Development of prolonged focal cerebral edema and regional cation changes following experimental brain injury in the rat

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.

Spatial Distribution of Neuropathology and Neuroinflammation Elucidate the Biomechanics of Fluid Percussion Injury

Diffuse brain injury is better described as multi-focal, where pathology can be found adjacent to seemingly uninjured neural tissue. In experimental diffuse brain injury, pathology and pathophysiology have been reported far more lateral than predicted by the impact site. We hypothesized that local thickening of the rodent skull at the temporal ridges serves to focus the intracranial mechanical forces experienced during brain injury and generate predictable pathology. We demonstrated local thickening of the skull at the temporal ridges using contour analysis on magnetic resonance imaging. After diffuse brain injury induced by midline fluid percussion injury (mFPI), pathological foci along the anterior-posterior length of cortex under the temporal ridges were evident acutely (1, 2, and 7 days) and chronically (28 days) post-injury by deposition of argyophilic reaction product. Area CA3 of the hippocampus and lateral nuclei of the thalamus showed pathological change, suggesting that mechanical forces to or from the temporal ridges shear subcortical regions. A proposed model of mFPI biomechanics suggests that injury force vectors reflect off the skull base and radiate toward the temporal ridge, thereby injuring ventral thalamus, dorsolateral hippocampus, and sensorimotor cortex. Surgically thinning the temporal ridge before injury reduced injury-induced inflammation in the sensorimotor cortex. These data build evidence for temporal ridges of the rodent skull to contribute to the observed pathology, whether by focusing extracranial forces to enter the cranium or intracranial forces to escape the cranium. Pre-clinical investigations can take advantage of the predicted pathology to explore injury mechanisms and treatment efficacy.

Effects of pregabalin on brain edema, neurologic and histologic outcomes in experimental traumatic brain injury

Brain edema and increased intracranial pressure (ICP) are among the main causes of neurological disturbance and mortality following traumatic brain injury (TBI). Since pregabalin neuroprotective effects have been shown, this study was performed to evaluate the possible neuroprotective effects of pregabalin in experimental TBI of male rats. Adult male Wistar rats were divided into 4 groups: sham, vehicle, pregabalin 30 mg/kg and pregabalin 60 mg/kg. TBI was induced in vehicle and pregabalin groups by Marmarou method. Pregabalin was administered 30 min after TBI. Sham and vehicle groups received saline. Brain water and Evans blue content and histopathological changes were evaluated 24, 5 and 24 h after TBI, respectively. The ICP and neurological outcomes (veterinary coma scale, VCS) were recorded before, 1 h and 24 h post TBI. The results showed a significant reduction in brain water content and ICP, and a significant increase in VCS of pregabalin group (60 mg/kg) as compared to vehicle group (P < 0.05). Also, pregabalin reduced brain edema and apoptosis score as compared to vehicle group. Post TBI pregabalin administration revealed a delayed but significant improvement in ICP and neurological outcomes in experimental TBI. The underlying mechanism(s) was not determined and needs further investigation.

Unfolded Maps for Quantitative Analysis of Cortical Lesion Location and Extent after Traumatic Brain Injury

We aimed to generate two-dimensional (2D) unfolded cortical maps from magnetic resonance (MR) images to delineate the location of traumatic brain injury (TBI)-induced cortical damage in functionally diverse cytoarchitectonic areas of the cerebral cortex, and to predict the severity of functional impairment after TBI based on the lesion location and extent. Lateral fluid-percussion injury was induced in adult rats and T2 maps were acquired with magnetic resonance imaging (MRI) at 3 days post-TBI. Somatomotor deficits were assessed based on the composite neuroscore and beam balance test, and spatial learning was assessed in the Morris water maze. Animals were perfused for histology at 13 days post-injury. A 2D template was generated by unfolding the cerebral cortex from 26 sections of the rat brain atlas, covering the lesion extent. Next, 2D unfolded maps were generated from T2 maps and thionin-stained histological sections from the same animals. Unfolding of the T2 maps revealed the lesion core in the auditory, somatosensory, and visual cortices. The unfolded histological lesion at 13 days post-injury was 12% greater than the MRI lesion at 3 days post-TBI, as the lesion area increased laterally and caudally; the larger the MRI lesion area, the larger the histological lesion area. Further, the larger the MRI lesion area in the barrel field of the primary somatosensory cortex (S1BF), upper lip of the primary somatosensory cortex (S1ULp), secondary somatosensory division (S2), and ectorhinal (Ect) and perirhinal (PRh) cortices, the more impaired the performance in the beam balance and Morris water maze tests. Subsequent receiver operating characteristic analysis indicated that severity of the MRI lesion in S1ULp and S2 was a sensitive and specific predictor of poor performance in the beam balance test. Moreover, MRI lesions in the S1ULp, S2, S1BF, and Ect and PRh cortices predicted poor performance in the Morris water maze test. Our findings indicate that 2D-unfolded cortical maps generated from MR images delineate the distribution of cortical lesions in functionally different cytoarchitectonic regions, which can be used to predict the TBI-induced functional impairment.

The Impact of Previous Physical Training on Redox Signaling after Traumatic Brain Injury in Rats: A Behavioral and Neurochemical Approach

Throughout the world, traumatic brain injury (TBI) is one of the major causes of disability, which can include deficits in motor function and memory, as well as acquired epilepsy. Although some studies have shown the beneficial effects of physical exercise after TBI, the prophylactic effects are poorly understood. In the current study, we demonstrated that TBI induced by fluid percussion injury (FPI) in adult male Wistar rats caused early motor impairment (24 h), learning deficit (15 days), spontaneous epileptiform events (SEE), and hilar cell loss in the hippocampus (35 days) after TBI. The hippocampal alterations in the redox status, which were characterized by dichlorofluorescein diacetate oxidation and superoxide dismutase (SOD) activity inhibition, led to the impairment of protein function (Na(+), K(+)-adenosine triphosphatase [ATPase] activity inhibition) and glutamate uptake inhibition 24 h after neuronal injury. The molecular adaptations elicited by previous swim training protected against the glutamate uptake inhibition, oxidative stress, and inhibition of selected targets for free radicals (e.g., Na(+), K(+)-ATPase) 24 h after neuronal injury. Our data indicate that this protocol of exercise protected against FPI-induced motor impairment, learning deficits, and SEE. In addition, the enhancement of the hippocampal phosphorylated nuclear factor erythroid 2-related factor (P-Nrf2)/Nrf2, heat shock protein 70, and brain-derived neurotrophic factor immune content in the trained injured rats suggests that protein expression modulation associated with an antioxidant defense elicited by previous physical exercise can prevent toxicity induced by TBI, which is characterized by cell loss in the dentate gyrus hilus at 35 days after TBI. Therefore, this report suggests that previous physical exercise can decrease lesion progression in this model of brain damage.

Making Waves in the Brain: What Are Oscillations, and Why Modulating Them Makes Sense for Brain Injury

Traumatic brain injury (TBI) can result in persistent cognitive, behavioral and emotional deficits. However, the vast majority of patients are not chronically hospitalized; rather they have to manage their disabilities once they are discharged to home. Promoting recovery to pre-injury level is important from a patient care as well as a societal perspective. Electrical neuromodulation is one approach that has shown promise in alleviating symptoms associated with neurological disorders such as in Parkinson’s disease (PD) and epilepsy. Consistent with this perspective, both animal and clinical studies have revealed that TBI alters physiological oscillatory rhythms. More recently several studies demonstrated that low frequency stimulation improves cognitive outcome in models of TBI. Specifically, stimulation of the septohippocampal circuit in the theta frequency entrained oscillations and improved spatial learning following TBI. In order to evaluate the potential of electrical deep brain stimulation for clinical translation we review the basic neurophysiology of oscillations, their role in cognition and how they are changed post-TBI. Furthermore, we highlight several factors for future pre-clinical and clinical studies to consider, with the hope that it will promote a hypothesis driven approach to subsequent experimental designs and ultimately successful translation to improve outcome in patients with TBI.

