The staining patterns of 24 biotinylated lectins were analyzed in serial sections of the mandible of 13- to 21-day-old rat embryos by means of the avidin-biotin-peroxidase method. A ubiquitous distribution of binding sites was demonstrated after incubation with Con A (Canavalia ensiformis), DSL (Datura stramonium; except bone matrix), and WGA (Triticum vulgare). ECL (Erythrina cristagalli), GSL I (Griffonia simplicifolia), SJA (Saphora japonica), VVL (Vicia villosa), DBA (Dolichus biflorus), UEA I (Ulex europeus), and LTA (Lotus tetragonobolus) were constantly negative. In early stages of development, GSL II (Griffonia simplicifolia II) was a selective marker of prechondral blastema. In contrast, PNA (Arachis hypogaea) did not stain condensing mesenchyme. During chondrogenesis of Meckels's cartilage a general decrease of lectin binding was observed. Mature cartilage matrix was constantly negative. Chondrocytes were marked by the lectins PSA (Pisum sativum), WGA, PHA-E, and PHA-L (Phaseolus vulgaris E and L). A strong GSL II binding was restricted to the mesial-superior region of the perichondrium. In later stages, several lectins revealed significant differences between preskeletal ("central") areas and the remaining ("peripheral") mesenchyme. A clear binding reaction was noted in central regions by applying LEA (Lycopersicon esculentum) and STL (Solanum tuberosum), while the peripheral tissue was only faintly stained. Developing bone was specifically marked by succinylated WGA (sWGA). The lectins LCA (Lens culinaris) and RCA (Ricinus communis) bound to fibers and extracellular matrix of the connective tissue. Jacalin (Artocarpus integrifolia) and SBA (Glycine max) binding sites were found in macrophages. Affinity of VAA (Viscum album) increased parallel with maturation of endothelial cells. Specific lectin-binding patterns revealed no correlation with the distribution of glycosaminoglycans. The results demonstrate a general reduction of oligosaccharide structures during development of Meckel's cartilage. From our observations we conclude that intralaminar glucose and/or mannose sequences as well as terminal sialic acid molecules are ubiquitously distributed, while terminal alpha-fucose was constantly negative. Lectin-binding patterns of macrophages may reflect the presence of specifically linked terminal galactose. Our findings indicate that oligosaccharides terminating in N-acetylglucosamine are bone-specific. The significance of the restricted staining of the perichondrium by GSL II remains to be elucidated.
The distribution of complex carbohydrate structures during the embryonic development of the rat palate was analysed by examining lectin-binding patterns in serial paraffin and cryostat sections. With few exceptions, the binding patterns showed a general increase in lectin receptors in the more developed stages of palatogenesis. High mannose oligosaccharides were especially amplified during development. Terminal fucose molecules were not expressed. In contrast, terminal sialic acid molecules were ubiquitously distributed in epithelial and mesenchymal tissues. Non-sialylated terminal N-acetylglucosamine was specifically restricted to evolving bone matrix. Before palatal fusion, quantitative but not qualitative differences were detected between oral, nasal, and medial-edge epithelial surfaces. The only exception was LCA, which specifically marked epithelial cells at the tip of palatal shelves. A very selective affinity for Jacalin was demonstrated in the oral epithelium of the palate after day 16, suggesting the presence of sialylated terminal galactose-(beta-1,3)-N-acetylgalactosamine. PNA specifically marked the basal lamina of the oral side of palatal processes. The binding patterns of DBA, GSL IA, SBA, and VVA indicated that the epithelium of the tongue is characterized by terminal alpha- and beta-galactose residues, whereas palatine cells possess only molecules with beta-anomery. During palatogenesis, glycosaminoglycans patterns were significantly modified. Our data suggest that alteration of complex carbohydrate structures may play a central role in modulating cell-cell and cell-matrix interactions. The significance of these findings, however, remains to be elucidated.
Pleocytosis in cerebrospinal fluid and infiltration of the leptomeningeal tissue have been studied after injection of ferritin into the subarachnoid space (SAS) of cats. The most important source of granulocytes in the leptomeninges are the relatively large veins of the pia mater, which have very thin walls. Passing between the lining cells of the pia mater the granulocytes leave the connective tissue space of the pia mater and reach the SAS. Leukodiapedesis has also been observed in veins crossing the SAS. During this process, gaps between the lining cells of the perivascular leptomeningeal sheath may develop. There are two possible ways for the granulocytes to pass from the vascular pia mater to the avascular arachnoidea: either they migrate actively on the surface of the leptomeningeal trabeculae or they reach the arachnoidea passively by the circulation of the cerebrospinal fluid. Leukodiapedesis in the vessels of the dura mater occurs relatively seldom and would not be able to cause the occasionally massive infiltration of the arachnoidea.
In 2 cats nerves of the spinal pia mater were studied by means of electron microscopy. These nerves possessed no perineurium. However, it has been observed that flat cells of the surrounding connective tissue can form an incomplete covering for small nerve bundles. In addition the perivascular nervous plexus of subarachnoid arteries of the brain stem, which were examined in 1 animal, also showed no perineural sheath. These results are discussed with those reported in the literature dealing with the perineurium of other peripheral nerves. The observations concerning the distribution and the composition of leptomeningeal nerves are in accordance with those obtained by light microscopic investigations.
After intracisternal injection of heparinised autologous blood in cats, spinal nerve exits (SNE) of the subarachnoid space (SAS) were examined by scanning and transmission electron microscopy. Phagocytes, erythrocytes and erythrophages (= macrophages which had phagocytosed red blood cells) were found at SNE. Some lining cells of the SAS had retracted from the adjacent cells and had rounded up. Cells which formed an integral part of the subarachnoid lining cells also had phagocytosed erythrocytes. Debris of an exhausted erythrophage was phagocytosed by other macrophages. Finally the observation has been made that erythrophages are capable of leaving the SAS actively by migrating through the layer of lining cells, thus getting into the leptomeningeal connective tissue space.
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