Archives d'anatomie microscopique et de morphologie experimentale最新文献

By radioactive or trypan blue induced fluorescence yolk labelling (used at certain developmental stages as intravital cytoplasmic markers), it can be demonstrated that the constituent yolk layers of quail blastoderms are formed when the precursor oocyte is growing from 3 to approximately 18 mm (rapid growth period). A previous study ( Callebaut , 1974) and the present study demonstrate that 2 cytoplasmic regions, each with a different constitution and behaviour, can be discerned in the avian germinal disc: 1) a deep and paraxial region, containing yolk that has been in contact with the t.i.c.o.s. (3H-thymidine incorporating cytoplasmic organelles) during oogenesis; 2) a superficial and peripheral region, which has not been in contact with the t.i.c.o. material and which penetrates into the first region along with the cleavage furrows. In the large blastomeres, the originally superficial ooplasm surrounds the deep ooplasm. The area centralis of the unincubated blastoderm must be considered as a heterogeneous cell population, containing both deep and superficial material in variable amounts. After laying and incubation, extra-embryonic tissues such as yolk endoderm and margin of overgrowth develop in the superficial and peripheral region. The embryonic mesoderm also develops from the latter. The yolk, which will be incorporated in the primordial germ cells (germinal yolk), derives only from the original deep and paraxial region of the oocytal germinal disc, i.e. from the region which has been in contact with the t.i.c.o.s. The germinal yolk plasm can be traced in the deep paraxial region of the oocytal germinal disc, in the central region of the unincubated blastoderm, in the endophyll (early primitive streak stage) and finally in the primordial germ cells (P.G.C.s.) at the moment of their separation from the endophyll wall (early somite stage). Thus our results provide evidence for the existence of a germ cell plasm in the avian postlampbrush oocyte.

A new microsurgical procedure is described through which the thymus can be completely removed bilaterally prior to its seeding by lymphoid precursor cells in the chick embryo. 53% of the embryos operated at 5 days of incubation and sacrificed either before or after hatching were totally thymectomized as controlled on serial sections of the neck. Hatchability is low, as it normally is when operations are performed on embryos in ovo. However totally thymectomized viable chicken could be recovered. In certain series of experiments, the graft of a 5-day quail embryonic thymus was performed into the site of excision of the chick thymus. The quail thymic rudiment then became colonized by chick lymphoid precursor cells and developed normally. The possibility of using this excision-graft technique is suggested to study the role of MHC gene products in T-cell differentiation.

The embryonic development of Grantia compressa is studied by means of the electron microscope from the blastula inside the mesenchyme to the mature amphi-blastula released in the excurrent canals. The study of the different cellular categories of the embryon shows the distribution of the vitellin inclusions and their evolution. The ultrastructure of the "cellules en croix" is not in favour of a photoreceptor part.

Isografts of sciatic nerve, skeletal muscle, submaxillary gland and, as control experiments, of optice nerve, were transplanted into the non transected spinal cord of young albino mice, through a punctiform pial aperture. Under these conditions, local cellular reactions were reduced and the sensori motor behavior of the operated animals remained apparently undisturbed throughout the experimental period. Within a few days, axonal sprouts issuing mainly from the terminal clubs of intraspinal nerve fibres severed by the grafting procedure were seen elongating and growing into--and presumably throughout--the nervous as well as the muscular and glandular transplants. The Schwann cells of these grafts, either sedentary or migrating towards the cord and intermingling with host reactive glial cells, appeared to guide the growth of the axonal sprouts they ensheathed (from day 3 to day 10) and generally myelinated (as early as day 6). Optic nerve transplants, lacking Schwann cells, were never reinnervated. Furthermore, in control microinjuries without grafting, limited growth of axonal sprouts was observed only when a few host Schwann cells were present. Mouse spinal neurons, therefore, demonstrate a marked capacity for regrowth when minimal damage to the spinal cord is associated with an adequate supply of Schwann cells. In contrast, host as well as transplanted glial cells, were unable, at least when they were not associated with Schwannian elements, to promote regenerative expression of these central neurons.

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 .

By means of the indirect immunofluorescence method, somatostatin-like immunoreactive (SLI) cells are detected in the esophagus of the ascidian Styela plicata. They are of the "open" type; they act probably by a paracrine mechanism on the esophageal secretin-like cells. The ascidian SLI cells are negative to all the specific cytochemical methods characteristic of vertebrate somatostatin (D) cells, which were applied in this work. In consequence, special SLI cells are probably present in ascidians.

A morphological study of in vitro wound healing has been performed by light, transmission and scanning electron microscopy in dorsal thoraco-lumbar skin of 7-day chick embryos. A circular wound, 750 microns in diameter, was punched out of dorsal skin, removing epidermis and the underlying dense dermis. Wound closure was completed within 96 to 120 hours. Feather bud development was not observed at the wound site. The epidermis began to migrate some 24 h after the wounding; the migration of peridermal cells preceded that of basal epidermal cells by some 12 hours. Mechanisms of the epidermal migration were similar to those observed in situ during wound healing of the integument in 5-day chick embryos (THEVENET, 1981), Superficial epithelization of bare dermis occurred as soon as 12 h after the injury. Cytoplasm of dermal cells exhibited many microtubules and a dilated rough endoplasmic reticulum. During the first 48 h, the epidermal cells established direct contacts and zones of close parallel apposition with epithelized dermal cell processes. The basement membrane lamina densa was maintained at the edges of the wound without retraction or ruffling. It was reconstituted concomitantly with the epidermal migration within 72 h. Cytoplasm of migratory epidermal and epithelized dermal cells exhibited many cytoskeleton structures.

In the present report tubulated granules are described for the first time in a freshwater teleost (Pimelodus maculatus) endothelial cells. Some ultrastructural characteristics as well as the localization and distribution suggest that tubulated bodies represent the teleost counterpart of the Weibel-Palade bodies described in other animal classes.

This report describes the fine structure of the "wheel" cells and of epithelial structures which both characterize the interstitial tissue of hypophysectomized and intact senescent rats. The regressive changes induced in normal ovarian interstitial cells of 25-26 day-old hypophysectomized rats were studied from 7 days to 15 months after the operation. They mainly consist in a rapid cytoplasmic dedifferentiation of these steroidogenic cells which, by one month after hypophysectomy, could be only identified by their specific nuclear pattern ("wheel" cells). Further changes of their organelles are only quantitative. These interstitial cells become perennial cells with no ultrastructural signs of senescence. In one year-old animals, the presence of both epithelial testis-like tubes and epithelial cellular cords provides evidence that these structures represent two different morphological arrangements for a similar cellular aspect. Unlike established "wheel" cells, these epithelial structures are evolutive and the thickening of their basement membrane can be considered as an age criterion. The follicular origin of the testis-like tubes and the complex formation of the cords are discussed in the light of our previous photonic study and compared with similar structures occurring in the senile rat ovary and in other situations.

The effects of a commercial spray preparation of ammonium salt ppf fosamine (a defoliant) on quail and chick eggs have been studied. The results lead us to conclude that under the stated conditions the product has little embryotoxicity. However, it does have teratogenic effects on the steal and on the cervical, dorsal and posterior axial skeleton. The observed malformations are more severe and appear more frequently in quail than in chick embryos.