A single dose of PPARγ agonist pioglitazone reduces cortical oxidative damage and microglial reaction following lateral fluid percussion brain injury in rats

Neuroprotective actions of the peroxisome proliferator-activated receptor-γ (PPARγ) agonists have been observed in various animal models of the brain injuries. In this study we examined the effects of a single dose of pioglitazone on oxidative and inflammatory parameters as well as on neurodegeneration and the edema formation in the rat parietal cortex following traumatic brain injury (TBI) induced by the lateral fluid percussion injury (LFPI) method. Pioglitazone was administered in a dose of 1mg/kg at 10min after the brain trauma. The animals of the control group were sham-operated and injected by vehicle. The rats were decapitated 24h after LFPI and their parietal cortices were analyzed by biochemical and histological methods. Cortical edema was evaluated in rats sacrificed 48h following TBI. Brain trauma caused statistically significant oxidative damage of lipids and proteins, an increase of glutathione peroxidase (GSH-Px) activity, the cyclooxygenase-2 (COX-2) overexpression, reactive astrocytosis, the microglia activation, neurodegeneration, and edema, but it did not influence the superoxide dismutase activity and the expressions of interleukin-1 beta, interleukin-6 and tumor necrosis factor-alpha in the rat parietal cortex. Pioglitazone significantly decreased the cortical lipid and protein oxidative damage, increased the GSH-Px activity and reduced microglial reaction. Although a certain degree of the TBI-induced COX-2 overexpression, neurodegeneration and edema decrease was detected in pioglitazone treated rats, it was not significant. In the injured animals, cortical reactive astrocytosis was unchanged by the tested PPARγ agonist. These findings demonstrate that pioglitazone, administered only in a single dose, early following LFPI, reduced cortical oxidative damage, increased antioxidant defense and had limited anti-inflammatory effect, suggesting the need for further studies of this drug in the treatment of TBI.

Long-Term Effects of Enriched Environment on Neurofunctional Outcome and CNS Lesion Volume After Traumatic Brain Injury in Rats

To determine whether the exposure to long term enriched environment (EE) would result in a continuous improvement of neurological recovery and ameliorate the loss of brain tissue after traumatic brain injury (TBI) vs. standard housing (SH). Male Sprague-Dawley rats (300-350 g, n=28) underwent lateral fluid percussion brain injury or SHAM operation. One TBI group was held under complex EE for 90 days, the other under SH. Neuromotor and sensorimotor dysfunction and recovery were assessed after injury and at days 7, 15, and 90 via Composite Neuroscore (NS), RotaRod test, and Barnes Circular Maze (BCM). Cortical tissue loss was assessed using serial brain sections. After day 7 EE animals showed similar latencies and errors as SHAM in the BCM. SH animals performed notably worse with differences still significant on day 90 (p<0.001). RotaRod test and NS revealed superior results for EE animals after day 7. The mean cortical volume was significantly higher in EE vs. SH animals (p=0.003). In summary, EE animals after lateral fluid percussion (LFP) brain injury performed significantly better than SH animals after 90 days of recovery. The window of opportunity may be wide and also lends further credibility to the importance of long term interventions in patients suffering from TBI.

Animal models of traumatic brain injury

Traumatic brain injury (TBI) is a major health issue comprising a heterogeneous and complex array of pathologies. Over the last several decades, numerous animal models have been developed to address the diverse nature of human TBI. The clinical relevance of these models has been a major point of reflection given the poor translation of pharmacologic TBI interventions to the clinic. While previously characterized broadly as either focal or diffuse, this classification is falling out of favor with increased awareness of the overlap in pathologic outcomes between models and an emerging consensus that no one model is sufficient. Moreover, an appreciation of injury biomechanics is essential in recapitulating and interpreting the spectrum of TBI neuropathology observed in various established models of dynamic closed-head TBI. While these models have replicated many specific features of human TBI, an enhanced context with clinical relevancy will facilitate the further elucidation of the mechanisms and treatment of injury.

Overexpression of netrin-1 increases the expression of tight junction-associated proteins, claudin-5, occludin, and ZO-1, following traumatic brain injury in rats

The function of the blood-brain barrier (BBB) depends on the integrity of tight junction (TJ)-associated proteins. Netrin-1 is known to promote angiogenesis and may also regulate the BBB. To understand the association between netrin-1 and the TJ-associated proteins, the expression levels of proteins involved in maintaining the integrity of the BBB, including netrin-1, claudin-5, occludin and zonula occluden (ZO)-1, were investigated in the present study using quantitative polymerase chain reaction, western blot analysis and immunofluorescence. The aim of the present study was to determine the changes in BBB permeability and whether pZsGreen1-N1 mediated overexpression of netrin-1 increased the expression of the TJ-associated proteins following traumatic brain injury (TBI). The results demonstrated that the levels of mRNA transcription and protein expression of the TJ-associated proteins, claudin-5, occludin and ZO-1, were significantly reduced following TBI. Furthermore, the changes in the expression of these three TJ proteins were consistent with the changes in the BBB permeability, indicating that weakening intercellular junctions leads to BBB opening. The present study also demonstrated that netrin-1 significantly increased the downregulation of claudin-5, occludin and ZO-1 expression levels induced by TBI, which provided a basis for further investigation on the role of netrin-1 in the integrity of TJs and proper functioning of the BBB.

Functional assessment of long-term deficits in rodent models of traumatic brain injury

Traumatic brain injury (TBI) ranks as the leading cause of mortality and disability in the young population worldwide. The annual US incidence of TBI in the general population is estimated at 1.7 million per year, with an estimated financial burden in excess of US$75 billion a year in the USA alone. Despite the prevalence and cost of TBI to individuals and society, no treatments have passed clinical trial to clinical implementation. The rapid expansion of stem cell research and technology offers an alternative to traditional pharmacological approaches targeting acute neuroprotection. However, preclinical testing of these approaches depends on the selection and characterization of appropriate animal models. In this article we consider the underlying pathophysiology for the focal and diffuse TBI subtypes, discuss the existing preclinical TBI models and functional outcome tasks used for assessment of injury and recovery, identify criteria particular to preclinical animal models of TBI in which stem cell therapies can be tested for safety and efficacy, and review these criteria in the context of the existing TBI literature. We suggest that 2 months post-TBI is the minimum period needed to evaluate human cell transplant efficacy and safety. Comprehensive review of the published TBI literature revealed that only 32% of rodent TBI papers evaluated functional outcome ≥1 month post-TBI, and only 10% evaluated functional outcomes ≥2 months post-TBI. Not all published papers that evaluated functional deficits at a minimum of 2 months post-TBI reported deficits; hence, only 8.6% of overall TBI papers captured in this review demonstrated functional deficits at 2 months or more postinjury. A 2-month survival and assessment period would allow sufficient time for differentiation and integration of human neural stem cells with the host. Critically, while trophic effects might be observed at earlier time points, it will also be important to demonstrate the sustainability of such an effect, supporting the importance of an extended period of in vivo observation. Furthermore, regulatory bodies will likely require at least 6 months survival post-transplantation for assessment of toxicology/safety, particularly in the context of assessing cell abnormalities.

Purinergic 2Y1 receptor stimulation decreases cerebral edema and reactive gliosis in a traumatic brain injury model

Traumatic brain injury (TBI) is the leading cause of death and disability in children and young adults. Neuroprotective agents that may promote repair or counteract damage after injury do not currently exist. We recently reported that stimulation of the purinergic receptor subtype P2Y(1)R using 2-methylthioladenosine 5' diphosphate (2MeSADP) significantly reduced cytotoxic edema induced by photothrombosis. Here, we tested whether P2Y(1)R stimulation was neuroprotective after TBI. A controlled closed head injury model was established for mice using a pneumatic impact device. Brains were harvested at 1, 3, or 7 days post-injury and assayed for morphological changes by immunocytochemistry, Western blot analysis, and wet/dry weight. Cerebral edema and expression of both aquaporin type 4 and glial fibrillary acidic protein were increased at all time points examined. Immunocytochemical measurements in both cortical and hippocampal slices also revealed significant neuronal swelling and reactive gliosis. Treatment of mice with 2MeSADP (100 μM) or MRS2365 (100 μM) 30 min after trauma significantly reduced all post-injury symptoms of TBI including edema, neuronal swelling, reactive gliosis, and AQ4 expression. The neuroprotective effect was lost in IP(3)R2-/- mice treated with 2MeSADP. Immunocytochemical labeling of brain slices confirmed that P2Y(1)R expression was defined to cortical and hippocampal astrocytes, but not neurons. Taken together, the data show that stimulation of astrocytic P2Y(1)Rs significantly reduces brain injury after acute trauma and is mediated by the IP(3)-signaling pathway. We suggest that enhancing astrocyte mitochondrial metabolism offers a promising neuroprotective strategy for a broad range of brain injuries.

