A model of diffuse traumatic brain injury in the immature rat

Pediatric Traumatic Brain Injury: An Update on Preclinical Models, Clinical Biomarkers, and the Implications of Cerebrovascular Dysfunction

Traumatic brain injury (TBI) is a leading cause of pediatric morbidity and mortality. Recent studies suggest that children and adolescents have worse post-TBI outcomes and take longer to recover than adults. However, the pathophysiology and progression of TBI in the pediatric population are studied to a far lesser extent compared to the adult population. Common causes of TBI in children are falls, sports/recreation-related injuries, non-accidental trauma, and motor vehicle-related injuries. A fundamental understanding of TBI pathophysiology is crucial in preventing long-term brain injury sequelae. Animal models of TBI have played an essential role in addressing the knowledge gaps relating to pTBI pathophysiology. Moreover, a better understanding of clinical biomarkers is crucial to diagnose pTBI and accurately predict long-term outcomes. This review examines the current preclinical models of pTBI, the implications of pTBI on the brain’s vasculature, and clinical pTBI biomarkers. Finally, we conclude the review by speculating on the emerging role of the gut-brain axis in pTBI pathophysiology.

Morphine attenuates neuroinflammation and blood-brain barrier disruption following traumatic brain injury through the opioidergic system

Endogenous opiates are suggested to have a role in the pathophysiology of traumatic brain injury (TBI). Furthermore, administration of opioidergic agents in TBI injured animals have been shown to affect the brain injury and provide neuroprotection post-TBI. This study aims to investigate the potential neuroprotective effects of morphine through inhibition of neuroinflammatory pathways in acute severe TBI. Male Wistar rats were divided into seven groups (24 rats per group): Sham, Vehicle (TBI + intraperitoneal (i.p) injection of normal saline), TBI + i.p injection of morphine in 1, 5 and 10 mg/kg doses (MOR 1, MOR 5 and MOR 10 groups), TBI + morphine (5 mg/kg i.p) + Naloxone (NAL + MOR), and TBI + morphine (5 mg/kg i.p) + Naltrindole (NALT + MOR). A severe diffuse TBI model (weight dropping Marmarou model) was used to induce TBI in rats. The veterinary coma scale (VCS), beam-walk, and beam-balance tasks were used to assess short-term neurological deficits. Histolopathological changes of brain tissue was evaluated using light microscopy and hematoxilin and eosin staining. Blood-Brain barrier (BBB) disruption was evaluated by the Evans Blue method 6 h post-injury. Brain water content and cerebrospinal fluid (CSF) content of IL-1β and IL-10 were assessed by the wet-dry method and enzyme-linked immunosorbent assay (ELISA), respectively. Morphine (1 and 5 mg/kg doses) attenuated BBB leakage, improved VCS score, pathological changes of brain tissue, and vestibulomotor function compared to the vehicle group (p < 0.0001). Only 5 mg/kg morphine attenuated brain edema (p < 0.0001). Furthermore, 1 and 5 mg/kg morphine significantly changed CSF concentration of IL-1β and IL-10 compared to the vehicle group (p < 0.0001). Inhibition of opioid receptors by naloxone and naltrindole abolished morphine neuroprotective effects (p < 0.0001 vs. MOR 5 group). This study suggests that morphine administration inhibits TBI-mediated neuroinflammation via opioid receptors and improves neurobehavioral function following TBI, which provides a potential therapeutic opportunity in the treatment of traumatic brain injury.

A new model of repeat mTBI in adolescent rats

Sports-related injury is frequently associated with repeated diffuse and mild traumatic brain injury (mTBI). We combined two existing models for inducing TBI in rats, the Impact Acceleration and Controlled Cortical Impact models, to create a new method relevant to the study of cognitive sequelae of repeat mTBI in adolescent athletes. Repeated mTBI, such as those incurred in sports, can result in a wide range of outcomes, with many individuals experiencing no chronic sequela while others develop profound cognitive and behavioral impairments, typically in the absence of lasting motor symptoms or gross tissue loss appreciable antemortem. It is critical to develop models of mTBI and repeat mTBI that have the flexibility to assess multiple parameters related to injury (e.g. number and magnitude of impacts, inter-injury interval, etc) that are associated with brain vulnerability compared to normal recovery. We designed a 3D-printed plastic implant to permanently secure a metal disc to the skull of adolescent rats in order to induce multiple injuries without performing multiple survival surgeries and also to minimize pre-injury anesthesia time. Rats were randomly assigned to sham injury (n = 12), single injury (n = 12; injury on P41), or repeat injury (n = 14; injuries on P35, P38, and P41) groups. Compared to single injury and sham injury, repeat injuries caused increased toe pinch reflex latency (F(2,34) = 4.126, p < .05) and diminished weight gain (F(2, 34) = 4.767, p < .05). Spatial navigation was tested using Morris water maze, beginning one week after the final injury (P48). While there were no differences between groups during acquisition, both single and repeat injuries resulted in deficits on probe trial performance (p < .01 and p < .05 respectively). Single injury animals also exhibited a deficit in working memory deficit across three days of testing (p < .05). Neither injury group had neuronal loss in the hilus or CA3, according to stereological quantification of NeuN. Therefore, by implanting a helmet we have created a relevant model of sports-related injury and repeated mTBI that results in subtle but significant changes in cognitive outcome in the absence of significant hippocampal cell death.

Neuro-Inflammation in Pediatric Traumatic Brain Injury-from Mechanisms to Inflammatory Networks

Compared to traumatic brain injury (TBI) in the adult population, pediatric TBI has received less research attention, despite its potential long-term impact on the lives of many children around the world. After numerous clinical trials and preclinical research studies examining various secondary mechanisms of injury, no definitive treatment has been found for pediatric TBIs of any severity. With the advent of high-throughput and high-resolution molecular biology and imaging techniques, inflammation has become an appealing target, due to its mixed effects on outcome, depending on the time point examined. In this review, we outline key mechanisms of inflammation, the contribution and interactions of the peripheral and CNS-based immune cells, and highlight knowledge gaps pertaining to inflammation in pediatric TBI. We also introduce the application of network analysis to leverage growing multivariate and non-linear inflammation data sets with the goal to gain a more comprehensive view of inflammation and develop prognostic and treatment tools in pediatric TBI.

