The fine structure of the pia mater of the rat

Abstract

Abstract Tissue from the central nervous system of 11 adult Sprague‐Dawley rats fixed by vascular perfusion with buffered aldehydes was used in a study of the fine structure of the pia mater. Surface tissue from the cerebral and cerebellar cortices, ventral pons, olfactory bulb, tuber cinereum, spinal cord, superior colliculus, optic chiasm, and median longitudinal fissure was examined. Variations in pial composition occurred within each of these selected areas although a basic pattern prevailed throughout. The components of the pia mater are described under three categories: pial cells, extracellular elements, and macrophages. The pial cells are the more numerous cell type, possessing long, flattened cytoplasmic processes which contain few inclusions. These cells vary in thickness in any one area and there may be from one to six distinct cytoplasmic layers. Fenestrations between pial cell processes or total absence of pial cells are occasionally encountered. Unit collagen fibrils make up most of the extracellular material of the pia. These have a major period of about 550 Å and are about 400 Å wide. Macrophages are rounded up and contain various cytoplasmic inclusions. In normal animals evidence of active phagocytosis is rare.