Effect of Decompression Craniotomy on Increase of Contusion Volume and Functional Outcome after Controlled Cortical Impact in Mice

Bradykinin 2 Receptors Mediate Long-Term Neurocognitive Deficits After Experimental Traumatic Brain Injury

The kallikrein-kinin system is one of the first inflammatory pathways to be activated following traumatic brain injury (TBI) and has been shown to exacerbate brain edema formation in the acute phase through activation of bradykinin 2 receptors (B2R). However, the influence of B2R on chronic post-traumatic damage and outcome is unclear. In the current study, we assessed long-term effects of B2R-knockout (KO) after experimental TBI. B2R KO mice (heterozygous, homozygous) and wild-type (WT) littermates (n = 10/group) were subjected to controlled cortical impact (CCI) TBI. Lesion size was evaluated by magnetic resonance imaging up to 90 days after CCI. Motor and memory function were regularly assessed by Neurological Severity Score, Beam Walk, and Barnes maze test. Ninety days after TBI, brains were harvested for immunohistochemical analysis. There was no difference in cortical lesion size between B2R-deficient and WT animals 3 months after injury; however, hippocampal damage was reduced in B2R KO mice (p = 0.03). Protection of hippocampal tissue was accompanied by a significant improvement of learning and memory function 3 months after TBI (p = 0.02 WT vs. KO), whereas motor function was not influenced. Scar formation and astrogliosis were unaffected, but B2R deficiency led to a gene-dose-dependent attenuation of microglial activation and a reduction of CD45+ cells 3 months after TBI in cortex (p = 0.0003) and hippocampus (p < 0.0001). These results suggest that chronic hippocampal neurodegeneration and subsequent cognitive impairment are mediated by prolonged neuroinflammation and B2R. Inhibition of B2R may therefore represent a novel strategy to reduce long-term neurocognitive deficits after TBI.

Characterization of Vasogenic and Cytotoxic Brain Edema Formation After Experimental Traumatic Brain Injury by Free Water Diffusion Magnetic Resonance Imaging

Brain edema formation is a key factor for secondary tissue damage after traumatic brain injury (TBI), however, the type of brain edema and the temporal profile of edema formation are still unclear. We performed free water imaging, a bi-tensor model based diffusion MRI analysis, to characterize vasogenic brain edema (VBE) and cytotoxic edema (CBE) formation up to 7 days after experimental TBI. Male C57/Bl6 mice were subjected to controlled cortical impact (CCI) or sham surgery and investigated by MRI 4h, 1, 2, 3, 5, and 7 days thereafter (n = 8/group). We determined mean diffusivity (MD) and free water (FW) in contusion, pericontusional area, ipsi- and contralateral brain tissue. Free (i.e., non-restricted) water was interpreted as VBE, restricted water as CBE. To verify the results, VBE formation was investigated by in-vivo 2-Photon Microscopy (2-PM) 48h after surgery. We found that MD and FW values decreased for 48h within the contusion, indicating the occurrence of CBE. In pericontusional tissue, MD and FW indices were increased at all time points, suggesting the formation of VBE. This was consistent with our results obtained by 2-PM. Taken together, CBE formation occurs for 48h after trauma and is restricted to the contusion, while VBE forms in pericontusional tissue up to 7 days after TBI. Our results indicate that free water magnetic resonance imaging may represent a promising tool to investigate vasogenic and cytotoxic brain edema in the laboratory and in patients.

Prolonged course of brain edema and neurological recovery in a translational model of decompressive craniectomy after closed head injury in mice

Background

The use of decompressive craniectomy in traumatic brain injury (TBI) remains a matter of debate. According to the DECRA trial, craniectomy may have a negative impact on functional outcome, while the RescueICP trial revealed a positive effect of surgical decompression, which is evolving over time. This ambivalence of craniectomy has not been studied extensively in controlled laboratory experiments.

Objective

The goal of the current study was to investigate the prolonged effects of decompressive craniectomy (both positive and negative) in an animal model.

Methods

Male mice were assigned to the following groups: sham, decompressive craniectomy, TBI and TBI followed by craniectomy. The analysis of functional outcome was performed at time points 3d, 7d, 14d and 28d post trauma according to the Neurological Severity Score and Beam Balance Score. At the same time points, magnetic resonance imaging was performed, and brain edema was analyzed.

Results

Animals subjected to both trauma and craniectomy presented the exacerbation of the neurological impairment that was apparent mostly in the early course (up to 7d) after injury. Decompressive craniectomy also caused a significant increase in brain edema volume (initially cytotoxic with a secondary shift to vasogenic edema and gliosis). Notably, delayed edema plus gliosis appeared also after decompression even without preceding trauma.

Conclusion

In prolonged outcomes, craniectomy applied after closed head injury in mice aggravates posttraumatic brain edema, leading to additional functional impairment. This effect is, however, transient. Treatment options that reduce brain swelling after decompression may accelerate neurological recovery and should be explored in future experiments.

The Single-Dose Application of Interleukin-4 Ameliorates Secondary Brain Damage in the Early Phase after Moderate Experimental Traumatic Brain Injury in Mice

Activation of the interleukin-4 (IL-4) pathway ameliorates secondary injury mechanisms after experimental traumatic brain injury (TBI); therefore, we assessed the effect of a therapeutic IL-4 administration on secondary brain damage after experimental TBI. We subjected 100 C57/Bl6 wildtype mice to controlled cortical impact (CCI) and administered IL-4 or a placebo control subcutaneously 15 min thereafter. Contusion volume (Nissl staining), neurological function (hole board, video open field, and CatWalkXT®), and the immune response (immunofluorescent staining) were analyzed up to 28 days post injury (dpi). Contusion volumes were significantly reduced after IL-4 treatment up to 14 dpi (e.g., 6.47 ± 0.41 mm3 vs. 3.80 ± 0.85 mm3, p = 0.011 3 dpi). Macrophage invasion and microglial response were significantly attenuated in the IL-4 group in the acute phase after CCI (e.g., 1.79 ± 0.15 Iba-1+/CD86+ cells/sROI vs. 1.06 ± 0.21 Iba-1/CD86+ cells/sROI, p = 0.030 in the penumbra 3 dpi), whereas we observed an increased neuroinflammation thereafter (e.g., mean GFAP intensity of 3296.04 ± 354.21 U vs. 6408.65 ± 999.54 U, p = 0.026 in the ipsilateral hippocampus 7 dpi). In terms of functional outcome, several gait parameters were improved in the acute phase following IL-4 treatment (e.g., a difference in max intensity of -7.58 ± 2.00 U vs. -2.71 ± 2.44 U, p = 0.041 3 dpi). In conclusion, the early single-dose administration of IL-4 significantly reduces secondary brain damage in the acute phase after experimental TBI in mice, which seems to be mediated by attenuation of macrophage and microglial invasion.

Evaluation of decompressive craniectomy in mice after severe traumatic brain injury

Decompressive craniectomy (DC) is of great significance for relieving acute intracranial hypertension and saving lives after traumatic brain injury (TBI). In this study, a severe TBI mouse model was created using controlled cortical impact (CCI), and a surgical model of DC was established. Furthermore, a series of neurological function assessments were performed to better understand the pathophysiological changes after DC. In this study, mice were randomly allocated into three groups, namely, CCI group, CCI+DC group, and Sham group. The mice in the CCI and CCI+DC groups received CCI after opening a bone window, and after brain injury, immediately returned the bone window to simulate skull condition after a TBI. The CCI+DC group underwent DC and contused tissue removal 6 h after CCI. The mice in the CCI group underwent the same anesthesia process; however, no further treatment of the bone window and trauma was performed. The mice in the Sham group underwent anesthesia and the process of opening the skin and bone window, but not in the CCI group. Changes in Modified Neurological Severity Score, rotarod performance, Morris water maze, intracranial pressure (ICP), cerebral blood flow (CBF), brain edema, blood–brain barrier (BBB), inflammatory factors, neuronal apoptosis, and glial cell expression were evaluated. Compared with the CCI group, the CCI+DC group had significantly lower ICP, superior neurological and motor function at 24 h after injury, and less severe BBB damage after injury. Most inflammatory cytokine expressions and the number of apoptotic cells in the brain tissue of mice in the CCI+DC group were lower than in the CCI group at 3 days after injury, with markedly reduced astrocyte and microglia expression. However, the degree of brain edema in the CCI+DC group was greater than in the CCI group, and neurological and motor functions, as well as spatial cognitive and learning ability, were significantly poorer at 14 days after injury.

