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.     

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.     

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.     

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.     

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.     

Significance of serotonin in the activity of the taste receptor apparatus of the frog Rana temporaria

Studies have been made of the effect of exogeneous serotonin on responses of taste receptors recorded from the hypoglossal nerve during adequate stimulation. It was shown that serotonin evokes afferent discharge in this nerve and significantly increases responses of taste receptors. Stimulating effect of serotonin appears 15-20 min after its application and gradually develops reaching maximum within 60 min after injection. Competitive antagonist of serotonin, 7-methyltryptamine, inhibits taste afferent responses and blocks stimulating effect of serotonin. Possible role of serotoninergic mechanism in afferent impulse activity of the taste receptive apparatus is discussed.     

The response characteristics of vibration-sensitive saccular fibers in the grassfrog,Rana temporaria

Summary The response characteristics of saccular nerve fibers in European grassfrogs (Rana temporaria) subjected to dorso-ventral, 10–200 Hz sinusoidal vibrations were studied.Only 4 fibers out of a total of 129 did not respond to the vibrations.70 fibers had an irregular spontaneous activity of 2–48 spikes/s. These fibers were very vibration-sensitive. The synchronization thresholds at 10–20 Hz varied from below 0.005 to 0.02 cm/s².In contrast to earlier results, all these fibers had low-pass characteristics (with respect to acceleration) and responded maximally at 10 and 20 Hz.55 fibers had spontaneous activities from 0–2 spikes/s. These fibers were less sensitive than the fibers with higher spontaneous activity. The spike-rate thresholds varied from about 0.04 to above 1.28 cm/s², giving a considerable range fractionation. Most of these fibers also had low-pass characteristics with respect to acceleration, but 8 fibers showed band-pass characteristics with maximal synchronizations and spike-rates occurring at 40–80 Hz.At high acceleration levels, most spikes fell within 5–10 degrees of the stimulus cycle. The phase-locking of the saccular fibers is therefore very acute at low frequencies.The phase angles preferred by the fibers at 10 Hz were bimodally distributed with the two peaks about 180° apart. This finding probably reflects the morphological observation that the saccular macula contains two oppositely oriented hair-cell populations. The results also indicate that the actual motion of the otolith relative to the macula is complex.No behavioral role of a vibration receptor has been demonstrated in the grassfrog. A use in predator avoidance is likely, and it is possible that the sacculus is used for detection of water surface-waves. The vibration sense could therefore be of importance in the detection and localization of conspecifics in the breeding ponds.     

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     

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.     

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.     

Appearance of dendritic cells in the basal layer of the corneal epithelium during metamorphosis of the grass frog Rana temporaria L

A population of dendritic cells was found at the light optic level in the basal layer of the corneal epithelium in Rana temporaria L. The cells had wide short processes which penetrated between neighboring epithelial cells. The 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.