Differences in pathological changes between two rat models of severe traumatic brain injury

The rat high-impact free weight drop model mimics the diffuse axonal injury caused by severe traumatic brain injury in humans, while severe controlled cortical impact can produce a severe traumatic brain injury model using precise strike parameters. In this study, we compare the pathological mechanisms and pathological changes between two rat severe brain injury models to identify the similarities and differences. The severe controlled cortical impact model was produced by an electronic controlled cortical impact device, while the severe free weight drop model was produced by dropping a 500 g free weight from a height of 1.8 m through a plastic tube. Body temperature and mortality were recorded, and neurological deficits were assessed with the modified neurological severity score. Brain edema and blood-brain barrier damage were evaluated by assessing brain water content and Evans blue extravasation. In addition, a cytokine array kit was used to detect inflammatory cytokines. Neuronal apoptosis in the brain and brainstem was quantified by immunofluorescence staining. Both the severe controlled cortical impact and severe free weight drop models exhibited significant neurological impairments and body temperature fluctuations. More severe motor dysfunction was observed in the severe controlled cortical impact model, while more severe cognitive dysfunction was observed in the severe free weight drop model. Brain edema, inflammatory cytokine changes and cortical neuronal apoptosis were more substantial and blood-brain barrier damage was more focal in the severe controlled cortical impact group compared with the severe free weight drop group. The severe free weight drop model presented with more significant apoptosis in the brainstem and diffused blood-brain barrier damage, with higher mortality and lower repeatability compared with the severe controlled cortical impact group. Severe brainstem damage was not found in the severe controlled cortical impact model. These results indicate that the severe controlled cortical impact model is relatively more stable, more reproducible, and shows obvious cerebral pathological changes at an earlier stage. Therefore, the severe controlled cortical impact model is likely more suitable for studies on severe focal traumatic brain injury, while the severe free weight drop model may be more apt for studies on diffuse axonal injury. All experimental procedures were approved by the Ethics Committee of Animal Experiments of Tianjin Medical University, China (approval No. IRB2012-028-02) in February 2012.

Toward development of clinically translatable diagnostic and prognostic metrics of traumatic brain injury using animal models: A review and a look forward

Traumatic brain injury is a leading cause of cognitive and behavioral deficits in children in the US each year. There is an increasing interest in both clinical and pre-clinical studies to discover biomarkers to accurately diagnose traumatic brain injury (TBI), predict its outcomes, and monitor its progression especially in the developing brain. In humans, the heterogeneity of TBI in terms of clinical presentation, injury causation, and mechanism has contributed to the many challenges associated with finding unifying diagnosis, treatment, and management practices. In addition, findings from adult human research may have little application to pediatric TBI, as age and maturation levels affect the injury biomechanics and neurophysiological consequences of injury. Animal models of TBI are vital to address the variability and heterogeneity of TBI seen in human by isolating the causation and mechanism of injury in reproducible manner. However, a gap between the pre-clinical findings and clinical applications remains in TBI research today. To take a step toward bridging this gap, we reviewed several potential TBI tools such as biofluid biomarkers, electroencephalography (EEG), actigraphy, eye responses, and balance that have been explored in both clinical and pre-clinical studies and have shown potential diagnostic, prognostic, or monitoring utility for TBI. Each of these tools measures specific deficits following TBI, is easily accessible, non/minimally invasive, and is potentially highly translatable between animals and human outcomes because they involve effort-independent and non-verbal tasks. Especially conspicuous is the fact that these biomarkers and techniques can be tailored for infants and toddlers. However, translation of preclinical outcomes to clinical applications of these tools necessitates addressing several challenges. Among the challenges are the heterogeneity of clinical TBI, age dependency of some of the biomarkers, different brain structure, life span, and possible variation between temporal profiles of biomarkers in human and animals. Conducting parallel clinical and pre-clinical research, in addition to the integration of findings across species from several pre-clinical models to generate a spectrum of TBI mechanisms and severities is a path toward overcoming some of these challenges. This effort is possible through large scale collaborative research and data sharing across multiple centers. In addition, TBI causes dynamic deficits in multiple domains, and thus, a panel of biomarkers combining these measures to consider different deficits is more promising than a single biomarker for TBI. In this review, each of these tools are presented along with the clinical and pre-clinical findings, advantages, challenges and prospects of translating the pre-clinical knowledge into the human clinical setting.

Harmonization of lateral fluid-percussion injury model production and post-injury monitoring in a preclinical multicenter biomarker discovery study on post-traumatic epileptogenesis

Multi-center preclinical studies can facilitate the discovery of biomarkers of antiepileptogenesis and thus facilitate the diagnosis and treatment development of patients at risk of developing post-traumatic epilepsy. However, these studies are often limited by the difficulty in harmonizing experimental protocols between laboratories. Here, we assess whether the production of traumatic brain injury (TBI) using the lateral fluid-percussion injury (FPI) in adult male Sprague-Dawley rats (12 weeks at the time of injury) was harmonized between three laboratories - located in the University of Eastern Finland (UEF), Monash University in Melbourne, Australia (Melbourne) and The University of California, Los Angeles, USA (UCLA). These laboratories are part of the international multicenter-based project, the Epilepsy Bioinformatics Study for Antiepileptogenesis Therapy (EpiBioS4Rx). Lateral FPI was induced in adult male Sprague-Dawley rats. The success of methodological harmonization was assessed by performing inter-site comparison of injury parameters including duration of anesthesia during surgery, impact pressure, post-impact transient apnea, post-impact seizure-like behavior, acute mortality (<72 h post-injury), time to self-right after the impact, and severity of the injury (assessed with the neuroscore). The data was collected using Common Data Elements and Case Report Forms. The acute mortality was 15% (UEF), 50% (Melbourne) and 57% (UCLA) (p < 0.001). The sites differed in the duration of anesthesia, the shortest being at UEF < Melbourne < UCLA (p < 0.001). The impact pressure used also differed between the sites, the highest being in UEF > Melbourne > UCLA (p < 0.001). The impact pressure associated with the severity of the functional deficits (low neuroscore) (P < 0.05) only at UEF, but not at any of the other sites. Additionally, the sites differed in the duration of post-impact transient apnea (p < 0.001) and time to self-right (P < 0.001), the highest values in both parameters was registered in Melbourne. Post-impact seizure-like behavior was observed in 51% (UEF), 25% (Melbourne) and 2% (UCLA) of rats (p < 0.001). Despite the differences in means when all sites were compared there was significant overlap in injury parameters between the sites. The data reflects the technical difficulties in the production of lateral FPI across multiple sites. On the other hand, the data can be used to model the heterogeneity in human cohorts with closed-head injury. Our animal cohort will provide a good starting point to investigate the factors associated with epileptogenesis after lateral FPI.