Cerebral venous hemodynamic responses in a mouse model of traumatic brain injury

Traumatic brain injury (TBI) is a serious public health problem that endangers human health and is divided into primary and secondary injuries. Previous work has confirmed that changes in cerebral blood flow (CBF) are related to the progression of secondary injury, although clinical studies have shown that CBF monitoring cannot fully and accurately evaluate disease progression. These studies have almost ignored the monitoring of venous blood flow; however, as an outflow channel of the cerebral circulation, it warrants discussion. To explore the regulation of venous blood flow after TBI, the present study established TBI mouse models of different severities, observed changes in cerebral venous blood flow by laser speckle flow imaging, and recorded intracranial pressure (ICP) after brain injury to evaluate the correlation between venous blood flow and ICP. Behavioral and histopathological assessments were performed after the intervention. The results showed that there was a significant negative correlation between ICP and venous blood flow (r = -0.795, P < 0.01), and both recovered to varying degrees in the later stages of observation. The blood flow changes in regional microvessels were similar to those in venous, and the expression of angiogenesis proteins around the impact area was significantly increased. In conclusion, this study based on the TBI mouse model, recorded the changes in venous blood flow and ICP and revealed that venous blood flow can be used as an indicator of the progression of secondary brain injury.

Interleukin-4 reduces lesion volume and improves neurological function in the acute phase after experimental traumatic brain injury in mice

Little is known about the impact of Interleukin-4 (IL-4) on secondary brain damage in the acute phase after experimental traumatic brain injury (TBI). Therefore, we evaluated the effect of IL-4-Knockout on structural damage as well as functional impairment in the acute phase after experimental TBI in mice. 28 C57Bl/6 wildtype and 20 C57BL/6-Il4tm1Nnt/J Interleukin-4-Knockout (IL-4-KO) mice were subjected to Controlled Cortical Impact (CCI). Contusion volumes, body weight and functional outcome (Video Open Field Test (VOF), Hole Board Test (HB), CatWalkXT®) were determined on postoperative days one (D1), three (D3) and seven (D7). Contusion volume (13.45 +/- 0.88 mm³ vs. 9.50 +/- 0.97 mm³, p=0.015) and weight loss (-2.92 +/- 0.52% vs. -0.85 +/- 0.67%, p=0.027) were significantly higher and exploration behavior significantly more impaired (e.g., 150.44 +/- 18.71 fields explored vs. 211.56 +/- 18.90 fields explored, p=0.028 in the VOF; 23.31 +/- 2.03 holes explored vs. 35.65 +/- 1.93 holes explored, p<0.001 in the HB) in IL-4-KO mice on D1. Gait impairment was significantly more pronounced in IL-4-KO mice throughout the first week after CCI (e.g., 0.07 +/- 0.01s vs. 0.00 +/- 0.01s, p=0.047 for right hindpaw Swing on D1; -1.76 +/- 1.34 U vs. 2.53 +/- 0.90 U, p=0.01 for right forepaw Mean Intensity on D3; -0.01 +/- 0.01cm² vs. 0.05 +/- 0.01cm², p=0.015 for left forepaw Mean Area on D7). In conclusion, IL-4 reduces structural damage and improves functional outcome in the acute phase after CCI. Neurobehavioral outcome assessment in IL-4-related studies should focus on motor function on the first three days after trauma induction.

Focal lesion size poorly correlates with motor function after experimental traumatic brain injury in mice

Background

It remains unclear whether neurobehavioral testing adds significant information to histologic assessment of experimental traumatic brain injury (TBI) and if automated gait assessment using the CatWalk XT^®, while shown to be effective in in the acute phase, is also effective in the chronic phase after experimental TBI. Therefore, we evaluated the correlation of CatWalk XT^® parameters with histologic lesion volume and analyzed their temporal and spatial patterns over four weeks after trauma induction.

Methods

C57Bl/6 mice were subjected to controlled cortical impact (CCI). CatWalk XT^® analysis was performed one day prior to surgery and together with the histological evaluation of lesion volume on postoperative days one, three, seven, 14 and 28. Temporal and spatial profiles of gait impairment were analyzed and a total of 100 CatWalk XT^® parameters were correlated to lesion size.

Results

While in the first week after CCI, there was significant impairment of nearly all CatWalk XT^® parameters, impairment of paw prints, intensities and dynamic movement parameters resolved thereafter; however, impairment of dynamic single paw parameters persisted up to four weeks. Correlation of the CatWalk XT^® parameters with lesion volume was poor at all timepoints.

Conclusion

As CatWalk XT^® parameters do not correlate with focal lesion size after CCI, gait assessment using the CatWalk XT^® might add valuable information to solitary histologic evaluation of the injury site. While all CatWalk XT^® parameters can be used for gait assessments in the first week after CCI, dynamic single paw parameters might be more relevant in the chronic phase after experimental TBI.

Mutated neuronal voltage-gated CaV2.1 channels causing familial hemiplegic migraine 1 increase the susceptibility for cortical spreading depolarization and seizures and worsen outcome after experimental traumatic brain injury

Patients suffering from familial hemiplegic migraine type 1 (FHM1) may have a disproportionally severe outcome after head trauma, but the underlying mechanisms are unclear. Hence, we subjected knock-in mice carrying the severer S218L or milder R192Q FHM1 gain-of-function missense mutation in the CACNA1A gene that encodes the α_1A subunit of neuronal voltage-gated Ca_V2.1 (P/Q-type) calcium channels and their wild-type (WT) littermates to experimental traumatic brain injury (TBI) by controlled cortical impact and investigated cortical spreading depolarizations (CSDs), lesion volume, brain edema formation, and functional outcome. After TBI, all mutant mice displayed considerably more CSDs and seizures than WT mice, while S218L mutant mice had a substantially higher mortality. Brain edema formation and the resulting increase in intracranial pressure were more pronounced in mutant mice, while only S218L mutant mice had larger lesion volumes and worse functional outcome. Here, we show that gain of Ca_V2.1 channel function worsens histopathological and functional outcome after TBI in mice. This phenotype was associated with a higher number of CSDs, increased seizure activity, and more pronounced brain edema formation. Hence, our results suggest increased susceptibility for CSDs and seizures as potential mechanisms for bad outcome after TBI in FHM1 mutation carriers.

RIPK1 or RIPK3 deletion prevents progressive neuronal cell death and improves memory function after traumatic brain injury

Traumatic brain injury (TBI) causes acute and subacute tissue damage, but is also associated with chronic inflammation and progressive loss of brain tissue months and years after the initial event. The trigger and the subsequent molecular mechanisms causing chronic brain injury after TBI are not well understood. The aim of the current study was therefore to investigate the hypothesis that necroptosis, a form a programmed cell death mediated by the interaction of Receptor Interacting Protein Kinases (RIPK) 1 and 3, is involved in this process. Neuron-specific RIPK1- or RIPK3-deficient mice and their wild-type littermates were subjected to experimental TBI by controlled cortical impact. Posttraumatic brain damage and functional outcome were assessed longitudinally by repetitive magnetic resonance imaging (MRI) and behavioral tests (beam walk, Barnes maze, and tail suspension), respectively, for up to three months after injury. Thereafter, brains were investigated by immunohistochemistry for the necroptotic marker phosphorylated mixed lineage kinase like protein(pMLKL) and activation of astrocytes and microglia. WT mice showed progressive chronic brain damage in cortex and hippocampus and increased levels of pMLKL after TBI. Chronic brain damage occurred almost exclusively in areas with iron deposits and was significantly reduced in RIPK1- or RIPK3-deficient mice by up to 80%. Neuroprotection was accompanied by a reduction of astrocyte and microglia activation and improved memory function. The data of the current study suggest that progressive chronic brain damage and cognitive decline after TBI depend on the expression of RIPK1/3 in neurons. Hence, inhibition of necroptosis signaling may represent a novel therapeutic target for the prevention of chronic post-traumatic brain damage.

