Early white blood cell dynamics after traumatic brain injury: effects on the cerebral microcirculation

The Surgical Method of Craniectomy Differentially Affects Acute Seizures, Brain Deformation and Behavior in a TBI Animal Model

Traumatic brain injury (TBI) is the leading cause of morbidity and mortality worldwide. Multiple injury models have been developed to study this neurological disorder. One such model is the lateral fluid-percussion injury (LFPI) rodent model. The LFPI model can be generated with different surgical procedures that could affect the injury and be reflected in neurobehavioral dysfunction and acute EEG changes. A craniectomy was performed either with a trephine hand drill or with a trephine electric drill that was centered over the left hemisphere of adult, male Sprague Dawley rats. Sham craniectomy groups were assessed by hand-drilled (ShamHMRI) and electric-drilled (ShamEMRI) to evaluate by MRI. Then, TBI was induced in separate groups (TBIH) and (TBIE) using a fluid-percussion device. Sham-injured rats (ShamH/ShamE) underwent the same surgical procedures as the TBI rats. During the same surgery session, rats were implanted with screw and microwire electrodes positioned in the neocortex and hippocampus and the EEG activity was recorded 24 hours for the first 7 days after TBI for assessing the acute EEG seizure and Gamma Event Coupling (GEC). The electric drilling craniectomy induced greater tissue damage and sensorimotor deficits compared to the hand drill. Analysis of the EEG revealed acute seizures in at least one animal from each group after the procedure. Both TBI and Sham rats from the electric drill groups had a significant greater total number of seizures than the animals that were craniectomized manually (p<0.05). Similarly, EEG functional connectivity was lower in ShamE compared to ShamH rats. These results suggest that electrical versus hand drilling craniectomies produce cortical injury in addition to the LFPI which increases the likelihood for acute post-traumatic seizures. Differences in the surgical approach could be one reason for the variability in the injury that makes it difficult to replicate results between preclinical TBI studies.

Association between white blood cells and ultra-early hematoma growth in patients with spontaneous intracerebral hemorrhage

Background

Ultra-early inflammatory reaction after spontaneous intracerebral hemorrhage (sICH) plays an important role in the coagulation process and is closely related to early hematoma expansion. However, the relationship between ultra-early hematoma growth (uHG) and ultra-early inflammatory reaction remains unknown.

Objective

To evaluate the association between ultra-early inflammatory indicators and uHG in patients with sICH.

Methods

We retrospectively included 225 patients with acute sICH who were divided into the uHG ≤4.7 ml/h group and the uHG >4.7 ml/h group, respectively. The uHG was defined as hematoma volume (milliliter) at the primary computed tomography (CT) scan divided by time (hour) from onset to the performance of primary CT within 6 h after onset. The white blood cells (WBC), blood hypersensitive C-reactive protein, National Institutes of Health Stroke Scale (NIHSS) score and other related baseline data were collected and compared between the two groups. The multivariate regression analysis and receiver operating characteristic (ROC) curve were used to evaluate the independent risk factors for uHG >4.7 ml/h.

Results

NIHSS score and WBC were independent risk factors for uHG in patients with acute sICH (OR 1.188, 95% CI: 1.111-1.271, p < 0.001; OR 1.151, 95% CI: 1.018-1.300, p = 0.024; respectively). The area under curve of ROC for WBC and NIHSS score was 0.658 and 0.754, respectively (all p < 0.001), while the WBC combined with NIHSS score was 0.773 (p < 0.001).

Conclusion

WBC count within 6h after onset might be an independent risk factor for the increase of uHG in patients with sICH.

Insights from Rodent Models for Improving Bench-to-Bedside Translation in Traumatic Brain Injury

Road accidents, domestic falls, and persons associated with sports and military services exhibited the concussion or contusion type of traumatic brain injury (TBI) that resulted in chronic traumatic encephalopathy. In some instances, these complex neurological aberrations pose severe brain damage and devastating long-term neurological sequelae. Several preclinical (rat and mouse) TBI models simulate the clinical TBI endophenotypes. Moreover, many investigational neuroprotective candidates showed promising effects in these models; however, the therapeutic success of these screening candidates has been discouraging at various stages of clinical trials. Thus, a correct selection of screening model that recapitulates the clinical neurobiology and endophenotypes of concussion or contusion is essential. Herein, we summarize the advantages and caveats of different preclinical models adopted for TBI research. We suggest that an accurate selection of experimental TBI models may improve the translational viability of the investigational entity.

PRMT7 can prevent neurovascular uncoupling, blood-brain barrier permeability, and mitochondrial dysfunction in repetitive and mild traumatic brain injury

Mild traumatic brain injury (TBI) comprises the largest percentage of TBI-related injuries, with pathophysiological and functional deficits that persist in a subset of TBI patients. In our three-hit paradigm of repetitive and mild traumatic brain injury (rmTBI), we observed neurovascular uncoupling via decreased red blood cell velocity, microvessel diameter, and leukocyte rolling velocity 3 days post-rmTBI via intra-vital two-photon laser scanning microscopy. Furthermore, our data suggest increased blood-brain barrier (BBB) permeability (leakage), with corresponding decrease in junctional protein expression post-rmTBI. Mitochondrial oxygen consumption rates (measured via Seahorse XFe24) were also altered 3 days post-rmTBI, along with disrupted mitochondrial dynamics of fission and fusion. Overall, these pathophysiological findings correlated with decreased protein arginine methyltransferase 7 (PRMT7) protein levels and activity post-rmTBI. Here, we increased PRMT7 levels in vivo to assess the role of the neurovasculature and mitochondria post-rmTBI. In vivo overexpression of PRMT7 using a neuronal specific AAV vector led to restoration of neurovascular coupling, prevented BBB leakage, and promoted mitochondrial respiration, altogether to suggest a protective and functional role of PRMT7 in rmTBI.

Persistent Blunting of Penumbral Leukocyte Mobilization by Beta Blockade Administered for Two Weeks After Traumatic Brain Injury

INTRODUCTION

Beta-blockers (BB) after traumatic brain injury (TBI) accelerate cognitive recovery weeks after injury. BBs also inhibit leukocyte (LEU) mobilization to the penumbral blood brain barrier (BBB) 48-h after TBI. It is unclear whether the latter effects persist longer and accompany the persistent cognitive improvement. We hypothesized that 2 wk of BB after TBI reduce penumbral BBB leukocyte-endothelial interactions.

METHODS

Thirty CD1 mice underwent TBI (controlled cortical impact, CCI: 6 m/s velocity, 1 mm depth, 3 mm diameter) or sham craniotomy followed by i.p. saline (NS) or propranolol (1, 2, 4 mg/kg) every 12 h for 14 d. On day 14, in vivo pial intravital microscopy visualized endothelial-LEU interactions and BBB microvascular leakage. Day 14 Garcia neurological test scores and animal weights were compared to preinjury levels reflecting concurrent clinical recovery.

RESULTS

LEU rolling was greatest in CCI + NS when compared to sham (P = 0.03). 4 mg/kg propranolol significantly reduced postCCI LEU rolling down to uninjured sham levels (P = 0.03). LEU adhesion and microvascular permeability were not impacted at this time interval. Untreated injured animals (CCI + NS) scored lower Garcia neurological test and greater weight loss recovery at day 14 when compared to preinjury (P < 0.05). Treatment with higher doses of propranolol (2, 4 mg/kg), improved weight loss recovery (P < 0.001).

CONCLUSIONS

LEU rolling alone, was influenced by BB therapy 14 d after TBI suggesting that certain penumbral neuroinflammatory cellular effects of BB therapy after TBI persist up to 2 wk after injury potentially explaining the pervasive beneficial effects of BBs on learning and memory.

