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

The splitting pattern and the spatial arrangement of the musculature were studied in the chick tibiotarsal segment. All 15 muscles evolve from the two opposed premuscular masses which become dorsal and ventral to the chondrogenic core before day 5 of incubation. Binary and tertiary divisions and subdivisions of these muscle masses between day 5 and day 7.5 of incubation produce the muscular pattern characteristic of the hind limb zeugopod.

Cell proliferation kinetics were investigated in the thymus of the newt Pleurodeles waltlii during larval life and metamorphosis. Cell cycles lengthened continuously, particularly G1 and G2 phases. Relative durations of G1 and G2 (differentiation phases) lengthened, while relative durations of S and M (multiplication phases) shortened. Consequently, multiplication rate decreased regularly. Mitotic index, labelling index and growth fraction increase up to stage 50, then decreased markedly. Stage 50 is an important one, as cell cycles duration and growth fraction vary inversely from this point onwards; it marks the end of the period of intense proliferation and rapid growth of the thymus, and also the beginning of the period during which all differentiated cell types are present, cell proliferation decreasing and becoming markedly diminished after the end of metamorphosis.

Morphological, morphometrical and histochemical studies of the cell types in the salivary glands of Philodryas patagoniensis have been performed. It is concluded: 1) the acini of supra, infralabial and premaxillary glands are formed by mucous and mucoserous cells; the Duvernoy's gland by seromucous cells; 2) mucous cells show neutral and sulphated mucosubstances and sialic acid; mucoserous cells show neutral mucosubstance, sialic acid and protein radicals; seromucous cells of Duvernoy's gland show neutral mucosubstance and protein radicals. The acinar area, height of tubule and duct cells, and nuclear volume of acinar, tubule and duct cells were evaluated morphometrically.

Rostral gonadotrophs of the teiid lizard Cnemidopohorus lemniscatus are mainly situated in the rostral zone of the anterior hypophysis, but partially invade the caudal region when hyperactive. They are rounded or ovoid cells in which the dilated granular endoplasmic reticulum, containing a flocculent substance, forms large disseminated vesicles and, frequently, an expanded basal cisterna. Numerous free ribosomes lie in the hyaloplasm, and the Golgi apparatus has often a spherical arrangement. Secretory granules are round, homogeneous, of medium opacity, and closely bound by a membrane. They vary considerably in size, their largest diameters being four times greater than those of the smallest granules in most cells. Characteristic membrane-bound polymorphic bodies exist among the granules; they contain a filamentous substance and opaque or crystalline inclusions. The mitochondria are very elongated. Rostral gonadotrophs undergo marked variations throughout the year; in May they are voluminous, with vesicular nuclei, abundant secretory granules, large polymorphic bodies, conspicuous Golgi apparatuses and widely scattered vesicles of endoplasmic reticulum, whereas the small cells present in January show opposite features. Gonadectomy, in both sexes, produces activation of these cells, with progressive reduction in the number and size of secretory granules, until almost complete degranulation of many elements after sixty days. Metyrapone administration for eight days results in a striking regression of rostral gonadotrophs, which appear small, with shrunken nuclei, poorly developed organelles, and few, often large secretory granules.

An electron microscope study was conducted on the origin of the dorsal longitudinal muscles of a Nematocerous Diptera (Chironomus). These imaginal muscles arise from three pairs of slender larval muscles that are characterized by the presence of myoblasts located beneath the basal lamina and adhering to the sarcoplasmic membrane. During the last larval instar the myoblasts increase in number, each of the associated muscle fibers loses its contractile material and splits longitudinally into two to form six columns of sarcoplasm. Differentiation of the fibrillar material begins in each of the six muscle rudiments after the adhering myoblasts have become incorporated. There are several possible origins for these myoblasts: they may be embryonic cells that persist in association with the larval muscle fibers; or --as in the case of Cyclorrhaphous Diptera-- they may migrate from elsewhere to invest these fibers.

Differentiation of cartilage from mesodermal cells of the chick embryo wing bud is controlled by the ectoderm. Transfilter cultures have shown that this interaction cannot take place at a distance but requires contact conditions as established between mesodermal cells outgrowths and the ectodermal basement membrane in vivo and in vitro. Induction does not pass from one cell to another: when cultured in vitro cartilage differentiating cells do not provoke chondrogenic differentiation of mesodermal cells incapable of autonomous differentiation. During in vitro culture, cartilage differentiation of limb mesodermal cells is obtained in the absence of ectoderm at stage 17 (H. and H.) and rarely at stages 15-16. Is the inductive contact established at these stages for all the cells concerned or is it a continuous phenomenon which lasts as long as condensation formation proceeds? Ultrastructural studies of the space between ectoderm and mesoderm show that at stage 13 (18 to 20 somites), all limb somatopleural cells are capable of establishing a contact with the ectodermal basement membrane. But numerous contacts are also observed up to late stages, when condensations develop. However, at the stages and at the levels of formation of precartilaginous condensations, no movement of cells is observed from the external mesodermal layers towards the condensations, in chimeric quail-chick limbs. It seems therefore that the inductive contact takes place early (24-32 somites, stages 15 to 17 H. and H.), possibly a little later, but long before the formation of precartilaginous condensations (stages 23 to 30 H. and H.). The time between inductive contact and differentiation of the cell differs greatly therefore according to the final localization of the chondrocyte among the proximo-distal axis. This conclusions is discussed in relation to the Progress Zone (P.Z) concept.

