Intracerebral Inflammatory Response And Experimental Glucocorticoid Intervention After Traumatic Brain Injury In Rats

Although inflammation is a basic response to injury, for many years the brain has been considered an exception to this rule due to its separation from peripheral circulation mediated by the blood-brain barrier. Only in recent years has it been shown that the cerebral inflammatory response to processes such as trauma and stroke are pronounced, and contribute to secondary brain injury. Conversely, it is becoming clear that inhibiting the inflammatory response in the brain may help protect against injury and may improve outcome. This thesis comprises three parts, chapter 1 and chapter 2 are about cerebral inflammatoy response after traumatic brain injury in rats: Kinetic of polymorphonuclear leukocyte infiltration and upregulation of ICAM-1; chapter 3 is about Glucocorticoid inhibitory effects on acute inflammatory response and brain edema after traumatic brain injury in rats. ChapterⅠ: Kinetic of polymorphonuclear leukocyte infiltration after traumatic brain injury in rats Objective: The purpose of this study was to investigate the temporal and regional profile of polymorphonuclear leukocyte (PMNL) infiltration into the injured parenchyma and the time course of PMNL after traumatic brain injury (TBI) using the free-falling weight model, also to evaluate the contributions of inflammatory response to the secondary brain injury (SBI). Methods: Using the Feeney's free-falling weight model, 32 male Sprague-Dawley (SD) rats were randomly separated into sham-injured groups and injured groups, the damaged region of brain were removed in different time plases, stained with hematoxylin and eosin (HE) to evaluate the histopathologic changes, assayed myeloperoxidase (MPO) activity to study the duration of PMNL aggregation infiltration on the cortical and subcortical regions 3, 6, 12, 24, 48, 72 hours and 7 days post-trauma. Results: There are no PMNL infiltration in control sham-injured brain. PMNL aggregation and infiltration in injured brain progressively increased following histopathologic exacebation. MPO activity occurred in injured brain from 3 hours post-trauma, maximum at 12-48 hours, reduced at 72 hours and resolved by 7 days after trauma. Conclusion: 1. A local inflammatory response was initiated immediately following TBI and is characterized by the accumulation and infiltration of PMNL. 2. Proinflammatory cytokines production are thought to be partially responsible for the PMNLs infiltration contribute to inflammatory response and the inflammation may play an important role in the pathogenesis of secondary cerebral injury after traumatic brain injury. 3. The information explosion relative to inflammatory response mechanisms of secondary injury identified a potential targets for intervention, and PMNL infiltration into the brain parenchyma is a delayed phenomenon in the physiopathology of TBI. antagonism of PMNL action may be beneficial in neurological outcomes. ChapterⅡ: Up-regulation of ICAM-1 after trauma brain injury in rats Objective The purpose of this study was made to investigate on the expression of the intercellular adhesion molecule 1 (ICAM-1) in cerebralmicrovessels after cortical contusion trauma of the rat brain and the time course of ICAM-1 after traumatic brain injury (TBI) using the free-falling weight model. We also to discuss the cntributions of Up-regulation of ICAM-1 after trauma brain injury to neutrophil infiltration and the secondary brain injury (SBI). Methods Using the Feeney's free-falling weight model, 32 male Sprague-Dawley (SD) rats were randomly separated into sham-injured groups and injured groups, the damaged region of brain was removed in different time phases and analyzed immunohistochemically for ICAM-1 expression from 3 hour up to 7 days after trauma. Immunohistochemistry was done on paraffin sections using a monoclonal antibody. and studied the duration of ICAM-1 expression in cerebral microvessels on the cortical and subcortical regions 3, 6, 12, 24, 48, 72 hour and 7 days post-trauma. Results Sham-injured rats showed immunostaining of some penetrating arteries of the cerebral cortex, the epithelial cells of the choroid plexus and occasional microvessels of the brain parenchyma. All rats with contusion trauma showed a substantial increase in the number of immunostained microvessles throughout the site of the lesion. In the first 3 hr after trauma, the number of ICAM-1 positive vessels increased up to 11-fold in cortical and subcortical regions compared with sham injured controls (P < 0.01). Maximal ICAM-1 expression (up to 22-fold increase) was detected after 6-24 hrs (P < 0.001), returning to sham-injured groups levels in all brain regions by 7 days after trauma. The ipsilateral cortical and subcortical regions showed a abrupt increase in the number of immunostained microvascular profiles. The staining was seen as an uninterrupted line at the position of the endothelial cells, indicating an upregulation of this adhesion molecule after brain trauma. In contrast, neutrophil infiltration and up-regulation of ICAM-1 both events relevantin traumatic brain injury, and ICAM-1 upregulation is more earlier than PMNL infiltration , but paralleled by neutrophil infiltration. In the tests, a significant inflammation was observed in traumatized rats as compared with sham-injured animals from 6 hr post-injury (P<0.001). Conclusions 1. After traumatic brain injury ICAM-1 upregulation has been demonstrated is paralleled by neutrophil infiltration, pointing out that ICAM-1 upregulation is the important molecular base of PMNL infiltration and individual and distinct inflammatory events occur after TBI. 2. ICAM-1 may be involved in the production of several post-traumatic events such as leukocyte adhesion, microcirculatory disturbances and edema formation. 3. ICAM-1 upregulation in the early pathologic process of traumatic brain injury suggested blockage of ICAM-1 expression during early injury period may reduce the secondary brain damage. ChapterⅢ: Glucocorticoid effects on acute inflammatory response after traumatic brain injury Objective: To study the local inflammatory response and traumatic cerebral edema in injured rat brain suppressed by Methylprednisolone, and to survey recent data as to the possible mechanisms underlying the anti-inflammation actions of glucocorticoids, Raise the possibility that methylprednisolone is a novel target for therapeutic intervention in secondary brain injury. Methods: Forty-eight male SD rats were randomly assigned to thecontral groups(n=24) and methyprednisolone treatment groups(n=24). Based on the result of chapter I and Ⅱ, at the early time after injury, methyprednisolone was administrated to rats in treatment groups through the tail vein at the time when the more PMNL sequestration was observed in brain, and at the same time, physiological saline was administrated to rats in control groups: The expression of MPO activity and ICAM-1 and the changes of the histopathology and cerebral edema were studied at 6 hours, 12 hours and 24 hours after TBI. Results: Comparision to the rats receiving a control physiological saline, MPO activity and postive expression of ICAM-1 in brain area obviously reduced with methylprednisolone treatment (p<0.01), and the histopathological changes were also improved. and cerebral edema (p<0.05) were also decreased. Condusion: 1. Administration of glucocorticoids in the early time after traumatic brain injury prevented expression of MPO activity and ICAM-1, attenuated local inflammation injury and reduced cerebral edema. 2. Glucocorticoids shows anti-inflammatory effect which is closely related to the regulatory role of glucocorticoids on the NF-κB activiation and cytokine secretion and attenuated secondary brain injury after TBI.