ICAM-1 on the luminal surface of endothelial cells is induced to a greater extent in mouse retina than in other tissues in diabetes

AIMS/HYPOTHESIS

Induction of intercellular adhesion molecule-1 (ICAM-1) has been implicated in the development of macrovascular and microvascular diseases such as diabetic retinopathy. Lesions of diabetic retinopathy are unique to the retina but the reason for this is unclear, as all tissues are exposed to the same hyperglycaemic insult. We tested whether diabetes induces ICAM-1 on the luminal surface of endothelial cells to a greater extent in the retina than in other tissues and the role of vision itself in that induction.

METHODS

Experimental diabetes was induced in C57Bl/6J, P23H opsin mutant and Gnat1-/- × Gnat2-/- double knockout mice using streptozotocin. The relative abundance of ICAM-1 on the luminal surface of endothelial cells in retina and other tissues was determined by conjugating anti-ICAM-1 antibodies to fluorescent microspheres (2 μm), injecting them intravenously and allowing them to circulate for 30 min. After transcardial perfusion, quantification of microspheres adherent to the endothelium in tissues throughout the body was carried out by fluorescent microscopy or flow cytometry. Mice injected with lipopolysaccharide (LPS) were used as positive controls. The difference in leucostasis between retinal and non-retinal vasculature was evaluated.

RESULTS

Diabetes significantly increased ICAM-1-mediated adherence of microspheres to retinal microvessels by almost threefold, independent of sex. In contrast, diabetes had a much smaller effect on endothelial ICAM-1 in other tissues, and more tissues showed a significant induction of endothelial ICAM-1 with LPS than with diabetes. The diabetes-induced increase in endothelial ICAM-1 in retinal vasculature was inhibited by blocking phototransduction in photoreceptor cells. Diabetes significantly increased leucostasis in the retina by threefold compared with a non-ocular tissue (cremaster).

CONCLUSIONS/INTERPRETATION

The diabetes-induced upregulation of ICAM-1 on the luminal surface of the vascular endothelium varies considerably among tissues and is highest in the retina. Induction of ICAM-1 on retinal vascular endothelial cells in diabetes is influenced by vision-related processes in photoreceptor cells. The unique presence of photoreceptors in the retina might contribute to the greater susceptibility of this tissue to vascular disease in diabetes.

Emerging Roles of T Helper Cells in Non-Infectious Neuroinflammation: Savior or Sinner

CD4⁺ T cells, also known as T helper (Th) cells, contribute to the adaptive immunity both in the periphery and in the central nervous system (CNS). At least seven subsets of Th cells along with their signature cytokines have been identified nowadays. Neuroinflammation denotes the brain’s immune response to inflammatory conditions. In recent years, various CNS disorders have been related to the dysregulation of adaptive immunity, especially the process concerning Th cells and their cytokines. However, as the functions of Th cells are being discovered, it’s also found that their roles in different neuroinflammatory conditions, or even the participation of a specific Th subset in one CNS disorder may differ, and sometimes contrast. Based on those recent and contradictory evidence, the conflicting roles of Th cells in multiple sclerosis, Alzheimer’s disease, Parkinson’s disease, epilepsy, traumatic brain injury as well as some typical mental disorders will be reviewed herein. Research progress, limitations and novel approaches concerning different neuroinflammatory conditions will also be mentioned and compared.

Levels of lncRNA GAS5 in Plasma of Patients with Severe Traumatic Brain Injury: Correlation with Systemic Inflammation and Early Outcome

Scientific efforts continue to concentrate on elucidating the complex molecular mechanisms underlying traumatic brain injury (TBI), and recent reports suggest that epigenetic regulation including long non-coding RNA (lncRNA) is involved. The present study aimed to investigate the plasma concentration of a long non-coding RNA, named growth arrest-specific 5 (GAS5), in a group of 45 patients with severe TBI (sTBI), and to analyze the correlations of GAS5 with TBI onset, injury severity, systemic inflammation, and early outcome of the patients. It was found that plasma GAS5 levels were substantially increased in sTBI patients compared with the relative controls (p < 0.001). Further, significantly higher expression of plasma GAS5 was observed in patients with a Glasgow Coma Scale (GCS) score of less than five (p = 0.002) or unfavorable outcome at discharge (p < 0.001). Circulating GAS5 expression had a negative correlation with GCS score (r = −0.406, p = 0.006), and positive correlations with white blood cell count (r = 0.473, p = 0.001), neutrophil count (r = 0.502, p < 0.001), and neutrophil/lymphocyte ratio (NLR) (r = 0.398, p = 0.007). Univariate and multivariate logistic regression analyses revealed that GCS score (OR = 0.318, 95% CI 0.132−0.767, p = 0.011) and GAS5 (OR = 2.771, 95% CI 1.025−7.494, p = 0.045) were the two independent predictors for early outcome of patients. The receiver operating characteristic (ROC) curves showed good prognostic values of GCS score (AUC = 0.856, 95% CI: 0.719−0.943) and GAS5 expression (AUC = 0.798, 95% CI: 0.651−0.903). Importantly, the combined use of them can improve the prognostic ability of TBI with an AUC of 0.895 (95% CI: 0.767−0.966). Collectively, our study indicated that the levels of lncRNA GAS5 in circulation were elevated following severe TBI and correlated well with injury severity and inflammatory parameters. In addition, GAS5 as well as GCS scores may have the potential to predict the early outcome of TBI patients.

Clinical and radiographic factors involved in achieving a hematoma evacuation rate of more than 70% through minimally invasive catheter drainage for spontaneous intracerebral hemorrhage

Although stereotactic or neuronavigation-guided hematoma drainage for spontaneous intracerebral hemorrhage (ICH) is widely used, its clinical efficacy and factors for predictive results remain to be fully elucidated. This study sought to determine the efficacy of hematoma evacuation for spontaneous ICH, in addition to the factors affecting it. We retrospectively reviewed patients who underwent stereotactic or neuronavigation-guided catheter insertion for spontaneous ICH at our institute between April 2010 and December 2019. We identified and compared the clinical and radiographic factors between groups according to the hematoma evacuation rate of 70%. Logistic regression analyses were performed to identify factors affecting hematoma evacuation. We investigated whether the hematoma evacuation rate was associated with patient survival. A total of 95 patients who underwent stereotactic or neuronavigation-guided catheter insertion and hematoma drainage for spontaneous ICH were included. A multivariate analysis indicated that a hematoma volume of 30-60 cm³ (odds ratio [OR] = 8.064, 95% confidence interval [CI] = 2.285-28.468, P = 0.001), blend sign (OR = 6.790, 95% CI = 1.239-37.210, P = 0.027), diabetes (OR = 0.188, 95% CI = 0.041-0.870, P = 0.032), and leukocytosis (OR = 3.061, 95% CI = 1.094-8.563, P = 0.033) were significantly associated with a higher hematoma evacuation. The mean hematoma evacuation rate in patients with 1-month mortality was lower than that in survivors (P = 0.051). Our study revealed that a hematoma volume of 30-60 cm³, the presence of a blend sign and leukocytosis, and the absence of diabetes are independent predictors that affect more than 70% of hematoma evacuations.

The Flow Limiting Operator: A New Approach to Environmental Control in Flow Bioreactors

Bioreactors have become a critical step for the testing of new biomaterials and pharmaceuticals. They need to be controllable, ideally high-throughput, and produce a biologically relevant environment. For example, in the brain, it is essential to recreate multiple flow–pressure profiles daily and mimic brain fluid movement for a bioreactor to be more physiologic. In this study, we demonstrate a scalable system that regulates flow rate, pressure, and pulsation amplitude. We also show that with new microcontroller technology, up to 15 chambers running in parallel is theoretically possible. Our system, the Flow Limiting Operator (FLO), achieves these goals by multiplexing a series of valves and pumps to control pressure and volumetric flow rate instead of relying on head gas pressure. With the ability to control multiple parameters and its ease of use, both scientists and clinicians can use FLO to study the effects of pulsation amplitude of the fluid flow, flow rate, and pressure on intercellular interactions for both biomaterials and pharmaceuticals.

