Tecto-thalamo-telencephalic visual system of the brain in 13-day-old chick embryos

Light and electron microscopic studies have been made of the nervous tissue in three parts of the tecto-thalamo-telencephalic visual system--i.e. tectum opticum, nucleus rotundus of thalamus and ectostriatum of telencephalon--of 13-day chick embryos. Neuroblasts and neurones at various stages of differentiation were described together with various types of synaptic and nonsynaptic intercellular contacts in the neuropil of these brain structures. Heterochronous maturation of these parts of the visual system in embryogenesis was noted which reflects the level of their phylogenetic maturity. Being phylogenetically more ancient structures, tectum opticum and nucleus rotundus reveal differentiation earlier than ectostriatum which is phylogenetically younger.     

Estradiol secretion by the ovary of 19-day-old hypophysectomized and sham-operated chick embryos

The amounts of estradiol released into culture media by ovaries from 19-day-old hypophysectomized (decapitated) and sham-operated chick embryos were determined by RIA. Per single ovary, ovaries from decapitated embryos secreted slightly less estradiol than ovaries from sham-operated ones during a 4-h culture period (837 +/- 413 vs 935 +/- 378 pg), but this difference was not significant. On an ovarian weight basis, ovaries from decapitated embryos secreted slightly more estradiol than ovaries from sham-operated ones (1.15 vs 0.91 ng), but this difference was not significant either. It is concluded from these results that the hypophysis does not control estradiol secretion by the ovary in the 19-day-old chick embryo.     

Biochemical characteristics of adhesion factors isolated from the retina of 8-day-old chick embryos

While isoelectrofocusing the extracts obtained after dissociation of the retina of eight day old chick embryos, two active protein fractions were found: AF I with pI 3 and AF II with pI below 3. The content of these fractions in the extracts depended on the method of dissociation: treatment with EDTA increased the content of AF II, whereas trypsin treatment increased the yield of AF I. After electrophoresis in the denaturating conditions both fractions were divided in two components. The effect of AF I on aggregation of retinal cells, unlike that of AF II, does not depend on the presence of bivalent cations in the medium and is realized within 1 h of interaction with the cells at 4 degrees. It is suggested that the retinal extracts of eight day old chick embryos contain substances providing two types of adhesiveness: Ca2+-independent (AF I) and Ca2+-dependent (AF II).     

Fate mapping study of the endoderm of the 1.5-day-old chick embryo

Various portions of the endoderm between the levels of the first and the 10th somite of 1.5-day-old chick embryos were marked by local application of the vital dye Dil, and the fate of marked cells was analyzed after cultivation of the embryos for 2 days in vitro.The presumptive area of digestive tract ranging from the posterior pharynx to the jejunum was found to extend bilaterally from the midline of the 1.5-day embryo with a width two or three times as great as the distance between the midline and the lateral edge of the somite. Either side of this area contributed to the same side of the endodermal tube of digestive tract. The anterior and posterior portions generally contributed to the anterior and posterior regions of the digestive tract, respectively, and the cells originating from the portion farther from the midline took the more ventral and posterior position in the digestive tract endoderm. Most of the presumptive areas of the digestive organs in the endoderm of 1.5-day embryo were located in a more anterior position than those in the splanchnic mesoderm.     

The development of connections in the tecto-thalamo-telencephalic visual system of the brain in 13-day-old chick embryos

Light and electron microscopic studies have been made on degenerative changes in the nervous tissue induced by experimental destruction of the median brain bulb at the 5th day of incubation, in parts of the tecto-thalamo-telencephalic visual system in 13-day chick embryos (in the visual tectum, round nucleus of the thalamus and ectostriatum of the telencephalon). It was shown that to this period tecto-thalamic connections are already formed in the visual system, whereas thalamo-telencephalic connections are, presumably, indirect ones.     