Volatile anesthetics influence blood-brain barrier integrity by modulation of tight junction protein expression in traumatic brain injury

Disruption of the blood-brain barrier (BBB) results in cerebral edema formation, which is a major cause for high mortality after traumatic brain injury (TBI). As anesthetic care is mandatory in patients suffering from severe TBI it may be important to elucidate the effect of different anesthetics on cerebral edema formation. Tight junction proteins (TJ) such as zonula occludens-1 (ZO-1) and claudin-5 (cl5) play a central role for BBB stability. First, the influence of the volatile anesthetics sevoflurane and isoflurane on in-vitro BBB integrity was investigated by quantification of the electrical resistance (TEER) in murine brain endothelial monolayers and neurovascular co-cultures of the BBB. Secondly brain edema and TJ expression of ZO-1 and cl5 were measured in-vivo after exposure towards volatile anesthetics in native mice and after controlled cortical impact (CCI). In in-vitro endothelial monocultures, both anesthetics significantly reduced TEER within 24 hours after exposure. In BBB co-cultures mimicking the neurovascular unit (NVU) volatile anesthetics had no impact on TEER. In healthy mice, anesthesia did not influence brain water content and TJ expression, while 24 hours after CCI brain water content increased significantly stronger with isoflurane compared to sevoflurane. In line with the brain edema data, ZO-1 expression was significantly higher in sevoflurane compared to isoflurane exposed CCI animals. Immunohistochemical analyses revealed disruption of ZO-1 at the cerebrovascular level, while cl5 was less affected in the pericontusional area. The study demonstrates that anesthetics influence brain edema formation after experimental TBI. This effect may be attributed to modulation of BBB permeability by differential TJ protein expression. Therefore, selection of anesthetics may influence the barrier function and introduce a strong bias in experimental research on pathophysiology of BBB dysfunction. Future research is required to investigate adverse or beneficial effects of volatile anesthetics on patients at risk for cerebral edema.

Topiramate promotes neurological recovery in a new model of traumatic brain injury in rats

The aim of this study is to investigate the neuroprotective effects of the anticonvulsant topiramate in a new model of traumatic brain injury in rats. A new model of traumatic brain injury, based on the weight-drop technique, was developed for the purpose of this study. Seventy-five male Wistar rats weighing 320-470 g were studied. All rats were anesthetized, subsequently submitted to a round craniectomy in the left parietal region and a weight of 50 g was used for the production of a cortical contusion. In study I, 44 rats were randomized in three groups to receive either topiramate 40 mg/kg (n=13), topiramate 60 mg/kg (n=14), or water for injection (n=17) i.p. 30 min after the injury and every 12 h thereafter for 3 days. The rats were tested clinically 24 h, 72 h, 10 days and 20 days after the injury. On day 21 the animals were sacrificed and the brains were removed and prepared for histopathological analysis. In study II, 19 rats were randomized to receive either topiramate 60 mg/kg (n=10) or water for injection (n=9) i.p. 30 min after the injury and every 12 h (four doses in total). 48 h after the injury the animals were sacrificed and the brains were rapidly removed and analyzed for water content with the dry-wet weight technique. The animals that received topiramate performed significantly better in neurological tests compared to the animals that received vehicle ten (P<0.05) and 20 (P<0.001) days after the injury. There was no difference between the high and the low dose of the drug. Topiramate had no effect on the anatomic volume of the lesion. The animals that received topiramate had a tendency to present with less cerebral edema formation, but the difference was not statistically significant (P>0.05). These findings suggest that topiramate promotes neurological recovery in rats after traumatic brain injury without affecting the final size of the traumatic lesion and that it might play a role in the reduction of post-traumatic cerebral edema.

Transplantation of marrow stromal cells restores cerebral blood flow and reduces cerebral atrophy in rats with traumatic brain injury: in vivo MRI study

Cell therapy promotes brain remodeling and improves functional recovery after various central nervous system disorders, including traumatic brain injury (TBI). We tested the hypothesis that treatment of TBI with intravenous administration of human marrow stromal cells (hMSCs) provides therapeutic benefit in modifying hemodynamic and structural abnormalities, which are detectable by in vivo MRI. hMSCs were labeled with superparamagnetic iron oxide (SPIO) nanoparticles. Male Wistar rats (300-350 g, n=18) subjected to controlled cortical impact TBI were intravenously injected with 1 mL of saline (n=9) or hMSCs in suspension (n=9, approximately 3 × 10(6) SPIO-labeled hMSCs) 5 days post-TBI. In vivo MRI measurements consisting of cerebral blood flow (CBF), T2-weighted imaging, and 3D gradient echo imaging were performed for all animals 2 days post-TBI and weekly for 6 weeks. Functional outcome was evaluated with modified neurological severity score and Morris water maze test. Cell engraftment was detected in vivo by 3D MRI and confirmed by double staining. Ventricle and lesion volumetric alterations were measured using T2 maps, and hemodynamic abnormality was tracked by MRI CBF measurements. Our data demonstrate that treatment with hMSCs following TBI diminishes hemodynamic abnormalities by early restoration and preservation of CBF in the brain regions adjacent to and remote from the impact site, and reduces generalized cerebral atrophy, all of which may contribute to the observed improvement of functional outcome.

Experimental traumatic brain injury

Traumatic brain injury, a leading cause of death and disability, is a result of an outside force causing mechanical disruption of brain tissue and delayed pathogenic events which collectively exacerbate the injury. These pathogenic injury processes are poorly understood and accordingly no effective neuroprotective treatment is available so far. Experimental models are essential for further clarification of the highly complex pathology of traumatic brain injury towards the development of novel treatments. Among the rodent models of traumatic brain injury the most commonly used are the weight-drop, the fluid percussion, and the cortical contusion injury models. As the entire spectrum of events that might occur in traumatic brain injury cannot be covered by one single rodent model, the design and choice of a specific model represents a major challenge for neuroscientists. This review summarizes and evaluates the strengths and weaknesses of the currently available rodent models for traumatic brain injury.

Inhibition of myosin light chain kinase reduces brain edema formation after traumatic brain injury

The role of the endothelial contractile apparatus in the process of brain edema formation after brain trauma is not characterized. Phosphorylation of myosin light chains by myosin light chain kinases (MLCK) activates endothelial contractile elements and results in a rearrangement of the cytoskeleton. This may enhance post-traumatic blood-brain barrier dysfunction. In order to investigate the role of the MLCK on brain edema formation and blood-brain barrier permeability after brain injury, mice were anesthetized and subjected to a controlled cortical impact (CCI). MLCK expression is significantly up-regulated after CCI with a maximum 12 h post-injury. Specific inhibition of MLCK by ML-7 resulted in a reduction of phosphorylation of myosin light chains and improved blood-brain-barrier integrity. Accordingly, ML-7 attenuated post-traumatic brain edema formation and intracranial hypertension 24 h after CCI. Prevention of brain edema formation did not translate into improved neurological outcome or reduced brain lesion. In conclusion, the results confirm that the endothelial contractile apparatus is activated by CCI and opens the endothelial barrier leading to vasogenic brain edema formation. Lack of neurological and histological improvement suggests that specific targeting of vasogenic brain edema at the endothelial level is not sufficient to limit secondary brain damage and has, therefore, to be combined with other potential neuroprotective strategies.

