Anton Švajger

Separation of germ layers in presomite rat embryos

Les feuillets du cylindre-Æuf du rat ont été disjoints par une solution composée de deux enzymes: 0,5% de trypsine et 2,5% de pancréatine. La séparation a été achevée par une aiguille de tungstène. Les feuillets ainsi détachés retiennent leur pouvoir de croissance et de différenciation comme homogreffes, sous la capsule rénale.

The effect of intermittent cold treatment on the adipose tissue of the cat. Apparent transformation from white to brown adipose tissue.

Young cats (Felis domestica), aged 10-13 weeks, were intermittently exposed to a temperature of -30 degrees C for two periods of 1 hr per day. Animals were sacrificed on the 7th day and adipose tissue from the perirenal, pericardial, axillary, interscapular, and subcutaneous-inguinal depots was examined by electron microscopy and analysed stereologically. All examined depots were morphologically changed after cold treatment. Adipose tissue of perirenal, pericardial, and axillary depots showed a greater decrease in lipid content than the interscapular and subcutaneous-inguinal depots, but other changes were similar. Compared to the control group, which consisted of typical white adipose tissue, the diameter of adipose cells examined after cold treatment was diminished, in extreme cases to 18 micron (from 75 micron in the control group). The number of capillaries per cell was doubled (as evaluated on semithin sections). The most dramatic changes were observed in the mitochondria. Their volume increased to 0.48 micron 3 (from 0.13 micron 3 in the control), and the surface density of mitochondrial cristae per mitochondrial volume increased to 50 micron 2/micron 3 (from 32 in the control). Pleomorphism in mitochondrial size and inner structure and the presence of intramitochondrial electron-dense bodies and crystalline structures led us to conclude that the cold stress induced an increase in the absolute number of mitochondria in the adipose cells. The adipose tissue after cold treatment thus morphologically resembled the brown adipose tissue of cold-acclimated rodents. This implies that the adipose tissue of young cats can change its morphology and function, depending on the requirements of the organism.

Differentiation of endodermal tissues in homografts of primitive ectoderm from two-layered rat embryonic shields

Die innere und die äussere Zellschicht 8 Tage alter Rattenkeimscheiben wurden enzymatisch voneinander getrennt und unter die Nierenkapsel erwachsener Ratten verpflanzt. Die isolierte innere Zellschicht (primitives Ektoderm) differenzierte sich nicht nur in ektodermale und mesodermale, sondern auch in typisch endodermale Gewebe (Darmepithel). Es wird daraus gefolgert, dass in diesem Entwicklungsstadium die innere bzw. äussere Zellschicht noch nicht als das definitive Ekto- bzw. Endoderm angesehen werden können.

Origin of the notochord in the rat embryo tail

SummaryThe origin of the notochord in the rat tail was investigated on transverse serial semi-thin and ultra-thin sections of 12- and 13-day embryo tails. It was found that the notochord develops from a mass of condensed mesenchymal cells which is located ventrally to the secondary neural tube, and which subsequently splits into a) a thin cord which becomes notochord and b) a thick portion which gives rise to the tail gut. By analogy with the secondary neurulation and the secondary gut formation, one might therefore speak of a secondary notochord formation in the tail. It occurs in close relationship with the formation of the tail gut.

Histogenetic capacity of rat and mouse embryonic shields cultivatedin vitro

SummaryThe organ culture technique was used for the study of early cytodifferentiation in explanted rat and mouse embryonic shields. After 15 daysin vitro the main tissues were differentiated in explants. The full differentiation depended on the presence of homologous serum in the culture medium. 95% oxygen in the atmosphere was either deleterious or without measurable effect if introduced from the beginning or toward the end of the cultivation period, respectively. Some chemically defined media supported the development for only a limited time span during the initial period of cultivation.

Morphological and immunohistochemical characteristics of axial structures in the transitory human tail.

