Hypoxemia has detrimental effects after traumatic brain injury (TBI) in both experimental models and humans. The purpose of this study was to determine the effect of mild or moderate hypoxemia on early histologic and motor functional outcome after controlled cortical impact (CCI) in rats. Anesthetized rats underwent CCI and were randomized to receive mild (FiO2 = 13%, n = 6), moderate (FiO2 = 11%, n = 9), or no (FiO2 = 33%, n = 6) hypoxemia for 30 min after trauma. Sham-operated rats without hypoxemia (n = 7) were used as controls. Motor function (beam balance latency) was assessed on days 0-5. Rats were killed 7 days after injury and their brains removed for assessment of survival of hippocampal neurons and contusion volume. Terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick end labeling (TUNEL) was performed on brain sections from rats killed at 6, 24, and 72 h after CCI and moderate hypoxemia to assess DNA fragmentation in situ. Mild and moderate hypoxemia augmented motor function deficits after CCI in a dose-dependent manner. Moderate hypoxemia after CCI reduced 7-day survival of CA3 neurons but not CA1 neurons vs. sham (55 [46-86] vs. 99 [95-130], p < 0.05, and 79 [63-86] vs. 101 [81-123], NS, respectively; % uninjured hemisphere, median [range]). The addition of mild or moderate hypoxemia did not increase contusion volume. TUNEL-positive neurons were seen in ipsilateral cortex and dentate gyrus at 6, 24, and 72 h after trauma, and in ipsilateral CA3 hippocampal neurons and thalamus at 24 and 72 h. Moderate hypoxemia augments CA3 neuronal death and early motor functional deficits after CCI. The pattern of DNA fragmentation in selectively vulnerable neurons suggests that apoptosis may play a role in the delayed neuronal death seen after TBI.

Controlled cortical impact (CCI) produces blood-brain barrier (BBB) permeability and an acute inflammatory response in injured brain, associated with upregulation of cell adhesion molecules and accumulation of neutrophils. Nevertheless, the role of acute inflammation in the pathogenesis of BBB permeability after traumatic brain injury (TBI) is undefined. The purpose of this study was to examine the time course of acute inflammation and BBB permeability after CCI in rats and to determine the effect of neutrophil depletion on BBB permeability early after CCI. In the first protocol, four groups of rats (n = 4-7/group) were subjected to CCI. Expression of endothelial (E)-selectin on cerebrovascular endothelium, accumulation of neutrophils, and BBB permeability were measured in brain at 1, 4, 8, and 24 hours after injury by immunohistochemistry or spectrophotometric quantification of Evans blue. E-selectin upregulation and neutrophil accumulation in injured brain occurred at later times than maximal BBB permeability. In a second protocol, rats made neutropenic with a murine monoclonal IgM antibody (RP-3) specific for rat neutrophils were subjected to CCI, given Evans blue at 3.5 hours, and sacrificed at 4 hours after injury. Neutrophil depletion did not affect BBB permeability at 4 hours after CCI. We conclude that events other than those mediated by neutrophils initiate BBB permeability early after CCI.

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.

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