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.

Relations between development of the capillary wall and myoarchitecture of the rat heart.

The type of the blood supply to the myocardium appears to be closely related to its structural arrangement. The heart of adult poikilotherm animals is either entirely spongious, supplied from the ventricular cavity or its spongious musculature is covered by an outer compact layer with vascular supply. The size of the compact layer increases with increasing heart weight. The changes in the heart size during the ontogenetic development of honoiotherms are accompanied by the gradual transformation of the vascularless spongious musculature into a compact myocardium supplied thrugh coronary vessels. Up to the development of coronary arteries (in the rat up to the 17th day of embryonic life - ed) the myocardium is entirely spongious and supplied from mentricular cavity. Two types of primitive vascular bed are characteristic for this period: a) intertrabecular spaces, which penetrate deep into the ventricular wall as direct continuation of the endocardium, and b) intramyocardial clefts without endothelial lining. During further development of the terminal mascular bed, the outgrowth of endothelial cells into the myocardial clefts is important. The first capillaries with closed endothelial wall can be observed on the 18th ed. At this time various developmental stages o the terminal blood bed can be observed simultaneously. Within the following period (20-21 ed) the thick capillary walls become narrow and pericytes occur. The process of differentiation spreads in both ventricles and in septum from the base to the cardiac apex and is practically finished by the 14th day of postnatal life. The longitudinal orientations of myofibres starts between the 20th and 22nd ed. The final arrangement of muscle cells and capillaries into three layers (outer and inner longitudinal, central circular) is terminated during the second postnatal week.

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.

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.

Quantitative development of choroid plexuses in chick embryo cerebral ventricles.

Quantitative development of choroid plexuses in cerebral ventricles of chick embryos was investigated by means of the planary projection of the choroid plexuses from the time the plexuses reached a consistent flattened structure. Choroid plexuses in the lateral cerbral ventricles were studied from day 6, the plexus in the third cerebral ventricle from day 8, and the plexus in the fourth cerebral ventricle from day 11 of incubation. Regardless of the microscopic origin of these choroid plexuses, their development reached a growth maximum on day 15 of incubation, after which there was a slight regression. The regression was gradual in the plexus of the third cerebral ventricle but a transient enlargement of plexuses in the laternal and in the fourth cerebral ventricle was observed between days 18 and 19. The enlargement of choroid plexuses in the lateral cerebral ventricles was caused by a flattening of the villi, whereas that of the plexus in the fourth cerebral ventricle was caused by thinning and yawning of the villi. The area of choroid plexuses in the lateral cerebral ventricles was six or seven times larger than the sum of the areas of the remaining choroid plexuses.

Effect of hydrocortisone on the growth of choroid plexus and composition of cerebrospinal fluid in the developing chick embryo.

The effect of hydrocortisone on the telencephalic choroid plexus and on the osmolarity and ionic compositon of CSF was studied 48 hours after its administration onto the chorio-allantoic membrane of chick embryos on days 11 and 13 (20 mug per egg) or on day 17 (40 mug per egg). Hydrocortisone significantly reduced the choroid plexus area on days 13 and 15 but was ineffective on day 19. The topical analysis of these choroid plexuses, influenced by the steroid, pointed to a decrease of the growth activity in those parts whose proliferation was intensive. The transient population of villi in the apical part of these plexuses was the most sensitive. Those parts, being morphogenetically inactive or whose morphogenetic changes were not caused by the cellular proliferstion, were not affected significantly. The osmolarity of CSF increased significantly during the investigated period simultaneously with an increase in the sodium and chloride concentration while the concentrations of potassium did not change significantly. Hydrocortisone evoked a precocious increase in the osmolarity of CSF on days 13 and 15. Contemporarily, the potassium concentration in CSF was elevated while the steroid failed to change the sodium and chloride concentrations.

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.

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.