Fate mapping study of the splanchnopleural mesoderm of the 1.5-day-old chick embryo

Various portions of the splanchnopleural mesoderm lateral to the somites of 1.5-day chick embryos were marked in ovo by local injection of Dil, and the distribution of the labelled cells in the digestive-tract mesoderm formed after 3 days' reincubation was analysed. The presumptive area of the digestive organs was confined to bands of splanchnic mesoderm lying lateral to the somites, on both sides, with a width two or three times that between the midline of the embryo and the lateral edge of the somite. Each band generally contributed cells to its own side of the digestive-tract mesoderm, except for the region around the bile duct. The anterior and posterior portion of the pre-gut area contributed cells to the anterior and posterior region of the digestive tract, respectively, but label originating from the portion furthest from the somite took the more ventral and posterior position. Thus, the presumptive areas of the respective digestive organs were located anteroposteriorly in the same order as in the digestive tract with their boundaries lying oblique to the embryonic axis.     

Chronotropism and blood flow patterns following teratogenic doses of catecholamines in 5-day-old chick embryos.

In vivo heart rates of 5-day-old chick embryos were recorded from electrodes placed in close proximity to the heart. L-epinephrine (4X10(-10) mole), 1-norepinephrine (1X10(-9)mole) and 1-isoproterenol (1.6X10(-10)mole) in 5 microliter of isotonic saline transiently accerlerated the mean heart rate by almost 9 percent. L-phenylephrine (2X10(-9)mole/5microliter) and the experimental procedure produced no appreciable effect. The positive chronotropic effect of the catecholamines was found to be highly significant (P less than 0.0005) as computed by Student's t test. However, no direct relationship could be established between the chronotropic response and the aortic arch anomalies produced. A prolonged reduction of blood flow in the primitive heart tube and the sixth aortic arch after administration of epinephrine and isoproterenol is apparently related to the induction of hypoplastic right pulmonary artery with absent or hypoplastic right ductus arteriosus.     

Transepithelial potential in mesonephric nephrons of 7-day-old chick embryos in relation to the histochemically detected sodium pump

In order to obtain basic information on the transport properties of differentiating embryonic nephrons, we examined the 7-day-old chick mesonephros by measuring the transtubular epithelial potential difference (TPD) and by histochemical detection of Na,K-ATPase activity. TPD as an indicator of the electrogenic transport was measured in individual segments of superficial nephrons in vivo. Their electric polarity was always lumen-negative. TPD was reduced by addition of 10 mM KCN applied to the mesonephric nephrons from the outside. In the proximal tubules, TPD was significantly lower (mean+/-SD: -1.0+/-0.5 mV) than in the distal and collecting tubules (-2.2+/-1.0 mV, p< or =0.05). Activity of the sodium pump was evaluated histochemically by detection of ouabain-sensitive potassium-dependent p-nitrophenyl phosphatase in cryostat sections of the mesonephros. The enzyme activity was demonstrated only in distal tubules and in the collecting ducts, but not in the proximal tubules. These findings have revealed significant differences between embryonic nephron segments: the distal tubule, in contrast to the proximal one, is supplied by the sodium pump and is able to generate higher TPD. Therefore, we consider that it is only the distal nephron, which possesses the ability of active transport.     

A cytogenetical study of 7-day-old bovine embryos of poor morphological quality

Seven-day-old embryos were collected from Canadian Holstein and Ayrshire heifers after superovulation with pregnant mare's serum gonadotropin (PMSG) or follicle-stimulating hormone (FSH). A total of 103 morphologically abnormal (type C) and 23 morphologically normal (type A) embryos were cytogenetically analyzed after 4, 20-24, or 44-48 h of culture in enriched phosphate-buffered saline or Eagles minimum essential medium. Twenty-one of 23 (91.3%) type A and 75 of 103 (72.8%) type C embryos had cells in metaphase. Among the 21 type C embryos produced by PMSG stimulation, 17 (80.9%) could be analyzed: 6 were mixoploid (two 2n/3n, three 2n/4n, one 2n/6n), 2 were aneuploid (61 XXY), and 9 were diploid. Among the 82 type C embryos produced by FSH stimulation, 58 (70.7%) could be analyzed: 6 were mixoploid (one n/2n, one 2n/3n, three 2n/4n, one 2n/4n/8n), 2 were polyploid (4n), and 50 were diploid. No abnormalities were observed in the type A embryos.     

