Acute excitotoxic injury induces expression of monocyte chemoattractant protein-1 and its receptor, CCR2, in neonatal rat brain

Chemokines are a family of structurally related cytokines that activate and recruit leukocytes into areas of inflammation. The "CC" chemokine, monocyt e chemoattractant protein (MCP)-1 may regulate the microglia/monocyte respo nse to acute brain injury. Recent studies have documented increased express ion of MCP-1 in diverse acute and chronic experimental brain injury models; in contrast, there is little information regarding expression of the MCP-1 receptor, CCR2, in the brain. In the neonatal rat brain, acute excitotoxic injury elicits a rapid and intense microglial response. To determine if MC P-1 could be a regulator of this response, we evaluated the impact of excit otoxic injury on MCP-1 and CCR2 expression in the neonatal rat brain. We us ed a reproducible model of focal excitotoxic brain injury elicited by intra hippocampal injection of NMDA (10 nmol) in 7-day-old rats, to examine injur y-induced alterations in MCP-1 and CCR2 expression. RT-PCR assays demonstra ted rapid stimulation of both MCP-1 and CCR2 mRNA expression. MCP-1 protein content, measured by ELISA in tissue extracts, increased >30-fold in lesio ned tissue 8-12 h after lesioning. CCR2 protein was also detectable in tiss ue extracts. Double-immunofluorescent labeling enabled localization of CCR2 both to activated microglia/monocytes in the corpus callosum adjacent to t he lesioned hippocampus and subsequently in microglia/monocytes infiltratin g the pyramidal cell layer of the lesioned hippocampus. These results demon strate that in the neonatal brain, acute excitotoxic injury stimulates expr ession of both MCP-1 and its receptor, CCR2, and suggests that MCP-1 regula tes the microglial/monocyte response to acute brain injury. (C) 2000 Academ ic Press.