Acid-Ion Sensing Channel 1a Deletion Reduces Chronic Brain Damage and Neurological Deficits after Experimental Traumatic Brain Injury

Traumatic brain injury (TBI) causes long-lasting neurodegeneration and cognitive impairments; however, the underlying mechanisms of these processes are not fully understood. Acid-sensing ion channels 1a (ASIC1a) are voltage-gated Na⁺- and Ca²⁺-channels shown to be involved in neuronal cell death; however, their role for chronic post-traumatic brain damage is largely unknown. To address this issue, we used ASIC1a-deficient mice and investigated their outcome up to 6 months after TBI. ASIC1a-deficient mice and their wild-type (WT) littermates were subjected to controlled cortical impact (CCI) or sham surgery. Brain water content was analyzed 24 h and behavioral outcome up to 6 months after CCI. Lesion volume was assessed longitudinally by magnetic resonance imaging and 6 months after injury by histology. Brain water content was significantly reduced in ASIC1a^-/- animals compared to WT controls. Over time, ASIC1a^-/- mice showed significantly reduced lesion volume and reduced hippocampal damage. This translated into improved cognitive function and reduced depression-like behavior. Microglial activation was significantly reduced in ASIC1a^-/- mice. In conclusion, ASIC1a deficiency resulted in reduced edema formation acutely after TBI and less brain damage, functional impairments, and neuroinflammation up to 6 months after injury. Hence, ASIC1a seems to be involved in chronic neurodegeneration after TBI.

Influence of Organic Solvents on Secondary Brain Damage after Experimental Traumatic Brain Injury

Many compounds tested for a possible neuroprotective effect after traumatic brain injury (TBI) are not readily soluble and therefore organic solvents need to be used as a vehicle. It is, however, unclear whether these organic solvents have intrinsic pharmacological effects on secondary brain damage and may therefore interfere with experimental results. Thus, the aim of the current study was to evaluate the effect of four widely used organic solvents, dimethylsulfoxide (DMSO), Miglyol 812 (Miglyol^®), polyethyleneglycol 40 (PEG 40), and N-2-methyl-pyrrolidone (NMP) on outcome after TBI in mice. A total of 143 male C57Bl/6 mice were subjected to controlled cortical impact (CCI). Contusion volume, brain edema formation, and neurological function were assessed 24 h after TBI. Test substances or saline were injected intraperitoneally (i.p.) 10 min before CCI. DMSO, Miglyol, and PEG 40 had no effect on post-traumatic contusion volume after CCI; NMP, however, significantly reduced contusion volume and brain edema formation at different concentrations. The use of DMSO, Miglyol, and PEG 40 is unproblematic for studies investigating neuroprotective treatment strategies as they do not influence post-traumatic brain damage. NMP seems to have an intrinsic neuroprotective effect that should be considered when using this agent in pharmacological experiments; further, a putative therapeutic effect of NMP needs to be elucidated in future studies.

Longitudinal Characterization of Blood-Brain Barrier Permeability after Experimental Traumatic Brain Injury by In Vivo 2-Photon Microscopy

Vasogenic brain edema (VBE) formation remains an important factor determining the fate of patients with traumatic brain injury (TBI). The spatial and temporal development of VBE, however, remains poorly understood because of the lack of sufficiently sensitive measurement techniques. To close this knowledge gap, we directly visualized the full time course of vascular leakage after TBI by in vivo 2-photon microscopy (2-PM). Male C57BL/6 mice (n = 6/group, 6-8 weeks old) were assigned randomly to sham operation or brain trauma by controlled cortical impact. A cranial window was prepared, and tetramethylrhodamine-dextran (TMRM, MW 40,000 Da) was injected intravenously to visualize blood plasma 4 h, 24 h, 48 h, 72 h, or seven days after surgery or trauma. Three regions with increasing distance to the primary contusion were investigated up to a depth of 300 μm by 2-PM. No TMRM extravasation was detected in sham-operated mice, while already 4 h after TBI vascular leakage was significantly increased (p < 0.05 vs. sham) and reached its maximum at 48 h after injury. Vascular leakage was most pronounced in the vicinity of the contusion. The rate of extravasation showed a biphasic pattern, peaking 4 h and 48-72 h after trauma. Taken together, longitudinal quantification of vascular leakage after TBI in vivo demonstrates that VBE formation after TBI develops in a biphasic manner suggestive of acute and delayed mechanisms. Further studies using the currently developed dynamic in vivo imaging modalities are needed to investigate these mechanisms and potential therapeutic strategies in more detail.

A Systematic Review and Meta-Analysis of Hypothermia in Experimental Traumatic Brain Injury: Why Have Promising Animal Studies Not Been Replicated in Pragmatic Clinical Trials?

Therapeutic hypothermia was a mainstay of severe traumatic brain injury (TBI) management for half a century. Recent trials have suggested that its effect on long-term functional outcome is neutral or negative, despite apparently promising pre-clinical data. Systematic review and meta-analysis is a useful tool to collate experimental data and investigate the basis of its conclusions. We searched three online databases to identify studies testing systemic hypothermia as monotherapy for treatment of animals subjected to a TBI. Data pertaining to TBI paradigm, animal subjects, and hypothermia management were extracted as well as those relating to risk of bias. We pooled outcome data where sufficient numbers allowed and investigated heterogeneity in neurobehavioral outcomes using multi-variate meta-regression. We identified 90 publications reporting 272 experiments testing hypothermia in animals subject to TBI. The subjects were mostly small animals, with well-established models predominating. Target temperature was comparable to clinical trial data but treatment was initiated very early. Study quality was low and there was some evidence of publication bias. Delay to treatment, comorbidity, and blinded outcome assessment appeared to predict neurobehavioral outcome on multi-variate meta-regression. Therapeutic hypothermia appears to be an efficacious treatment in experimental TBI, which differs from the clinical evidence. The pre-clinical literature showed limitations in quality and design and these both appeared to affect neurobehavioral experiment outcome. These should be acknowledged when designing and interpreting pre-clinical TBI studies in the future.

Vasopressin V1a Receptors Regulate Cerebral Aquaporin 1 after Traumatic Brain Injury

Brain edema formation contributes to secondary brain damage and unfavorable outcome after traumatic brain injury (TBI). Aquaporins (AQP), highly selective water channels, are involved in the formation of post-trauma brain edema; however, their regulation is largely unknown. Because vasopressin receptors are involved in AQP-mediated water transport in the kidney and inhibition of V1a receptors reduces post-trauma brain edema formation, we hypothesize that cerebral AQPs may be regulated by V1a receptors. Cerebral Aqp1 and Aqp4 messenger ribonucleic acid (mRNA) and AQP1 and AQP4 protein levels were quantified in wild-type and V1a receptor knockout (V1a-/-) mice before and 15 min, 1, 3, 6, 12, or 24 h after experimental TBI by controlled cortical impact. In non-traumatized mice, we found AQP1 and AQP4 expression in cortical neurons and astrocytes, respectively. Experimental TBI had no effect on Aqp4 mRNA or AQP4 protein expression, but increased Aqp1 mRNA (p < 0.05) and AQP1 protein expression (p < 0.05) in both hemispheres. The Aqp1 mRNA and AQP1 protein regulation was blunted in V1a receptor knockout mice. The V1a receptors regulate cerebral AQP1 expression after experimental TBI, thereby unraveling the molecular mechanism by which these receptors may mediate brain edema formation after TBI.

