Cell activation and inflammatory response following traumatic axonal injury in the rat

In a rat model of traumatic brain injury cell activation was characterized immunohistochemically from 2 h up to 2 weeks. Reactive astrocytosis became apparent perivascularly and in the grey matter within 4 h after trauma. Inc reased OX42 immunoreactivity indicated microglial activation in cortex and hippocampus as early as 4 h, whereas up-regulation of MHC class II (OX6) wa s evident in white matter tracts at 24 h. Although macrophage (EDI) numbers increased in the meninges and perivascularly, brain infiltration appeared marginal. Accumulation of lymphocytes and granulocytes was not observed. Ou r results show that traumatic axonal injury induces a rapid and sustained g lial activation in the absence of leukocyte infiltration. Thus, cell activa tion following diffuse trauma strongly differs from that found after focal brain damage, awaiting further functional characterization. NeuroReport 11: 2587-2590 (C) 2000 Lippincott Williams & Wilkins.