Therapeutic strategies to target acute and long-term sequelae of pediatric traumatic brain injury

Pediatric traumatic brain injury (TBI) remains one of the leading causes of morbidity and mortality in children. Experimental and clinical studies demonstrate that the developmental age, the type of injury (diffuse vs. focal) and sex may play important roles in the response of the developing brain to a traumatic injury. Advancements in acute neurosurgical interventions and neurocritical care have improved and led to a decrease in mortality rates over the past decades. However, survivors are left with life-long behavioral deficits underscoring the need to better define the cellular mechanisms underlying these functional changes. A better understanding of these mechanisms some of which begin in the acute post-traumatic period may likely lead to targeted treatment strategies. Key considerations in designing pre-clinical experiments to test therapeutic strategies in pediatric TBI include the use of age-appropriate and pathologically-relevant models, functional outcomes that are tested as animals age into adolescence and beyond, sex as a biological variable and the recognition that doses and dosing strategies that have been demonstrated to be effective in animal models of adult TBI may not be effective in the developing brain. This article is part of the Special Issue entitled "Novel Treatments for Traumatic Brain Injury".

Single low-dose lipopolysaccharide preconditioning: neuroprotective against axonal injury and modulates glial cells

Aim

Over 7 million traumatic brain injuries (TBI) are reported each year in the United States. However, treatments and neuroprotection following TBI are limited because secondary injury cascades are poorly understood. Lipopolysaccharide (LPS) administration before controlled cortical impact can contribute to neuroprotection. However, the underlying mechanisms and whether LPS preconditioning confers neuroprotection against closed-head injuries remains unclear.

Methods

The authors hypothesized that preconditioning with a low dose of LPS (0.2 mg/kg) would regulate glial reactivity and protect against diffuse axonal injury induced by weight drop. LPS was administered 7 days prior to TBI. LPS administration reduced locomotion, which recovered completely by time of injury.

Results

LPS preconditioning significantly reduced the post-injury gliosis response near the corpus callosum, possibly by downregulating the oncostatin M receptor. These novel findings demonstrate a protective role of LPS preconditioning against diffuse axonal injury. LPS preconditioning successfully prevented neurodegeneration near the corpus callosum, as measured by fluorojade B.

Conclusion

Further work is required to elucidate whether LPS preconditioning confers long-term protection against behavioral deficits and to elucidate the biochemical mechanisms responsible for LPS-induced neuroprotective effects.

Imaging and serum biomarkers reflecting the functional efficacy of extended erythropoietin treatment in rats following infantile traumatic brain injury

OBJECTIVE Traumatic brain injury (TBI) is a leading cause of death and severe morbidity for otherwise healthy full-term infants around the world. Currently, the primary treatment for infant TBI is supportive, as no targeted therapies exist to actively promote recovery. The developing infant brain, in particular, has a unique response to injury and the potential for repair, both of which vary with maturation. Targeted interventions and objective measures of therapeutic efficacy are needed in this special population. The authors hypothesized that MRI and serum biomarkers can be used to quantify outcomes following infantile TBI in a preclinical rat model and that the potential efficacy of the neuro-reparative agent erythropoietin (EPO) in promoting recovery can be tested using these biomarkers as surrogates for functional outcomes. METHODS With institutional approval, a controlled cortical impact (CCI) was delivered to postnatal Day (P)12 rats of both sexes (76 rats). On postinjury Day (PID)1, the 49 CCI rats designated for chronic studies were randomized to EPO (3000 U/kg/dose, CCI-EPO, 24 rats) or vehicle (CCI-veh, 25 rats) administered intraperitoneally on PID1-4, 6, and 8. Acute injury (PID3) was evaluated with an immunoassay of injured cortex and serum, and chronic injury (PID13-28) was evaluated with digitized gait analyses, MRI, and serum immunoassay. The CCI-veh and CCI-EPO rats were compared with shams (49 rats) primarily using 2-way ANOVA with Bonferroni post hoc correction. RESULTS Following CCI, there was 4.8% mortality and 55% of injured rats exhibited convulsions. Of the injured rats designated for chronic analyses, 8.1% developed leptomeningeal cyst-like lesions verified with MRI and were excluded from further study. On PID3, Western blot showed that EPO receptor expression was increased in the injured cortex (p = 0.008). These Western blots also showed elevated ipsilateral cortex calpain degradation products for αII-spectrin (αII-SDPs; p < 0.001), potassium chloride cotransporter 2 (KCC2-DPs; p = 0.037), and glial fibrillary acidic protein (GFAP-DPs; p = 0.002), as well as serum GFAP (serum GFAP-DPs; p = 0.001). In injured rats multiplex electrochemiluminescence analyses on PID3 revealed elevated serum tumor necrosis factor alpha (TNFα p = 0.01) and chemokine (CXC) ligand 1 (CXCL1). Chronically, that is, in PID13-16 CCI-veh rats, as compared with sham rats, gait deficits were demonstrated (p = 0.033) but then were reversed (p = 0.022) with EPO treatment. Diffusion tensor MRI of the ipsilateral and contralateral cortex and white matter in PID16-23 CCI-veh rats showed widespread injury and significant abnormalities of functional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD); MD, AD, and RD improved after EPO treatment. Chronically, P13-P28 CCI-veh rats also had elevated serum CXCL1 levels, which normalized in CCI-EPO rats. CONCLUSIONS Efficient translation of emerging neuro-reparative interventions dictates the use of age-appropriate preclinical models with human clinical trial-compatible biomarkers. In the present study, the authors showed that CCI produced chronic gait deficits in P12 rats that resolved with EPO treatment and that chronic imaging and serum biomarkers correlated with this improvement.

Impact brain apnoea - A forgotten cause of cardiovascular collapse in trauma

OBJECTIVE

Early death following cranial trauma is often considered unsurvivable traumatic brain injury (TBI). However, Impact Brain Apnoea (IBA), the phenomenon of apnoea following TBI, may be a significant and preventable contributor to death attributed to primary injury. This paper reviews the history of IBA, cites case examples and reports a survey of emergency responder experience.

