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.     

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.     

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.     

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.     

Middle ear transmission in the grass frog, Rana temporaria

The anuran middle ear serves to transmit eardrum vibrations to the inner ear. In order to do this efficiently, the eardrum and middle ear must operate as an impedance transformer matching the low impedance of air to the higher impedance of the fluid-filled inner ear. In amniotes, one of the mechanisms used to achieve impedance transformation is to have the middle ear work as a force-amplifying lever system. Here, we present evidence that the grass frog middle ear also implements a lever system. The columellar footplate, which sits in the oval window, is firmly connected to the otic capsule along its ventral edge. Therefore, simple in-out movement of the columella is prevented while a rotational movement around the footplate's ventral edge is possible. The latter movement pattern was confirmed by laser vibrometry measurements of eardrum and footplate vibrations. The results showed that the footplate vibrations were 20–30 dB weaker than those of the eardrum and that the two structures vibrated 180° out of phase (at low frequencies). The lever ratio was approximately 6, i.e. somewhat higher than lever ratios reported for amniotes. Hence, the middle ear lever probably makes a significant contribution to impedance matching in frogs. Accepted: 1 July 1997     

Interdigitating cells in the thymus of the frog, Rana temporaria

Interdigitating cells (IDC) of the thymic medulla of the frog, Rana temporaria, collected in the summer, were examined by electron microscopy. The most characteristic cytological features of IDC are voluminous electron-lucent cytoplasm and widespread interdigitations and invaginations of the cell membrane. IDC possess an excentrically located nucleus with pronounced nucleoli and a thin rim of a dense chromatine as well as a perinuclear area with characteristic tubulo-vesicular complex. In our material Birbeck granules were absent. Some IDC contain phagocytized material. A few transitional forms between monocytes and IDC were observed. On the basis of these observations it is highly probable that the amphibian IDC belong to the mononuclear phagocyte system.     

Refrigerated storage of European common frog Rana temporaria oocytes

Reproduction technologies (RTs) for the storage and use of amphibian gametes have rapidly developed since the recognition of the amphibian conservation crisis in the late 20th Century. Of these RTs, the refrigerated storage of oocytes and sperm can help to achieve reliable pair-matching when unexpected deaths could lead to critical gaps in studbook programs, and also to enable gamete transport between facilities or when sampled from field populations. Viable sperm can be reliably stored in vitro in testes, as suspensions in refrigerators for weeks and in situ in refrigerated carcasses for days. However, oocytes have only been reliably stored in vitro and then only for a few hours. We stored mature oocytes of the European common frog Rana temporaria refrigerated at 4 °C: in situ in the oviduct of carcasses for 1–5 days, in vivo in the oviduct of live frogs for 30 days, and in vitro in plastic boxes for 1–5 days. Oocyte viability was measured as the percentage of fertilisation relative to controls and as the percentage hatch of fertilised oocytes. Rana temporaria oocytes in situ or in vitro retained some viability to hatch for up to 5 days. In contrast, when stored in vivo, oocytes showed little loss of viability to hatch after 10 days and moderate viability up to 30 days.     

GABA immunoreactivity in the main olfactory bulb of the frog Rana temporaria

Immunoreactivity for gamma-aminobutyric acid (GABA) was localized at the light microscopic level in the main olfactory bulb (MOB) of the frog, Rana temporaria. By means of free-floating peroxidase-antiperoxidase immunocytochemical technique, GABA was found in a large number of neurons in the granular cell layer, in a few small somata in the mitral cell layer and in two different types of cell somata in the glomerular layer. Individual GABA-immunopositive cells were found in the olfactory nerve layer. GABA immunostaining was also localized in cell processes and fiber fragments. There were many immunoreactive puncta in all layers of the MOB. GABA-positive punctate structures often outlined immunonegative cells in the mitral cell and glomerular layers. Rounded tightly packed groups of immunoreactive puncta were found only along ventral border of the glomerular layer. The results are discussed in comparison with data obtained on mammalian MOB in terms of MOB functional organization.     

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.     

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".     

The temperature hysteresis of water-salt metabolism in the frog Rana temporaria]

Frogs acclimated to 4 degrees C were transported to a medium with temperature 20 degrees C, which caused polyuria; recovery of normal diuresis took about 24 h. During this period, hypernatremia was observed together with the increase in natriuresis, the rate of renal excretion of potassium ions with urea remaining constant. Water content of skeletal muscles decreased. Transportation of frogs acclimated to 20 degrees C into a medium with a temperature 4 degrees C decreased their diuresis. Renal excretion of sodium, calcium and magnesium ions remained unchanged, whereas that of potassium ions significantly decreased. The content of potassium and magnesium in the blood serum increased, that of sodium--decreased. Hydratation of muscled and kidneys was accompanied by the decrease of calcium, potassium and magnesium ions calculated per wet weight of the tissues, the level of sodium remaining unaffected. The data obtained indicate significant changes in the pattern of water and salt metabolism in frogs during temperature hysteresis.     

Histochemical study of skeletal muscles of the frog, Rana temporaria

Histochemical profiles of muscles were identified based on staining for myosin ATPase activity. They reveal typical arrangement of muscular fibres with a zoned pattern. Tonic fibres have a unique histochemical profile and are mixed with the most oxydative fast fibres to form toxic zones. Muscles show fast profiles in thigh and tonic or mixed profiles in fore-arm.