FLO is a high-throughput bioreactor for testing biomaterials in more physiologically similar environments including pulsation amplitude, flow rate, and pressure waveforms which is done through the manipulation of fluid velocity.

Neutrophil to lymphocyte ratio as a predictive biomarker for computed tomography scan use in mild traumatic brain injury

Aim: Traumatic brain injury (TBI) is a serious health concern. We set out to investigate the role of neutrophil-to-lymphocytes ratio (NLR) at admission for predicting the need for computed tomography (CT) in mild-TBI. Materials & methods: A retrospective study of adult patients who presented with mild-TBI Results: One hundred and thirty patients met the inclusion criteria. Seventy-four patients had positive CT-findings. The mean NLR-levels at presentations were 5.6 ± 4.8. Patients with positive CT-findings had significant higher NLR-levels. Receiver operating characteristic curve analysis was conducted and the threshold of NLR-levels for detecting the cases with positive CT-findings was 2.5, with 78.1% sensitivity and 63% specificity Conclusion: To the best of our knowledge no previous study has assessed the value of NLR-levels for predicting the need for CT in mild-TBI.

Endothelial-specific Crif1 deletion induces BBB maturation and disruption via the alteration of actin dynamics by impaired mitochondrial respiration

Cerebral endothelial cells (ECs) require junctional proteins to maintain blood-brain barrier (BBB) integrity, restricting toxic substances and controlling peripheral immune cells with a higher concentration of mitochondria than ECs of peripheral capillaries. The mechanism underlying BBB disruption by defective mitochondrial oxidative phosphorylation (OxPhos) is unclear in a mitochondria-related gene-targeted animal model. To assess the role of EC mitochondrial OxPhos function in the maintenance of the BBB, we developed an EC-specific CR6-interactin factor1 (Crif1) deletion mouse. We clearly observed defects in motor behavior, uncompacted myelin and leukocyte infiltration caused by BBB maturation and disruption in this mice. Furthermore, we investigated the alteration in the actin cytoskeleton, which interacts with junctional proteins to support BBB integrity. Loss of Crif1 led to reorganization of the actin cytoskeleton and a decrease in tight junction-associated protein expression through an ATP production defect in vitro and in vivo. Based on these results, we suggest that mitochondrial OxPhos is important for the maturation and maintenance of BBB integrity by supplying ATP to cerebral ECs.

The emerging role of neutrophils as modifiers of recovery after traumatic injury to the developing brain

The innate immune response plays a critical role in traumatic brain injury (TBI), contributing to ongoing pathogenesis and worsening long-term outcomes. Here we focus on neutrophils, one of the "first responders" to TBI. These leukocytes are recruited to the injured brain where they release a host of toxic molecules including free radicals, proteases, and pro-inflammatory cytokines, all of which promote secondary tissue damage. There is mounting evidence that the developing brain is more vulnerable to injury that the adult brain. This vulnerability to greater damage from TBI is, in part, attributed to relatively low antioxidant reserves coupled with an early robust immune response. The latter is reflected in enhanced sensitivity to cytokines and a prolonged recruitment of neutrophils into both cortical and subcortical regions. This review considers the contribution of neutrophils to early secondary pathogenesis in the injured developing brain and raises the distinct possibility that these leukocytes, which exhibit phenotypic plasticity, may also be poised to support wound healing. We provide a basic review of the development, life cycle, and granular contents of neutrophils and evaluate their potential as therapeutic targets for early neuroprotection and functional recovery after injury at early age. While neutrophils have been broadly studied in neurotrauma, we are only beginning to appreciate their diverse roles in the developing brain and the extent to which their acute manipulation may result in enduring neurological recovery when TBI is superimposed upon brain development.

The immune system in traumatic brain injury

Traumatic brain injury (TBI) is the major cause of death in children and young adults and one of the major reasons for long-term disability worldwide, however, no specific clinical treatment option could be established so far. This is surprising since it is well known that following the initial mechanical damage to the brain a plethora of delayed processes are activated which ultimately result in additional brain damage. Among these secondary mechanisms, acute and chronic activation of the innate and adaptive immune system is increasingly believed to play an important role for the pathogenesis of TBI. Understanding these processes may results in new, clinically applicable therapeutic options for TBI patients.

Endothelial nitric oxide synthase mediates arteriolar vasodilatation after traumatic brain injury in mice

Brain edema and increased cerebral blood volume (CBV) contribute to intracranial hypertension and hence to unfavorable outcome after traumatic brain injury (TBI). The increased post-traumatic CBV may be caused in part by arterial vasodilatation. The aim of the current study was to uncover the largely unknown mechanisms of post-traumatic arteriolar vasodilatation. The diameter of pial arterioles and venules was monitored by intravital fluorescence microscopy before (baseline) and for 30 min after controlled cortical impact in C57BL/6 and endothelial nitric oxide synthase (eNOS)-/- mice (n=5-6/group) and in C57BL/6 mice (n=6/group) receiving vehicle (phosphate-buffered saline [PBS]) or 4-amino-tetrahydro-L-biopterine (VAS203), a NOS inhibitor previously shown to reduce post-traumatic intracranial hypertension. Temperature, end-tidal partial pressure of carbon dioxide (pCO₂), and mean arterial blood pressure were kept within the physiological range throughout the experiments. Arteriolar diameters were stable during baseline monitoring but increased significantly in C57BL/6 mice after controlled cortical impact (136±7% of baseline; p<0.001 vs. baseline). This response was reduced by 78% in eNOS-/- mice (108±3% of baseline; p<0.005 vs. wild-type). Application of VAS203, a NOS inhibitor, or PBS did not affect vessels diameter before TBI. After trauma, however, administration of VAS203 reduced arteriolar diameter to 92±2% of baseline (p<0.05). The diameter of pial veins was not affected. Our results suggest that arteriolar vasodilatation after TBI is largely mediated by excess production of endothelial nitric oxide. Accordingly, our data may explain the beneficial effects of the NOS inhibitor VAS203 in the early phase after TBI and suggest that inhibition of excess endothelial nitric oxide production may represent a novel therapeutic strategy following TBI.

Contributions of the immune system to the pathophysiology of traumatic brain injury - evidence by intravital microscopy

Traumatic brain injury (TBI) results in immediate brain damage that is caused by the mechanical impact and is non-reversible. This initiates a cascade of delayed processes which cause additional—secondary—brain damage. Among these secondary mechanisms, the inflammatory response is believed to play an important role, mediating actions that can have both protective and detrimental effects on the progression of secondary brain damage. Histological data generated extensive information; however, this is only a snapshot of processes that are, in fact, very dynamic. In contrast, in vivo microscopy provides detailed insight into the temporal and spatial patterns of cellular dynamics. In this review, we aim to summarize data which was generated by in vivo microscopy, specifically investigating the immune response following brain trauma, and its potential effects on secondary brain damage.

Early initiation of prophylactic heparin in severe traumatic brain injury is associated with accelerated improvement on brain imaging

Background:

Venous thromboembolic prophylaxis (VTEp) is often delayed following traumatic brain injury (TBI), yet animal data suggest that it may reduce cerebral inflammation and improve cognitive recovery. We hypothesized that earlier VTEp initiation in severe TBI patients would result in more rapid neurologic recovery and reduced progression of brain injury on radiologic imaging.

Study Design:

Medical charts of severe TBI patients admitted to a level 1 trauma center in 2009-2010 were queried for admission Glasgow Coma Scale (GCS), head Abbreviated Injury Scale, Injury Severity Score (ISS), osmotherapy use, emergency neurosurgery, and delay to VTEp initiation. Progression (+1 = better, 0 = no change, −1 = worse) of brain injury on head CTs and neurologic exam (by bedside MD, nurse) was collected from patient charts. Head CT scan Marshall scores were calculated from the initial head CT results.

