A histochemical study of epithelial mucin in the chick chorioallantois

Histochemical methods demonstrate the accumulation of two types of mucous inclusion in the allantoic epithelial cells of the chick embryo. One type of inclusion contains a sialomucin that is PAS-reactive, unstained by Alcian blue and other anionophilic dyes and is susceptible to digestion by Vibrio cholerae neuraminidase. The second inclusion contains an apparent sulfomucin which is Alcianophilic at pH 1.0, unstained by anionophilic dyes after a methylation-demethylation sequence and resistant to testicular hyaluronidase. This sulfomucin exhibits PAS reactivity after desulfation procedures. Both types of mucus occur in individual cells and are normal components of the chorioallantois. Accumulation of the inclusions is enhanced by lowering the pH of the allantoic fluid or as a result of organ transplantation.     

A model of the human lumbar vertebral column: a preliminary study

Summary Finite element modelling of the human lumbar vertebral column employs data-processing procedures for study of the linear and nonlinear elasticity of materials such as are currently used in mechanics or in civil engineering. Thanks to developments in computer science, requiring a close collaboration between doctors and engineers, we put forward in this preliminary study a linear computerised model of the lumbar column comprising 4824 meshes and 6813 nodes. By reducing the simplificatory hypotheses and integrating new parameters, this model as developed is capable of important clinical applications in surgery and ergonomics.

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Modélisation de la colonne lombaire humaine. Etude préliminaire

Résumé La modélisation en éléments finis de la colonne lombaire humaine utilise les procédés informatisés d'étude de l'élasticité linéaire et non linéaire des matériaux telle qu'elle est couramment employée en mécanique ou en génie civil. Grâce au développement de l'informatique, nécessitant une collaboration étroite entre médecins et ingénieurs, nous proposons, dans cette étude préliminaire, un modèle informatisé linéaire de la colonne lombaire comportant 4824 mailles et 6813 noeuds. En réduisant les hypothèses simplificatrices et en intégrant de nouveaux paramètres, ce modèle évolué est susceptible d'importantes applications cliniques en chirurgie et en ergonomie.

     

Kinetics and differentiation of somite cells forming the vertebral column: studies on human and chick embryos

We have studied the kinetics of somite cells with an antibody against proliferating cell nuclear antigen (PCNA/cyclin) in human and chick embryos, and with the BrdU anti-BrdU method in chick embryos, to investigate whether the metameric pattern of the developing vertebral column can be explained by different proliferation rates. Furthermore we applied antibodies against differentiation markers of chondrogenic and myogenic cells of the somites in order to study the correlation between proliferation and differentiation. There are no principal differences in the proliferation pattern of the vertebral column between human and chick embryos. In all stages examined, the cell density is higher in the caudal sclerotome halves than in the cranial halves. Laterally, the caudal sclerotome halves, which give rise to the neural arches, are characterized by a higher proliferative activity than the cranial halves. Although there is a high variability, the labelling indices show significant differences between the two halves with both proliferation markers. With the onset of chondrogenic differentiation, only the perichondrial cells retain a high proliferation rate. During fetal development, the neural arches and their processes grow appositionally. Even at the earliest stages, there is practically no immunostaining for PCNA or BrdU in the desmin-positive myotome cells of human and chick embryos. Axially, a higher proliferation rate is found in the condensed mesenchyme of the anlagen of the intervertebral discs than in the anlagen of the vertebral bodies. During fetal development, cells at the borders between vertebral bodies and intervertebral discs proliferate, indicating appositional growth. Our results show that local differences in the proliferation rates of the paraxial mesoderm exist, and may be an important mechanism for the establishment of the metameric pattern of the vertebral column in human and chick embryos.     

A radiographic study of the growth in width of the human fetal vertebral column

Only a few studies have concerned themselves with the development of the fetal vertebral column, and this paper attempts to extend the literature. Standards are presented for the growth in width of the human vertebral column between 10 and 26 weeks of conceptual age. The growth patterns show that cervical and lumbar enlargements are not present at 8 weeks but develop slowly and become clearly present at 26 weeks. The growth equations also show that groups of vertebrae have their own growth patterns, indicating that the vertebral column could be separated into five groups: C1–C5, C6–C7, T1–T12, L1–S1, and S2–S5. Furthermore, comparisons with growth patterns available for growth in length from other studies reveal that some vertebrae appear to develop in one dimension independently of another.     

