Assessment of Posttraumatic Polymorphonuclear Leukocyte Accumulation in Rat Brain Using Tissue Myeloperoxidase Assay and Vinblastine Treatment

Polymorphonuclear leukocytes (PMN) are implicated in the pathogenesis of traumatic brain injury. We tested the following hypotheses: (1) leukocyte accumulation is present in brain tissue 24 h posttrauma, (2) leukocyte accumulation represents PMN, and (3) prior systemic PMN depletion attenuates brain tissue PMN accumulation. Trauma was induced in exposed right parietal cortex by weightdrop in anesthetized Wistar rats (n = 24). Of the traumatized rats, 12 were PMN-depleted with vinblastine sulfate i.v. Controls were 12 normal rats and 5 sham-operated rats (craniotomy). Sections of traumatized and contralateral hemispheres were analyzed for myeloperoxidase (MPO) activity. Brain MPO activity was increased fivefold at 24 h posttrauma, but only in the traumatized hemisphere (0.448 ± 0.133 U/g vs 0.090 ± 0.022 U/g in trauma vs normal, respectively, p < 0.05, mean ± SEM). PMN depletion attenuated this increase in MPO activity and decreased circulating PMN counts (0.07 ± 0.032 × 10⁹/L vs 0.894 ± 0.294 × 10⁹/L PMN-depleted–trauma vs trauma rats, respectively, p < 0.05). Leukocyte accumulation in the brain posttrauma was confirmed by MPO assay. Inhibition of MPO activity in the PMN-depleted group and the specificity of vinblastine treatment for depletion of circulating PMN suggest that leukocyte accumulation in the brain at 24 h posttrauma is largely due to PMN.