ELECTRON MICROSCOPIC DEMONSTRATION OF THE PERINEURAL EPITHELIUM IN RAT PERIPHERAL NERVE

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Abstract
The perineural epithelium, which was demonstrated by light microscopy as a multiple-layered sheet of flat epithelial cells surrounding each peripheral nerve fasciculus, has been shown by electron microscopy as having the same character. Up to seven layers were demonstrated in rat sciatic nerve fasciculus and four layers in the fasciculi of the finer divisions of the same nerve, indicating that the number of layers goes on decreasing as the nerve goes on dividing. A basement membrane was found on both sides of the epithelial cells, and collagen bundles were found in between the epithelial cell layers. Evidence from other workers and from electron microscopic studies confirms that the perineural epithelium is an extension of the pia-arachnoid mater from the central nervous system over peripheral nerves up to their termination in motor and sensory endings, for example the Pacinian corpuscle, muscle spindle, motor end plate etc., thus separating the peripheral nervous tissue from surrounding body fluids. Indications are that blood vessels also become invested with a layer of perineural epithelium when they enter the nerve fasciculus, thus simulating the blood vessels of the central nervous system. It is suggested that the capsule which surrounds specialized end-organs such as the cold end bulbs of Krause, Meissner''s corpuscle, Herbst corpuscle and the heat receptors of Ruffini, may also be composed of extensions of this perineural epithelial cell membrane.