Early changes of macrophage-like immunoreactivity in the rat inferior olive after intraperitoneal 3-acetylpyridine...

Early changes of macrophage-like immunoreactivity were observed in the inferior olive after intraperitoneal injection of 3-acetylpyridine (3AP) using seven monoclonal antibodies recognizing macrophage subpopulations (OX-42, OX-6, ED-1, RM-1, TRPM-1, TRPM-2, and TRPM-3). Both resting and activated forms of microglia were stained with OX-42 and TRPM-2. Some of activated microglia reacted to OX-6 and/or ED-1. Neither resting nor activated microglia reacted to any of RM-1, TRPM-1, and TRPM-3. Four h after 3AP injection, the processes of OX-42-positive microglia had increased in number and became thicker than resting microglia. Between 24 h and the 7th day after 3AP injection (day 7), OX-42-positive microglia gradually increased in number. At 24 h after 3AP injection, round cells appeared that stained with all seven antibodies. These disappeared by day 3. Double staining indicated that OX-42-positive activated microglia on day 7 were divided into subpopulations by their immunoreactivity to ED-1. We suggest that the round cells derived from blood monocytes and entered the brain only transiently while OX-42-positive activated microglia originated from parenchymal resting microglia and continued to increase in number after the disappearance of the round cells.