METHODS

Literature and narrative review and focused survey of pre-hospital physicians.

RESULTS

IBA was first reported in the medical literature in 1705 but has been demonstrated in multiple animal studies and is frequently anecdotally witnessed in the pre-hospital arena following human TBI. It is characterised by the cessation of spontaneous breathing following a TBI and is commonly accompanied by a catecholamine surge witnessed as hypertension followed by cardiovascular collapse. This contradicts the belief that isolated traumatic brain injury cannot be the cause of shock, raising the possibility that brain injury may be misinterpreted and therefore mismanaged in patients with isolated brain injury. Current trauma management techniques (e.g. rolling patients supine, compression only cardiopulmonary resuscitation) could theoretically compound hypoxia and worsen the effects of IBA. Anecdotal examples from clinicians attending head injured patients within a few minutes of injury are described. Proposals for the study and intervention for IBA using advances in remote technology are discussed.

CONCLUSION

IBA is a potential cause of early death in some head injured patients. The precise mechanisms in humans are poorly understood but it is likely that early, simple interventions to prevent apnoea could improve clinical outcomes.

Impact Acceleration Model of Diffuse Traumatic Brain Injury

The impact acceleration (I/A) model of traumatic brain injury (TBI) was developed to reliably induce diffuse traumatic axonal injury in rats in the absence of skull fractures and parenchymal focal lesions. This model replicates a pathophysiology that is commonly observed in humans with diffuse axonal injury (DAI) caused by acceleration-deceleration forces. Such injuries are typical consequences of motor vehicle accidents and falls, which do not necessarily require a direct impact to the closed skull. There are several desirable characteristics of the I/A model, including the extensive axonal injury produced in the absence of a focal contusion, the suitability for secondary insult modeling, and the adaptability for mild/moderate injury through alteration of height and/or weight. Furthermore, the trauma device is inexpensive and readily manufactured in any laboratory, and the induction of injury is rapid (~45 min per animal from weighing to post-injury recovery) allowing multiple animal experiments per day. In this chapter, we describe in detail the methodology and materials required to produce the rat model of I/A in the laboratory. We also review current adaptations to the model to alter injury severity, discuss frequent complications and technical issues encountered using this model, and provide recommendations to ensure technically sound injury induction.

Weight Drop Models in Traumatic Brain Injury

Weight drop models in rodents have been used for several decades to advance our understanding of the pathophysiology of traumatic brain injury. Weight drop models have been used to replicate focal cerebral contusion as well as diffuse brain injury characterized by axonal damage. More recently, closed head injury models with free head rotation have been developed to model sports concussions, which feature functional disturbances in the absence of overt brain damage assessed by conventional imaging techniques. Here, we describe the history of development of closed head injury models in the first part of the chapter. In the second part, we describe the development of our own weight drop closed head injury model that features impact plus rapid downward head rotation, no structural brain injury, and long-term cognitive deficits in the case of multiple injuries. This rodent model was developed to reproduce key aspects of sports concussion so that a mechanistic understanding of how long-term cognitive deficits might develop will eventually follow. Such knowledge is hoped to impact athletes and war fighters and others who suffer concussive head injuries by leading to targeted therapies aimed at preventing cognitive and other neurological sequelae in these high-risk groups.

Found in translation: Understanding the biology and behavior of experimental traumatic brain injury

The aim of this review is to discuss in greater detail the topics covered in the recent symposium entitled "Traumatic brain injury: laboratory and clinical perspectives," presented at the 2014 International Behavioral Neuroscience Society annual meeting. Herein, we review contemporary laboratory models of traumatic brain injury (TBI) including common assays for sensorimotor and cognitive behavior. New modalities to evaluate social behavior after injury to the developing brain, as well as the attentional set-shifting test (AST) as a measure of executive function in TBI, will be highlighted. Environmental enrichment (EE) will be discussed as a preclinical model of neurorehabilitation, and finally, an evidence-based approach to sports-related concussion will be considered. The review consists predominantly of published data, but some discussion of ongoing or future directions is provided.

Real-time optical diagnosis of the rat brain exposed to a laser-induced shock wave: observation of spreading depolarization, vasoconstriction and hypoxemia-oligemia

Despite many efforts, the pathophysiology and mechanism of blast-induced traumatic brain injury (bTBI) have not yet been elucidated, partially due to the difficulty of real-time diagnosis and extremely complex factors determining the outcome. In this study, we topically applied a laser-induced shock wave (LISW) to the rat brain through the skull, for which real-time measurements of optical diffuse reflectance and electroencephalogram (EEG) were performed. Even under conditions showing no clear changes in systemic physiological parameters, the brain showed a drastic light scattering change accompanied by EEG suppression, which indicated the occurrence of spreading depression, long-lasting hypoxemia and signal change indicating mitochondrial energy impairment. Under the standard LISW conditions examined, hemorrhage and contusion were not apparent in the cortex. To investigate events associated with spreading depression, measurement of direct current (DC) potential, light scattering imaging and stereomicroscopic observation of blood vessels were also conducted for the brain. After LISW application, we observed a distinct negative shift in the DC potential, which temporally coincided with the transit of a light scattering wave, showing the occurrence of spreading depolarization and concomitant change in light scattering. Blood vessels in the brain surface initially showed vasodilatation for 3-4 min, which was followed by long-lasting vasoconstriction, corresponding to hypoxemia. Computer simulation based on the inverse Monte Carlo method showed that hemoglobin oxygen saturation declined to as low as ∼35% in the long-term hypoxemic phase. Overall, we found that topical application of a shock wave to the brain caused spreading depolarization/depression and prolonged severe hypoxemia-oligemia, which might lead to pathological conditions in the brain. Although further study is needed, our findings suggest that spreading depolarization/depression is one of the key events determining the outcome in bTBI. Furthermore, a rat exposed to an LISW(s) can be a reliable laboratory animal model for blast injury research.

