0.085 and x=10.584+/-0.085 pg, respectively). These results are in line with the interpretation that males in the common frog are the heterogametic sex, and that there exists large (up to 12%) geographic variation in genome size in this species. However, the sex differences in the genome size are too small to be useful in individual sex identification.     

A physico-chemical investigation of the jelly capsules surrounding eggs of the Common frog (Rana temporaria temporaria)

The mucopolysaccharide capsules surrounding eggs of the Common frog, Rana temporaria temporaria L. were investigated. Frogs were obtained from ponds in northern England ranging in altitude from 46 to 838 m. Egg capsules acted as insulators, keeping the centre of an egg mass warmer on average than the surrounding water. The size of an egg capsule and its insulating efficiency varied in different pond waters. Egg capsules in water from highland ponds were larger and more efficient insulators than egg capsules in water from lowland ponds. In a series of laboratory experiments the factors controlling capsular swelling were investigated). The ionic concentration of the fluid surrounding the eggs was found to be the principal factor involved, but the temperature and pH of the fluid and the valency and identity of the ions in solution were also important. The water chemistry of ponds varied with altitude. This accounted for the differential swelling of egg jelly in highland and lowland ponds. The fact that egg capsules are larger in highland pond water may increase egg survival at low temperatures. This is probably fortuitous as there is no evidence to suggest that frogs select their breeding ponds because the water in them will promote capsular swelling.     

Ultrastructure of the joint receptors in the frog (Rana temporaria).

The ultrastructure of sensory nerve endings was examined in joint capsules of large limb joints in three adult frogs (Rana temporaria). The joint receptors are represented by the only one kind of sensory nerve endings--by free nerve endings. The unmyelinized preterminal desintegrates into single terminals. This branching is bound on the most peripheral cell of the Schwann cell by means of mesaxons, they pass from the pericaryum of the Schwann cell peripherally. The branches of the nerve terminal are surrounded by a cover of 1...3 cytoplasmatic processes of the Schwann cell. The surface lamella is covered by a distinct basal membrane. Bundles of collagenous fibrils pass along the branches of the nerve terminal. Quite naked nerve endings were not observed. The axoplasma of the nerve terminal contains strikingly few cell organels. Besides axially passing neurofilaments and neurotubules only sporadic mitochondria and clear vesicles were observed. The accumulation of mitochondria, characteristic for the axoplasma of nerve terminals, was observed in no case. Free nerve endings which were found in the joint capsules of the frog belong among so called "free penicillate nerve endings".     

Genetic variability predicts common frog (Rana temporaria) size at metamorphosis in the wild

We investigated associations between genetic variability and two fitness-related traits--size and age at metamorphosis--in two subartic populations of the common frog, Rana temporaria. We found that metamorphic size was positively correlated with individual heterozygosity (as estimated using eight microsatellite loci) and that maternal heterozygosity also explained a significant amount of variation in this trait. In contrast, age at metamorphosis was only explained by environmental factors. Since size at metamorphosis is positively correlated with fitness in amphibians, these results suggest that genetic variability may be an important component of individual fitness in common frogs. The environmental variation underlying timing of metamorphosis may indicate that strong selection pressure on this trait in the Nordic environment is likely to override genetic effects.     

Stretch receptors of the lungs in the frog Rana temporaria

In experiments on isolated lungs, studies have been made on the activity of single afferent fibers during simulated expiration and inspiration. Both slowly adapting and rapidly adapting voluminous stretch receptors were found in the frog lungs. The latter type exhibits the activity also during fast simulated expiration. Using acetylcholine and histamine, it was shown that the level of excitability of the receptors investigated depends on functional condition of the plain muscles in the pulmonary wall.