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At least 37 records · Page 2Linked to original sources
PubMed1990

Optic nerves in plethodontid salamanders (amphibia, urodela): neuroglia, fiber spectrum and myelination.

In five species of lungless salamanders, family Plethodontidae, which all show highly developed visual abilities, the ultrastructure of the optic nerve was investigated and the total number of retinal ganglion cell axons, the percentage of myelinated axons, and the volume densities of glia and axons were determined. More than 80% of all axons were smaller than 0.4 micron and only 2-3% were larger than 0.8 micron. In individual nerves the degree of myelination varied between 1 and 9% which is in the range reported for other amphibian species. The miniaturized and highly paedomorphic species Batrachoseps attenuatus was an exception because only very few or even no myelinated axons were present in the nerve, which is unique among gnathostome vertebrates. The five investigated species had total numbers of axons ranging from 26,000 in Batrachoseps attenuatus to about 50,000 in Plethodon jordani. These numbers are the lowest found among vertebrates with an elaborated visual system. The amount of glial material in the optic nerve varied between 25 and 50%, with larger nerves possessing more glia than smaller ones. Ultrastructural analysis revealed that the optic nerve of each species contained both astrocytes and oligodendrocytes, although often in immature form. In Batrachoseps attenuatus the glia showed features of both astrocytes and oligodendrocytes which reflect an undifferentiated state.

Animals↗
PubMed1977

A Golgi study on the hypothalamus of amphibia. The neuronal typology.

The neuronal typology in the hypothalamus of the frog and the crested newt was studied by the Golgi technique. In the newt, piriform, multipolar or cerebrospinal fluid (CSF)-contacting neurons of relatively primitive type, according to the classification of Ramón-Moliner, are encountered in the preoptic area. Moreover, magnocellular neurons are impregnated. In the frog the preoptic area shows a more varied typology. The posterior hypothalami of the frog and the newt exhibit mainly bipolar CSF-contacting and piriform neurons. These latter are generally "tufted", but some bipolar of multipolar cells are encountered, especially in the frog. The simple anatomical organization of the amphibian hypothalamus corresponds well with the pattern of "generalized" integrative area where multimodal sensory inputs converge--including visceral information from cerebrospinal fluid by means of hypothalamic CSF-contacting sensors--to regulate the neuroendocrine outflow.

Animals↗
PubMed1977

Comparative ultrastructural investigations of the uterine epithelium in the viviparous Salamandra atra Laur. and the ovoviviparous Salamandra salamandra (l.) (amphibia, urodela).

The uterine epithelium of the viviparous Salamandra atra and the ovoviviparous Salamandra salamandra was studied in non pregnant and ovulating females and in females during different stages of pregnancy. The epithelium of both species is organized in a monolayer. The epithelial cells are characterized by a moderate secretory activity, a variable amount of apical granules which include PAS-positive material and by some apical and basal exo- or endocytotic vesicles. Adjacent cells are joined by junctional complexes. The lateral surfaces form a tortuous boundary with adjoining cells which suggest that the epithelium is involved in transport. Sporadic light cells possess highly variable cytoplasmic inclusions and are not joined with neighbouring cells. Possibly they represent migratory cells. The entire epithelium, except for a small cranial portion of the uterus in S. atra, undergoes no remarkable morphological changes during the different physiological stages examined except that flattened cells seem to be more numerous in pregnant females. The results are discussed with regard to the possible supply of the developing young by the mother.

Animals↗
PubMed1977

The vascularization of the neural stalk and the pars nervosa of the hypophysis in the toad, Bufo bufo (L.) (amphibia, anura). A comparative light microscopical and scanning electron microscopical study.