Inhibition of Myosin light-chain kinase attenuates cerebral edema after traumatic brain injury in postnatal mice

Traumatic brain injury (TBI) in children less than 8 years of age leads to decline in intelligence and executive functioning. Neurological outcomes after TBI correlate to development of cerebral edema, which affect survival rates after TBI. It has been shown that myosin light-chain kinase (MLCK) increases cerebral edema and that pretreatment with an MLCK inhibitor (ML-7) reduces cerebral edema. The aim of this study was to determine whether inhibition of MLCK after TBI in postnatal day 24 (PND-24) mice would prevent breakdown of the blood-brain barrier (BBB) and development of cerebral edema and improve neurological outcome. We used a closed head injury model of TBI. ML-7 or saline treatment was administered at 4 h and every 24 h until sacrifice or 5 days after TBI. Mice were sacrificed at 24 h, 48 h, and 72 h and 7 days after impact. Mice treated with ML-7 after TBI had decreased levels of MLCK-expressing cells (20.7±4.8 vs. 149.3±40.6), less albumin extravasation (28.3±11.2 vs. 116.2±60.7 mm(2)) into surrounding parenchymal tissue, less Evans Blue extravasation (339±314 vs. 4017±560 ng/g), and showed a significant difference in wet/dry weight ratio (1.9±0.07 vs. 2.2±0.05 g), compared to saline-treated groups. Treatment with ML-7 also resulted in preserved neurological function measured by the wire hang test (57 vs. 21 sec) and two-object novel recognition test (old vs. new, 10.5 touches). We concluded that inhibition of MLCK reduces cerebral edema and preserves neurological function in PND-24 mice.

Morris water maze function and histologic characterization of two age-at-injury experimental models of controlled cortical impact in the immature rat

PURPOSE

Controlled cortical impact (CCI) is commonly used in adult animals to study focal traumatic brain injury (TBI). Our study aims to further study injury mechanisms in children and variable models of pathology in the developing brain.

METHODS

Develop a focal injury model of experimental TBI in the immature, postnatal days (PND) 7 and 17 rats that underwent a CCI at varying depths of deflection, 1.5-2.5 mm compared with sham and then tested using the Morris water maze (MWM) beginning on post-injury day (PID) 11. Histopathologic analysis was performed at PID 1 and 28.

RESULTS

In PND 7, the 1.75- and 2.0-mm deflections (diameter (d) = 3 mm; velocity = 4 m/s; and duration = 500 ms) resulted in significant MWM deficits while the 1.5-mm injury did not produce MWM deficits vs. sham controls. In PND 17, all injury levels resulted in significant MWM deficits vs. sham controls with a graded response; the 1.5-mm deflection (d = 6 mm; velocity = 4 m/s; and duration = 500 ms) produced significantly less deficits as compared WITH the 2.0- and 2.5-mm injuries. Histologically, a graded injury response was also seen in both ages at injury with cortical and more severe injuries, hippocampal damage. Cortical contusion volume increased in most injury severities from PID 1 to 28 in both ages at injury while hippocampal volumes subsequently decreased.

CONCLUSIONS

CCI in PND 7 and 17 rat results in significant MWM deficits and cortical histopathology providing two different and unique experimental models of TBI in immature rats that may be useful in further investigations into the mechanisms and treatments of pediatric TBI.

Alterations in cerebral oxygen metabolism after traumatic brain injury in children

Traumatic brain injury (TBI) is the most common cause of acquired disability in children. Metabolic defects, and in particular mitochondrial dysfunction, are important contributors to brain injury after TBI. Studies of metabolic dysfunction are limited, but magnetic resonance methods suitable for use in children are overcoming this limitation. We performed noninvasive measurements of cerebral blood flow and oxygen metabolic index (OMI) to assess metabolic dysfunction in children with severe TBI. Cerebral blood flow is variable after TBI but hypoperfusion and low OMI are predominant, supporting metabolic dysfunction. This finding is consistent with preclinical and adult clinical studies of brain metabolism and mitochondrial dysfunction after TBI.

Preconditioning for traumatic brain injury

Traumatic brain injury (TBI) treatment is now focused on the prevention of primary injury and reduction of secondary injury. However, no single effective treatment is available as yet for the mitigation of traumatic brain damage in humans. Both chemical and environmental stresses applied before injury have been shown to induce consequent protection against post-TBI neuronal death. This concept termed "preconditioning" is achieved by exposure to different pre-injury stressors to achieve the induction of "tolerance" to the effect of the TBI. However, the precise mechanisms underlying this "tolerance" phenomenon are not fully understood in TBI, and therefore even less information is available about possible indications in clinical TBI patients. In this review, we will summarize TBI pathophysiology, and discuss existing animal studies demonstrating the efficacy of preconditioning in diffuse and focal type of TBI. We will also review other non-TBI preconditioning studies, including ischemic, environmental, and chemical preconditioning, which maybe relevant to TBI. To date, no clinical studies exist in this field, and we speculate on possible future clinical situations, in which pre-TBI preconditioning could be considered.

Closed head injury in rats: histopathological aspects in an experimental weight drop model

PURPOSE

To study histopathological findings due to a model of closed head injury by weight loss in rats.

METHODS

A platform was used to induce closed cranial lesion controlled by weight loss with a known and predefined energy. 25 male Wistar rats (Rattus novergicus albinus) were divided in five equal groups which received different cranial impact energy levels: G1, G2, G3 and G4 with 0.234J, 0.5J, 0.762J and 1J respectively and G5 (Sham). Under the effect of analgesia, the brain of each group was collected and prepared for histopathological analysis by conventional optic microscopy.

RESULTS

It was observed greater number of injured neurons in animals of group 4, however neuronal death also could be noticed in animals of group 5. Intraparenchymal hemorrhages were more frequent in animals of group 4 and the cytotoxic brain swelling and vascular congestion were more intense in this group

CONCLUSION

The histopathological analysis of these findings allowed to observe typical cranial trauma alterations and these keep close relation with impact energy.

Traumatic brain injury: clinical and pathological parameters in an experimental weightdrop model

PURPOSE

To investigate the function of an experimental cranium trauma model in rats.

METHODS

The equipment, already described in the literature and under discreet adaptations, is composed by a platform that produces closed head impact controlled by weight drop with pre-defined and known energy. 25 Wistar male rats (Rattus norvegicus albinus) were divided into five equal groups that received different quantities of cranial impact energy: G1, G2, G3 and G4 with 0,234J, 0,5J, 0,762J and 1J respectively and G5 (Sham). Under intense analgesia, each group was evaluated clinically in a sequence of intervals and had their encephalon removed for pathologic analysis.

RESULTS

Important clinical alterations (convulsions, bradycardia, bradypnea and abnormal postures) and focal pathologic (hematomas and hemorrhages) kept proportion with the intensity of the impact. No fracture was observed and the group 4 had 80% mortality rate.