Cell lineage restrictions in the chick embryo hindbrain.

During development of the chick embryo, early neuronal differentiation and axonogenesis in the hindbrain follow a segmented pattern in register with the segmented morphology of this region. Cell marking experiments have shown that the segments, or rhombomeres, are lineage-restriction units each constructing a defined piece of the hindbrain. This raises the interesting possibility that, as in the developing fly, metamerism is used to generate level-specific anatomical structures with great and reliable precision. In the hindbrain, as for many invertebrates, lineage ancestry may be important in the determination of cell fate. The segmentation seen in this body region could therefore reflect a similar condition once present in the ancestor common to vertebrates and invertebrates.     

Ultrastructural changes in the neural tube of 10-day-old mouse embryos exposed to colchicine and hydroxyurea

The ultrastructural changes in the neural tube of 10-day-old mouse embryos were investigated between 1.5 hr and 4 hr after application of either 1 mg/kg colchicine (Col) or 500 mg/kg hydroxyurea (HU) or simultaneous application of both substances. During the investigated period, the shape of the nuclei of the neuroepithelial cells had changed from elongated to round after Col application. The chromatin in the nuclei was condensed and arranged in clusters. A breakdown of polysomes into ribosomes and an enlargement of the rough ER was observed in the cytoplasm. At the luminal surface, bleb-like cytoplasmic processes of the neuroepithelial cells containing monoribosomes protruded into the lumen. No cell necroses were visible in the neural tube after Col application. A condensation of chromatin in the nuclei of some neuroepithelial cells was visible 1.5 hr after HU application. Shortly thereafter, cell necroses appeared in the neural tube and 4 hr after HU application the entire spinal cord was strongly damaged. After simultaneous application of Col and HU, the ultrastructural changes in the neuroepithelial cells of the neural tube did not differ from the results obtained after Col application alone. In contrast to the results obtained after HU application alone, no necroses occurred after simultaneous application of Col and HU.     

Convergent inductive signals specify midbrain, hindbrain, and spinal cord identity in gastrula stage chick embryos.

In the chick embryo, neural cells acquire midbrain, hindbrain, and spinal cord character over a approximately 6 hr period during gastrulation. The convergent actions of four signals appear to specify caudal neural character. Fibroblast growth factors (FGFs) and a paraxial mesoderm-caudalizing (PMC) activity are involved, but neither signal is sufficient to induce any single region. FGFs act indirectly by inducing mesoderm that expresses PMC and retinoid activity and also directly on prospective neural cells, in combination with PMC activity and a rostralizing signal, to induce midbrain character. Hindbrain character emerges from cells that possess the potential to acquire midbrain character upon exposure to higher levels of PMC activity. Induction of spinal cord character appears to involve PMC and retinoid activities.     

Fate mapping study of the endoderm in the posterior part of the 1.5-day-old chick embryo

Various endodermal sites posterior to the caudal-most somite were marked in ovo with the vital dye Dil, and the fate of marked endoderm was analyzed after 2 or 3 days' reincubation. The endoderm in this area became gut epithelium posterior to the caudal jejunum and yolk sac. The area occupied by the cells that were to contribute to the dorsal part of the digestive tube lay centrally around the area overlaid by axial and paraxial mesoderm, with the preventral digestive area lying outside with considerable overlapping, which was surrounded by the preyolk sac area. During the formation of the posterior digestive tube, the endoderm was elongated anteroposteriorly to a considerable degree. Cells that contributed to the cloaca and those that produced descendants in the large intestine occupied similar areas posterior to the center of the sinus rhomboidalis, which were included in the pre-ileal area extending more anteriorly. Prejejunal cells generally localized in a more anterior position than pre-ileal cells. Pre-allantoic cells were located in a rather small area around the posterior primitive streak.