Intracranial Pressure Monitoring in Experimental Traumatic Brain Injury: Implications for Clinical Management

Traumatic brain injury (TBI) is often associated with long-term disability and chronic neurological sequelae. One common contributor to unfavorable outcomes is secondary brain injury, which is potentially treatable and preventable through appropriate management of patients in the neurosurgical intensive care unit. Intracranial pressure (ICP) is currently the predominant neurological-specific physiological parameter used to direct the care of severe TBI (sTBI) patients. However, recent clinical evidence has called into question the association of ICP monitoring with improved clinical outcome. The detailed cellular and molecular derangements associated with intracranial hypertension (IC-HTN) and their relationship to injury phenotype and neurological outcomes are not completely understood. Various animal models of TBI have been developed, but the clinical applicability of ICP monitoring in the pre-clinical setting has not been well-characterized. Linking basic mechanistic studies in translational TBI models with investigation of ICP monitoring that more faithfully replicates the clinical setting will provide clinical investigators with a more informed understanding of the pathophysiology of IC-HTN, thus facilitating development of improved therapies for sTBI patients.

Variability and uncertainty in the rodent controlled cortical impact model of traumatic brain injury

BACKGROUND

Controlled cortical impact (CCI) has emerged as one of the most flexible and clinically applicable approaches for the induction of traumatic brain injury (TBI) in rodents and other species. Although this approach has been shown to model cognitive and functional outcomes associated with TBI in humans, recent work has shown that CCI is limited by excessive variability in lesion size despite attempts to control velocity, impact depth, and dwell time.

NEW METHOD

Thus, this work used high-speed imaging to evaluate the delivery of cortical impact and permit the identification of specific parameters associated with technical variability in the CCI model.

RESULTS

Variability is introduced by vertical oscillations that result in multiple impacts of varying depths, lateral movements after impact, and changes in velocity, particularly at the prescribed impact depth.

CONCLUSIONS

Together these data can inform future work to design modifications to commonly used CCI devices that produce TBI with less variability in severity and lesion size.

Changes in Posttraumatic Brain Edema in Craniectomy-Selective Brain Hypothermia Model Are Associated With Modulation of Aquaporin-4 Level

Both hypothermia and decompressive craniectomy have been considered as a treatment for traumatic brain injury. In previous experiments we established a murine model of decompressive craniectomy and we presented attenuated edema formation due to focal brain cooling. Since edema development is regulated via function of water channel proteins, our hypothesis was that the effects of decompressive craniectomy and of hypothermia are associated with a change in aquaporin-4 (AQP4) concentration. Male CD-1 mice were assigned into following groups (n = 5): sham, decompressive craniectomy, trauma, trauma followed by decompressive craniectomy and trauma + decompressive craniectomy followed by focal hypothermia. After 24 h, magnetic resonance imaging with volumetric evaluation of edema and contusion were performed, followed by ELISA analysis of AQP4 concentration in brain homogenates. Additional histopathological analysis of AQP4 immunoreactivity has been performed at more remote time point of 28d. Correlation analysis revealed a relationship between AQP4 level and both volume of edema (r² = 0.45, p < 0.01, ^**) and contusion (r² = 0.41, p < 0.01, ^**) 24 h after injury. Aggregated analysis of AQP4 level (mean ± SEM) presented increased AQP4 concentration in animals subjected to trauma and decompressive craniectomy (52.1 ± 5.2 pg/mL, p = 0.01; ^*), but not to trauma, decompressive craniectomy and hypothermia (45.3 ± 3.6 pg/mL, p > 0.05; ns) as compared with animals subjected to decompressive craniectomy only (32.8 ± 2.4 pg/mL). However, semiquantitative histopathological analysis at remote time point revealed no significant difference in AQP4 immunoreactivity across the experimental groups. This suggests that AQP4 is involved in early stages of brain edema formation after surgical decompression. The protective effect of selective brain cooling may be related to change in AQP4 response after decompressive craniectomy. The therapeutic potential of this interaction should be further explored.

Reduction of Cerebral Edema via an Osmotic Transport Device Improves Functional Outcome after Traumatic Brain Injury in Mice

Traumatic brain injury (TBI), the foremost cause of morbidity and mortality in persons under 45 years of age worldwide, leads to about 200,000 victims requiring hospitalization and approximately 52,000 deaths per year in the United States. TBI is characterized by cerebral edema leading to raised intracranial pressure, brain herniation, and subsequent death. Current therapies for TBI treatment are often ineffective, thus novel therapies are needed. Recent studies have shown that an osmotic transport device (OTD) is capable of reducing brain water content and improving survival in mice with severe cerebral edema. Here we compare the effects of a craniectomy and an OTD plus craniectomy on neurological function in mice after TBI. Animals treated with a craniectomy plus an OTD had significantly better neurological function 2 days after TBI compared with those treated with craniectomy only. This study suggests that an OTD for severe brain swelling may improve patient functional outcome. Future studies include a more comprehensive neurological examination, including long-term memory tests.

Decreased Secondary Lesion Growth and Attenuated Immune Response after Traumatic Brain Injury in Tlr2/4-/- Mice

Danger-associated molecular patterns are released by damaged cells and trigger neuroinflammation through activation of non-specific pattern recognition receptors, e.g., toll-like receptors (TLRs). Since the role of TLR2 and 4 after traumatic brain injury (TBI) is still unclear, we examined the outcome and the expression of pro-inflammatory mediators after experimental TBI in Tlr2/4^−/− and wild-type (WT) mice. Tlr2/4^−/− and WT mice were subjected to controlled cortical injury and contusion volume and brain edema formation were assessed 24 h thereafter. Expression of inflammatory markers in brain tissue was measured by quantitative PCR 15 min, 3 h, 6 h, 12 h, and 24 h after controlled cortical impact (CCI). Contusion volume was significantly attenuated in Tlr2/4^−/− mice (29.7 ± 0.7 mm³ as compared to 33.5 ± 0.8 mm³ in WT; p < 0.05) after CCI while brain edema was not affected. Only interleukin (IL)-1β gene expression was increased after CCI in the Tlr2/4^−/− relative to WT mice. Inducible nitric oxide synthetase, TNF, IL-6, and COX-2 were similar in injured WT and Tlr2/4^−/− mice, while the increase in high-mobility group box 1 was attenuated at 6 h. TLR2 and 4 are consequently shown to potentially promote secondary brain injury after experimental CCI via neuroinflammation and may therefore represent a novel therapeutic target for the treatment of TBI.

Selective Brain Hypothermia Mitigates Brain Damage and Improves Neurological Outcome after Post-Traumatic Decompressive Craniectomy in Mice

Hypothermia and decompressive craniectomy (DC) have been considered as treatment for traumatic brain injury. The present study investigates whether selective brain hypothermia added to craniectomy could improve neurological outcome after brain trauma. Male CD-1 mice were assigned into the following groups: sham; DC; closed head injury (CHI); CHI followed by craniectomy (CHI+DC); and CHI+DC followed by focal hypothermia (CHI+DC+H). At 24 h post-trauma, animals were subjected to Neurological Severity Score (NSS) test and Beam Balance Score test. At the same time point, magnetic resonance imaging using a 9.4 Tesla scanner and subsequent volumetric evaluation of edema and contusion were performed. Thereafter, the animals were sacrificed and subjected to histopathological analysis. According to NSS, there was a significant impairment among all the groups subjected to trauma. Animals with both trauma and craniectomy performed significantly worse than animals with craniectomy alone. This deleterious effect disappeared when additional hypothermia was applied. BBS was significantly worse in the CHI and CHI+DC groups, but not in the CHI+DC+H group, compared to the sham animals. Edema and contusion volumes were significantly increased in CHI+DC animals, but not in the CHI+DC+H group, compared to the DC group. Histopathological analysis showed that neuronal loss and contusional blossoming could be attenuated by application of selective brain hypothermia. Selective brain cooling applied post-trauma and craniectomy improved neurological function and reduced structural damage and may be therefore an alternative to complication-burdened systemic hypothermia. Clinical studies are recommended in order to explore the potential of this treatment.