Results:

A total of 22, 34, and 19 patients received VTEp at early (<3 days), intermediate (3-5 days), and late (>5 days) time intervals, respectively. Clinical and radiologic brain injury characteristics on admission were similar among the three groups (P > 0.05), but ISS was greatest in the early group (P < 0.05). Initial head CT Marshall scores were similar in early and late groups. The slowest progression of brain injury on repeated head CT scans was in the early VTEp group up to 10 days after admission.

Conclusion:

Early initiation of prophylactic heparin in severe TBI is not associated with deterioration neurologic exam and may result in less progression of injury on brain imaging. Possible neuroprotective effects of heparin in humans need further investigation.

In vivo temporal and spatial profile of leukocyte adhesion and migration after experimental traumatic brain injury in mice

Background

Leukocytes are believed to be involved in delayed cell death following traumatic brain injury (TBI). However, data demonstrating that blood-borne inflammatory cells are present in the injured brain prior to the onset of secondary brain damage have been inconclusive. We therefore investigated both the interaction between leukocytes and the cerebrovascular endothelium using in vivo imaging and the accumulation of leukocytes in the penumbra following experimentally induced TBI.

Methods

Experimental TBI was induced in C57/Bl6 mice (n = 42) using the controlled cortical impact (CCI) injury model, and leukocyte-endothelium interactions (LEI) were quantified using both intravital fluorescence microscopy (IVM) of superficial vessels and 2-photon microscopy of cortical vessels for up to 14 h post-CCI. In a separate experimental group, leukocyte accumulation and secondary lesion expansion were analyzed in mice that were sacrificed 15 min, 2, 6, 12, 24, or 48 h after CCI (n = 48). Finally, leukocyte adhesion was blocked with anti-CD18 antibodies, and the effects on LEI and secondary lesion expansion were determined 16 (n = 12) and 24 h (n = 21), respectively, following TBI.

Results

One hour after TBI leukocytes and leukocyte-platelet aggregates started to roll on the endothelium of pial venules, whereas no significant LEI were observed in pial arterioles or in sham-operated mice. With a delay of >4 h, leukocytes and aggregates did also firmly adhere to the venular endothelium. In deep cortical vessels (250 μm) LEIs were much less pronounced. Transmigration of leukocytes into the brain parenchyma only became significant after the tissue became necrotic. Treatment with anti-CD18 antibodies reduced adhesion by 65%; however, this treatment had no effect on secondary lesion expansion.

Conclusions

LEI occurred primarily in pial venules, whereas little or no LEI occurred in arterioles or deep cortical vessels. Inhibiting LEI did not affect secondary lesion expansion. Importantly, the majority of migrating leukocytes entered the injured brain parenchyma only after the tissue became necrotic. Our results therefore suggest that neither intravascular leukocyte adhesion nor the migration of leukocytes into cerebral tissue play a significant role in the development of secondary lesion expansion following TBI.

Correlation of leukocytosis with early neurological deterioration following supratentorial intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating and common admitting diagnosis to intensive care units in the USA. Despite advances in critical care, patients with ICH often experience early neurological deterioration (END) in the first 72 hours after admission due to a variety of factors, including hematoma and cerebral edema evolution. The purpose of this study was to determine factors associated with END after ICH. Using the Duke University Hospital Neuroscience Critical Care Unit Database, we retrospectively identified patients with an admitting diagnosis of supratentorial ICH from January to December 2010, verified by CT imaging. END was defined as a decrease in the Glasgow Coma Scale score of ≥3 or death within the first 72 hours after hemorrhage. The chi-squared or t-test analysis was used to compare the groups, as appropriate. Multiple logistical regression modeling was performed to test for associations between likely predictors of END. Of the 89 subjects admitted with supratentorial ICH, we included 83 in the analysis based on complete datasets. Of these, 31 experienced END within 72 hours after onset of symptoms. ICH score, presence of midline shift on imaging, and white blood cell (WBC) count were used in a regression model for predicting END. WBC count demonstrated the greatest association with END. Patients with ICH are prone to END within the first few days after hemorrhage. Elevated WBC count appears predictive of deterioration. These data demonstrate that heightened inflammatory state after ICH may be related to early deterioration after injury.

Neutrophil depletion reduces edema formation and tissue loss following traumatic brain injury in mice

Background

Brain edema as a result of secondary injury following traumatic brain injury (TBI) is a major clinical concern. Neutrophils are known to cause increased vascular permeability leading to edema formation in peripheral tissue, but their role in the pathology following TBI remains unclear.

Methods

In this study we used controlled cortical impact (CCI) as a model for TBI and investigated the role of neutrophils in the response to injury. The outcome of mice that were depleted of neutrophils using an anti-Gr-1 antibody was compared to that in mice with intact neutrophil count. The effect of neutrophil depletion on blood-brain barrier function was assessed by Evan's blue dye extravasation, and analysis of brain water content was used as a measurement of brain edema formation (24 and 48 hours after CCI). Lesion volume was measured 7 and 14 days after CCI. Immunohistochemistry was used to assess cell death, using a marker for cleaved caspase-3 at 24 hours after injury, and microglial/macrophage activation 7 days after CCI. Data were analyzed using Mann-Whitney test for non-parametric data.

Results

Neutrophil depletion did not significantly affect Evan's blue extravasation at any time-point after CCI. However, neutrophil-depleted mice exhibited a decreased water content both at 24 and 48 hours after CCI indicating reduced edema formation. Furthermore, brain tissue loss was attenuated in neutropenic mice at 7 and 14 days after injury. Additionally, these mice had a significantly reduced number of activated microglia/macrophages 7 days after CCI, and of cleaved caspase-3 positive cells 24 h after injury.

Conclusion

Our results suggest that neutrophils are involved in the edema formation, but not the extravasation of large proteins, as well as contributing to cell death and tissue loss following TBI in mice.

Effects of hemodilution after traumatic brain injury in juvenile rats

BACKGROUND

Normovolemic hemodilution (HD) in adult animal studies has shown exacerbation of traumatic brain injury (TBI) lesion volumes. Similar studies in juvenile rats have not been reported and outcomes are likely to be different. This study investigated the effects of normovolemic hemodilution (21% hematocrit) in a juvenile TBI (jTBI) model.

METHODS

Twenty 17-day-old rats underwent moderate cortical contusion impact injury (CCI) and were divided into four groups: CCI/hemodilution (HD) (group HD), CCI/no HD (group C), Sham/HD (group SHD), and Sham/no HD (group S). Regional laser Doppler flowmetry (LDF), edema formation (MRI-T2WI), water mobility assessed using diffusion weighted imaging (MRI-DWI), open field activity tests, and histological analyses were evaluated for lesion characteristics.

RESULTS

Hemodilution significantly increased blood flow in the HD compared to the C group after TBI. T2WI revealed a significantly increased extravascular blood volume in HD at 1, 7, and 14 days post-CCI. Edematous tissue and total contusional lesion volume were higher in HD-treated animals at 1 and 14 days. DWI revealed that HD, SHD, and C groups had elevated water mobility compared to S groups in the ipsilateral cortex and striatum. Histology showed a larger cortical lesion in the C than HD group. Open field activity was increased in HD, C, and SHD groups compared to the S group.

CONCLUSIONS

Hemodilution results in significant brain hyperemia with increased edema formation, extravascular blood volume, and water mobility after jTBI. Hemodilution results in less cortical damage but did not alter behavior. Hemodilution is likely not to be clinically beneficial following jTBI.