CONCLUSION

The experimental cranium trauma animal model by weight drop is an alternative of low cost and easy reproduction that allows evaluating clinical and pathological alterations in accordance with studies in experimental surgery aims for new traumatic brain injury approach in rats.

A brief history of behavioral assessment following experimental traumatic brain injury in juveniles

This review focuses on assessment of behavioral outcomes following traumatic brain injury in juvenile animal models. In the 15 years since the first publication in this field, the majority of studies have used rats roughly equivalent to human toddlers in terms of brain development. Few studies have tested ages closer to human neonates, and fewer have assessed ages closer to human adolescents. Closed head impact has been the most commonly used model, causing relatively consistent motor and cognitive deficits. Additionally, closed head impacts of a more severe nature have generally led to behavioral deficits of a more severe nature. Impact models (both closed and open skull) have produced more severe deficits in younger animals than in older animals, similar to patterns observed in juvenile humans with traumatic brain injury. In contrast, the fluid percussion model has produced relatively subtle deficits that did not get worse with a more severe injury and were worse for older animals than younger animals. Most of the studies have looked at relatively short postinjury time points, and none so far have assessed behavior in old adult animals injured as juveniles. The review ends with a discussion of possible directions for future animal research into juvenile traumatic brain injury.

Pathophysiological response to experimental diffuse brain trauma differs as a function of developmental age

The purpose of experimental models of traumatic brain injury (TBI) is to reproduce selected aspects of human head injury such as brain edema, contusion or concussion, and functional deficits, among others. As the immature brain may be particularly vulnerable to injury during critical periods of development, and pediatric TBI may cause neurobehavioral deficits, our aim was to develop and characterize as a function of developmental age a model of diffuse TBI (DTBI) with quantifiable functional deficits. We modified a DTBI rat model initially developed by us in adult animals to study the graded response to injury as a function of developmental age - 7-, 14- and 21-day-old rats compared to young adult (3-month-old) animals. Our model caused motor deficits that persisted even after the pups reached adulthood, as well as reduced cognitive performance 2 weeks after injury. Moreover, our model induced prominent edema often seen in pediatric TBI, particularly evident in 7- and 14-day-old animals, as measured by both the wet weight/dry weight method and diffusion-weighted MRI. Blood-brain barrier permeability, as measured by the Evans blue dye technique, peaked at 20 min after trauma in all age groups, with a second peak found only in adult animals at 24 h after injury. Phosphorus MR spectroscopy showed no significant changes in the brain energy metabolism of immature rats with moderate DTBI, in contrast to significant decreases previously identified in adult animals.

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.

N-methyl-D-aspartate preconditioning improves short-term motor deficits outcome after mild traumatic brain injury in mice

Traumatic brain injury (TBI) causes impairment of fine motor functions in humans and nonhuman mammals that often persists for months after the injury occurs. Neuroprotective strategies for prevention of the sequelae of TBI and understanding the molecular mechanisms and cellular pathways are related to the glutamatergic system. It has been suggested that cellular damage subsequent to TBI is mediated by the excitatory neurotransmitters, glutamate and aspartate, through the excessive activation of the N-methyl-D-aspartate (NMDA) receptors. Thus, preconditioning with a low dose of NMDA was used as a strategy for protection against locomotor deficits observed after TBI in mice. Male adult mice CF-1 were preconditioned with NMDA (75 mg/kg) 24 hr before the TBI induction. Under anesthesia with O(2)/N(2)O (33%: 66%) inhalation, the animals were subjected to the experimental model of trauma that occurs by the impact of a 25 g weight on the skull. Sensorimotor gating was evaluated at 1.5, 6, or 24 hr after TBI induction by using footprint and rotarod tests. Cellular damage also was assessed 24 hr after occurrence of cortical trauma. Mice preconditioned with NMDA were protected against all motor deficits revealed by footprint tests, but not those observed in rotarod tasks. Although mice showed motor deficits after TBI, no cellular damage was observed. These data corroborate the hypothesis that glutamatergic excitotoxicity, especially via NMDA receptors, contributes to severity of trauma. They also point to a putative neuroprotective mechanism induced by a sublethal dose of NMDA to improve motor behavioral deficits after TBI.

Flumazenil administration attenuates cognitive impairment in immature rats after controlled cortical impact

Evidence suggests that the gamma-aminobutyric acid (GABA)ergic system may be involved in cognitive dysfunction following traumatic brain injury (TBI). We investigated the effect of flumazenil treatment, a benzodiazepine antagonist approved by the U.S. Food and Drug Administration, on learning and memory in the immature rat following experimental brain injury. Post-natal day 17 rats were injured using controlled cortical impact. Systemic treatment with flumazenil at 1, 5, and 10 mg/kg was initiated on post-injury day 1 and administered for 13 days via daily intraperitoneal injections. Morris water maze (MWM) testing was used to measure latency to find a submerged platform and the results from experimental and control animals were compared. We demonstrated a significant dose-dependent improvement in MWM performance in drug-treated animals. This is the first study demonstrating the efficacy of flumazenil in reducing post-TBI cognitive deficits and we propose that these effects may be related to modulation of the GABA(A) receptor.

Glutathione peroxidase overexpression does not rescue impaired neurogenesis in the injured immature brain

Traumatic brain injury (TBI) is a leading cause of disability among young children and is associated with long-term cognitive deficits. These clinical findings have prompted an investigation of the hippocampus in an experimental model of trauma to the developing brain at postnatal day (p21). Previous studies using this model have revealed a progressive loss of neurons in the hippocampus as brain-injured animals mature to young adulthood. Here we determined whether this hippocampal vulnerability is likewise reflected in altered neurogenesis and whether the antioxidant glutathione peroxidase (GPx) modulates neurogenesis during maturation of the injured immature brain. Male transgenic mice that overexpress GPx and wild-type littermates were subjected to controlled cortical impact or sham surgery on p21. At 2 weeks postinjury, the numbers of proliferating cells and immature neurons within the subgranular zone were measured by using Ki-67 and doublecortin, respectively. Bromodeoxyuridine (BrdU) was used to label dividing cells beginning 2 weeks postinjury. Survival (BrdU(+)) and neuronal differentiation (BrdU(+)/NeuN(+)) were then measured 4 weeks later via confocal microscopy. Two-way ANOVA revealed no significant interaction between genotype and injury. Subsequent analysis of the individual effects of injury and genotype, however, showed a significant reduction in subgranular zone proliferation (Ki-67) at 2 weeks postinjury (P = 0.0003) and precursor cell survival (BrdU(+)) at 6 weeks postinjury (P = 0.016) and a trend toward reduced neuronal differentiation (BrdU(+)/NeuN(+)) at 6 weeks postinjury (P = 0.087). Overall, these data demonstrate that traumatic injury to the injured immature brain impairs neurogenesis during maturation and suggest that GPx cannot rescue this reduced neurogenesis.