Effects of early surgical decompression on functional and histological outcomes after severe experimental thoracic spinal cord injury

OBJECTIVE

In acute traumatic brain injury, decompressive craniectomy is a common treatment that involves the removal of bone from the cranium to relieve intracranial pressure. The present study investigated whether neurological function following a severe spinal cord injury improves after utilizing either a durotomy to decompress the intradural space and/or a duraplasty to maintain proper flow of cerebrospinal fluid.

METHODS

Sixty-four adult female rats (n = 64) were randomly assigned to receive either a 3- or 5-level decompressive laminectomy (Groups A and B), laminectomy + durotomy (Groups C and D), or laminectomy + duraplasty with graft (Group E and F) at 24 hours following a severe thoracic contusion injury (200 kilodynes). Duraplasty involved the use of DuraSeal, a hydrogel dural sealant. Uninjured and injured control groups were included (Groups G, H). Hindlimb locomotor function was assessed by open field locomotor testing (BBB) and CatWalk gait analysis at 35 days postinjury. Bladder function was analyzed and bladder wall thickness was assessed histologically. At 35 days postinjury, mechanical and thermal allodynia were assessed by the Von Frey hair filament and hotplate paw withdrawal tests, respectively. Thereafter, the spinal cords were dissected, examined for gross anomalies at the injury site, and harvested for histological analyses to assess lesion volumes and white matter sparing. ANOVA was used for statistical analyses.

RESULTS

There was no significant improvement in motor function recovery in any treatment groups compared with injured controls. CatWalk gait analysis indicated a significant decrease in interlimb coordination in Groups B, C, and D (p < 0.05) and swing speed in Groups A, B, and D. Increased mechanical pain sensitivity was observed in Groups A, C, and F (p < 0.05). Rats in Group C also developed thermal pain hypersensitivity. Examination of spinal cords demonstrated increased lesion volumes in Groups C and F and increased white matter sparing in Group E (p < 0.05). The return of bladder automaticity was similar in all groups. Examination of the injury site during tissue harvest revealed that, in some instances, expansion of the hydrogel dural sealant caused compression of the spinal cord.

CONCLUSIONS

Surgical decompression provided no benefit in terms of neurological improvement in the setting of a severe thoracic spinal cord contusion injury in rats at 24 hours postinjury. Decompressive laminectomy and durotomy did not improve motor function recovery, and rats in both of these treatment modalities developed neuropathic pain. Performing a durotomy also led to increased lesion volumes. Placement of DuraSeal was shown to cause compression in some rats in the duraplasty treatment groups. Decompressive duraplasty of 3 levels does not affect functional outcomes after injury but did increase white matter sparing. Decompressive duraplasty of 5 levels led to neuropathic pain development and increased lesion volumes. Further comparison of dural repair techniques is necessary.

Comparison of speed-vacuum method and heat-drying method to measure brain water content of small brain samples

BACKGROUND

A reliable measurement of brain water content (wet-to-dry ratio) is an important prerequisite for conducting research on mechanisms of brain edema formation. The conventionally used oven-drying method suffers from several limitations, especially in small samples. A technically demanding and time-consuming alternative is freeze-drying.

NEW METHOD

Centrifugal vacuum concentrators (e.g. SpeedVac/speed-vacuum drying) are a combination of vacuum-drying and centrifugation, used to reduce the boiling temperature. These concentrators have the key advantages of improving the freeze-drying speed and maintaining the integrity of dried samples, thus, allowing e.g. DNA analyses. In the present study, we compared the heat-oven with speed-vacuum technique with regard to efficacy to remove moisture from water and brain samples and their effectiveness to distinguish treatment paradigms after experimental traumatic brain injury (TBI) caused by controlled cortical impact (CCI).

RESULTS

Both techniques effectively removed water, the oven technique taking 24h and vacuum-drying taking 48h. Vacuum-drying showed lower variations in small samples (30-45mg) and was suitable for genomic analysis as exemplified by sex genotyping. The effect of sodium bicarbonate (NaBic8.4%) on brain edema formation after CCI was investigated in small samples (2×1mm). Only vacuum-drying showed low variation and significant improvement under NaBic8.4% treatment.

COMPARISON WITH AN EXISTING METHOD

The receiver operating curves (ROC) analysis demonstrated that vacuum-drying (area under the curve (AUC):0.867-0.967) was superior to the conventional heat-drying method (AUC:0.367-0.567).

CONCLUSIONS

The vacuum method is superior in terms of quantifying water content in small samples. In addition, vacuum-dried samples can also be used for subsequent analyses, e.g., PCR analysis.

Early Decompression of Acute Subdural Hematoma for Postoperative Neurological Improvement: A Single Center Retrospective Review of 10 Years

Objective

This study was conducted to investigate survival related factors, as well as to evaluate the effects of early decompression on acute subdural hematoma (ASDH).

Methods

We retrospectively reviewed cases of decompressive craniectomy (DC) for decade. In total, 198 cases of DC involved ASDH were available for review, and 65 cases were excluded due to missing data on onset time and a delayed operation after closed observation with medical care. Finally, 133 cases of DC with ASDH were included in this study, and various factors including the time interval between trauma onset and operation were evaluated.

Results

In the present study, survival rate after DC in patients with ASDH was shown to be related to patient age (50 years old, p=0.012), brain compression ratio (p=0.042) and brain stem compression (p=0.020). Sex, preoperative mental status, and time interval between trauma onset and operation were not related with survival rate. Among those that survived (n=78), improvements in Glasgow Coma Scale (GCS) score of more than three points, compared to preoperative measurement, were more frequently observed among the early (less than 3 hours between trauma onset and operation) decompressed cases (p=0.013). However, improvements of more than 4 or 5 points on the GCS were not affected by early decompression.

Conclusion

Early decompression of ASDH was not correlated with survival rate, but was related with neurological improvement (more than three points on the GCS). Accordingly, early decompression in ASDH, if indicated, may be of particular benefit.

Mannose-binding lectin is expressed after clinical and experimental traumatic brain injury and its deletion is protective

OBJECTIVE

Mannose-binding lectin protein is the activator of the lectin complement pathway. Goals were (1) to investigate mannose-binding lectin expression after human and experimental traumatic brain injury induced by controlled cortical impact and (2) to evaluate whether mannose-binding lectin deletion is associated with reduced sequelae after controlled cortical impact.

DESIGN

Translational research, combining a human/experimental observational study and a prospective experimental study.

SETTING

University hospital/research laboratory.

PATIENTS AND SUBJECTS

Brain-injured patients, C57Bl/6 mice, and mannose-binding lectin-A and mannose-binding lectin-C double-knockout (-/-) mice.

INTERVENTIONS

Using anti-human mannose-binding lectin antibody, we evaluated mannose-binding lectin expression in tissue samples from six patients who underwent surgery for a cerebral contusion. Immunohistochemistry was also performed on tissues obtained from mice at 30 minutes; 6, 12, 24, 48, and 96 hours; and 1 week after controlled cortical impact using anti-mouse mannose-binding lectin-A and mannose-binding lectin-C antibodies. We evaluated the effects of mannose-binding lectin deletion in wild-type and mannose-binding lectin-A and mannose-binding lectin-C double-knockout mice. Functional outcome was evaluated using the neuroscore and beam walk tests for 4 weeks postinjury (n = 11). Histological injury was evaluated by comparing neuronal cell counts in the cortex adjacent to the contusion (n = 11).

MEASUREMENTS AND MAIN RESULTS

Following human traumatic brain injury, we observed mannose-binding lectin-positive immunostaining in the injured cortex as early as few hours and up to 5 days postinjury. Similarly in mice, we observed mannose-binding lectin-C-positive immunoreactivity in the injured cortex beginning 30 minutes and persisting up to 1 week postinjury. The extent of mannose-binding lectin-A expression was lower when compared with that of mannose-binding lectin-C. We observed attenuated sensorimotor deficits in mannose-binding lectin (-/-) mice compared with wild-type mice at 2-4 weeks postinjury. Furthermore, we observed reduced cortical cell loss at 5 weeks postinjury in mannose-binding lectin (-/-) mice compared with wild-type mice.