Age is a determinant of leukocyte infiltration and loss of cortical volume after traumatic brain injury

There is increasing evidence that the inflammatory response differs in the injured developing brain as compared to the adult brain. Here we compared cerebral blood flow and profiled the inflammatory response in mice that had been subjected to traumatic brain injury (TBI) at postnatal day (P)21 or at adulthood. Relative blood flow, determined by laser Doppler, revealed a 30% decrease in flow immediately after injury followed by prominent hyperemia between 7 and 35 days after injury in both age groups. The animals were euthanized at 1-35 days after injury and the brains prepared for the immunolocalization and quantification of CD45-, GR-1-, CD4- and CD8-positive (+) cells. On average, the number of CD45+ leukocytes in the cortex was significantly higher in the P21 as compared to the adult group. A similar trend was seen for GR-1+ granulocytes, whereas no age-related differences were noted for CD4+ and CD8+ cells. While CD45+ and GR-1+ cells in the P21 group remained elevated, relative to shams, over the first 2 weeks after injury, the adult group showed a time course limited to the first 3 days after injury. The loss of ipsilateral cortical volumes at 2 weeks after injury was significantly greater in the adult relative to the P21 group. While the adult group showed no further change in cortical volumes, there was a significant loss of cortical volumes between 2 and 5 weeks after injury in the P21 group, reaching values similar to that of the adult group by 5 weeks after injury. Together, these findings demonstrate age-dependent temporal patterns of leukocyte infiltration and loss of cortical volume after TBI.

Fluid-percussion-induced traumatic brain injury model in rats

Traumatic brain injury (TBI) is a major cause of mortality and morbidity. Various attempts have been made to replicate clinical TBI using animal models. The fluid-percussion model (FP) is one of the oldest and most commonly used models of experimentally induced TBI. Both central (CFP) and lateral (LFP) variations of the model have been used. Developed initially for use in larger species, the standard FP device was adapted more than 20 years ago to induce consistent degrees of brain injury in rodents. Recently, we developed a microprocessor-controlled, pneumatically driven instrument, micro-FP (MFP), to address operational concerns associated with the use of the standard FP device in rodents. We have characterized the MFP model with regard to injury severity according to behavioral and histological outcomes. In this protocol, we review the FP models and detail surgical procedures for LFP. The surgery involves tracheal intubation, craniotomy and fixation of Luer fittings, and induction of injury. The surgical procedure can be performed within 45-50 min.

Temporal profile of thrombogenesis in the cerebral microcirculation after traumatic brain injury in mice

Traumatic brain injury (TBI) is associated with an almost immediate reduction in cerebral blood flow (CBF). Because cerebral perfusion pressure is often normal under these circumstances it was hypothesized that the reduction of post-traumatic CBF has to occur at the level of the microcirculation. The aim of the current study was to investigate whether cerebral microvessels are involved in the development of blood flow disturbances following experimental TBI. C57/BL6 mice (n = 12) were intubated and ventilated under control of end-tidal Pco(2) ((ET)P(CO2)). After preparation of a cranial window and baseline recordings, the animals were subjected to experimental TBI by controlled cortical impact (CCI; 6 m/sec, 0.5 mm). Vessel lumina and intravascular cells were visualized by in vivo fluorescence microscopy (IVM) using the fluorescent dyes FITC-dextran and rhodamine 6G, respectively. Vessel diameter, cell-endothelial interactions, and thrombus formation were quantified within the traumatic penumbra by IVM up to 2 h after CCI. Arteriolar diameters increased after CCI by 26.2 +/- 2.5% (mean +/- SEM, p < 0.01 versus baseline), and remained at this level until the end of the observation period. Rolling of leukocytes on the cerebrovascular endothelium was observed both in arterioles and venules, while leukocyte-platelet aggregates were found only in venules. Microthrombi occluded up to 70% of venules and 33% of arterioles. The current data suggest that the immediate post-traumatic decrease in peri-contusional blood flow is not caused by arteriolar vasoconstriction, but by platelet activation and the subsequent formation of thrombi in the cerebral microcirculation.

Dynamic in vivo imaging of cerebral blood flow and blood-brain barrier permeability

The brain is characterized by an extremely rich blood supply, regulated by changes in blood vessel diameter and blood flow, depending on metabolic demands. The blood-brain barrier (BBB)-a functional and structural barrier separating the intravascular and neuropil compartments-characterizes the brain's vascular bed and is essential for normal brain functions. Disruptions to the regional cerebral blood supply, to blood drainage and to BBB properties have been described in most common neurological disorders, but there is a lack of quantitative methods for assessing blood flow dynamics and BBB permeability in small blood vessels under both physiological and pathological conditions. Here, we present a quantitative image analysis approach that allows the characterization of relative changes in the regional cerebral blood flow (rCBF) and BBB properties in small surface cortical vessels. In experiments conducted using the open window technique in rats, a fluorescent tracer was injected into the tail vein, and images of the small vessels at the surface of the cortex were taken using a fast CCD camera. Pixel-based image analysis included registration and characterization of the changes in fluorescent intensity, followed by cluster analysis. This analysis enabled the characterization of rCBF in small arterioles and venules and changes in BBB permeability. The method was implemented successfully under experimental conditions, including increased rCBF induced by neural stimulation, bile salt-induced BBB breakdown, and photothrombosis-mediated local ischemia. The new approach may be used to study changes in rCBF, neurovascular coupling and BBB permeability under normal and pathological brain conditions.

Continuous hypertonic saline therapy and the occurrence of complications in neurocritically ill patients

OBJECTIVE

To evaluate potential side effects of continuous hypertonic 3% saline (CHS) as maintenance fluid in patients with brain injury.

METHODS

Retrospective chart analysis of prospectively collected data.

PATIENTS

Patients admitted to the neurosurgical intensive care unit for >4 days with traumatic brain injury, stroke, or subarachnoid hemorrhage with a Glasgow Coma Scale <9 and elevated intracranial pressure (ICP) or at risk of developing elevated ICP were included. Based on physician preference, one group was treated with 3% CHS at a rate of 1.5 mL/kg/bw as maintenance fluid. The other group received 0.9% normal saline (NS). Two percent saline was used in the CHS group to wean patients off 3% CHS or when sodium was above 155. Data on serum sodium, blood urea nitrogen, creatinine, ICP, infection rate, length of stay, rates of deep vein thrombosis, and pulmonary emboli and dural thrombosis were collected prospectively.

RESULTS

One hundred seven patients in the CHS group and 80 in the NS group met the inclusion criteria. The incidence of moderate hypernatremia (Na >155 mmol/L) and severe hypernatremia (Na >160 mmol/L) was significantly higher in the CHS therapy group than in the NS group. No significant relationship between CHS infusion and renal dysfunction was found. Moderate and severe hypernatremia was associated with a higher risk of elevated blood urea nitrogen and creatinine levels. Acute renal failure was not seen in these patients. A total of 53.3% in the CHS group and in 16.3% in the NS group (p < 0.0001) had raised ICP (>25 mm Hg), consistent with the physicians decision to use CHS in patients with elevated ICP.

CONCLUSIONS

CHS therapy was not associated with an increased rate of infection, deep vein thrombosis, or renal failure. However, there was a significant risk of developing hypernatremia. We conclude that CHS administration in patients with severe injuries is safe as long as sodium levels are carefully monitored.

Neuroinflammatory responses after experimental diffuse traumatic brain injury

Little is known about microglial activation and macrophage localization after diffuse brain injury (DBI). DBI-mediated perisomatic traumatic axonal injury (TAI) was recently identified within the neocortex, hippocampus, and thalamus, providing an opportunity to characterize immune cell responses within diffusely injured brain loci uncomplicated by contusion. By using moderate midline/central fluid percussion injury, microglial/macrophage responses were examined with antibodies targeting immune cell phenotypes and amyloid precursor protein, a marker of TAI. Parallel assessments of blood-brain barrier alterations were also performed. Within 6 to 48 hours postinjury, microglial activation within injured loci was observed, whereas microglia within non-TAI-containing regions maintained a resting phenotype. Microglial activation shared a spatiotemporal relationship with TAI though no clear interactions were observed. By 7 to 28 days postinjury, activated microglia contained myelin debris, yet revealed limited aggregation. Immunophenotypic macrophages were also localized to injured loci. Select macrophages approximated somatic membranes of perisomatically axotomized neurons with evidence of bouton disruption. No causality was established between blood-brain barrier alterations and these inflammatory responses. These findings indicate rapid, yet initially nonspecific, and persistent microglial/macrophage responses to DBI. DBI-mediated inflammatory responses suggest further expansion of traumatic brain injury histopathologic evaluations to identify neuroinflammation indicative of diffuse pathology.