Hypothermia following pediatric traumatic brain injury

Preclinical as well as clinical studies in traumatic brain injury (TBI) have established the likely association of secondary injury and outcome in adults in children following severe injury. Similarly, there is growing evidence in experimental laboratory studies that moderate hypothermia has a beneficial effect on outcome, though the exact mechanisms remain to be absolutely defined. The Pediatric TBI Guidelines provided the knowledge and background for standard management of children following severe TBI and highlighted that there are very few clinical studies to date. In particular with respect to temperature regulation and the use of hypothermia, initial findings of case series of small numbers were promising. Further preliminary randomized clinical trials, both single institution and multicenter, have provided the initial data on safety and efficacy, though larger, Phase III studies are necessary to ensure both the safety and efficacy of hypothermia in pediatric TBI prior to implementation as part of the standard of care. It is expected that hypothermia initiated early after severe TBI will have a protective effect on the pediatric brain and can be done safely, but this still remains to be definitively tested.

Traumatic brain injury research priorities: the Conemaugh International Brain Injury Symposium

In 2005, an international symposium was convened with over 100 neuroscientists from 13 countries and major research centers to review current research in traumatic brain injury (TBI) and develop a consensus document on research issues and priorities. Four levels of TBI research were the focus of the discussion: basic science, acute care, post-acute neurorehabilitation, and improving quality of life (QOL). Each working group or committee was charged with reviewing current research, discussion and prioritizing future research directions, identifying critical issues that impede research in brain injury, and establishing a research agenda that will drive research over the next five years, leading to significantly improved outcomes and QOL for individuals suffering brain injuries. This symposium was organized at the request of the Congressional Brain Injury Task Force, to follow up on the National Institutes of Health Consensus Conference on TBI as mandated by the TBI ACT of 1996. The goal was to review what progress had been made since the National Institutes of Health (NIH) Consensus Conference, and also to follow up on the 1990's Decade of the Brain Project. The major purpose of the symposium was to provide recommendations to the U.S. Congress on a priority basis for research, treatment, and training in TBI over the next five years.

Hitting a moving target: Basic mechanisms of recovery from acquired developmental brain injury

Acquired brain injuries represent a major cause of disability in the pediatric population. Understanding responses to developmental acquired brain injuries requires knowledge of the neurobiology of normal development, age-at-injury effects and experience-dependent neuroplasticity. In the developing brain, full recovery cannot be considered as a return to the premorbid baseline, since ongoing maturation means that cerebral functioning in normal individuals will continue to advance. Thus, the recovering immature brain has to 'hit a moving target' to achieve full functional recovery, defined as parity with age-matched uninjured peers. This review will discuss the consequences of developmental injuries such as focal lesions, diffuse hypoxia and traumatic brain injury (TBI). Underlying cellular and physiological mechanisms relevant to age-at-injury effects will be described in considerable detail, including but not limited to alterations in neurotransmission, connectivity/network functioning, the extracellular matrix, response to oxidative stress and changes in cerebral metabolism. Finally, mechanisms of experience-dependent plasticity will be reviewed in conjunction with their effects on neural repair and recovery.

Midline brain injury in the immature rat induces sustained cognitive deficits, bihemispheric axonal injury and neurodegeneration

Infants and children less than 4 years old suffer chronic cognitive deficits following mild, moderate or severe diffuse traumatic brain injury (TBI). It has been suggested that the underlying neuropathologic basis for behavioral deficits following severe TBI is acute brain swelling, subarachnoid hemorrhage and axonal injury. To better understand mechanisms of cognitive dysfunction in mild-moderate TBI, a closed head injury model of midline TBI in the immature rat was developed. Following an impact over the midline suture of the intact skull, 17-day-old rats exhibited short apnea times (3-15 s), did not require ventilatory support and suffered no mortality, suggestive of mild TBI. Compared to un-injured rats, brain-injured rats exhibited significant learning deficits over the first week post-injury (p<0.0005), and, significant learning (p<0.005) and memory deficits (p<0.05) in the third post-injury week. Between 6 and 72 h, blood-brain barrier breakdown, extensive traumatic axonal injury in the subcortical white matter and thalamus, and focal areas of neurodegeneration in the cortex and hippocampus were observed in both hemispheres of the injured brain. At 8 to 18 days post-injury, reactive astrocytosis in the cortex, axonal degeneration in the subcortical white matter tracts, and degeneration of neuronal cell bodies and processes in the thalamus of both hemispheres were observed; however, cortical volumes were not different between un-injured and injured rat brains. These data suggest that diffuse TBI in the immature rat can lead to ongoing degeneration of both cell soma and axonal compartments of neurons, which may contribute, in part, to the observed sustained cognitive deficits.

Mild traumatic brain injury to the infant mouse causes robust white matter axonal degeneration which precedes apoptotic death of cortical and thalamic neurons

The immature brain in the first several years of childhood is very vulnerable to trauma. Traumatic brain injury (TBI) during this critical period often leads to neuropathological and cognitive impairment. Previous experimental studies in rodent models of infant TBI were mostly concentrated on neuronal degeneration, while axonal injury and its relationship to cell death have attracted much less attention. To address this, we developed a closed controlled head injury model in infant (P7) mice and characterized the temporospatial pattern of axonal degeneration and neuronal cell death in the brain following mild injury. Using amyloid precursor protein (APP) as marker of axonal injury we found that mild head trauma causes robust axonal degeneration in the cingulum/external capsule as early as 30 min post-impact. These levels of axonal injury persisted throughout a 24 h period, but significantly declined by 48 h. During the first 24 h injured axons underwent significant and rapid pathomorphological changes. Initial small axonal swellings evolved into larger spheroids and club-like swellings indicating the early disconnection of axons. Ultrastructural analysis revealed compaction of organelles, axolemmal and cytoskeletal defects. Axonal degeneration was followed by profound apoptotic cell death in the posterior cingulate and retrosplenial cortex and anterior thalamus which peaked between 16 and 24 h post-injury. At early stages post-injury no evidence of excitotoxic neuronal death at the impact site was found. At 48 h apoptotic cell death was reduced and paralleled with the reduction in the number of APP-labeled axonal profiles. Our data suggest that early degenerative response to injury in axons of the cingulum and external capsule may cause disconnection between cortical and thalamic neurons, and lead to their delayed apoptotic death.