Quantitative T2 mapping as a potential marker for the initial assessment of the severity of damage after traumatic brain injury in rat

Severity of traumatic brain injury (TBI) positively correlates with the risk of post-traumatic epilepsy (PTE). Studies on post-traumatic epileptogenesis would greatly benefit from markers that at acute phase would reliably predict the extent and severity of histologic brain damage caused by TBI in individual subjects. Currently in experimental models, severity of TBI is determined by the pressure of applied load that does not directly reflect the extent of inflicted brain injury, mortality within experimental population, or impairment in behavioral tests that are laborious to perform. We aimed to compare MRI markers measured at acute post-injury phase to previously used indicators of injury severity in the ability to predict the extent of histologically determined post-traumatic tissue damage. We used lateral fluid-percussion injury model in rat that is a clinically relevant model of closed head injury in humans, and results in PTE in severe cases. Rats (48 injured, 12 controls) were divided into moderate (mTBI) and severe (sTBI) groups according to impact strength. MRI data (T2, T2*, lesion volume) were acquired 3 days post-injury. Motor deficits were analysed using neuroscore (NS) and beam balance (BB) tests 2 and 3 days post-injury, respectively. Histological evaluation of lesion volume (Fluoro-Jade B) was used as the reference outcome measure, and was performed 2 weeks after TBI. From MRI parameters studied, quantitative T2 values of cortical lesion not only correlated with histologic lesion volume (P<0.001, r=0.6, N=34), as well as NS (P<0.01, r=-0.5, N=34) and BB (P<0.01, r=-0.5, N=34) results, but also successfully differentiated animals with mTBI from those with sTBI 70.6 +/- 6.2 6.2 ms vs. 75.9 +/- 2.6 ms, P<0.001). Quantitative T2 of the lesion early after TBI can serve as an indicator of the severity of post-traumatic cortical damage and neuro-motor impairment, and has a potential as a clinical marker for identification of individuals with elevated risk of PTE.

Traumatic brain injury in the rat using the fluid-percussion model

Traumatic brain injury is a leading cause of death and disability, particularly among young adults. During closed head trauma, the injury process is initiated by the impact of the brain against the inner table of the calvarium. Subsequently, there is prompt initiation of a complex biochemical, cellular, and physiological injury cascade that may take days to complete. From a functional standpoint, this culminates in neurologic dysfunction and, if severe, death. This unit describes an impact-induced brain trauma model in rats which replicates nonpenetrating head injury. It does not model either penetrating or ischemic brain injuries.

Cortical edema in moderate fluid percussion brain injury is attenuated by vagus nerve stimulation

Development of cerebral edema (intracellular and/or extracellular water accumulation) following traumatic brain injury contributes to mortality and morbidity that accompanies brain injury. Chronic intermittent vagus nerve stimulation (VNS) initiated at either 2 h or 24 h (VNS: 30 s train of 0.5 mA, 20 Hz, biphasic pulses every 30 min) following traumatic brain injury enhances recovery of motor and cognitive function in rats in the weeks following brain injury; however, the mechanisms of facilitated recovery are unknown. The present study examines the effects of VNS on development of acute cerebral edema following unilateral fluid percussion brain injury (FPI) in rats, concomitant with assessment of their behavioral recovery. Two hours following FPI, VNS was initiated. Behavioral testing, using both beam walk and locomotor placing tasks, was conducted at 1 and 2 days following FPI. Edema was measured 48 h post-FPI by the customary method of region-specific brain weights before and after complete dehydration. Results of this study replicated that VNS initiated at 2 h after FPI: 1) effectively facilitated the recovery of vestibulomotor function at 2 days after FPI assessed by beam walk performance (P<0.01); and 2) tended to improve locomotor placing performance at the same time point (P=0.18). Most interestingly, results of this study showed that development of edema within the cerebral cortex ipsilateral to FPI was significantly attenuated at 48 h in FPI rats receiving VNS compared with non-VNS FPI rats (P<0.04). Finally, a correlation analysis between beam walk performance and cerebral edema following FPI revealed a significant inverse correlation between behavior performance and cerebral edema. Together, these results suggest that VNS facilitation of motor recovery following experimental brain injury in rats is associated with VNS-mediated attenuation of cerebral edema.

Late effects of enriched environment (EE) plus multimodal early onset stimulation (MEOS) after traumatic brain injury in rats: Ongoing improvement of neuromotor function despite sustained volume of the CNS lesion

Recently we showed that the combination between MEOS and EE applied to rats for 7-15 days after traumatic brain injury (TBI) was associated with reduced CNS lesion volume and enhanced reversal of neuromotor dysfunction. In a continuation of this work, we tested whether these effects persisted for longer post-operative periods, e.g. 30 days post-injury (dpi). Rats were subjected to lateral fluid percussion (LFP) or to sham injury. After LFP, one third of the animals (injured and sham) was placed under conditions of standard housing (SH), one third was kept in EE-only, and one third received EE+MEOS. Standardized composite neuroscore (NS) for neurological functions and computerized analysis of the vibrissal motor performance were used to assess post-traumatic neuromotor deficits. These were followed by evaluation of the cortical lesion volume (CLV) after immunostaining for neuron-specific enolase, caspase 3 active, and GFAP. Finally, the volume of cortical lesion containing regeneration-associated proteins (CLV-RAP) was determined in sections stained for GAP-43, MAP2, and neuronal class III beta-tubulin. We found (i) no differences in the vibrissal motor performance; (ii) EE+MEOS rats performed significantly better than SH rats in NS; (iii) EE-only and EE+MEOS animals, but not SH rats, showed better recovery at 30 dpi than at 15 dpi; (iv) no differences among all groups in CLV (larger than that at 15 dpi) and CLV-RAP, despite a clear tendency to reduction in the EE-only and EE+MEOS rats. We conclude that EE+MEOS retards, but cannot prevent the increase of lesion volume. This retardation is sufficient for a continuous restoration of neurological functions.

Temporal window of vulnerability to repetitive experimental concussive brain injury

OBJECTIVE

Repetitive concussive brain injury (CBI) is associated with cognitive alterations and increased risk of neurodegenerative disease.

METHODS

To evaluate the temporal window during which the concussed brain remains vulnerable to a second concussion, anesthetized mice were subjected to either sham injury or single or repetitive CBI (either 3, 5, or 7 days apart) using a clinically relevant model of CBI. Cognitive, vestibular, and sensorimotor function (balance and coordination) were evaluated, and postmortem histological analyses were performed to detect neuronal degeneration, cytoskeletal proteolysis, and axonal injury.

RESULTS

No cognitive deficits were observed in sham-injured animals or those concussed once. Mice subjected to a second concussion within 3 or 5 days exhibited significantly impaired cognitive function compared with either sham-injured animals (P < 0.05) or mice receiving a single concussion (P < 0.01). No cognitive deficits were observed when the interconcussion interval was extended to 7 days, suggestive of a transient vulnerability of the brain during the first 5 days after an initial concussion. Although all concussed mice showed transient motor deficits, vestibulomotor dysfunction was more pronounced in the group that sustained two concussions 3 days apart (P < 0.01 compared with all other groups). Although scattered degenerating neurons, evidence of cytoskeletal damage, and axonal injury were detected in selective brain regions between 72 hours and 1 week after injury in all animals sustaining a single concussion, the occurrence of a second concussion 3 days later resulted in significantly greater traumatic axonal injury (P < 0.05) than that resulting from a single CBI.

CONCLUSION

These data suggest that a single concussion is associated with behavioral dysfunction and subcellular alterations that may contribute to a transiently vulnerable state during which a second concussion within 3 to 5 days can lead to exacerbated and more prolonged axonal damage and greater behavioral dysfunction.

Excitotoxic mechanisms and the role of astrocytic glutamate transporters in traumatic brain injury

Glutamate excitotoxicity plays an important role in the development of secondary injuries that occur following traumatic brain injury (TBI), and contributes significantly to expansion of the total volume of injury. Acute increases in extracellular glutamate levels have been detected in both experimental brain trauma models and in human patients, and can lead to over-stimulation of glutamate receptors, resulting in a cascade of excitotoxic-related mechanisms culminating in neuronal damage. These elevated levels of glutamate can be effectively controlled by the astrocytic glutamate transporters GLAST (EAAT1) and GLT-1 (EAAT2). However, evidence indicate these transporters and splice variant are downregulated shortly following the insult, which then precipitates glutamate-mediated excitotoxic conditions. Lack of success with glutamate receptor antagonists as a potential source of clinical intervention treatment following TBI has resulted in the necessity for a better understanding of the mechanisms that underlie the process of excitotoxicity, including the function and regulation of glutamate transporters. Such new insight should improve the likelihood of development of novel avenues for therapeutic intervention following TBI.

