Ultrastructure of the perineurial cell of the sciatic nerve in rats--a transmission and scanning electron microscopic study.

The perineurial cells of the sciatic nerve of mature albino rats were investigated by using light microscope (LM), transmission electron microscope (TEM) and scanning electron microscope (SEM). The perineurium of the sciatic nerve was composed of several lamellae of thin perineurial cells which were held together by the zonula occludens and also by the zonula adherens. The TEM view of the perineurium revealed that the plasmalemma of the perineurial cells presented numerous caveolae similar to those described in the endothelial cells of blood capillaries. By SEM, the perineurial cells were very thin, flattened out with various shapes from rectangular to hexagonal, and arranged closely to each other in the fashion of a stone pavement around the nerve fascicles. It was possible to isolate the perineurium from the nerve and to demonstrate the cellular border of the perineurial cells by silver impregnation method. The SEM observation of the perineurial cells ascertained the figure of the cells which were seen in the silver-impregnated specimen under LM. The present authors have interest in the fact that shape and arrangement of the perineurial cells of spinal nerves resemble closely those of the myoid cells in the limiting lamina of the seminiferous tubules of the mammalian testes. The meaning and significance of the similarity between these two types of cells was discussed.