The Effect of Brain Temperature on Acute Inflammation after Traumatic Brain Injury in Rats

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Abstract
The effect of varying brain temperature on neutrophil accumulation in brain and the expression of E-selectin and intercellular adhesion molecule-1 (ICAM-1) on cerebrovascular endothelium after controlled cortical impact (CCI) was studied in rats. Sprague Dawley rats were anesthetized and subjected to CCI to the left parietal cortex. Ten minutes after CCI, brain temperature was modulated and maintained at 32 degrees C, 37 degrees C, or 39 degrees C (n = 8 per group) for 4 h. Rats were then decapitated and immunohistochemistry on brain sections was performed using monoclonal antibodies (MoAb) that recognize neutrophils (RP-3), ICAM-1 (TM-8, Athena Neurosciences), or MoAb that react with E-selectin (La-Roche). Each of these markers was quantified in 100 x fields. Neutrophil accumulation was also quantified with myeloperoxidase (MPO) assay. Absolute neutrophil count (ANC) was measured in blood samples before and 1 h and 4 h after CCI. Neutrophil accumulation in injured brain was decreased in rats maintained at 32 degrees C vs 39 degrees C (4-fold difference as assessed by immunohistochemistry, p < 0.05; 8-fold difference as assessed by MPO assay, p < 0.05). Peripheral blood ANC was not affected by temperature. E-selectin was induced on cerebrovascular endothelium after CCI (p < 0.05), but was only decreased modestly at 32 degrees C versus 39 degrees C (p = 0.11). ICAM-1 was not upregulated on cerebrovascular endothelium at this early time following CCI. Neutrophil accumulation is directly dependent on brain temperature during the initial 4 h after CCI. This appears to be mediated by mechanisms other than effects of temperature on E-selectin or ICAM-1 expression or systemic ANC.