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At least 1,009 records · Page 56Linked to original sources
PubMed1983

Somitogenesis in amphibia. IV. The dynamics of tail development.

Following neurulation, the frog segments c.40 somites and concurrently undergoes a striking elongation along the anteroposterior axis. This elongation (excluding the head) is largely the result of a presegmental extension of posterior tissue with a lesser contribution from the extension of segmented tissue. Presegmental extension is entirely the result of activity within a narrow zone of extension that occupies the central region in the tail bud. Within the zone of extension, a minimum of six prospective somites undergo an eight- to ten-fold extension along the axis. The zone passes posteriorly across the tissue of the tail tip. The anterior of the tail bud contains three extended prospective somites in the course of segmentation. The anterior boundary of the zone of extension coincides in space exactly with the anterior boundary of the zone of abnormal segmentation that results from temperature shock. This means that extension ceases immediately before the sudden tissue change associated with segmentation.

Animals↗
PubMed1983

Development and differentiation of the brain ventricular system in tadpoles of Xenopus laeris (Daudin) (Amphibia, Anura).

The development and the differentiation of the ventricular system of the brain of tadpoles of the South African Clawed Toad, Xenopus laevis (Daudin), is studied by light microscopy (stages 45 to 66) and scanning and transmission electron microscopy (stages 50 to 66). Special interest is paid to the ependymal structures of the foramen of Monroe, the ventricles of the diencephalon, the mesencephalon, and the rhombencephalon, and to the ependymal of the central canal and the choroid plexus of the third and fourth ventricle. At early developmental stages the lower two thirds of the ventricles are dominated by blebs, cytoplasmatic protrusions of the ependymal cells. During the development they become reduced and replaced by cilia. The number of cilia and microvilli increases strongly towards the end of the metamorphosis. The surface structures demonstrated by scanning electron microscopy are discussed in respect to morphology and physiology.

Animals↗
PubMed1983

[Quantitative and qualitative analysis of the effects of various doses of beta-irradiation (50-5000 rads) on epidermal cells of embryos and larvae of Pleurodeles waltlii Mich. (Amphibia, Urodela)].

Embryos of Pleurodeles waltlii at the hatching stage were irradiated with doses of 50 to 5 000 rad. From 70 to 500 rad chromosomal aberrations appear; they are studied respectively 24,48 hours and 3 weeks after the treatment. Breakages are observed, that may be followed by rearrangements, i.e. acentric, telocentric and dicentric fragments, chromatid translocations and chromosome translocations. With time, the cells showing the most severe abnormalities are eliminated by the developing larvae. From 1 000 rad cytoplasmic structures (membrane systems and mitochondria) are alterated .

Animals↗
PubMed1984

Scanning electron microscopy of the oviduct of Salamandra salamandra (L.) (Amphibia, Urodela).

The oviduct of non-pregnant females of the ovoviviparous salamander, Salamandra salamandra, was examined using SEM-techniques. In the luminal epithelium polygonal ciliated cells were found along the entire surface of the oviduct, except the uterus, and non-ciliated cells with a varying number of short or long microvilli. The ciliated cells occur in the most anterior portion of the oviduct, the pars recta; they are sparsely distributed in the p. convoluta I, but abundant in the p. convoluta II and III. Non-ciliated cells comprise several small gland cells, restricted to the p. convoluta I, II, III, and undifferentiated cells both provided with microvilli, but difficult to be discerned from their surface appearance. The p. convoluta I, II, III is characterized by three types of secretory cells forming tubular glands, each type confined to a given zone. The secretory cells have slender microvilli at their surfaces. In freeze-cracked glands details of their secretory products can be visualized. The findings are compared to previously published TEM-investigations and discussed with regard to some functions of the oviduct during reproduction.

Animals↗
PubMed1984

[Secondary development of minced muscle tissue of amphibia during transplantation and cultivation in diffusion chambers].

The development of the skeletal muscular tissue from the frog Rana ridibunda was studied under autotransplantation and cultivation in diffusion chambers of the minced gastrocnemius muscle implanted intraperitoneally to other species of the same family. The material was examined by light or scanning electron microscopy. In both series of experiments, the muscular tissue from adult frogs retained its viability and reconstructive activity for a long time. The muscle material underwent reconstruction starting from myoblast formation by means of their separation and migration from disintegrating muscle fibers. The reconstruction eventuated in the formation of differentiated muscle fibers. The development of the muscular tissue proceeded more rapidly during cultivation in diffusion chambers under homo-implantation as compared with the process occurring in the minced muscle autotransplant.

Animals↗
PubMed1980

[Quantitative analysis of adult morphology in eudiploids and three types of trisomics of Pleurodeles waltlii (Amphibia, Urodela) (author's transl)].

The results of a comparative quantitive study of morphology in eudiploids and three types of trisomics of adult Pleurodeles waltlii are discussed. General morphologies are specified by mean measurement values. Statistical bivariate analysis demonstrate differential growths and give some new details on sexual dimorphism. Trisomies 8 and 11 have opposite effects on growth allometries, while no significant effect of trisomy 10 has been detected. As a rule, characters of trisomics are more variable than those of diploids.

Animals↗
PubMed1980

On spontaneous skin tumours in amphibia.

In 7 from 320 Rana temporaria grass frogs and 16 from 978 Rana ridibunda pond frogs, the 31 and 47 spontaneous skin tumors respectively, were observed. The tumors were represented by cystadenopapillomas and adenocarcinomas, and developed from epithelium of skin mucous glands. The spontaneous pigment tumors (melanophoromas) were found in 2 axolotls Ambistoma mexicanum. These tumors developed from hyperplastic melanophores in pigment spots and focal proliferations of melanophores located deeply in derma.

Ambystoma mexicanum↗
PubMed1981

Tissue interactions during axial structure pattern formation in amphibia.

Tissue interactions have traditionally been assigned important roles in establishing the pattern of amphibian axial structure morphogenesis. Those interactions have been postulated to generate the patterns of neural fold morphogenesis, neural tube formation, and somite development. A review of axial structure development together with a brief discussion of the classical viewpoint, is presented. A re-examination of axis formation has recently been carried out with the SEM. Embryos which displayed major defects in notochord development, ranging from diminished length to complete obliteration, were produced by irradiating fertile eggs prior to first cleavage. A comparative SEM analysis of normal and "notochord defective" embryos revealed that, contrary to previous reports, the notochord is apparently a dispensable component of the developing axial structure system. Lastly, TEM examination of the notochord defective embryos allowed some insight into the ultrastructural alterations which occur in the notochord and neural tube cells of irradiated embryos. Additional information about the structure of the notochord, and the cellular mechanics of somitogenesis emerged from those studies.

Animals↗