Pericytes and Macrophages in the Cat Cerebral Capillaries: Some Fine Structural Implications
The cerebral capillaries were examined electron microscopically, in cats receiving horseradish peroxidase (HRP) either intraventricularly or intracerebrally to enhance the morphological and functional characteristics between pericytes and macrophages. Pericytes and macrophages were collectively referred to as perithelial cells, and these two cell types were distinguished by their morphological features. Pericytes were located only around capillaries or post-capillary venules and were completely enveloped and separated from the surrounding cerebral parenchyma by thick basal laminae. In the pericyte cytoplasm, microfilaments and plasmalemmal caveolae were found in the adluminal and abluminal sides, respectively. Macrophages were located around microvessels throughout from arterioles to venules. Macrophage lacked both basal laminae and plasmalemmal caveolae. The differences between pericytes and macrophages were clearly illustrated by their reaction to HRP. HRP was actively ingested into the cytoplasm of macrophages, whereas pericytes did not ingest HRP even after long exposure to the tracers. The pericytes of cerebral capillaries are distinct from other perithelial cells such as macrophages of scavenger cells.