Tacrolimus depresses local immune cell infiltration but fails to reduce cortical contusion volume in brain-injured rats

The immunosuppressant drug tacrolimus (FK-506) failed to show an anti-edematous effect despite suppressing pro-inflammatory cytokines in cerebrospinal fluid following focal traumatic brain injury. By questioning the role of the inflammatory response as a pharmacological target, we investigated the effects of FK-506 on immune cell infiltration in brain-injured rats. Following induction of a cortical contusion, male Sprague-Dawley rats received FK-506 or physiological saline intraperitoneally. Brains were removed at 24 h, 72 h or 7 days, respectively. Frozen brain sections (7 microm) were stained immunohistologically for markers of endothelial activation (intercellular adhesion molecule-1--ICAM-1), neutrophil infiltration (His-48), and microglial and macrophage activation (Ox-6; ED-1), respectively. Immunopositive cells were counted microscopically. Contusion volume (CV) was quantified morphometrically 7 days after trauma. Inflammatory response was confined to the ipsilateral cortex and hippocampal formation, predominating in the contusion and pericontusional cortex. Strongest ICAM-1 expression coincided with sustained granulocyte accumulation at 72h which was suppressed by FK-506. Ox-6+ cells prevailing at 72 h were also significantly reduced by FK-506. ED-1+ cells reaching highest intensity at 7 days were significantly attenuated at 72 h. Cortical CV was not influenced. FK-506 significantly decreased post-traumatic local inflammation which, however, was not associated with a reduction in cortical CV. These results question the importance of post-traumatic local immune cell infiltration in the secondary growth of a cortical contusion.

Small volume resuscitation with HyperHaes improves pericontusional perfusion and reduces lesion volume following controlled cortical impact injury in rats

The hyperosmolar and hyperoncotic properties of HyperHaes (HHES) might improve impaired posttraumatic cerebral perfusion. Possible beneficial effects on pericontusional perfusion, brain edema, and contusion volume were investigated in rats subjected to controlled cortical impact (CCI). Male Sprague-Dawley rats (n = 60) anesthetized with isoflurane were subjected to a left temporoparietal CCI. Thereafter, rats were randomized to receive HHES (10% hydroxyethylstarch, 7.5% NaCl) or physiological saline solution (4 mL/kg body weight) intravenously. Mean arterial blood pressure (MABP) and intracranial pressure (ICP) were determined before and following CCI, after drug administration and 24 h later. Regional pericontusional cortical perfusion was determined by scanning laser Doppler flowmetry before CCI, and 30 min, 4 and 24 h after injury. At 24 h brain swelling and water content were measured gravimetrically. At 7 days, cortical contusion volume was determined planimetrically. MABP was not influenced by HHES. ICP was significantly decreased immediately after HHES infusion (5.7 +/- 0.4 vs. 7.1 +/- 1.0 mm Hg; p < 0.05). Pericontusional cortical perfusion was significantly decreased by 44% compared to pre-injury levels (p < 0.05). HHES significantly improved cortical perfusion at 4 h after CCI, approaching baseline values (85 +/- 12%). While increased posttraumatic brain edema was not reduced by HHES at 24 h, cortical contusion volume was significantly decreased in the HHES-treated rats at 7 days after CCI (23.4 +/- 3.5 vs. 39.6 +/- 6.2 mm3; p < 0.05). Intravaneous administration of HHES within 15 min after CCI has a neuroprotective potential, as it significantly attenuated impaired pericontusional perfusion and markedly reduced the extent of induced structural damage.

Responses of posttraumatic pericontusional cerebral blood flow and blood volume to an increase in cerebral perfusion pressure

In and around traumatic contusions, cerebral blood flow (CBF) is often near or below the threshold for ischemia. Increasing cerebral perfusion pressure (CPP) in patients with head injuries may improve CBF in these regions. However, the pericontusional response to this intervention has not been studied. Using positron emission tomography (PET), we have quantified the response to an increase in CPP in and around contusions in 18 contusions in 18 patients. Regional CBF and cerebral blood volume (CBV) were measured with PET at CPPs of 70 and 90 mmHg using norepinephrine to control CPP. Based upon computed tomography, regions of interest (ROIs) were placed as two concentric ellipsoids, each of 1-cm width, around the core of the contusions. Measurements were compared with a control ROI in tissue with normal anatomic appearance. Baseline CBF and CBV increased significantly with increasing distance from the core of the lesion. The increase in CPP led to small increases in CBF in all ROIs except the core. The largest absolute CBF increase was found in the control ROI. Relative CBF increases did not differ between ROIs so that ischemic areas remained ischemic. Pericontusional oedema on computed tomography was associated with lower absolute values of CBF and CBV but did not differ from nonoedematous tissue in the relative response to CPP elevation.

Traumatic Cerebral Vascular Injury: The Effects of Concussive Brain Injury on the Cerebral Vasculature

In terms of human suffering, medical expenses, and lost productivity, head injury is one of the major health care problems in the United States, and inadequate cerebral blood flow is an important contributor to mortality and morbidity after traumatic brain injury. Despite the importance of cerebral vascular dysfunction in the pathophysiology of traumatic brain injury, the effects of trauma on the cerebral circulation have been less well studied than the effects of trauma on the brain. Recent research has led to a better understanding of the physiologic, cellular, and molecular components and causes of traumatic cerebral vascular injury. A more thorough understanding of the direct and indirect effects of trauma on the cerebral vasculature will lead to improvements in current treatments of brain trauma as well as to the development of novel and, hopefully, more effective therapeutic strategies.

Segmental vascular resistance after mild controlled cortical impact injury in the rat

In an effort to localize the site at which increased resistance occurs after brain trauma, pial arteriole diameter and pressure were assessed after mild controlled cortical impact (CCI) injury in rats using an open cranial window technique. The authors tested the hypothesis that an increase in resistance accompanied by vasoconstriction occurs at the level of the pial arterioles within the injured cortex of the brain. At 1 hour after mild CCI injury, ipsilateral cerebral blood flow was significantly reduced by 42% compared with sham injury (n = 4; < 0.05). Pial arteriole diameter and pressure remained unchanged. Resistance in the larger arteries (proximal resistance), however, was significantly greater after CCI injury (1.87 +/- 0.26 mm Hg/[mL. 100 g. min]) compared with sham injury (0.91 +/- 0.21 mm Hg/[mL. 100 g. min]; < 0.0001). Resistance in small vessels, arterioles, and venules (distal resistance) was also significantly greater after CCI injury (1.13 +/- 0.05 mm Hg/[mL. 100 g. min]) compared with sham injury (0.74 +/- 0.13 mm Hg/[mL. 100 g. min]; = 0.0001). The authors conclude that, at 1 hour after mild CCI injury, changes in vascular resistance comprise a 53% increase in the resistance distal to the area of injury and, surprisingly, a 105% increase in resistance in the arteries proximal to the injury site.

