The topogenesis of the thyroid in chick embryos.

Using the technique of linar marking on the embryonic thyroid of chicken, it was proven that the thyroid anlage after its evagination from the primitive pharynx, does not undergo any caudal migration. Its topogenesis is influenced by two main mechanisms. First, the relative craniocaudal displacement follows from the cranially oriented growth of the neck and second, the enlarging oesophagus presses the trachea ventrally against the thyroid anlage promoting its division and separation of both lobes.

Uncoupling protein in embryonic brown adipose tissue--existence of nonthermogenic and thermogenic mitochondria.

Embryonic development of mouse and rat brown adipose tissue was characterized by electron microscopy and by quantifying the mitochondrial oxidative, phosphorylating and thermogenic capacities immunochemically, using antibodies against cytochrome oxidase, F1-ATPase and uncoupling protein, respectively. Mitochondria and cytochrome oxidase were detected from the 15-16th day of pregnancy and their amounts continuously increased toward birth. F1-ATPase was also found on the 15th day but it reached a maximum level already on the 19th day when the uncoupling protein appeared and rapidly increased during further maturation of brown adipose tissue. It thus appears that mitochondria in early prenatal brown adipose tissue lack completely uncoupling protein and are nonthermogenic. They transform into typical thermogenic mitochondria abruptly only 2 days before birth.

Age dependence of selenite uptake in rat eye lenses.

75Se-selenite was administered to young and adult rats in subcutaneous injection or added into the medium in which eye lenses were incubated. The 75Se uptake in lenses of the young was significantly higher in comparison with adults both in vivo and in vitro. The in vivo 75Se uptake, referred to unit of lens weight, was almost 500 times higher in young animals while in vitro it was only five times higher, which apparently reflects the age-dependent differences in the structure and function of membranes and/or system barriers.

Fibrillar centres and condensed nucleolar chromatin in resting and stimulated human lymphocytes.

To provide more information on the ultrastructural morphology of fibrillar centres and condensed nucleolar chromatin, both these nucleolar components were studied in ultrathin sections of resting and phytohemagglutinin stimulated human lymphocytes. In comparison with resting cells, in stimulated lymphocytes fibrillar centres increased in number but their total size was smaller. In stimulated cells the size of individual fibrillar centers remained about the same. The size of the intranucleolar condensed chromatin was larger in stimulated than in resting cells. The proportion of the intranucleolar areas with condensed chromatin to the whole nucleolar area was relatively constant since no difference was noted between resting and stimulated cells. On the other hand, the proportion of the condensed intranucleolar chromatin to the condensed perinucleolar chromatin increased in stimulated lymphocytes in comparison with resting cells. The close morphological relationship between fibrillar centres and condensed intranucleolar chromatin was noted in ring shaped nucleoli of resting lymphocytes, this relationship was frequently remaining in nucleoli with less or more distinct nucleolonemata of stimulated cells.

Analysis of the cardiotoxic effect of isoproterenol in chick embryo.

Intraamnial administration of isoproterenol (IPRO) to chick embryo induces different types of pathological changes of the myocardial and liver tissue: their character depends upon the developmental period during which the drug was administered. Analysis of the embryotoxic effect of IPRO has revealed that the time-course of in vivo uptake of [3H]IPRO by the developing heart appears to present the same pattern as the embryonic liver tissue; both peak values (10 min and 6 h after injection) were, however, significantly higher in the liver as compared with the myocardium. IPRO is rapidly metabolized to 3-o-methyl-IPRO; the proportion of this fraction in both organs represents approximately 40% of total radioactivity as early as 5 min after administration. Intraamnial administration of IPRO significantly increases the cAMP content in the myocardium; dibutyryl cAMP-induced myocardial lesions occurred, however, only occasionally and in comparison with IPRO they were significantly less pronounced. The cardiotoxic effect of IPRO can be significantly reduced by beta-blockade; calcium antagonist, verapamil, was found to have no protective effect. Our results suggest that the following factors may participate in the IPRO-induced embryotoxicity: (1) IPRO, (2) its toxic metabolites, (3) cAMP.

The carotid body of the pheasant (Phasianus colchicus L.). An electron microscopy study.

In the pheasant, the carotid body lies laterally to the common carotid artery, is partly surrounded by parathyroid tissue and is immediately adjacent to the ultimobranchial body. In some cases these tissues intermingle. The cellular component of the carotid body consists primarily of granular endocrine cells, which are arranged in islands and lie in immediate proximity to wide capillaries and nerve fibres. A quantitative evaluation of granule size frequencies in these main cells, which we divided into three types, showed, inter alia, that the types represented three stages of cell differentiation, type III being the most mature cells. Only this last, i.e. mature, type can be used for differentiation from the granular cells of the ultimobranchial body of the same species, from which they differ. In addition, the main carotid body cells are typically surrounded by sustentacular cells. Numerous contacts with the terminal parts of axons were found on the main cells.

Morphogenetic systems and screening for embryotoxicity.

While mutagenesis appears to be a single-cell phenomenon, the target for teratogenesis are the groups of cell populations constituting the morphogenetic system (MGS). The sensitivity of MGSs is of two kinds. First, it is the sensitivity to general cytotoxic agents. It is non-specific and reaches its maximum during early embryogenesis. The second type of sensitivity manifests itself at the more advanced stages of development, and it is intimately connected with the specific cell differentiation. The basic parameters of embryotoxicity can be estimated from the direct exposure of the selected MGSs both to the test substance and to its metabolites occurring in man. Based upon these principles a rapid and inexpensive screening test (CHEST) has been introduced using the embryonic chick. The test is capable of demonstrating the embryotoxicity effect level, the gross dose-effect relationships as well as estimating the general type of embryotoxic action. The predictive value of this procedure is comparable to that of the current routine techniques. A multilevel combined test for embryotoxicity is proposed in which CHEST is engaged as a priority selection system.

Fine structure of the ultimobranchial body of the pheasant (Phasianus colchicus L.).

The pheasant's ultimobranchial body is characterized by the presence, in the connective tissue stroma, of epithelial cells between which two types of granulated cells comprising the main part of the glandular portion of the body are formed. Type I is characterized chiefly by the presence of nonrounded electron-dense secretory granules measuring 65-240 nm in the cytoplasm and by a very well-developed Golgi apparatus. The cytoplasm of type II cells also contains dark secretory granules, but somewhat smaller (50-150 nm). This type is very frequently in close contact with specific and often branching tubular structures from whose cells microvilli project into the lumen. The dark cytoplasm of the cells lining these structures contains a relatively large number of mitochondria and dense bodies, but no secretory granules.

Formation of the heart loop and proliferation structure of its wall as a base for ventricular septation.

Controversial criteria for definition and classification of univentricular hearts are discussed from the point of view of proliferation pattern in the wall of heart tube and heart loop stage. The persistence of the primitive diffuse proliferation structure is the condition for the development of univentricular heart in which the morphogenetic mechanism forming the ventricular septum does not operate. Pseudouniventricular heart, i.e. the heart with the large main chamber accompanied by a small accessory cavity, is the result of total or partial right or left hypoplasia in which the extent of operation of the above mentioned mechanism is determined by the degree of ventricular hypoplasy. The morphogenesis of the heart wall structure and relief including the atrioventricular and arterial valves is a secondary feature, mostly dependent on the changed hemodynamic conditions.