Abstract
We found that amoeboid-shaped microglia expressing NG2 proteoglycan accumulated in stab wounds in the brain. Some of the NG2-positive microglia expressing nestin and GFAP turned into cells with neuroectodermal phenotypes in vitro. To elucidate whether such amoeboid NG2-positive microglia are blood-borne or the activated form of resident microglia, we compared the nature of cells expressing microglia markers using three kinds of brain pathology models using Wistar rats; stab-wound, middle cerebral artery occlusion (MCAO), and facial nerve axotomy models. The former two models accompanies breakdown of blood brain barrier (BBB), while the axotomy model does not. A huge number of NG2-positive amoeboid shaped cells expressing Iba1, a marker of microglia/macrophages, accumulated in the stab wounds and the core lesions of MCAO. The majority of the amoeboid cells were proliferating as revealed by Ki67-immunostaining. In contrast, microglial cells in the axotomied facial nerve nucleus enlarged somata but still kept ramified shapes, and none of them were Ki67-negative. Most of resident microglial cells died within 2 days after the stab-lesioning or MCAO, while none of microglia died in the facial nerve nucleus. These observations suggest that multipotent NG2-positive microglia in the brain lesions are blood-borne and distinct from resident ramified microglial cells. [J Physiol Sci. 2006;56 Suppl:S121]