Transmission and scanning electron microscope appearances of epithelium in a pregnant uterine horn at and between the eggs, in a non-gravid horn of a unilaterally pregnant animal, and in the uterine horn of a pseudopregnant animal provided evidence of short-, medium- and long-range blastocyst effects. While cessation of mitotic division at 5 to 6 days post-coitum is solely the result of ovarian activity, the changes that occur in the shape of uterine epithelial cells apex seem to be due to the combined actions of ovaries and eggs. The development of apical club-shaped structures between 4 and 6 days, more pronounced in the pregnant horn compared with the pseudopregnant horn is apparently determined by ovarian and ovular effects. On the other hand, blastocysts induce the apparition of crater-cells at days 4 and 5 only in the pregnant horn : this could involve a mechanical or a chemical action of short- and medium-range egg effects. Similarly, on days 5 and 6, apical elongations are seen in the uterine regions occupied by the eggs, this finding points to a possible short-range blastocyst action.

Thyrotrophs do not abound in the anterior hypophysis of the teiid lizard, Cnemidophorus lemniscatus. Situated in the ventral and caudal regions, they are medium-sized rounded cells, with some angulation, having an eccentric, indented nucleus, coarse chromatin, a rather dense hyaloplasm and numerous free ribosomes. The rough endoplasmic reticulum is composed of vesicles, some tubules and, often, an isolated basal flat cisterna. The Golgi apparatus tends to be angular; small new secretory granules and many coated vesicles occur in this zone. Mitochondria are ovoid or elongate, with a dense matrix. Well constituted cilia, of the type 9 + 2, may be found in these cells. The secretory granules are spherical and small, relatively uniform in size, and somewhat variable in density. Less opaque granules show a fine structural granularity; this difference is probably due to a maturation process. A narrow light space, or halo, usually exists between the bounding membrane and the core. The number of thyrotrophs is considerably increased by 15 days after thyroidectomy. Possibly many new cells differentiate from apparent syncytial foci of amitotic divisions. At the same time, thyrotrophs become highly hypertrophic, exhibiting vesicular nuclei with dispersed chromatin, greatly expanded Golgi apparatus, and very elongated mitochondria, as well as an extensive degranulation.

The following products were tested: 1) the purified new synthetic pyrethroid decamethrin; 2) its commercial solution; 3) the excipient of the commercial solution; and 4) the main constituent of the excipient xylene. Eggs were treated either directly by spraying of the shell with 2% and 0.05% aqueous suspensions of commercial decamethrin, excipient and xylene; or indirectly by repeated ingestion by the parental quails of fed contaminated with the four chemicals. All these constituents significantly acted upon the quail biotic potential; they reduced the hatching rate and the embryonic viability and, on the contrary, increased the fecundation rate and the weight of eggs, chickens and adults. Moreover, they reversed the sex-ratio, what brought about the male birds to have the advantage in number. At last, they acted more specifically on the embryonic genital development. The comparative study of effects of both the pesticide and its excipient showed that the later, and more exactly the xylene, was the main responsible factor.

In embryos and very young dogfish made hypothyroidian by various treatments (radiothyroidectomy, surgical thyroidectomy and PTU treatment), ultrastructural abnormalities have been observed in all tested cartilages : Meckel's, branchial and pelvic cartilages. Many chondrocytes show a dark nucleus, enlarged REG vesicles and very electron dense hyaloplasm giving the cell a very peculiar reticulated aspect. Other chondrocytes appear unaffected. Cartilage ultrastructure is almost fully restored after a 21 days' recovery time. Around abnormal chondrocytes, extracellular matrix components are scarce. Moreover, matrix mineralization occurs around some abnormal chondrocytes by hydroxyapatite crystalization, never seen in normal embryos. During recovery, these crystals are preserved. When the antithyroid effects of PTU are compensated for by a simultaneous thyroxine treatment, cartilage abnormalities are minimized. If radiothyroidectomy is performed on young embryos, chondrocyte differentiation is delayed. It is concluded from these various experiments that thyroid hormones are required for the normal differentiation of cartilage and for the maintenance of its integrity in this fish.