Cortical hypoperfusion precedes hyperperfusion following controlled cortical impact injury

Impaired cerebral perfusion contributes to tissue damage following traumatic brain injury. In this longitudinal study persistence of reduced cortical perfusion employing laser doppler flowmetry was investigated following controlled cortical impact injury (CCII). Before, 30 minutes, 6, 24, and 48 hours after CCII, perfusion in pericontusional cortex was determined by moving a laser doppler probe in 50 x 0.2 mm steps over the traumatized hemisphere in 5 rats. Arterial blood gases and mean arterial blood pressure were monitored. Mean arterial blood pressure and arterial blood gases remained stable during the entire experiments. At 30 minutes and 6 hours following CCII, cortical perfusion was significantly diminished by 24% and 43% (p < 0.05), respectively compared to pre-trauma levels. At 24 and 48 hours after CCII, pericontusional blood flow was significantly increased by 64% and 123%. Cortical hypoperfusion found within the early phase following trauma is reversible and precedes a long lasting phase of hyperperfusion. Changes in tissue mediators (endothelin, acidosis, NO) could account for these findings.

Effect of posttraumatic hyperglycemia on contusion volume and neutrophil accumulation after moderate fluid-percussion brain injury in rats

The purpose of this study was to evaluate the effects of posttraumatic hyperglycemia on contusion volume and neutrophil accumulation following moderate traumatic brain injury (TBI) in rats. A parasagittal fluid-percussion (F-P) brain injury (1.8-2.1 atm) was induced in male Sprague-Dawley rats. Rats were then randomized into four trauma groups (n = 7/group) by the timing of dextrose injection (2.0 gm/kg/ip), which included (1) early (E) group: 5 min after TBI; (2) delayed (D) group: 4 h after TBI; (3) 24-h group: 24 h after TBI; or (4) control (C) group: no dextrose injection. A sham operated control group also received dextrose to document physiological parameters (n = 4). Rats were perfusion fixed 3 days following TBI, and the brains were processed for routine histopathological and immunocytochemical analysis. Contusion areas and volumes, as well as the frequency of myeloperoxidase immunoreactive polymorphonuclear leukocytes (PMNLs) were determined. Dextrose injections significantly increased blood glucose levels (p < 0.005) in all treated groups. Although acute hyperglycemia following TBI did not significantly affect total contusion volume, contusion area was significantly elevated in the early treatment group. In addition, early posttraumatic hyperglycemia enhanced neutrophil accumulation in the area of the cortical contusion (p < 0.005). In contrast, delayed induced hyperglycemia (i.e., 4 h, 24 h) did not significantly affect histopathological outcome or neutrophil accumulation. Taken together, these findings indicate that acute but not delayed hyperglycemia aggravates histopathological outcome and increased accumulation of PMNLs. Posttraumatic hyperglycemia in the acute phase may worsen traumatic outcome by enhancing secondary injury processes, including inflammation.

Temporal profile of cortical perfusion and microcirculation after controlled cortical impact injury in rats

Impaired cerebral perfusion contributes to evolving posttraumatic tissue damage. Spontaneous reversibility of reduced perfusion within the first days after injury could make a persisting impact on secondary tissue damage less likely and needs to be considered for possible therapeutic approaches. The present study was designed to characterize the temporal profile and impact of trauma severity on cortical perfusion and microcirculation during the first 48 h after controlled cortical impact injury (CCI). In 10 rats, pericontusional cortical perfusion and microcirculation using laser Doppler flowmetry (LDF) and orthogonal polarization spectral (OPS) imaging were assessed before, and at 4, 24, and 48 h after CCI. Influence of trauma severity was studied by varying the penetration depth of the impactor rod (0.5 vs. 1 mm), thereby inducing a less and a more severe contusion. Mean arterial blood pressure (MABP), arterial blood gases, and blood glucose were monitored. With unchanged MABP and paCO2, cortical perfusion and microcirculation were significantly impaired during the first 48 h following CCI. Hypoperfusion observed at 4 h related to vasoconstriction and microcirculatory stasis preceded a long-lasting phase of hyperperfusion at 24 and 48 h reflected by vasodilation and increased flow velocity in arterioles and venules. Hyperperfusion was mostly pronounced in rats with a less severe contusion. Following CCI, trauma severity markedly influences changes in pericontusional cortical perfusion and microcirculation. Overall, pericontusional cortical hypoperfusion observed within the early phase preceded a long lasting phase of hyperperfusion up to 48 h after CCI.

Platelet adhesion and arteriolar dilation in the photothrombosis: observation with the rat closed cranial and spinal windows

The mechanism of cerebral infarction, in which thrombus formation and platelet-endothelium interaction play an important part, have not yet been clearly elucidated in vivo. The aim of this study was to observe rolling and adherent platelets and to analyze adherent leukocytes and vessel diameter change in vivo using a photothrombotic vessel occlusion model.A photothrombosis, which is mediated by free radicals, was induced in male Wistar rats in the presence of a photosensitizing dye (Photofrin II) and exposure to a filtered light. Rhodamine 6G-labeled platelets and leukocytes were visualized with intravital fluorescence videomicroscopy through a closed cranial or spinal window. The vessel diameter, photothrombosis and leukocyte adhesion were analyzed. Rolling and adherent platelets were observed during irradiation through the cerebral and spinal window. Before the platelets were recognized, the irradiated arteriole dilated significantly. After the photochemical occlusion of an arteriole, other arterioles also dilated and the adherent leukocytes increased in the venules. The photothrombosis were almost completely composed of platelets according to electron microscopic analysis. The arteriolar dilation rate and the number of adherent leukocytes in the cerebrum were greater than those in the spinal cord. By combining the photochemical thrombus formation and the fluorescence microscope techniques, we were able for the first time to observe rolling and adherent platelets and microvascular responses during photothrombosis in the cerebral and spinal microvasculature. It is suggested that free radicals, which can lead to platelet aggregation, play an important role as a cerebral vasodilator. This model is useful for cerebral and spinal microcirculatory analysis to investigate the platelet-endothelium interaction, the platelet aggregation and the effect of free radicals on cerebral and spinal microcirculation.

Effects of the nitrone radical scavengers PBN and S-PBN on in vivo trapping of reactive oxygen species after traumatic brain injury in rats

In previous studies, the authors showed that the nitrone radical scavenger alpha-phenyl-N- tert -butyl nitrone (PBN) and its sulfo-derivative, 2-sulfo-phenyl-N- tert -butyl nitrone (S-PBN), attenuated cognitive disturbance and reduced tissue damage after traumatic brain injury (TBI) in rats. In the current study, the production of reactive oxygen species (ROS) after TBI was monitored with microdialysis and the 4-hydroxybenzoic acid (4-HBA) trapping method. A single dose of PBN (30 mg/kg) or an equimolar dose of S-PBN (47 mg/kg) was administered intravenously 30 minutes before a controlled cortical contusion injury in rats. Plasma and brain tissue drug concentrations were analyzed at the end of the microdialysis experiment (3 hours after injury) and, in a separate experiment with S-PBN, at 30 and 60 minutes after injury. Traumatic brain injury caused a significant increase in ROS formation that lasted for 60 minutes after the injury as evidenced by increased 3,4-dihydroxybenzoic acid (3,4-DHBA) concentrations in the dialysate. PBN and S-PBN equally and significantly attenuated the posttraumatic increase in 3,4-DHBA formation. High PBN concentrations were found bilaterally in brain tissue up to 3 hours after injury. In contrast, S-PBN was rapidly cleared from the circulation and was not detectable in brain at 30 minutes after injury or at any later time point. The results suggest that scavenging of ROS after TBI may contribute to the neuroprotective properties observed with nitrone spin-trapping agents. S-PBN, which remained undetectable even in traumatized brain tissue, reduced ROS production to the same extent as PBN that readily crossed the blood-brain barrier. This finding supports an important role for ROS production at the blood-endothelial interface in TBI.