CONCLUSIONS

Mannose-binding lectin expression was documented after traumatic brain injury. The reduced sequelae associated with mannose-binding lectin absence suggest that mannose-binding lectin modulation might be a potential target after traumatic brain injury.

The impact of cranioplasty on cerebral blood flow and its correlation with clinical outcome in patients underwent decompressive craniectomy

Context:

Decompressive craniectomy is commonly use as the treatment for medically refractory intracranial hypertension. Unexpected improvement in patient's neurological status has been observed among patients that underwent cranioplasty. Restoration of cerebral blood flow (CBF) hemodynamics is one of the contributing factors. This study was conducted to determine the impact of cranioplasty on CBF and its correlation with clinical outcome.

Aims:

This study was done to evaluate the effect of cranioplasty on CBF with computed tomography perfusion (CTP). It also aimed to determine the correlation between postcranioplasty CBF and clinical outcome.

Settings and Design:

Prospective observational study.

Subjects and Methods:

All patients had CTP done to determine precranioplasty CBF. CTP was repeated at 6 weeks postcranioplasty and clinical assessment at 6 and 24 weeks postcranioplasty.

Statistical Analysis Used:

Data analysis was done using Statistical Package for Social Sciences version 12.0.1.

Results:

The median value of the ipsilateral CBF was 48.87 and 61.10 ml/min/100 g at precranioplasty and 6 weeks postcranioplasty (P < 0.001). Contralateral CBF also showed improvement from 60.55 to 71.84 ml/min/100 g (P < 0.001). Median value for mini mental state examination showed a significant difference with value of 22, 25, and 25.5 at precranioplasty, 6 and 24 weeks postcranioplasty (P = 0.001 and P < 0.001). Median value for frontal assessment battery was 12, 14.5, and 15 (P = 0.002 and P = 0.001).

Conclusions:

Cranioplasty can remarkably improve cortical perfusion for both ipsilateral and contralateral hemisphere. Though we are unable to establish strong correlation, between CBF and clinical outcome, cranioplasty was observed to have a therapeutic role in terms of clinical outcome improvement.

The Formation of Microthrombi in Parenchymal Microvessels after Traumatic Brain Injury Is Independent of Coagulation Factor XI

Microthrombus formation and bleeding worsen the outcome after traumatic brain injury (TBI). The aim of the current study was to characterize these processes in the brain parenchyma after experimental TBI and to determine the involvement of coagulation factor XI (FXI). C57BL/6 mice (n = 101) and FXI-deficient mice (n = 15) were subjected to controlled cortical impact (CCI). Wild-type mice received an inhibitory antibody against FXI (14E11) or control immunoglobulin G 24 h before or 30 or 120 min after CCI. Cerebral microcirculation was visualized in vivo by 2-photon microscopy 2-3 h post-trauma and histopathological outcome was assessed after 24 h. TBI induced hemorrhage and microthrombus formation in the brain parenchyma (p < 0.001). Inhibition of FXI activation or FXI deficiency did not reduce cerebral thrombogenesis, lesion volume, or hemispheric swelling. However, it also did not increase intracranial hemorrhage. Formation of microthrombosis in the brain parenchyma after TBI is independent of the intrinsic coagulation cascade since it was not reduced by inhibition of FXI. However, since targeting FXI has well-established antithrombotic effects in humans and experimental animals, inhibition of FXI could represent a reasonable strategy for the prevention of deep venous thrombosis in immobilized patients with TBI.

Rodent Models of Traumatic Brain Injury: Methods and Challenges

Traumatic brain injury (TBI) has been named the most complex disease in the most complex organ of the body. It is the most common cause of death and disability in the Western world in people <40 years old and survivors commonly suffer from persisting cognitive deficits, impaired motor function, depression and personality changes. TBI may vary in severity from uniformly fatal to mild injuries with rapidly resolving symptoms and without doubt, it is a markedly heterogeneous disease. Its different subtypes differs in their pathophysiology, treatment options and long-term consequences and to date, there are no pharmacological treatments with proven clinical benefit available to TBI patients. To enable development of novel treatment options for TBI, clinically relevant animal models are needed. Due to their availability and low costs, numerous rodent models have been developed which have substantially contributed to our current understanding of the pathophysiology of TBI. The most common animal models used in laboratories worldwide are likely the controlled cortical impact (CCI) model, the central and lateral fluid percussion injury (FPI) models, and weight drop/impact acceleration (I/A) models. Each of these models has inherent advantages and disadvantages; these need to be thoroughly considered when selecting the rodent TBI model according to the hypothesis and design of the study. Since TBI is not one disease, refined animal models must take into account the clinical features and complexity of human TBI. To enhance the possibility of establishing preclinical efficacy of a novel treatment, the preclinical use of several different experimental models is encouraged as well as varying the species, gender, and age of the animal. In this chapter, the methods, limitations, and challenges of the CCI and FPI models of TBI used in rodents are described.

Decompressive Craniectomy Increases Brain Lesion Volume and Exacerbates Functional Impairment in Closed Head Injury in Mice

Decompressive craniectomy has been widely used in patients with head trauma. The randomized clinical trial on an early decompression (DECRA) demonstrated that craniectomy did not improve the neurological outcome, in contrast to previous animal experiments. The goal of our study was to analyze the effect of decompressive craniectomy in a murine model of head injury. Male mice were assigned into the following groups: sham, decompressive craniectomy, closed head injury (CHI), and CHI followed by craniectomy. At 24 h post-trauma, animals underwent the Neurological Severity Score test (NSS) and Beam Balance Score test (BBS). At the same time point, magnetic resonance imaging was performed, and volume of edema and contusion was assessed, followed by histopathological analysis. According to NSS, animals undergoing both trauma and craniectomy presented the most severe neurological impairment. Also, balancing time was reduced in this group compared with sham animals. Both edema and contusion volume were increased in the trauma and craniectomy group compared with sham animals. Histopathological analysis showed that all animals that underwent trauma presented substantial neuronal loss. In animals treated with craniectomy after trauma, a massive increase of edema with hemorrhagic transformation of contusion was documented. Decompressive craniectomy applied after closed head injury in mice leads to additional structural and functional impairment. The surgical decompression via craniectomy promotes brain edema formation and contusional blossoming in our model. This additive effect of combined mechanical and surgical trauma may explain the results of the DECRA trial and should be explored further in experiments.

Pre-Clinical Traumatic Brain Injury Common Data Elements: Toward a Common Language Across Laboratories

Traumatic brain injury (TBI) is a major public health issue exacting a substantial personal and economic burden globally. With the advent of "big data" approaches to understanding complex systems, there is the potential to greatly accelerate knowledge about mechanisms of injury and how to detect and modify them to improve patient outcomes. High quality, well-defined data are critical to the success of bioinformatics platforms, and a data dictionary of "common data elements" (CDEs), as well as "unique data elements" has been created for clinical TBI research. There is no data dictionary, however, for preclinical TBI research despite similar opportunities to accelerate knowledge. To address this gap, a committee of experts was tasked with creating a defined set of data elements to further collaboration across laboratories and enable the merging of data for meta-analysis. The CDEs were subdivided into a Core module for data elements relevant to most, if not all, studies, and Injury-Model-Specific modules for non-generalizable data elements. The purpose of this article is to provide both an overview of TBI models and the CDEs pertinent to these models to facilitate a common language for preclinical TBI research.

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.