The angioarchitecture of the neural stalk and the encephaloposthypophysial portal system of the hypophysis of the toad, Bufo bufo (L.), was studied using three different methods. The neural stalk is mainly supplied by branches of the arteria infundibularis superficialis which form a widemeshed vascular network. Dorsally this network continues into the plexus of the pars nervosa. The vascularization of the pars nervosa is made up of the encephalo-posthypophysial portal system. This portal system consists of a hypothalamic branch (=portion), a mesencephalic and a mesencephalicbulbar branch (=portion). The hypothalamic branch was found to drain the pars ventralis of the tuber cinereum as well as more dorsal regions of the diencephalon. The mesencephalic-bulbar trunk enters the hypothalamic branch. The resulting common stem of the encephalo-posthypophysial portal vein the curves around the retroinfundibular communicating artery, crosses its ventral side and runs caudally. The secondary capillary plexus of the pars nervosa is characterized by well defined capillary plexus of the pars nervosa is characterized by well defined capillary networks which are located at the periphery of the parenchyma of the pars nervosa, thus forming a rostral, dorsal and ventro-caudal net. The central region of the parenchyma of the pars nervosa is supplied only by main branches of the encephalo-postpophysial portal vein. The venous drainage of the pars nervosa is via the vena hypophysea transversa.

Animals↗
PubMed1975

Observations on the fine structure, enzyme histochemistry, and innervation of parathyroid gland and ultimobranchial body of Chthonerpeton indistinctum (Gymnophiona, Amphibia).

Fine structural and enzyme histochemical observations on ultimobranchial body and parathyroid gland of the caecilian Chthonerpeton are presented. The cell clusters and follicles of the ultimobranchial body consist mainly of granulated cells which are termed C-cells and obviously belong to the APUD cell series. In the larger follicles additional possibly exhausted degranulated cells and replacement cells occur. A rich supply of nerve fibres has been found in this gland. Frequently nerve terminals were observed to come into synaptic contact with the C-cells. Two categories of nerve fibres occur: a) fibres containing large polymorphic electron dense granules (probably purinergic fibres), b) fibres containing small electron transparent vesicles and a few electron dense granules (probably cholinergic fibres). The parathyroid gland consists of elongated cells (one cell type) poor in organelles and often containing fields of glycogen and lipid droplets. The cells are further characterized by fair amounts of lysosomal enzymes; they are interconnected by maculae adhaerentes and occludentes. No nerves and blood vessels have been found in the parathyroid gland of Chthonerpeton.

Acid Phosphatase↗
PubMed1976

The influence of temperature on the thyroid gland of Chthonerpeton indistinctum (Gymnophiona, Amphibia).

The thyroid gland of the tropical amphibian Chthonerpeton is markedly stimulated when the animal is exposed for two days to relatively high temperatures (36 degrees C). Control animals were kept at 20 degrees C. The stimulated gland exhibits collapsed follicles and a very tall follicular epithelium. At the ultrastructural level the activated epithelial cells were characterized by an increased number of apical microvilli, increased amounts of rough endoplasmic reticulum, an extended Golgi apparatus and a high number of various granular and vesicular inclusions. These differences in histology and fine structure were not paralleled by quantitative results, which were approximately the same in both groups of animals. The values of these determinations were relatively high.

Amphibians↗
PubMed1976

Temperature dependent changes in the thyroid gland of Mertensiella caucasica (Urodela, Amphibia).

The influence of temperature on the thyroid gland of the Caucasian salamander, Mertensiella caucasica has been studied (1) with the light- and electron microscopes, (2) with enzyme histochemical and quantitative methods. Animals which had been kept for years at 16 degrees C were exposed for 48 hrs to 4 degrees C or 27 degrees C. At 4 degrees C the follicular epithelium consisted of cuboidal cells with well-developed rough ER, occasional distended cisternae of the rough endoplasmic reticulum (ER) filling most of the cytoplasm, a relatively small Golgi apparatus and numerous round or oval shaped lysosomes. In animals kept at 27 degrees C the follicular wall was composed of markedly taller epithelial cells, the apices of which bulged into the follicular lumen. Compared to the animals at 4 degrees C, there appeared to be a decrease in the rough ER. The Golgi apparatus did not exhibit clear differences. The lysosomes increased in number and showed various shapes among which elongated ones with pointed ends were particularly striking. In the apical cytoplasm colloid droplets appeared indicating hormone release. The apical microvilli increased in number. The measurements of total T4 have shown that the hormone level in animals kept at 27 degrees C was about twice as high as in animals kept at 4 degrees C.

