Electron microscopic studies on NO-synthase activity in brain phagocytes of rat cerebral cortex after ischemic and...

In the present study we used a cytochemical method for electron microscopy for nitric oxide synthase (NOS) detection in rat cerebral cortex. The animals were subjected to total brain ischemia and mechanical trauma. Tissue was fixed in 3% paraformaldehyde and 0.5% glutaraldehyde which enabled excellent preservation of cellular ultrastructure and resulted in an increase in method reproducibility. The results show the distribution of the particles reflecting the sites of NOS activity in the capillaries and other, more distant locations. NOS activity was found in thrombocytes, endothelium and pericytes. Moreover, the morphologically differentiated perivascular phagocytes demonstrated NOS reaction product in their cytoplasm. These phagocytes containing polymorphic phagolysosomes, surrounded the fragments of damaged neurons. We propose that these cells are descendants of blood-borne monocytes and transformed pericytes. In the areas distant to the sites of injury we noticed cells showing ultrastructural features of activated microglia. These cells were in a close contact with neural perikarya and contained iNOS-specific reaction product in the cytoplasm. In conclusion, our studies revealed differentiated forms of brain phagocytes, the occurrence of which depended on the type of cerebral injury. These cells demonstrated NOS reaction product suggesting their role in cerebral NO production during ischemia and other forms of brain injury.