Identification of the Vascular Source of Vasogenic Brain Edema following Traumatic Brain Injury Using In Vivo 2-Photon Microscopy in Mice

Vasogenic brain edema due to vascular leakage is one of the most important factors determining the clinical outcome of patients following acute brain injury. To date, performing a detailed in vivo quantification of vascular leakage has not been possible. Here, we used in vivo 2-photon microscopy (2-PM) to determine the spatial (3D) and temporal development of vasogenic brain edema following traumatic brain injury (TBI) in mice; in addition, we identified the vessel types involved in vascular leakage. Thirteen male Tie2-GFP mice (6-8 weeks old) were subjected to controlled cortical impact (CCI) or a sham operation; subsequently, a cranial window was prepared adjacent to the injury site, and tetramethylrhodamine-dextran (TMRM, 40 mg/kg, MW 40,000) was injected intravenously to visualize blood plasma leakage. Parenchymal fluorescence intensity was monitored in three regions for 2-4 h post-CCI, reaching from the surface of the brain to a depth of 300 μm, and TMRM leakage was measured as an increase in TMRM fluorescence intensity outside the vessel lumen and in the parenchyma. In the CCI group, vascular leakage was detected in all investigated regions as early as 2.5 h post-injury. This leakage increased over time and was more pronounced proximal to the primary contusion. Both arterioles and venules contributed similarly to brain edema formation and their contribution was independent of vessel size; however, capillaries were the major contributor to leakage. In summary, using 2-PM to perform in vivo 3D deep-brain imaging, we found that TBI induces vascular leakage from capillaries, venules, and arterioles. Thus, all three vessel types are involved in trauma-induced brain edema and should be considered when developing novel therapies for preventing vasogenic brain edema.

Decompressive craniectomy reduces white matter injury after controlled cortical impact in mice

Reduction and avoidance of increases in intracranial pressure (ICP) after severe traumatic brain injury (TBI) continue to be the mainstays of treatment. Traumatic axonal injury is a major contributor to morbidity after TBI, but it remains unclear whether elevations in ICP influence axonal injury. Here we tested the hypothesis that reduction in elevations in ICP after experimental TBI would result in decreased axonal injury and white matter atrophy in mice. Six-week-old male mice (C57BL/6J) underwent either moderate controlled cortical impact (CCI) (n=48) or Sham surgery (Sham, n=12). Immediately after CCI, injured animals were randomized to a loose fitting plastic cap (Open) or replacement of the previously removed bone flap (Closed). Elevated ICP was observed in Closed animals compared with Open and Sham at 15 min (21.4±4.2 vs. 12.3±2.9 and 8.8±1.8 mm Hg, p<0.0001) and 1 day (17.8±3.7 vs. 10.6±2.0 and 8.9±1.9 mm Hg, p<0.0001) after injury. Beta amyloid precursor protein staining in the corpus callosum and ipsilateral external capsule revealed reduced axonal swellings and bulbs in Open compared with Closed animals (32% decrease, p<0.01 and 40% decrease, p<0.001 at 1 and 7 days post-injury, respectively). Open animals were also found to have decreased neurofilament-200 stained axonal swellings at 7 days post-injury compared with Open animals (32% decrease, p<0.001). At 4 weeks post-injury, Open animals had an 18% reduction in white matter volume compared with 34% in Closed animals (p<0.01). Thus, our results indicate that CCI with decompressive craniectomy was associated with reductions in ICP and reduced pericontusional axonal injury and white matter atrophy. If similar in humans, therapeutic interventions that ameliorate intracranial hypertension may positively influence white matter injury severity.

Effect of small molecule vasopressin V1a and V2 receptor antagonists on brain edema formation and secondary brain damage following traumatic brain injury in mice

The attenuation of brain edema is a major therapeutic target after traumatic brain injury (TBI). Vasopressin (AVP) is well known to play a major role in the regulation of brain water content and vasoendothelial functions and to be involved in brain edema formation. Therefore, the aim of the current study was to analyze the antiedematous efficacy of a clinically relevant, nonpeptidic AVP V1a and V2 receptor antagonists. C57Bl6 mice were subjected to controlled cortical impact (CCI) and V1a or V2 receptors were inhibited by using the highly selective antagonists SR-49059 or SR-121463A either by systemic (intraperitoneal, IP) or intracerebroventricular (ICV) application. After 24 h, brain edema, intracranial pressure (ICP), and contusion volume were assessed. Systemically applied AVP receptor antagonists could not reduce secondary lesion growth. In contrast, ICV administration of AVP V1a receptor antagonist decreased brain edema formation by 68%, diminished post-traumatic increase of ICP by 46%, and reduced secondary contusion expansion by 43% 24 h after CCI. The ICV inhibition of V2 receptors resulted in significant reduction of post-traumatic brain edema by 41% 24 h after CCI, but failed to show further influence on ICP and lesion growth. Hence, centrally applied vasopressin V1a receptor antagonists may be used to reduce brain edema formation after 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.

A novel mouse model of penetrating brain injury

Penetrating traumatic brain injury (pTBI) has been difficult to model in small laboratory animals, such as rats or mice. Previously, we have established a non-fatal, rat model for pTBI using a modified air-rifle that accelerates a pellet, which hits a small probe that then penetrates the experimental animal’s brain. Knockout and transgenic strains of mice offer attractive tools to study biological reactions induced by TBI. Hence, in the present study, we adapted and modified our model to be used with mice. The technical characterization of the impact device included depth and speed of impact, as well as dimensions of the temporary cavity formed in a brain surrogate material after impact. Biologically, we have focused on three distinct levels of severity (mild, moderate, and severe), and characterized the acute phase response to injury in terms of tissue destruction, neural degeneration, and gliosis. Functional outcome was assessed by measuring bodyweight and motor performance on rotarod. The results showed that this model is capable of reproducing major morphological and neurological changes of pTBI; as such, we recommend its utilization in research studies aiming to unravel the biological events underlying injury and regeneration after pTBI.

Moderately elevated intracranial pressure after diffuse traumatic brain injury is associated with exacerbated neuronal pathology and behavioral morbidity in the rat

Traumatic brain injury (TBI)-induced elevated intracranial pressure (ICP) is correlated with ensuing morbidity/mortality in humans. This relationship is assumed to rely mostly on the recognition that extremely elevated ICP either indicates hematoma/contusions capable of precipitating herniation or alters cerebral perfusion pressure (CPP), which precipitates global ischemia. However, whether subischemic levels of elevated ICP without hematoma/contusion contribute to increased morbidity/mortality remains unknown. To address this knowledge gap, we utilized a model of moderate diffuse TBI in rats followed by either intraventricular ICP monitoring or manual ICP elevation to 20 mm Hg, in which CPP was above ischemic levels. The effects of ICP elevation after TBI on acute and chronic histopathology, as well as on behavioral morbidity, were evaluated. ICP elevation after TBI resulted in increased acute neuronal membrane perturbation and was also associated with reduced neuronal density at 4 weeks after injury. Somatosensory hypersensitivity was exacerbated by ICP elevation and was correlated to the observed neuronal loss. In conclusion, this study indicates that morbidity and increased neuronal damage/death associated with elevated ICP can occur without concurrent global ischemia. Therefore, understanding the pathologies associated with subischemic levels of elevated ICP could lead to the development of better therapeutic strategies for the treatment and management of TBI patients.

The neuroprotective effect of 17β-estradiol is independent of its antioxidative properties

INTRODUCTION

17β-Estradiol (E2) is neuroprotective in experimental models of stroke. While some postulate a mainly antioxidative action due to E2׳s free C3 hydroxyl group at its A-ring, others suggest that neuroprotection is mediated by a hormonal, receptor mediated effect. The aim of the current study was to clarify this issue by testing whether E2 analogues lacking hormonal activity are also neuroprotective following cerebral ischemia.

MATERIAL & METHODS

Focal cerebral ischemia was induced in male C57/BL6 mice by laser-Doppler-controlled endovascular occlusion of the middle cerebral artery for 40min. Mice received either 1) memantine, a NMDA-receptor antagonist, as a positive control, 2) E2 (1400µg/kg b.w.), or 3) 2,4,6-trimethylphenol (TMP), an E2 analogue without hormonal activity (1400, 140, or 14µg/kg b.w.). Motor function was tested 3h and 24h after ischemia. Thereafter mice were sacrificed and brain damage was quantified by histomorphometry.

RESULTS

Treatment with memantine or E2 significantly reduced infarct volume by >40% and significantly improved neurological function while treatment with TMP had no effect.

CONCLUSION

E2 is equally neuroprotective as antagonization of NMDA receptors while E2 analogues without hormonal activity are not neuroprotective. Therefore the current data suggest that the neuroprotection activity of E2 is independent of its free-radical scavenging properties.