Animals↗
PubMed1975

Innervation of the male genital tract and kidney in the amphibia, Xenopus laevis Daudin, Rana temporaria L., and Bufo bufo L.

The innervation of the male genital tract and kidney in three anuran species was studied by the fluorescence histochemical method of Falck-Hillarp for the demonstration of monoamines whose identity was secured by thin-layer chromatography, and by electron microscopy including administration of 5- or 6- hydroxydopamine (5- and 6-ODHA). The genital tract comprises testis, intra- and extratesticular and intrarenal seminal efferent ducts, Bidder's canal, renal dorsal transverse ducts, and ureter. In addition--depending on the species studied--renal corpuscles and the various portions of uriniferous tubules may be involved in sperm transport. 1. Adrenaline is the main transmitter in nerves supplying the male genital tract and kidney. Only in Xenopus is it possible to demonstrate the presence of noradrenaline, which was confirmed in the chromatographic analysis. No obvious changes are observed with regard to the distribution, amount, and fluorescence intensity of adrenergic fibers and their susceptibility towards 5- and 6-OHDA when comparing animals killed in late autumn and winter, or in late spring, respectively. Non-adrenergic nerve fibers have not been observed. 2. The adrenergic innervation in the testis is only scarce and confined to blood vessels. Neuro-endocrine contacts on Leydig cells are not established. The gonadal ducts and the specific (i.e. non-vascular) are intratesticular smooth muscle cells in Xenopus are not innervated. 3. Apart from the uriniferous tubules (see below), only the ureter receives an adrenergic innervation which, however, is scarce even around the time of spermiation. Bundles of non-terminal and terminal axons are seen running contiguous to the superficial bundles of smooth muscle or smooth muscle-like cells. Neuromuscular relationships comprise synapses at distances of 2000-5--- A, but no close contacts. In the seminal vesicle of Rana the same mode of apposition of adrenergic terminals to muscle cells is observed. In addition, a direct innervation of the epithelium is seen in a few instances. 4. In the kidney the renal arteries, afferent arterioles, and the main branches of the kidney the renal arteries, afferent arterioles, and the main branches of the portal veins are supplied by a dense plexus of adrenergic nerves. Small groups of intensely fluorescent cells are found in the walls of the renal portal veins and veins proper. The density of the arteriolar plexus is more pronounced in Rana and Bufo than in Xenopus. In Rana and Bufo the arteriolar innervation comprises terminals at "ordinary" smooth musculature with membrane-to-membrane appositions, as well as contacts at a distance of 800 to 4000 A on juxtaglomerular epitheloid cells...

Animals↗
PubMed1992

Adaptations of the reed frog Hyperolius viridiflavus (Amphibia: Anura: Hyperoliidae) to its arid environment. VI. The iridophores in the skin as radiation reflectors.

Hyperolius viridiflavus possesses one complete layer of iridophores in the stratum spongiosum of its skin at about 8 days after metamorphosis. The high reflectance of this thin layer is almost certainly the result of multilayer interference reflection. In order to reflect a mean of about 35% of the incident radiation across a spectrum of 300-2900 nm only 30 layers of well-arranged crystals are required, resulting in a layer 10.5 microns thick. These theoretical values are in good agreement with the actual mean diameter of single iridophores (15.0 +/- 3.0 microns), the number of stacked platelets (40-100) and the measured reflectance of one complete layer of these cells (32.2 +/- 2.3%). Iridescence colours typical of multilayer interference reflectors were seen after severe dehydration. The skin colour turned from white (0-10% weight loss) through a copper-like iridescence (10-25% weight loss) to green iridescence (25-42%). In dry season state, H. viridiflavus needs a much higher reflectance to cope with the problems of high solar radiation load during long periods with severe dehydration stress. Dry-adapted skin contains about 4-6 layers of iridophores. The measured reflectance (up to 60% across the solar spectrum) of this thick layer (over 60 microns) is not in keeping with the results obtained by applying the multilayer interference theory. Light, scattered independently of wavelength from disordered crystals, superimposes on the multilayer-induced spectral reflectance. The initial parallel shift of the multilayer curves with increasing thickness and the almost constant ("white") reflectance of layers exceeding 60 microns clearly point to a changing physical basis with increasing layer thickness.