Selective temporal and regional alterations of Nogo-A and small proline-rich repeat protein 1A (SPRR1A) but not Nogo-66 receptor (NgR) occur following traumatic brain injury in the rat

Axons show a poor regenerative capacity following traumatic central nervous system (CNS) injury, partly due to the expression of inhibitors of axonal outgrowth, of which Nogo-A is considered the most important. We evaluated the acute expression of Nogo-A, the Nogo-66 receptor (NgR) and the novel small proline-rich repeat protein 1A (SPRR1A, previously undetected in brain), following experimental lateral fluid percussion (FP) brain injury in rats. Immunofluorescence with antibodies against Nogo-A, NgR and SPRR1A was combined with antibodies against the neuronal markers NeuN and microtubule-associated protein (MAP)-2 and the oligodendrocyte marker RIP, while Western blot analysis was performed for Nogo-A and NgR. Brain injury produced a significant increase in Nogo-A expression in injured cortex, ipsilateral external capsule and reticular thalamus from days 1-7 post-injury (P < 0.05) compared to controls. Increased expression of Nogo-A was observed in both RIP- and NeuN positive (+) cells in the ipsilateral cortex, in NeuN (+) cells in the CA3 region of the hippocampus and reticular thalamus and in RIP (+) cells in white matter tracts. Alterations in NgR expression were not observed following traumatic brain injury (TBI). Brain injury increased the extent of SPRR1A expression in the ipsilateral cortex and the CA3 at all post-injury time-points in NeuN (+) cells. The marked increases in Nogo-A and SPRR1A in several important brain regions suggest that although inhibitors of axonal growth may be upregulated, the injured brain is also capable of expressing proteins promoting axonal outgrowth following TBI.

Acute, transient hemorrhagic hypotension does not aggravate structural damage or neurologic motor deficits but delays the long-term cognitive recovery following mild to moderate traumatic brain injury

OBJECTIVES

Posttraumatic hypotension is believed to increase morbidity and mortality in traumatically brain-injured patients. Using a clinically relevant model of combined traumatic brain injury with superimposed hemorrhagic hypotension in rats, the present study evaluated whether a reduction in mean arterial blood pressure aggravates regional brain edema formation, regional cell death, and neurologic motor/cognitive deficits associated with traumatic brain injury.

DESIGN

Experimental prospective, randomized study in rodents.

SETTING

Experimental laboratory at a university hospital.

SUBJECTS

One hundred nineteen male Sprague-Dawley rats weighing 350-385 g.

INTERVENTIONS

Experimental traumatic brain injury of mild to moderate severity was induced using the lateral fluid percussion brain injury model in anesthetized rats (n = 89). Following traumatic brain injury, in surviving animals one group of animals was subjected to pressure-controlled hemorrhagic hypotension, maintaining the mean arterial blood pressure at 50-60 mm Hg for 30 mins (n = 47). The animals were subsequently either resuscitated with lactated Ringer's solution (three times shed blood volume, n = 18) or left uncompensated (n = 29). Other groups of animals included those with isolated traumatic brain injury (n = 34), those with isolated hemorrhagic hypotension (n = 8), and sham-injured control animals receiving anesthesia and surgery alone (n = 22).

MEASUREMENTS AND MAIN RESULTS

The withdrawal of 6-7 mL of arterial blood significantly reduced mean arterial blood pressure by 50% without decreasing arterial oxygen saturation or Pao2. Brain injury induced significant cerebral edema (p < .001) in vulnerable brain regions and cortical tissue loss (p < .01) compared with sham-injured animals. Neither regional brain edema formation at 24 hrs postinjury nor the extent of cortical tissue loss assessed at 7 days postinjury was significantly aggravated by superimposed hemorrhagic hypotension. Brain injury-induced neurologic deficits persisted up to 20 wks after injury and were also not aggravated by the hemorrhagic hypotension. Cognitive dysfunction persisted for up to 16 wks postinjury. The superimposition of hemorrhagic hypotension significantly delayed the time course of cognitive recovery.

CONCLUSIONS

A single, acute hypotensive event lasting 30 mins did not aggravate the short- and long-term structural and motor deficits but delayed the speed of recovery of cognitive function associated with experimental traumatic brain injury.

Activation of Rho after traumatic brain injury and seizure in rats

Traumatic brain injury (TBI) is characterized by a progressive cell loss and a lack of axonal regeneration. In the central nervous system (CNS), the Rho signaling pathway regulates the neuronal response to growth inhibitory proteins and regeneration of damaged axons, and Rho activation is also correlated with an increased susceptibility to apoptosis. To evaluate whether traumatic brain injury (TBI) results in changes in Rho activation in vulnerable regions of the brain, GTP-RhoA pull down assays were performed on rat cortical and hippocampal tissue homogenates obtained from 24 h to 3 days following lateral fluid percussion brain injury (FPI). Following FPI, a significantly increased RhoA activation was observed from 24 h to 3 days post-injury in the cortex and by 3 days in the hippocampus ipsilateral to the injury. We also detected activated RhoA in the cortex and hippocampus contralateral to the injury, without concomitant changes in total RhoA levels. To determine if immediate post-traumatic events such as seizures may activate Rho, we examined RhoA activation in the brains of rats with kainic acid-induced seizures. Severe seizures resulted in bilateral RhoA activation in the cortex and hippocampus. Together, these results indicate that RhoA is activated in vulnerable brain regions following traumatic and epileptic insults to the CNS.

Reversal of neuromotor and cognitive dysfunction in an enriched environment combined with multimodal early onset stimulation after traumatic brain injury in rats

This study was designed to investigate the additional benefits of a multimodal early onset stimulation (MEOS) paradigm when combined with enriched environment (EE) versus EE only and standard housing (SH) on the recovery after experimental traumatic brain injury (TBI). Male Sprague- Dawley rats were subjected to moderate lateral fluid percussion (LFP) brain injury (n = 40) or sham operation (n = 6). Thereafter, the injured and sham/EE + MEOS and EE only groups were placed into a complex EE consisting of tunnel-connected wide-bodied cages with various beddings, inclining platforms, and toys. Along with group living and environmental complexity, injured and sham/EE + MEOS animals were additionally exposed to a standardized paradigm of multimodal stimulation including auditory, visual, olfactory, and motor stimuli. In contrast, injured and sham/SH groups were housed individually without stimulation. A standardized composite neuroscore (NS) test was used to assess acute post-traumatic neuromotor deficits (24 h after injury) and recovery on days 7 and 15; recovery of cognitive function was assessed on days 11-15 using the Barnes maze. Neuromotor impairment was comparable in all injured animals at 24 h post-injury, but braininjured EE + MEOS rats performed significantly better than both brain-injured SH and EE groups when tested on post-injury days 7 and 15 (p = 0.004). Similarly, latencies to locate the hidden box under the Barnes maze platform were significantly shortened in EE + MEOS animals at day 15 (p = 0.003). These results indicate that the reversal of neuromotor and cognitive dysfunction after TBI can be substantially enhanced when MEOS is added to EE.

Multimodal early onset stimulation combined with enriched environment is associated with reduced CNS lesion volume and enhanced reversal of neuromotor dysfunction after traumatic brain injury in rats

This study was designed to determine whether exposure to multimodal early onset stimulation (MEOS) combined with environmental enrichment (EE) after traumatic brain injury (TBI) would improve neurological recovery and to elucidate its morphological correlates. Male Sprague-Dawley rats were subjected to lateral fluid percussion (LFP) brain injury or to sham operation. After LFP, one-third of the animals (injured and sham) were placed under conditions of standard housing (SH), one-third were kept in EE only, and one-third received EE + MEOS. Assessment of neuromotor function 24 h post-injury using a standardized composite neuroscore test revealed an identical pattern of neurological impairment in all animals subjected to LFP. Neuromotor dysfunction in SH animals remained on a similar level throughout the experiment, while improvements were noted in both other groups 7 days post-injury (dpi). On 15 dpi, reversal of neuromotor dysfunction was significantly better in EE + MEOS animals vs. SH- and EE-only groups. In parallel, the comparison of lesion volume in EE + MEOS- vs. EE-only vs. SH rats revealed that animals exposed to EE + MEOS had consistently the lowest values (mm3, mean +/- SD; n = 6 rats in each group) as measured in serial brain sections immunostained for neuron-specific enolase (5.2 +/- 3.4 < or = 5.5 +/- 4.1 < 9.5 +/- 1.9), caspase 3-active/C3A (5.9 +/- 4.0 < or = 6.4 +/- 3.9 < 10.3 +/- 1.8) and glial fibrillary acidic protein (6.0 +/- 3.4 < or = 6.5 +/- 4.3 < 10.7 +/- 1.2). This first report on the effect of EE + MEOS treatment strongly indicates that the combined exposure reduces CNS scar formation and reverses neuromotor deficits after TBI in rats.