Anesthesia for euthanasia influences mRNA expression in healthy mice and after traumatic brain injury

Tissue sampling for gene expression analysis is usually performed under general anesthesia. Anesthetics are known to modulate hemodynamics, receptor-mediated signaling cascades, and outcome parameters. The present study determined the influence of anesthetic paradigms typically used for euthanization and tissue sampling on cerebral mRNA expression in mice. Naïve mice and animals with acute traumatic brain injury induced by controlled cortical impact (CCI) were randomized to the following euthanasia protocols (n=10-11/group): no anesthesia (NA), 1 min of 4 vol% isoflurane in room air (ISO), 3 min of a combination of 5 mg/kg midazolam, 0.05 mg/kg fentanyl, and 0.5 mg/kg medetomidine intraperitoneally (COMB), or 3 min of 360 mg/kg chloral hydrate intraperitoneally (CH). mRNA expression of actin-1-related gene (Act1), FBJ murine osteosarcoma viral oncogene homolog B (FosB), tumor necrosis factor alpha (TNFα), heat shock protein beta-1 (HspB1), interleukin (IL)-6, tight junction protein 1 (ZO-1), IL-1ß, cyclophilin A, micro RNA 497 (miR497), and small cajal body-specific RNA 17 were determined by real-time polymerase chain reaction (PCR) in hippocampus samples. In naïve animals, Act1 expression was downregulated in the CH group compared with NA. FosB expression was downregulated in COMB and CH groups compared with NA. CCI reduced Act1 and FosB expression, whereas HspB1 and TNFα expression increased. After CCI, HspB1 expression was significantly higher in ISO, COMB, and CH groups, and TNFα expression was elevated in ISO and COMB groups. MiR497, IL-6, and IL-1ß were upregulated after CCI but not affected by anesthetics. Effects were independent of absolute mRNA copy numbers. The data demonstrate that a few minutes of anesthesia before tissue sampling are sufficient to induce immediate mRNA changes, which seem to predominate in the early-regulated gene cluster. Anesthesia-related effects on gene expression might explain limited reproduciblity of real-time PCR data between studies or research groups and should therefore be considered for quantitative PCR data.

Traumatic brain injury using mouse models

The use of mouse models in traumatic brain injury (TBI) has several advantages compared to other animal models including low cost of breeding, easy maintenance, and innovative technology to create genetically modified strains. Studies using knockout and transgenic mice demonstrating functional gain or loss of molecules provide insight into basic mechanisms of TBI. Mouse models provide powerful tools to screen for putative therapeutic targets in TBI. This article reviews currently available mouse models that replicate several clinical features of TBI such as closed head injuries (CHI), penetrating head injuries, and a combination of both. CHI may be caused by direct trauma creating cerebral concussion or contusion. Sudden acceleration-deceleration injuries of the head without direct trauma may also cause intracranial injury by the transmission of shock waves to the brain. Recapitulation of temporary cavities that are induced by high-velocity penetrating objects in the mouse brain are difficult to produce, but slow brain penetration injuries in mice are reviewed. Synergistic damaging effects on the brain following systemic complications are also described. Advantages and disadvantages of CHI mouse models induced by weight drop, fluid percussion, and controlled cortical impact injuries are compared. Differences in the anatomy, biomechanics, and behavioral evaluations between mice and humans are discussed. Although the use of mouse models for TBI research is promising, further development of these techniques is warranted.

Surgical management of traumatic brain injury: a comparative-effectiveness study of 2 centers

Object

Mass lesions from traumatic brain injury (TBI) often require surgical evacuation as a life-saving measure and to improve outcomes, but optimal timing and surgical technique, including decompressive craniectomy, have not been fully defined. The authors compared neurosurgical approaches in the treatment of TBI at 2 academic medical centers to document variations in real-world practice and evaluate the efficacies of different approaches on postsurgical course and long-term outcome.

Methods

Patients 18 years of age or older who required neurosurgical lesion evacuation or decompression for TBI were enrolled in the Co-Operative Studies on Brain Injury Depolarizations (COSBID) at King's College Hospital (KCH, n = 27) and Virginia Commonwealth University (VCU, n = 24) from July 2004 to March 2010. Subdural electrode strips were placed at the time of surgery for subsequent electrocorticographic monitoring of spreading depolarizations; injury characteristics, physiological monitoring data, and 6-month outcomes were collected prospectively. CT scans and medical records were reviewed retrospectively to determine lesion characteristics, surgical indications, and procedures performed.

Results

Patients enrolled at KCH were significantly older than those enrolled at VCU (48 vs 34 years, p < 0.01) and falls were more commonly the cause of TBI in the KCH group than in the VCU group. Otherwise, KCH and VCU patients had similar prognoses, lesion types (subdural hematomas: 30%–35%; parenchymal contusions: 48%–52%), signs of mass effect (midline shift ≥ 5 mm: 43%–52%), and preoperative intracranial pressure (ICP). At VCU, however, surgeries were performed earlier (median 0.51 vs 0.83 days posttrauma, p < 0.05), bone flaps were larger (mean 82 vs 53 cm2, p < 0.001), and craniectomies were more common (performed in 75% vs 44% of cases, p < 0.05). Postoperatively, maximum ICP values were lower at VCU (mean 22.5 vs 31.4 mm Hg, p < 0.01). Differences in incidence of spreading depolarizations (KCH: 63%, VCU: 42%, p = 0.13) and poor outcomes (KCH: 54%, VCU: 33%, p = 0.14) were not significant. In a subgroup analysis of only those patients who underwent early (< 24 hours) lesion evacuation (KCH: n = 14; VCU: n = 16), however, VCU patients fared significantly better. In the VCU patients, bone flaps were larger (mean 85 vs 48 cm2 at KCH, p < 0.001), spreading depolarizations were less common (31% vs 86% at KCH, p < 0.01), postoperative ICP values were lower (mean: 20.8 vs 30.2 mm Hg at KCH, p < 0.05), and good outcomes were more common (69% vs 29% at KCH, p < 0.05). Spreading depolarizations were the only significant predictor of outcome in multivariate analysis.

Conclusions

This comparative-effectiveness study provides evidence for major practice variation in surgical management of severe TBI. Although ages differed between the 2 cohorts, the results suggest that a more aggressive approach, including earlier surgery, larger craniotomy, and removal of bone flap, may reduce ICP, prevent cortical spreading depolarizations, and improve outcomes. In particular, patients requiring evacuation of subdural hematomas and contusions may benefit from decompressive craniectomy in conjunction with lesion evacuation, even when elevated ICP is not a factor in the decision to perform surgery.

Tumor necrosis factor in traumatic brain injury: effects of genetic deletion of p55 or p75 receptor

The role of tumor necrosis factor (TNF) and its receptors after traumatic brain injury (TBI) remains unclear. We evaluated the effects of genetic deletion of either p55 or p75 TNF receptor on neurobehavioral outcome, histopathology, DNA damage and apoptosis-related cell death/survival gene expression (bcl-2/bax), and microglia/macrophage (M/M) activation in wild-type (WT) and knockout mice after TBI. Injured p55 (-/-) mice showed a significant attenuation while p75 (-/-) mice showed a significant worsening of sensorimotor deficits compared with WT mice over 4 weeks postinjury. At the same time point, contusion volume in p55 (-/-) mice (11.1±3.3 mm(3)) was significantly reduced compared with WT (19.7±3.4 mm(3)) and p75 (-/-) mice (20.9±3.2 mm(3)). At 4 hours postinjury, bcl-2/bax ratio mRNA expression was increased in p55 (-/-) compared with p75 (-/-) mice and was associated with reduced DNA damage terminal deoxynucleotidyl transferaseYmediated dUTP nick end labeling (TUNEL-positivity), reduced CD11b expression and increased Ym1 expression at 24 hours postinjury in p55 (-/-) compared with p75 (-/-) mice, indicative of a protective M/M response. These data suggest that TNF may exacerbate neurobehavioral deficits and tissue damage via p55 TNF receptor whose inhibition may represent a specific therapeutic target after TBI.