Acclimatization↗
PubMed1977

Vascularization of the pars distalis of the hypophysis in the toad, Bufo bufo (L.) (Amphibia, Anura). A comparative light microscopical and scanning electron microscopical study. I.

The vascularization of the pars distalis of the hypophysis of the toad, Bufo bufo (L.), was studied by the traditional method of injecting a mixture of India-ink and gelatine into the circulatory system of the head via the arteria coratis communis. Further, methyl-methacrylate corrosion casts of the brains were made; the hypothalamo-adenohypophysial region of these corrosion casts was studied with the scanning electron microscope. The results showed that the portal vessels which arise from the median eminence do not supply distinct areas in the pars distalis as is supposed by the point-to-point-hypothesis. The portal vessels enter the ventro-median region of the pars distalis and branch off into a three-dimensional network of the secondary capillary plexus of the pars distalis. The plexus is made up mostly by four- to six-sided meshes. This angioarchitecture guarantees an optimal supply of the glandular cells of the pars distalis with nutritional factors and releasing hormones, on the one hand, and facilitates the removal of the hormones which are released by these cells, on the other hand. The venous drainage of the pars distalis is exerted mainly by two large veins, which bilaterally leave the dorso-lateral region (venous pole) of the pars distalis and by a few small veins, which drain into the wide, sinus-like vessel, which curves around the dorso-caudal region of the pars distalis and joins bilaterally the vena hypophysea transversa.

Animals↗
PubMed1977

Vascularization of the pars intermedia of the hypophysis in the toad, , Bufo bufo (L.) (Amphibia, Anura). A comparative light microscopical and scanning electron microscopical study. II.

The vascularization of the pars intermedia of the hypophysis of the toad, Bufo bufo (L.) was studied by injection of a mixture of India-ink and gelatine into the circulatory system of the head via the arteria carotis communis. Further methyl-methacrylate corrosion casts of brains were made and the hypophysial region of the corrosion casts was examined with the scanning electron microscope. The results showed that the vascularization of the pars intermedia of the toad hypophysis consists of a single-layered vascular network, which is located on the ventral surface of the pars intermedia. The network is formed by capillaries, which primarily run caudally in a fan-like manner and which show only a few cross-connections. In the rostral region of the pars intermedia this network lies rather superficially, while in the caudal region it slightly penetrates the parenchyma. The vascular network originates from vessels of the neural stalk and from wide capillaries of the rostro-ventral region of the neurointermediate junction. The venous drainage of the pars intermedia is exerted by veins, which leave the caudal region and drain into the veins leaving the venous pole of the pars distalis. The flat, wide meshed vascular net on the ventral side of the pars intermedia, demonstrated in this study, fits into the concept that the pars intermedia of the anuran hypophysis is under the control of nerve fibers coming from the hypothalamus.

Animals↗
PubMed1975

DNA replication in the amphibia.

Autoradiographic techniques were used to measure rate of replication and length of the replication unit in cultured cells of Scaphiopus couchi, Bufo cognatus, Rana clamitans, and Triturus viridescens, having nuclear DNA amounts in the ratio 1:4:7:39 respectively. The autoradiographic experiments were designed to show whether the larger amounts of nuclear DNA are correlated with more rapid rates of synthesis and/or with longer replication units. -- The DNA replication rate was 2.5 mu/minute (corrected for two growing points) with 10 minutes 3H-thymidine label at 22 degrees C, but decreased with longer labelling durations. The length of the replication unit (estimated by the distance from the center of one autoradiograph to the center of the next in sequence) was most commonly in the 10-25 mu range with a 30 minute label, in all four species. The average center-to-center distance was 8 mu at 10 minutes and increased with label duration, to over 45 mu with 24 hours label. Replication was predominantly but not exclusively bidirectional. Neither rate of replication nor length of the replication unit was proportional to the amount of DNA in these species.

