The fine structure of the perineural endothelium

Abstract

Fine strands of motor nerves were examined with the electron microscope using thin section as well as freeze-etching techniques. The specimens were taken from frog cutaneous pectoris nerve, rat sciatic nerve, mouse and shrew phrenic nerves and from human skin nerves. The perineural sheath (Henle, Ranvier, Key and Retzius) consists of one to several concentric laminae of endothelial cells; it encases nerve fascicles and eventually individual nerve fibers and terminals. The endothelial cells are extremely thin and fitted togeether smoothly by overlap and dove-tailing of their border zones. The cell contacts are formed by continuous zonulae occludentes, often reinforced by maculae adhaerentes, and in depth they comprise 3-15 strands with an average of 5-6 strands per junction. The membranes of endothelial cells are studded with attachment sites and stomata of plasmalemmal vesicles suggesting a high level of pinocytotic activity. This phenomenon is by no means restricted to the external laminae of the endothelial sheath. Each endothelial lamina is vested with basement membranes on both (epineural and endoneural) sides, and the spaces between laminae contain a few collagen fibers and fibroblasts. Occasionally, punctate tight junctions are seen between laminae. Cytological evidence supports the hypothesis that the perineural endothelium provides a relatively tight and highly selective barrier separating the peripheral nerves from surrounding tissue and its extracellular fluid spaces. This effect is achieved on the one hand by the sealing of pericellular spaces and on the other hand by a membrane controlled transcellular transport mechanism (pinocytosis), both of which are enhanced by their serial arrangement.

Organization of cell junctions in the peritoneal mesothelium

“…Forms transitional from one type to another are, however, occasionally encountered (1,20). In the case of the first two types, the cleavage plane usually leaves junctional strands and bars on P faces, and simple grooves on E faces.…”

Perineurial Glia

“…1) (Gamble and Eames 1964;Cravioto 1965;Shantha and Bourne 1968;Akert et al 1976;Nordlander et al 1981). Central to all sensory and motor nerves are axons.…”

“…Each mature peripheral nerve has multiple fascicles of these axon -Schwann cell complexes in endoneurium and they are individually ensheathed by the perineurium ( Fig. 1) Bourne 1962, 1963;Burkel 1967;Shantha and Bourne 1968;Akert et al 1976). This nerve component is made up of multiple perineurial cells that are connected via tight junctions, making this structure a component of the blood -nerve barrier, protecting the interior of the nerve from toxins, infection, and ionic flux (Shanthaveer-appa andBourne 1962, 1963;Burkel 1967;Shantha and Bourne 1968;Haller and Low 1971;Akert et al 1976).…”

“…1) Bourne 1962, 1963;Burkel 1967;Shantha and Bourne 1968;Akert et al 1976). This nerve component is made up of multiple perineurial cells that are connected via tight junctions, making this structure a component of the blood -nerve barrier, protecting the interior of the nerve from toxins, infection, and ionic flux (Shanthaveer-appa andBourne 1962, 1963;Burkel 1967;Shantha and Bourne 1968;Haller and Low 1971;Akert et al 1976). The final nerve element, the epineurium, which is composed of collagen and adipocytes, bundles all of the individual nerve fascicles together into a single nerve structure that is physically separated from surrounding tissue ( Fig.…”

Molecular mechanisms of perineural spread of cutaneous carcinoma: a potential role for receptor tyrosine kinases and other biomarkers

“…Electron microscopy of the perineural sheath reveals that it comprises concentric laminae of perineural cells joined by tight junctions (zonulae occludentes), vested with basement membrane on both sides. (18) Longitudinally disposed elastic and collagen fibres together with fibroblasts occupy the spaces between laminae. (19) It is this sheath that effectively forms the selective "blood-nerve barrier" that separates the peripheral nerve compartment from surrounding tissue.…”