Ultrastructural relationships between the notochord and neighboring spinal cord were examined during the regression of the human tail. Also, the presence of certain extracellular matrix components in the notochord was immuno-histochemically analysed in the 4th to 12th week old embryos. At the early stages, a close apposition of the notochord to the spinal cord exists in the entire tail region. The external surface of both structures is covered with a continuous basal lamina. The narrow tissue interspace contains interdigitating cell processes and both amorphous and fibrillar extracellular matrix material. With advancing embryonic age, separation of the two structures occurs in craniocaudal direction and the widening interspace becomes occupied by mesenchymal cells. During tail regression and spinal cord retraction, the appearance of large intercellular spaces and cell degeneration takes place in both tissues. With age, the extracellular matrix of the notochord, predominantly the perinotochordal sheath, increases in amount and antigenic complexity. While the intensity of laminin, collagen type IV and type III expression rises continuously during the period examined, the expression of fibronectin begins first at later stages, after the separation of the notochord from the spinal cord. The possible developmental significance of the described phenomena in the regression of the posterior end of the human tail remains to be elucidated.

Ultrastructure of elastic cartilage in the rat external ear.

SummaryThe structure of elastic cartilage in the external ear of the rat was investigated by transmission and scanning electron microscopy.The narrow subperichondrial, boundary zone contains predominantly ovoid cells rich in cell organelles: mitochondria, Golgi complex, granular endoplasmic reticulum and small (40–100 nm) vesicles. Scarce glycogen granules and bundles of 6–7 nm cytoplasmic filaments are also present. Deeper in the boundary zone, one or more cytoplasmic lipid droplets appear and cytofilaments become more abundant.Fully differentiated chondrocytes in the central zone of the cartilage plate resemble white adipose cells. They are globular and contain a single, large cytoplasmic lipid droplet. The cytoplasm is reduced to a thin peripheral rim; it contains a flattened nucleus, few cytoplasmic organelles and abundant, densely packed, cytoplasmic filaments.The intercellular matrix is very sparse. The pericellular ring consists of collagen fibrils about 20 nm in diameter and a proteoglycan cartilage matrix in the form of a “stellate reticulum”. The complex of these two structures appears in the scanning electron micrographs as a network of randomly oriented, ca 100 nm thick fibrils. Spaces between pericellular rings of matrix also contain thick elastic fibers or plates, apparently devoid of microfibrils. In scanning electron micrographs elastic fibers could be detected only in a few areas, in which they were not obscured by other constituents of the matrix. Immature forms of elastic fibers, oxytalan (pre-elastic) and elaunin fibers, were found in the perichondrial and boundary zones.

Morphological evidence for secondary formation of the tail gut in the rat embryo

The secondary body formation is a developmental mechanism occurring in the caudal part of the embryo in which embryonic structures arise from a mass of mesenchymal cells without previous formation of germ layers. The formation of the tail gut by this mechanism was investigated on transverse serial semithin and ultrathin sections of 12-, 13-, 14- and 15-day rat embryo tails. The tail gut, together with the tail portion of the notochord, originates from an axial mass of condensed mesenchymal cells named tail cord. Formation of the tail gut involves the appearance of large intercellular junctions among tail cord cells, and rearrangement of these cells around a newly formed lumen. Mesenchymal characteristics of these cells are gradually lost, and they simultaneously acquire the morphology of epithelial cells. Some cells of the tail cord, located ventral to the tail gut, do not participate in the tail gut formation and form a separate mass of cells without any definitive morphogenetic fate. This surplus group of cells is first evident in 12-day embryos, and it increases in mass during the following 3 days. In 15-day embryos, after the tail gut has completely disappeared, the surplus cells represent all that remains of the tail cord. The mesenchymal-epithelial transformation of the tail cord cells into the cells of the tail gut, and the appearance of the surplus cells, could be considered as the main morphological arguments for the secondary formation of the tail gut.

Light- and electron-microscopic observations on the presence of pre-elastic (oxytalan) fibres around the mature cartilage in the external ear of the rat

Im Perichondrium des Ohrknorpels erwachsener Ratten wurden licht- und elektronenmikroskopisch die sogenannten Oxytalanfasern beschrieben (Elastase-resistent), die mit saurem Orcein und Aldehydfuchsin nach der Oxydation färbbar sind (Bündel von 50–150 Å dicken Mikrofibrillen). Dieser Befund spricht für die Annahme, dass die Oxytalanfasern in elastischen Geweben als normale Vorstufen reifer elastischer Fasern zu betrachten sind.

Technique of separation of germ layers in rat embryonic shields

SummaryA microsurgical technique for the separation of germ layers in two- and three-layered rat embryonic shields is described.