Animal models of head trauma

Animal models of traumatic brain injury (TBI) are used to elucidate primary and secondary sequelae underlying human head injury in an effort to identify potential neuroprotective therapies for developing and adult brains. The choice of experimental model depends upon both the research goal and underlying objectives. The intrinsic ability to study injury-induced changes in behavior, physiology, metabolism, the blood/tissue interface, the blood brain barrier, and/or inflammatory- and immune-mediated responses, makes in vivo TBI models essential for neurotrauma research. Whereas human TBI is a highly complex multifactorial disorder, animal trauma models tend to replicate only single factors involved in the pathobiology of head injury using genetically well-defined inbred animals of a single sex. Although such an experimental approach is helpful to delineate key injury mechanisms, the simplicity and hence inability of animal models to reflect the complexity of clinical head injury may underlie the discrepancy between preclinical and clinical trials of neuroprotective therapeutics. Thus, a search continues for new animal models, which would more closely mimic the highly heterogeneous nature of human TBI, and address key factors in treatment optimization.

Lateral fluid percussion brain injury: a 15-year review and evaluation

This article comprehensively reviews the lateral fluid percussion (LFP) model of traumatic brain injury (TBI) in small animal species with particular emphasis on its validity, clinical relevance and reliability. The LFP model, initially described in 1989, has become the most extensively utilized animal model of TBI (to date, 232 PubMed citations), producing both focal and diffuse (mixed) brain injury. Despite subtle variations in injury parameters between laboratories, universal findings are evident across studies, including histological, physiological, metabolic, and behavioral changes that serve to increase the reliability of the model. Moreover, demonstrable histological damage and severity-dependent behavioral deficits, which partially recover over time, validate LFP as a clinically-relevant model of human TBI. The LFP model, also has been used extensively to evaluate potential therapeutic interventions, including resuscitation, pharmacologic therapies, transplantation, and other neuroprotective and neuroregenerative strategies. Although a number of positive studies have identified promising therapies for moderate TBI, the predictive validity of the model may be compromised when findings are translated to severely injured patients. Recently, the clinical relevance of LFP has been enhanced by combining the injury with secondary insults, as well as broadening studies to incorporate issues of gender and age to better approximate the range of human TBI within study design. We conclude that the LFP brain injury model is an appropriate tool to study the cellular and mechanistic aspects of human TBI that cannot be addressed in the clinical setting, as well as for the development and characterization of novel therapeutic interventions. Continued translation of pre-clinical findings to human TBI will enhance the predictive validity of the LFP model, and allow novel neuroprotective and neuroregenerative treatment strategies developed in the laboratory to reach the appropriate TBI patients.

CHARACTERIZATION OF A NEW RAT MODEL OF EXPERIMENTAL COMBINED NEUROTRAUMA

Traumatic brain injury (TBI) is present in two-thirds of patients with multiple injuries and in one-third combined with injuries of the extremities. Studies on interactive effects between central and peripheral injuries are scarce due to the absence of clinically relevant models. To meet the demand for "more-hit" models, an experimental model of combined neurotrauma (CNT) incorporating a standardized TBI via lateral fluid percussion (LFP) together with a peripheral bone fracture, i.e., tibia fracture, is introduced. Sprague-Dawley rats were randomized to four experimental groups: controls (n = 10), animals with TBI (n = 30), animals with tibia fracture (n = 30), and animals with CNT (n = 30). Morphological aspects of brain and bone injury were analyzed via standard histopathological procedures and x-ray. Trauma-induced neuromotor dysfunction was assessed using a standardized neuroscore. For interactive effects between injuries, we studied the extent and temporal pattern of circulating interleukin 6 (IL-6) levels via immunoassay and callus formation at fracture sites by means of microradiography. LFP produced an ipsilateral lesion with cortical contusion, hemorrhage, mass shift, and neuronal cell loss (adjacent cortex and hippocampus CA-2/-3), along with contralateral neuromotor dysfunction. X-rays confirmed complete fractures in the middle of the bone shaft. The type of injury (P < 0.001) and time (P = 0.022) were significantly associated with increased IL-6 levels. CNT produced the highest IL-6 plasma levels with a maximum peak at 6 h after trauma (P < 0.001). Similarly, callus formation at fracture sites in CNT was significantly increased versus fracture only (P < 0,01). The CNT model mimics a variety of clinically relevant features known from human multiple injury, including TBI, and offers novel approaches for investigation of interactive mechanisms and therapeutic approaches.

Differential Effects of the Anticonvulsant Topiramate on Neurobehavioral and Histological Outcomes following Traumatic Brain Injury in Rats

The efficacy of topiramate, a novel therapeutic agent approved for the treatment of seizure disorders, was evaluated in a model of traumatic brain injury (TBI). Adult male rats were anesthetized (sodium pentobarbital, 60 mg/kg, i.p.), subjected to lateral fluid percussion brain injury (n = 60) or sham injury (n = 47) and randomized to receive either topiramate or vehicle at 30 min (30 mg/kg, i.p.), and 8, 20 and 32 h postinjury (30 mg/kg, p.o.). In Study A, memory was evaluated using a Morris water maze at 48 h postinjury, after which brain tissue was evaluated for regional cerebral edema. In Study B, animals were evaluated for motor function at 48 h and 1, 2, 3, and 4 weeks postinjury using a composite neuroscore and the rotating pole test and for learning ability at 4 weeks. Brains were analyzed for hemispheric tissue loss and hippocampal CA3 cell loss. Topiramate had no effect on posttraumatic cerebral edema or histologic damage when compared to vehicle. At 48 h, topiramate treatment improved memory function in sham but not brain-injured animals, while at one month postinjury it impaired learning performance in brain-injured but not sham animals. Topiramate significantly improved composite neuroscores at 4 weeks postinjury and rotating pole performance at 1 and 4 weeks postinjury, suggesting a potentially beneficial effect on motor function following TBI.

Low-dose prostacyclin improves cortical perfusion following experimental brain injury in the rat

It was recently shown that prostacyclin at a low dose reduces cortical cell death following brain trauma in the rat. Conceivably, prostacyclin with its vasodilatory, anti-aggregatory, anti-adhesive and permeability-reducing properties improved a compromised perfusion caused by post-traumatic vasoconstriction, microthrombosis and increased microvascular permeability. The objective of the present study was therefore to investigate the hemodynamic effects of low-dose prostacyclin in the traumatized rat cortex. Following a fluid percussion brain injury or a sham procedure, animals were treated with a continuous intravenous infusion of prostacyclin of 1 or 2 ng x kg(-1) x min(-1), or vehicle. Blood flow ([(14)C]-iodoantipyrine), the permeability-surface area product (PS) for [(51)Cr]-EDTA, and brain water content were measured after 3 or 48 h of treatment. Blood flow values in the injured cortex were transiently reduced to 0.42 +/- 0.2 mL x min(-1) in the vehicle group 3 h following trauma from a corresponding value of about 1.6 mL x min(-1) in the sham group, with recovery of blood flow after 48 h. Prostacyclin treatment caused a dose-dependent increase in blood flow which reached statistical significance 48 h following trauma. Brain water content and PS increased in the injured cortex post trauma and the higher dose of prostacyclin increased these parameters further at 48 h compared to the vehicle group (p < 0.05). The latter effects of prostacyclin cannot be attributed to an increase in permeability, as prostacyclin did not influence PS or brain water content following sham trauma. In fact prostacyclin has been shown to have permeability-decreasing properties. We conclude that prostacyclin improves cortical perfusion following brain trauma. The simultaneous aggravation of brain edema can be explained by an increased surface area, perhaps in combination with increased capillary hydrostatic pressure.

