Macrophages in peripheral nerves. An ultrastructural and enzyme histochemical study on rats.

The cellular content of the endoneurium in peripheral nerves of normal adult rats was studied. Endoneurial cells with high light-microscopical activity of acid phosphatase were usually located close to blood vessels or near the perineurium. Cells with the ultrastructural appearance of macrophages showed the same distribution and accounted for 2--4% of the endoneurial cell nuclei profiles. These cells rapidly endocytosed carbon particles after endoneurial administration of colloidal carbon in vitro.