Expression of induced nitric oxide synthase in amoeboid microglia in postnatal rats following an exposure to hypoxia

The present study showed the expression of induced nitric oxide synthase (i NOS) immunoreactivity in amoeboid microglia following an exposure to transi ent hypoxia in postnatal rats. iNOS immunoreactivity was expressed mainly i n the amoeboid microglia in corpus callosum and subependymal regions of the ventricles within 3 h after hypoxia. The expression declined after 5 h, an d became undetectable after 15 h and in longer surviving rats. The immunore activity of these cells with OX-42, which is a marker for microglia cells a nd detects complement type three receptors (CR3), was comparable in the rat s exposed to hypoxia and the control rats. Immunoglobulin G (IgG) immunorea ctivity was observed in the amoeboid microglia up to 3 h after hypoxia but it was undetectable in longer surviving rats and in the control rats. The i NOS expression in the amoeboid, mircoglial cells may be related to the host defense and maintenance of structural integrity of the highly vulnerable p eriventricular white matter after hypoxia. The immunostaining of amoeboid m icroglial cells with IgG following hypoxia indicates leakage of plasma immu noglobulin from the blood vessels and its removal by the amoeboid microglia l cells. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.