Amphibians↗
PubMed1979

In vivo effects of gamma-irradiation on the functional architecture of the lampbrush chromosomes in Pleurodeles (Amphibia, Urodela).

In vivo irradiation of ovaries of Pleurodeles poireti by gamma-rays leads to structural rearrangement of lampbrush chromosomes in late vitellogenic oocytes (stages V and VI). The loops collapse into the chromomeres and the axes condense. Doses between 200 and 2,000 rads have been tested. We observed that such changes were dependent on the irradiation dose though the chronological order of the events was irrespective of the dose. The maximum effect was attained about 10 h after irradiation. The alterations are totally reversible. Over a period of 3 days chromosomes gradually relax regenerate loops and recover their normal appearance. In mid vitellogenic oocytes (stages III and IV) lampbrush chromosomes do not undergo radiation induced alterations. It seems that only full-grown oocytes are competent to respond to the ionizing-flow.

Amphibians↗
PubMed1979

On the arrangement of chromosomes in the elongated sperm nuclei of Anura (Amphibia).

The position of specific constitutive heterochromatic chromosome regions within the elongated sperm nuclei of eight species of Anura was examined with Q- and C-banding. These species differ widely with regard to the number, size and position of the brightly fluorescing heterochromatic regions. The empirical frequency distributions determined for the heterochromatic regions relative to the longitudinal axis of the sperm nuclei were compared with random frequency distributions calculated on the basis of two spatial models. None of the specifically stained heterochromatic regions occupy any definite preferential position within the sperm nuclei. In two instances, a specific sequence of the heterochromatic regions within the sperm nuclei could be excluded. The type of chromosomal arrangement within the elongated sperm nuclei of Anura is discussed on the basis of the distribution patterns obtained.

Amphibians↗
PubMed1978

Chromosome location of the ribosomal RNA genes in Triturus vulgaris meridionalis (Amphibia, Urodela).

The mitotic chromosomes of six specimens from Triturus vulgaris meridionalis have been examined by both in situ hybridization with 3H 18S + 28S rRNA and AS-SAT staining method. The results of these two sets of experiments can be summarized as follows: 1) in each specimen the NORs and the additional ribosomal sites, which react positively to in situ hybridization with 3H 18S + 28S rRNA, are also stained by silver; 2) other chromosomal regions, which do not hybridize in situ with 3H 18S + 28S rRNA, are on the other hand stained by the AS-SAT method. These latter AG-positive sites show a species-specific pattern of chromosomal distribution.

Animals↗
PubMed1977

Chromosome location of the ribosomal RNA genes in Triturus vulgaris meridionalis (Amphibia, Urodela). II. Intraspecific variability in number and position of the chromosome loci for 18S + 28S ribosomal RNA.

Ribosomal genes have been localized on mitotic and lampbrush chromosomes of 20 specimens of Triturus vulgaris meridionalis by in situ hybridization with 3H 18S + 28S rRNA. The results may be summarized as follows: 1) each individual shows positive in situ hybridization at the nucleolus organizing region (NOR) on chromosome XI; 2) in addition, many specimens exhibit a positive reaction in chromosomal sites other than the NOR (additional ribosomal sites); 3) the chromosomal distribution of the additional sites appears to be identical in different tissues from the same specimen and to follow a specific individual pattern; 4) the additional ribosomal sites are preferentially found at the telomeric, centromeric or C-band regions of the chromosomes involved.

Animals↗
PubMed1975

Neural crest and early fore limb development in amphibia.

Anterior trunk neural folds were exchanged between neurula stages 15 to 16 (Harrison) of several Triturus species and Ambystoma mexicanum. Donor neural crest cells migrated ventrad before and during initial bud formation. They lined the early lumb epidermis and became incorporated into the young blastema. Donor melanophores and non-melanophores contributed substantially to host limb buds.

Ambystoma↗