Endocrine cells of mucosal epithelium in the distal gut of the grass frog Rana temporaria

The epithelium of the distal part of Rana temporaria intestine has been studied by light and electron microscopy. It has been shown that the number of agrent-affined endocrinocytes in the mucosa of the frog intestinal epithelium decreases gradually from the small bowel to the colon, and then sharply increased in the distal part of colon (cloaca). Four types of endocrinocytes have been identified: EC, D, L and type IV. In frogs examined in March, endocrinocytes of the colon mucosal epithelium demonstrate structural features characteristic of the state of functional strain. These features are most pronounced in EC-cells. This seems to be due to the state of awakening from hibernation, serotonin (produced by EC-cells) playing an essential role in this process.     

Morpho-functional changes in small intestine epithelium of frog Rana temporaria during hibernation

Structure and function of small intestinal epithelium were studied in overwintering frogs Rana temporaria at various stages of hibernation. In the process of testing of absorption of arginine vasotocin (AVT) in experiments in vitro it is established that at the period of hibernation there is preserved the capability of the epithelium for absorption of this nonapeptide without hydrolysis. However, as compared with October-December, in January-February and later, a decrease of the AVT absorption takes place, which is the most pronounced in March-April. Changes in epithelial structures appear by the middle of winter and are progressing by spring. In April-May, as compared with the beginning of hibernation, the height of enterocytes, the length of microvilli, and the number of microvilli decrease by 33 %, 40 %, and 57 %, respectively. The absence of features of destruction indicates an adaptive character of the observed changes. Dynamics of the studied parameters indicates morphological plasticity of the small intestine epithelium of R. temporaria at the period of hibernation.     

Possible apical respiration in the olfactory epithelium of the frog Rana temporaria

Bioluminescent analysis has been made of the effect of oxygen supply on the content of ATP in the isolated olfactory epithelium of the frog. It was shown that storage of epithelium preparations in the air increases their ATP content. When preparations are kept in the atmosphere of an inert gas, ATP level in the epithelium rapidly decreases, being recovered after transition of preparations to the air medium. The data obtained indicate the existence of apical type of respiration in the olfactory epithelium of the frog.     

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.     

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.     

Appearance of Dendritic Cells in the Basal Layer of Corneal Epithelium during Metamorphosis in Rana temporaria L.

A population of dendritic cells was found at the light optic level in the basal layer of the corneal epithelium inRana temporaria L. The cells had wide short processes which penetrated between neighboring epithelial cells. The cell bases lied on the basal membrane while the bodies are slightly elongated perpendicularly to the epithelium surface. The appearance of dendritic cells coincided in time with the beginning of metamorphosis of the tadpoles and their number increased by the end of metamorphosis. The dendritic cells we described were similar in their morphology to the Langerhans cells.     

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.     

Electron microscopic study of colonic epithelial cells from the grass frog Rana temporaria under different intensity of water absorption

Three cell types have been revealed in the epithelium of the frog large intestine: granular, mitochondria-rich, and mucosal cells. Under a low water permeability (0.12 +/- 0.10 mkl/(min.cm2)) the distribution of intramembrane particles (IMP) in the apical cell membrane was the same as in the most cell plasma membranes studied with freeze-fracture method. Under rising osmotic permeability and water absorption (0.43 +/- 0.05 mkl/(min.cm2)) the IMP distribution did not change. In these conditions, the quantity of fusion sites between granule membranes and the apical membrane increased, and the intercellular spaces in basolateral epithelial region were diluted. A a low water permeability, in addition to usual microtubules, bundles of noncentrosomal microtubules with associated osmiophilic globules were revealed. A comparative analysis has been made of the present evidence and previously obtained data on the frog urinary bladder epithelium.     

The hypothalamo-hypophysial system of the frog Rana temporaria

Summary The median eminence (ME) of the adult frog, Rana temporaria, was studied by means of electron microscopy including quantitative electron-microscopic autoradiography. In frogs captured in May and June numerous peptidergic neurosecretory fibres extending via the internal zone to the pars nervosa display large swellings containing few granules, mitochondria, neurotubules and cisternae of the smooth endoplasmic reticulum. In addition, few secretory globules up to 1.5 m in diameter occur in these varicosities. In animals collected during the autumn period many of these neurosecretory swellings filled with neurosecretory granules and polymorphic inclusions resemble Herring bodies. Three types of granule-containing neurosecretory fibres were observed in the external zone (EZ) of the ME of adult R. temporaria. Peptidergic A₁- and A₂-type fibres are characterized by granules 150–220 nm and 100–160 nm in diameter, respectively. Monoaminergic fibres of type B with granules approximately 100 nm in diameter represent 50% of all neurosecretory elements in the EZ of the frog ME; 12% of the total number of granule-bearing axons in the EZ actively taking up radiolabelled 5-hydroxytryptophan are thought to be serotoninergic terminals. Neurosecretory terminals of all types and glial vascular endfeet establish direct contacts with the perivascular space of the primary portal capillaries. Some neurosecretory terminals are separated from the lumen of the third ventricle by a thin cytoplasmic lamella of tanycytes. The possible physiological significance of this structural pattern is discussed.     

Seasonal changes in the endocrine cells of the gastric epithelium of Rana temporaria

By means of the light and electron microscopy methods histotopography, quantity and ultramicroscopic organization of endocrine cells (EC) have been studied in gastric epithelium of the frog (Rana temporaria) during various periods of its life: hibernation, awakening, active life. At all the periods of life 8 types of EC are revealed. Depending on the season, certain changes both in their amount and ultrastructural organization are observed. Decreasing amount of EC is noted during hibernation and their increase in spring during awakening and in summer. Quantity of enterochromaffin cells is not subjected to seasonal fluctuations. This is explained by the fact that in hibernation these cells are also at their active functional state, since they produce serotonin necessary for maintaining deep hypothermia, specific for hibernating animals.     

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.     

Endocrine cells of the gastric mucosa of Rana temporaria L

The endocrine cells of the gastric mucosa of Rana temporaria have been studied according to the ultrastructure, the staining properties of the granules with Masson Fontana's and Grimelius' silver methods, silver impregnation of Davenport on deplasticised semithin sections and immunocytochemical techniques. Seven different types of endocrine cells have been described. Six were regarded as belonging to known types: G, A, EC, ECL, D and P cells. One type was considered as unclassifiable.     

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.