Effects of magnesium administration on brain edema and blood-brain barrier breakdown after experimental traumatic brain injury in rats

In this study, we examined the effects of magnesium sulfate administration on brain edema and blood-brain barrier breakdown after experimental traumatic brain injury in rats. Seventy-one adult male Sprague-Dawley rats were anesthetized, and experimental closed head trauma was induced by allowing a 450-g weight to fall from a 2-m height onto a metallic disk fixed to the intact skull. Sixty-eight surviving rats were randomly assigned to receive an intraperitoneal bolus of either 750 micromol/kg magnesium sulfate (group 4; n = 30) or 1 mL of saline (group 2; n = 30) 30 minutes after induction of traumatic brain injury; 39 nontraumatized animals received saline (group 1; n = 21) or magnesium sulfate (group 3; n = 18) with an identical protocol of administration. Brain water content and brain tissue specific gravity, as indicators of brain edema, were measured 24 hours after traumatic brain injury. Blood-brain barrier integrity was evaluated quantitatively 24 hours after injury by spectrophotometric assay of Evans blue dye extravasations. In the magnesium-treated injured group, brain water content was significantly reduced (left hemisphere: group 2, 83.2 +/- 0.8; group 4, 78.4 +/- 0.7 [P <.05]; right hemisphere: group 2, 83.1 +/- 0.7; group 4, 78.4 +/- 0.5. [P <.05]) and brain tissue specific gravity was significantly increased (left hemisphere: group 2, 1.0391 +/- 0.0008; group 4, 1.0437 +/- 0.001 [P <.05]; right hemisphere, group 2, 1.0384 +/- 0.001; group 4, 1.0442 +/- 0.005 [P <.05]) compared with the saline-treated injured group. Evans blue dye content in the brain tissue was significantly decreased in the magnesium-treated injured group (left hemisphere: group 2, 0.0204 +/- 0.03; group 4, 0.0013 +/- 0.0002 [P <.05]; right hemisphere: group 2, 0.0064 +/- 0.0009; group 4, 0.0013 +/- 0.0003 [P <.05]) compared with the saline-treated injured group. The findings of the present study support that beneficial effects of magnesium sulfate exist after severe traumatic brain injury in rats. These results also indicate that a blood-brain barrier permeability defect occurs after this model of diffuse traumatic brain injury, and magnesium seems to attenuate this defect.

The glutamate AMPA receptor antagonist, YM872, attenuates cortical tissue loss, regional cerebral edema, and neurological motor deficits after experimental brain injury in rats

A massive increase in extracellular glutamate is thought to contribute to brain damage after traumatic brain injury. We examined the neuroprotective effect of the AMPA receptor antagonist YM872 in a rat head injury model using the fluid-percussion procedure. Male Sprague-Dawley rats were subjected to right lateral (parasagittal) fluid-percussion brain injury or sham injury. At 15 min postinjury, they received either YM872 (20 mg/kg/h, 20 mg/3 mL) or normal saline (vehicle) intravenously for 4 h. The administration of YM872 significantly improved the composite neuroscore at 1 and 2 weeks postinjury (p < 0.05), and markedly reduced the volume of tissue loss in the injured cortex (p < 0.05). It also significantly reduced cerebral edema in the ipsilateral parietal cortex at 48 h postinjury (p < 0.01). These results indicate that the posttraumatic administration of YM872 may be neuroprotective by ameliorating cortical tissue loss and regional cerebral edema, and suggest the importance of AMPA receptors in traumatic brain damage involving secondary injury processes.

Structural and functional damage sustained by mitochondria after traumatic brain injury in the rat: evidence for differentially sensitive populations in the cortex and hippocampus

The cellular and molecular pathways initiated by traumatic brain injury (TBI) may compromise the function and structural integrity of mitochondria, thereby contributing to cerebral metabolic dysfunction and cell death. The extent to which TBI affects regional mitochondrial populations with respect to structure, function, and swelling was assessed 3 hours and 24 hours after lateral fluid-percussion brain injury in the rat. Significantly less mitochondrial protein was isolated from the injured compared with uninjured parietotemporal cortex, whereas comparable yields were obtained from the hippocampus. After injury, cortical and hippocampal tissue ATP concentrations declined significantly to 60% and 40% of control, respectively, in the absence of respiratory deficits in isolated mitochondria. Mitochondria with ultrastructural morphologic damage comprised a significantly greater percent of the population isolated from injured than uninjured brain. As determined by photon correlation spectroscopy, the mean mitochondrial radius decreased significantly in injured cortical populations (361 +/- 40 nm at 24 hours) and increased significantly in injured hippocampal populations (442 +/- 36 at 3 hours) compared with uninjured populations (Ctx: 418 +/- 44; Hipp: 393 +/- 24). Calcium-induced deenergized swelling rates of isolated mitochondrial populations were significantly slower in injured compared with uninjured samples, suggesting that injury alters the kinetics of mitochondrial permeability transition (MPT) pore activation. Cyclosporin A (CsA)-insensitive swelling was reduced in the cortex, and CsA-sensitive and CsA-insensitive swelling both were reduced in the hippocampus, demonstrating that regulated MPT pores remain in mitochondria isolated from injured brain. A proposed mitochondrial population model synthesizes these data and suggests that cortical mitochondria may be depleted after TBI, with a physically smaller, MPT-regulated population remaining. Hippocampal mitochondria may sustain damage associated with ballooned membranes and reduced MPT pore calcium sensitivity. The heterogeneous mitochondrial response to TBI may underlie posttraumatic metabolic dysfunction and contribute to the pathophysiology of TBI.

Modulation of aquaporin-4 water transport in a model of TBI

Our Laboratory has pursued the hypothesis that traumatic brain edema is predominantly cellular and recent supportive evidence has been obtained indicating a non-extracellular route for sodium and water entering brain. The aim of this study was to investigate if astrocytic endfeet are involved in this passage, using a potent activator of Protein Kinase C (phorbol ester) to modify and closing the Aquaporin 4 (AQP4), a water channel specific for astrocytic endfoot. Anaesthetized Sprague-Dawley rats were subjected to an intracerebroventricular bolus of phorbol ester (50 pmol/4 microl) or vehicle, in the right hemisphere and after 30 minutes they were exposed to the well-established conical contusion model (3 mm depth at 6 m/sec) on the same side. After trauma, they were subjected to 5 hours of drug continuous infusion, then sacrificed. Water content measurements for both right (injured) and left (uninjured) hemispheres were calculated using the wet weight/dry weight technique. Results of these experiments showed a significant decrease in water content in injured phorbol treated animals, underlying that AQP4 regulation plays an important role in brain edema following stroke, and supporting the concept of cellular formation for edema via astrocytic foot processes.

Novel therapies in development for the treatment of traumatic brain injury

In industrialised countries, the mean per capita incidence of traumatic brain injury (TBI) that results in a hospital presentation is 250 per 100,000. In Europe and North America alone, this translates to > 2 million TBI presentations annually. Approximately 25% of these presentations are admitted for hospitalisation. Despite the significance of these figures, there is no single interventional pharmacotherapy that has shown efficacy in the treatment of clinical TBI. This lack of efficacy in clinical trials may be due, in part, to the inherent heterogeneity of the traumatic brain injury population. However, it is the multifactorial nature of secondary injury that also poses a major hurdle, particularly for those therapies that have been designed to specifically target an individual injury factor. It is now becoming increasingly recognised that any successful TBI therapy may have to simultaneously affect multiple injury factors, somewhat analogous to other broad spectrum interventions. Recent efforts in experimental TBI have therefore focussed on developing novel pharmacotherapies that may affect multiple injury factors and thus improve the likelihood of a successful outcome. While a number of interventions are noteworthy in this regard, this review will focus on three novel compounds that show particular promise: magnesium, substance P antagonists and cyclosporin A.

Delayed changes in regional brain energy metabolism following cerebral concussion in rats

Traumatic brain injury (TBI) results in an acute altered metabolic profile of brain tissue which resolves within hours of initial insult and yet some of the functional deficits and cellular perturbations persist for days. It is hypothesized that a delayed change in energy status does occur and is a factor in the neural tissue's ability to survive and regain function. Regional metabolic profile and glucose consumption were determined at either 1 or 3 days following two different intensities of parasagittal fluid-percussion (F-P). A significant decrease in both 1CMRgluc and levels of ATP and P-creatine was evident in the hemisphere ipsilateral to the trauma at 1 day after the insult. The effect was greater in the cortical than the subcortical regions and was more pronounced at the higher trauma intensity. Normalization of glucose consumption and energy levels was essentially complete by 3 days. It would appear that the delayed metabolic changes at 1 day postinsult cannot be explained by a secondary ischemia since the changes in the metabolite profile do not elicit an increase in the consumption of glucose. These changes in energy metabolites may account for and contribute to the chronic neurological deficits following TBI.