The development of the avian vertebral column

Segmentation of the paraxial mesoderm leads to somite formation. The underlying molecular mechanisms involve the oscillation of ”clock-genes” like c-hairy-1 and lunatic fringe indicative of an implication of the Notch signaling pathway. The cranio-caudal polarity of each segment is already established in the cranial part of the segmental plate and accompanied by the expression of genes like Delta1, Mesp1, Mesp2, Uncx-1, and EphA4 which are restricted to one half of the prospective somite. Dorsoventral compartmentalization of somites leads to the development of the dermomyotome and the sclerotome, the latter forming as a consequence of an epithelio-to-mesenchymal transition of the ventral part of the somite. The sclerotome cells express Pax-1 and Pax-9, which are induced by notochordal signals mediated by sonic hedgehog (Shh) and noggin. The craniocaudal somite compartmentalization that becomes visible in the sclerotomes is the prerequisite for the segmental pattern of the peripheral nervous system and the formation of the vertebrae and ribs, whose boundaries are shifted half a segment compared to the sclerotome boundaries. Sclerotome development is characterized by the formation of three subcompartments giving rise to different parts of the axial skeleton and ribs. The lateral sclerotome gives rise to the laminae and pedicles of the neural arches and to the ribs. Its development depends on signals from the notochord and the myotome. The ventral sclerotome giving rise to the vertebral bodies and intervertebral discs is made up of Pax-1 expressing cells that have invaded the perinotochordal space. The dorsal sclerotome is formed by cells that migrate from the dorso-medial angle of the sclerotome into the space between the roof plate of the neural tube and the dermis. These cells express the genes Msx1 and Msx2, which are induced by BMP-4 secreted from the roof plate, and they later form the dorsal part of the neural arch and the spinous process. The formation of the ventral and dorsal sclerotome requires directed migration of sclerotome cells. The regionalization of the paraxial mesoderm occurs by a combination of functionally Hox genes, the Hox code, and determines the segment identity. The development of the vertebral column is a consequence of a segment-specific balance between proliferation, apoptosis and differentiation of cells. Accepted: 25 May 2000     

Ultrastructural histochemical and autoradiographic studies on the developing chick notochord

Summary The author examines by means of ultrastructural, histochemical and autoradiographic techniques the development of the notochord of the chick embryo in the period between Hamburger-Hamilton's Stages 9 and 26. The interest in this research is that, during this period, the notochord is transformed from an apparently undifferentiated organ into an organ with secretory activity, and at the same time becomes an inductive organ in the development of the axial skeleton.The study shows that, starting from Stage 10, the notochord cells become hypertrophic and acquire the characteristics of secretory elements, with the production of chondroitin sulphate (A and/or C) and probably of collagen microfibrils. Such substances not only cluster densely around the notochord, thus contributing to the formation of the perichordal sheath, but they also diffuse outwards, becoming distributed among the sclerotomic cells; the latter, on the other hand, start to differentiate into cartilaginous cells only after the halo deriving from the notochord has enlarged and diffused among them.It is also pointed out that there is a close temporal connection between the high degree of secretory activity of the notochord and the start of its inductive activity on the sclerotomes.     

Innervation of the canine thoracolumbar vertebral column

The pattern of innervation of the caudal thoracic and cranial lumbar vertebral column of the dog is described. Frozen sections stained with Schofield's silver impregnation method show that the dorsal longitudinal ligament is profusely innervated, while the anulus fibrosus contains a few nerves limited to its outermost layers; no nerves are present in the nucleus pulposus. Following injection of horseradish peroxidase (HRP) into the anulus fibrosus of the thoracolumbar intervertebral disc and subsequent removal and staining of dorsal root ganglia, the reaction product is found in ganglia as far as two segments cranially as well as caudally, demonstrating that the disc is innervated by nerves arising from several spinal cord segments. A meningeal ramus, which innervates the discs of man, could not be found by gross dissection. Dissections show each vertebral articular facet innervated by the medial branches of two contiguous spinal nerves, a pattern further confirmed by injections of HRP into facet joints with subsequent staining of dorsal root ganglia. The dorsal rami of spinal nerves often divide into medial, intermediate, and lateral branches rather than the traditionally described division into only medial and lateral branches.     

A method of rapid extraction of the whole vertebral column during autopsy

The method is a follows: the cervical part of the vertebral column is mobilized from the inner cranial base with the preservation of the occipito-atlantic joint and with subsequent cranio-caudal extraction. This method does not disturb the epidural space and allows the extraction of the vertebral column without any assistance within 30 minutes.     

Electron histochemical and developmental study of glycogen metabolism in the retina of the chick fetus.

The activities of glycogen synthetase and phosphorylase were electron histochemically examined in the retina of the fetal chick. These enzyme activities appeared in the cytoplasmic matrices of the developing paraboloid in the photoreceptor inner segment almost simultaneously at the 17th day of incubation. After the appearance of these 2 enzyme activities, glycogen particles were found in the developing paraboloid. It is concluded that glycogen is synthesized through the enzymatic pathway in the fetal retina and that glycogen is not found before the enzymes related to glycogen metabolism appear in the cell except the appearance of native glycogen in the egg. Branching glycosyltransferase seemed to appear after phosphorylase was activated and these enzymes became higher in their activity with the differentiation in the paraboloid in the fetal and early postnatal periods.     

The effects of somite removal on vertebral formation in the chick

We have examined the effects on vertebral development of various combinations of somite removal in two day old chick embryos as shown by vertebral formation after a further seven days of incubation. Each combination produced one of a variety of results ranging from completely normal vertebral formation, through fusion of various vertebral elements, to the absence of complete vertebral halves and the formation of hemivertebrae. Assessment of our operating ability showed that we were removing at least 90% of the somitic material and therefore these results suggest that there is a regulating mechanism available to the embryo, at least with regards to vertebral development. When two consecutive somites were removed, vertebrae frequently developed that were lacking certain elements. This suggests that the somitic cells are already determined with regards to formation of specific vertebral elements. Experiments involving the removal of a bilateral pair of somites (a repetitive unit) also provided evidence of a counting mechanism which ensures that the correct number of total vertebrae are present.