Visualization of rat pial microcirculation using the novel orthogonal polarized spectral (OPS) imaging after brain injury

Recently, the novel optical system, orthogonal polarized spectral (OPS) imaging was developed to visualize microcirculation. Investigation of changes in microcirculation is essential for physiological, pathophysiological, and pharmacological studies. In the present study applicability of OPS imaging was assessed to study pial microcirculation in normal and traumatized rat brain. High quality images of rat pial microcirculation in normal and traumatized rats were generated with the OPS imaging, allowing to easily differentiate arterioles and venules with the dura remaining intact. In non-traumatized rats, mean vessel diameter of arterioles and venules of five different cortical regions was 19.1+/-2.7 and 22.2+/-1.4 microm, respectively. In the early phase following focal cortical contusion vessel diameter was significantly decreased in arterioles by 28% while diameter in venules was significantly increased by 27%. For technical reasons velocity in arterioles was not measurable. In venules, mean flow velocity of 0.68+/-0.08 mm/s was significantly decreased by 50% at 30 min after trauma. OPS imaging is an easy to use optical system allowing to generate high quality images and to reliably investigate pial microcirculation without having to remove the dura. This technique opens the possibility to perform longitudinal studies investigating changes in pial microcirculation.

Cerebral blood flow velocity and inflammatory response after severe traumatic brain injury

OBJECTIVES

The cerebral blood flow velocity (CBVF) was measured by transcranial Doppler sonography in patients with severe traumatic brain injury (TBI) in order to determine, whether it depends on the posttraumatic inflammatory response.

MATERIAL AND METHODS

CBVF in both middle cerebral arteries (MCA) was recorded in 25 comatous TBI patients (male 20; female five; mean age +/- standard deviation (S.D.), 41 +/- 20 years) and correlated to the levels of interleukine-(IL) 6, IL-8 and IL-10 in corresponding CSF/plasma samples, to PaCO2 and to intracranial (ICP), mean arterial (MAP) and cranial perfusion pressure (CPP).

RESULTS

CSF IL-6 and IL-8 were clearly higher than the corresponding plasma levels (mean CSF/plasma quotient for IL-6: 159 +/- 582; for IL-8: 143 +/- 311). CBVF did not show large side-to-side differences at each examination indicating that CBFV in both MCAs was determined mostly by systemic conditions and not by severe regional abnormalities. Since all other evaluated variables including interleukines represent also systemic conditions we used the mean value (MCBFV) of both CBFVs for analysis. By stepwise regression analysis between MCBVF (mean +/- S.D., 80 +/- 26 cm/s) and the variables PaCO2 (33 +/- 4 mmHg), MAP (86 +/- 12 mmHg), ICP (20 +/- 11 mmHg), CPP (70 +/- 14 mmHg) and CSF or plasma IL-6, IL-8 and IL-10, it turned out that MCBFV correlated significantly with PaCO2 (r = 0.478; P < 0.01) and CSF IL-8 (r = -0.361; P < 0.05).

CONCLUSIONS

When CPP is adequate for brain perfusion, CBFV in large brain supplying arteries depends predominantly on PaCO2 and shows only a slight association to intrathecal IL-8 levels. For clinical interpretation of CBFV data, the inflammatory response seems to be of minor relevance.

Importance of posttraumatic hypothermia and hyperthermia on the inflammatory response after fluid percussion brain injury: biochemical and immunocytochemical studies

The purpose of this study was to investigate: 1) the temporal and regional profile of polymorphonuclear leukocyte (PMNL) infiltration after moderate traumatic brain injury using the parasagittal fluid percussion model and 2) the effects of posttraumatic hypothermia (30 degrees C) and hyperthermia (39 degrees C) on the acute and subacute inflammatory response. We hypothesized that posttraumatic hypothermia would reduce the degree of PMNL accumulation whereas hyperthermia would exacerbate this response to injury. In the first series of experiments we quantitated the temporal profile of altered myeloperoxidase activity under normothermic (37 degrees C) conditions (n = 20). The rats were allowed to survive for 3 hours, 24 hours, 3 days, or 7 days after trauma, and brains were dissected into cortical and subcortical regions ipsilateral and contralateral to injury. Additional animals were perfused and fixed for the immunocytochemical visualization of myeloperoxidase (n = 15). In the second series of experiments, rats (n = 25) were killed 3 hours or 3 days after the 3-hour monitoring period of normothermia (36.5 degrees C), hypothermia (30 degrees C), or hyperthermia (39 degrees C) (n = 4 to 5 per group), and myeloperoxidase activity was again quantitated. In normothermic rats, the enzymatic activity of myeloperoxidase was significantly increased (P < 0.05) at 3 hours within the anterior cortical segment (213.97 +/- 56.2 versus control 65.5 +/- 52.3 U/g of wet tissue; mean +/- SD) and posterior (injured) cortical and subcortical segments compared to sham-operated rats (305.76 +/- 27.8 and 258.67 +/- 101.4 U/g of wet tissue versus control 62.8 +/- 24.8 and 37.28 +/- 35.6 U/g of wet tissue; P < 0.0001, P < 0.05, respectively). At 24 hours and 7-days after trauma only the posterior cortical region (P < 0.005, P < 0.05, respectively) exhibited increased myeloperoxidase activity. However, 3 days after trauma, myeloperoxidase activity was also significantly increased within the anterior cortical segment (P < 0.05) and in posterior cortical and subcortical regions compared to sham-operated cortex (P < 0.0001, P < 0.05, respectively). Immunocytochemical analysis of myeloperoxidase reactivity at 3 hours, 24 hours, 3- and 7-days demonstrated large numbers of immunoreactive leukocytes within and associated with blood vessels, damaged tissues, and subarachnoid spaces. Posttraumatic hypothermia and hyperthermia had significant effects on myeloperoxidase activity at both 3 hours and 3 days after traumatic brain injury. Posttraumatic hypothermia reduced myeloperoxidase activity in the injured and noninjured cortical and subcortical segments compared to normothermic values (P < 0.05). In contrast, posttraumatic hyperthermia significantly elevated myeloperoxidase activity in the posterior cortical region compared to normothermic values at both 3 hours and 3 days (473.5 +/- 258.4 and 100.11 +/- 27.58 U/g of wet tissue, respectively, P < 0.05 versus controls). These results indicate that posttraumatic hypothermia decreases early and more prolonged myeloperoxidase activation whereas hyperthermia increases myeloperoxidase activity. Temperature-dependent alterations in PMNL accumulation appear to be a potential mechanism by which posttraumatic temperature manipulations may influence traumatic outcome.

Effects of moderate hypothermia on leukocyte- endothelium interaction in the rat pial microvasculature after transient middle cerebral artery occlusion

Background and Purpose--It has been demonstrated that moderate hypothermia attenuates brain damage, but the mechanism whereby this is achieved has not been clearly shown. Recently, the role of leukocytes as mediators of secondary brain damage after brain ischemia has been discussed. The aim of this study is to examine the effects of moderate hypothermia on leukocyte-endothelium interaction in the rat pial microvasculature after transient middle cerebral artery occlusion (MCAO). Methods--Rhodamine 6G-labeled leukocytes in brain surface were visualized with intravital fluorescence videomicroscopy through a closed cranial window. We analyzed the number of leukocytes adhering to the venular and arteriolar endothelium before ischemic insult and up to 3 hours after reperfusion. Rats were divided into 4 experimental groups. Group I (n=6) consisted of sham-operated animals. Groups II (n=6) and III (n=6) received left MCAO for 1 hour under normothermia (36 degrees C to 37 degrees C, group II) and under moderate hypothermia (30 degrees C to 32 degrees C, group III). Group IV (n=4) received left common carotid artery occlusion for 1 hour under normothermia. Results--The number of adhering leukocytes in venules in groups II and IV increased significantly (P<0.001) after reperfusion compared with the group I, but that in group III did not increase significantly (P>0.05). The number of adhering leukocytes in arterioles in group II increased significantly (P<0.01) compared with the other groups, although the adhering leukocytes were not as numerous as those seen in venules. Conclusions--It is demonstrated that hypothermia attenuates adhering leukocytes in venules and arterioles after reperfusion of MCAO. The inhibition of the leukocyte function may be an important factor in the neuroprotective effect of hypothermia.