Interleukin-1 beta is required for the early evolution of reactive astrogliosis following CNS lesion

The CNS response to injury is characterized by the rapid activation of astrocytes in a process known as astrogliosis. The function of reactive astrocytes is controversial, in that both beneficial and detrimental properties are postulated. Identification of the molecules involved in regulating astrogliosis is an important step towards understanding astrocyte functions and establishing suitable conditions for CNS regeneration. We previously reported that inflammatory cytokines are regulators of astrogliosis but the key cytokine involved in initiating astrogliosis was unclear. We describe here that the elevation of glial fibrillary acid protein (GFAP) transcripts follows the very early rise of interleukin (IL)-1beta mRNA in a murine corticectomy model of CNS lesion. Furthermore, the injury-induced upregulation of GFAP mRNA and protein did not occur in mice genetically deficient for IL-1beta compared to wild-type animals. This was correlated with an absence of an increase in GFAP-immunoreactivity (GFAP-ir) in IL-1beta-null mice at 2 and 3 days of injury. However, by 5 to 7 days after the lesion, GFAP-ir was not different between cytokine-deficient and wild-type controls. Functionally, mice lacking IL-1beta exhibited a significant impairment in reformation of the blood-brain barrier (BBB) following corticectomy compared to wild-type controls. These findings suggest that the rapid production of IL-1beta following trauma plays a beneficial role in initiating astrogliosis in an attempt to restore the integrity of the BBB and seal off the wound site.

Neuropathological protection after traumatic brain injury in intact female rats versus males or ovariectomized females

An important consideration in traumatic brain injury (TBI) in females is the influence of hormones on recovery. Recent studies in both cerebral ischemia and TBI have demonstrated an attenuation in both damage and neurologic recovery following hormonal treatment. However, the ability of endogenous hormone levels to provide neuropathological protection after fluid percussion (FP) brain injury has not been studied. The purpose of this experiment was to determine whether endogenous circulating hormones in the female rat could provide neuroprotection compared to males and ovariectomized female animals. Sixty-four Sprague-Dawley rats underwent a moderate (1.7-2.2 atm) right parasagittal FP injury. Intact females (i.e., nonovariectomized) were subjected to injury either during the proestrous (TBI-FP, n = 18) phase of their cycle or nonproestrous (TBI-FNP, n = 19) phase. A separate group of females were ovariectomized (TBI-OVX, n = 10) 10 days prior to FP injury in order to reduce hormone levels. Male animals were also traumatized (TBI-M, n = 17). Appropriate sham controls (Sham-FP, n = 2; Sham-FNP, n = 2; Sham-OVX, n = 2; Sham-M, n = 2) also underwent all aspects of surgery except for the actual FP injury. All groups were sacrificed 3 days following TBI for analysis. Both intact female groups had significantly (p < 0.05) smaller cortical contusions compared to male animals. In addition to this finding, the TBI-FNP group was significantly (p < 0.04) different from the ovariectomized female animals. Ovariectomized rats had larger areas of damage compared to intact females. The TBI-OVX group's cortical contusion volume was similar to male animals. These results provide evidence for endogenous hormonal histopathological protection following parasagittal FP brain injury. The use of hormone therapy after TBI warrants continued exploration.

The duality of the inflammatory response to traumatic brain injury

One and a half to two million people sustain a traumatic brain injury (TBI) in the US each year, of which approx 70,000-90,000 will suffer from long-term disability with dramatic impacts on their own and their families' lives and enormous socio-economic costs. Brain damage following traumatic injury is a result of direct (immediate mechanical disruption of brain tissue, or primary injury) and indirect (secondary or delayed) mechanisms. These secondary mechanisms involve the initiation of an acute inflammatory response, including breakdown of the blood-brain barrier (BBB), edema formation and swelling, infiltration of peripheral blood cells and activation of resident immunocompetent cells, as well as the intrathecal release of numerous immune mediators such as interleukins and chemotactic factors. An overview over the inflammatory response to trauma as observed in clinical and in experimental TBI is presented in this review. The possibly harmful/beneficial sequelae of post-traumatic inflammation in the central nervous system (CNS) are discussed using three model mediators of inflammation in the brain, tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and transforming growth factor-beta (TGF-beta). While the former two may act as important mediators for the initiation and the support of post-traumatic inflammation, thus causing additional cell death and neurologic dysfunction, they may also pave the way for reparative processes. TGF-beta, on the other hand, is a potent anti-inflammatory agent, which may also have some deleterious long-term effects in the injured brain. The implications of this duality of the post-traumatic inflammatory response for the treatment of brain-injured patients using anti-inflammatory strategies are discussed.

Small shifts in craniotomy position in the lateral fluid percussion injury model are associated with differential lesion development

Previous studies have shown that location and direction of injury may affect outcome in experimental models of traumatic brain injury. Significant variability in outcome data has also been noted in studies using the lateral fluid percussion brain injury model (FPI) in rats. In recent studies from our laboratory, we observed considerable variability in localization and severity of tissue damage as a function of small changes in craniotomy position. To further address this issue, we examined the relationship between craniotomy position and brain lesion size/location in rats subjected to moderate FPI (2.28 +/- 0.18 atmospheres). With placement of a 5-mm craniotomy adjacent to the sagittal suture, there was both ipsilateral and contralateral damage as detected at 3 weeks posttrauma using T2-weighted magnetic resonance imaging (MRI). The MRI lesions were generally restricted to the hippocampus and subcortical layers. Shifting of the craniotomy site laterally was associated with increased ipsilateral tissue damage and a greater cortical component that correlated with distance from the sagittal suture. In contrast, the contralateral MRI lesion did not change significantly in size or location unless the center of the craniotomy was placed more than 3.5 mm from the sagittal suture, under which condition contralateral damage could no longer be detected. Ipsilateral tissue damage as determined from the MRI scans was linearly correlated to motor outcome but not with cognitive outcome as assessed by the Morris Water Maze. We conclude that craniotomy position is critical in determining extent and location of tissue injury produced during the lateral FPI model in rats. Addressing such potential variability is essential for studies that address either injury mechanisms or therapeutic treatments.

Free radical scavenger posttreatment improves functional and morphological outcome after fluid percussion injury in the rat

Reactive oxygen species (ROS) are thought to contribute to the secondary injury process after traumatic brain injury (TBI). ROS scavenging compounds have shown neuroprotective properties in various models of experimental brain injury, including TBI. Administration of nitrone radical scavengers has emerged as a promising pharmacological concept in focal experimental ischemia due to their low toxicity and neuroprotective properties, with a time window of several hours. The aim of this study was to test the neuroprotective efficacy of two nitrones, the readily blood-brain barrier (BBB) penetrating alpha-phenyl-N-tert-butyl nitrone (PBN) and the poorly BBB penetrating sulfo-derivative, 2-sulfo-phenyl-N-tert-butyl nitrone (S-PBN) after moderate (2.20-2.45 atm) lateral fluid percussion injury (FPI) in rats. Twenty-six rats received a 24-h intravenous infusion (30 mg/kg/h) of saline, PBN, or an equimolar dose of S-PBN beginning 30 min after FPI. Eight sham-operated animals were used as controls. Cognitive function was assessed using the Morris Water Maze at day 11-15 after TBI, neurological status at day 1, 4, and 8 and morphological outcome at day 15. PBN and S-PBN treatment significantly reduced the loss of ipsilateral hemispheric tissue whereas only S-PBN tended to reduce the cortical lesion volume. PBN treatment caused a significant improvement in the neurological score as compared to saline-treated animals, while S-PBN alone attenuated the cognitive deficit. Our results suggest that nitrone radical scavengers are neuroprotective when administered 30 min after FPI in rats. Differences in pharmacokinetics may account for the observed individual neuroprotective profiles of the two nitrones.