Distribution of anionic sites on the basal lamina of Schwann cells

Immunohistochemical differentiation of Schwann and epithelial basal lamina in the rabbit cornea

Transmission electron microscopy has shown that at the point of entry of axons into corneal epithelium, Schwann cell lamina densa merges with lamina densa of epithelial origin. Staining properties and the thickness of lamina densa from these sources are similar. Immunostaining with monoclonal antibodies to laminin and type IV collagen revealed that while Schwann cell basal lamina fluoresced to both of these probes, epithelial basal lamina was visualized only with anti-laminin. Monoclonal antibodies to neurofilament protein (70 and 200 kDa) were used to visualize the neural tissue. Segments of the deep stromal and subepithelial innervation appeared similar to those seen following gold chloride impregnation. The results suggest that intercalation of lamina densa from these tissue sources and regulation of the production of basal lamina components by both the epithelial and the Schwann cells probably occur.

Basal laminae and Meissner corpuscle regeneration

Murine Meissner corpuscles (mouse digital corpuscles), located in pad skin at the toe tip, consist of lamellar cells with long cellular processes (lamellae) surrounding axon terminals in an onion-skin fashion. Lamellar cell bodies and processes were provided with a basal lamina. The present study was made to examine whether these lamellar cell basal laminae have any specific role in the differentiation of regenerating axons and Schwann cells into specialized axon terminals and lamellar cells, respectively. Pad skin at the toe tip was treated 3-5 X by freezing and thawing. By this treatment, cellular constituents of the corpuscles die and disintegrate into cell debris, leaving in situ basal laminae of the lamellar cells in stacked hollow loops, reminiscent of the original configuration of lamellae. Schwann cells and axons of the ordinary nerve fibers in the pad skin were similarly damaged, and basal laminae of the Schwann cells remained as basal lamina tubes. Three days after treatment, regenerating axons were seen extending through the basal lamina tubes of Schwann cells deep in the toe pad skin. However, no regenerating axons were found in the vicinity of the old corpuscles. Five days after treatment, regenerating axons, some of which were accompanied by migrating Schwann cells and others which were still naked, were noted at the subepidermal region, and began to enter the hollow basal lamina loops of the old corpuscles. Eight-15 days after treatment, regenerating axons which entered the basal lamina loops successively gave rise to branches, and at the same time, accompanying Schwann cells emanated cellular processes through well-preserved basal lamina loops. Fifteen-25 days after treatment, regenerating axons seemed to be morphologically specialized as axon terminals, and accompanying Schwann cells differentiated into definite lamellar cells which surrounded the axon terminals in the same manner as in the normal murine Meissner corpuscles. Although the incidence of good regeneration of the corpuscle was relatively low, these findings suggested that basal laminae of lamellar cells might have some specific properties which could be responsible for the differentiation as well as maintenance of lamellar cells and axon terminals in the Meissner corpuscles.

Localizations of ruthenium red positive material in rabbit peripheral nerves

The penetration and distribution of ruthenium red in the axon-myelin-Schwann cell complex of developing rabbit peripheral nerve fibers are investigated. Ruthenium red positive material is established in the axoplasm, axolemma, periaxonal space, major dense lines and intraperiod lines of the compact myelin, mesaxons, split peripheral myelin lamellae, Schmidt-Lanterman and longitudinal incisures, paranodal loops and axo-glial contacts, Schwann cell cytoplasm and basal lamina, nodal extracellular matrix, desmosome-like structures, endoneural collagen. Some features of the distribution of the contrast material in the developing myelin sheath are described. Regional differences of the axolemma and of the Schwann cell cytoplasm and plasmalemma are established. The prevalence of glycoproteins or glycolipids in the ruthenium red stained material in its different localizations is discussed on the basis of trypsin and hyaluronidase digestion performed.

The localization of lectin-binding sites on Schwann cell basal lamina

Basal laminae were separated from Schwann cells of mouse sciatic nerves by sonification, and the distributions of lectin-binding sites were demonstrated by electron microscopy using ferritin-conjugated lectins. Only three out of the 11 lectins examined were bound to the basal laminae of Schwann cells: they were Ricinus communis agglutinin-I (RCA-I), Canavalia ensiformis agglutinin (ConA) and Triticum vulgaris agglutinin (wheat germ agglutinin, WGA). It was notable that WGA was bound more densely to the cellular side than to the interstitial side, whereas in the case of RCA-I and ConA there were no differences in the binding density on the two sides of the basal lamina. These results indicate that there are sugar residues such as beta-D-galactose, alpha-D-mannose, alpha-D-glucose and beta(1-4) linked N-acetyl-D-glucosamine in the Schwann cell basal laminae. The first three sugar residues are almost equally densely distributed on the cellular and interstitial sides of the basal laminae, whereas beta(1-4) linked N-acetyl-D-glucosamine is more densely distributed on the cellular than on the interstitial side. This result suggests that the basal lamina has a polarity in chemical composition between the cellular and interstitial sides. These findings are discussed in the context of the preferential attachment of regenerating axons to the cellular side of the Schwann cell basal laminae.