Diffuse brain injury in the immature rat: evidence for an age-at-injury effect on cognitive function and histopathologic damage

Diffuse axonal injury is a significant component of the pathology of moderate-severe pediatric traumatic brain injury in children less than 4 years of age, and is associated with poor cognitive outcome. However, cognitive deficits or gross histopathologic abnormalities are typically not observed following moderate-severe diffuse brain injury in the immature (17-day-old) rat. In order to test whether the age of the immature animal may influence post-traumatic outcome, non-contusive brain trauma was induced in post-natal day (PND) 11 or 17 rats. Brain injury in the PND11 rat, but not in the PND17 rat, was associated with a significant acquisition deficit at 28 days post-injury (p<0.0005 compared with age-matched sham rats, and with brain-injured PND17 rats). All brain-injured animals exhibited a retention deficit in the probe trial (p<0.001), but also demonstrated a significant visual deficit in the visible platform trial (p<0.05 compared to sham animals). Although significantly longer times of apnea and loss of righting reflex were observed in brain-injured PND17 rats compared to PND11 rats (p<0.05), overt cytoarchitectural alterations and reactive gliosis were not observed in the older age group. No focal pathology was observed in the cortex below the impact site in the PND11 rat but by 28 days, the brain-injured PND11 rat exhibited atrophy in multiple brain regions and an enlarged lateral ventricle in the impact hemisphere. Quantitative analysis revealed a time-dependent increase in tissue loss in the injured hemisphere (7-10%) in the younger animals, and a modest extent of tissue loss in the older animals (3-4%). Traumatic axonal injury was observed to similar extents in the white matter and thalamus below the impact site in both brain-injured PND11 and 17 rats. These data demonstrate that non-contusive (diffuse) brain injury of moderate severity in the immature rat is associated with chronic cognitive deficits and long-term histopathologic alterations and suggest that the age-at-injury is an important parameter of behavioral and pathologic outcome following closed head injury in the immature age group.

Chronic cognitive deficits and long-term histopathological alterations following contusive brain injury in the immature rat

Although diffuse axonal injury is the primary pathology in pediatric brain trauma, the additional presence of focal contusions may contribute to the poor prognosis in brain-injured children younger than 4 years of age. Because existing models of pediatric brain trauma focus on diffuse brain injury, a model of contusive brain trauma was developed using postnatal day (PND) 11 and 17 rats, ages that are neurologically equivalent to a human infant and toddler, respectively. Closed head injury was modeled by subjecting the intact skull over the left parietal cortex of the immature rat to an impact with a metal-tipped indenter. Brain trauma on PND11 or PND17 led to significant spatial learning deficits at 28 days post-injury, compared to age-matched control rats (p < 0.05). Although both groups of rats sustained skull fractures on impact, the histopathologic response of the brain was distinctly age-dependent. At 3 days post-injury in PND11 rats, the cortex below the impact site was contused and hemorrhagic, and contained reactive astrocytes, while the subcortical white matter and thalamus contained injured (swollen) axons. At 14 and 28 days post-injury, the cortex, white matter, and hippocampus were substantially atrophied, and the lateral ventricle was enlarged. In contrast, in PND17 rats, the contused cortex observed at 3 days post-injury matured into a pronounced cavity lined with a glia limitans at 14 days; reactive astrocytes were present in both the hippocampus and thalamus up to 28 days post-injury. No evidence of traumatic axonal injury was observed in any region of the brain-injured PND17 rat. These data suggest that contusive brain trauma in the immature rat is associated with chronic cognitive deficits, but underscore the effect of the age-at-injury on behavioral and histopathologic outcomes.

New Rat Model for Diffuse Brain Injury Using Coronal Plane Angular Acceleration

A new experimental model was developed to induce diffuse brain injury (DBI) in rats through pure coronal plane angular acceleration. An impactor was propelled down a guide tube toward the lateral extension of the helmet fixture. Upon impactor-helmet contact, helmet and head were constrained to rotate in the coronal plane. In the present experimental series, the model was optimized to generate rotational kinematics necessary for concussion. Twenty-six rats were subjected to peak angular accelerations of 368 +/- 30 krad/sec2 (mean +/- standard deviation) with 2.1 +/- 0.5-msec durations. Following rotational loading, unconsciousness was defined as time between reversal agent administration and return of corneal reflex. All experimental rats demonstrated transient unconsciousness lasting 8.8 +/- 3.7 min that was significantly longer than control rats. Macroscopic damage was noted in 51% of experimental animals: 38% subarachnoid hemorrhage, and 15% intraparenchymal lesion. Microscopic analysis indicated no evidence of axonal swellings at sacrifice times of 24, 48, 72, and 96 h. All rats survived rotational loading without skull fracture. Injuries were classified as concussion based on transient unconsciousness, scaled biomechanics, limited macroscopic damage, and minimal histological abnormalities. The experimental methodology remains adjustable, permitting investigation of increasing DBI severities through modulation of model parameters, and inclusion of further functional and histological outcome measures.

Basic science; repetitive mild non-contusive brain trauma in immature rats exacerbates traumatic axonal injury and axonal calpain activation: a preliminary report

Infants who experience inflicted brain injury (shaken-impact syndrome) present with subdural hematoma, brain atrophy, and ventriculomegaly, pathologic features that are suggestive of multiple incidences of brain trauma. To develop a clinically relevant model of inflicted brain injury in infants, the skulls of anesthetized 11-day-old rat pups were subjected to one, two, or three successive mild impacts. While skull fractures were not observed, a single impact to the intact skull resulted in petechial hemorrhages in the subcortical white matter, and double or triple impacts led to hemorrhagic tissue tears at 1 day postinjury. Whereas the singly impacted brain did not exhibit overt damage at 7 days, two impacts resulted in an enlarged ventricle and white matter atrophy; three impacts to the brain led to similar pathology albeit at 3 days postinjury. By 7 days, cortical atrophy was observed following three impacts. Reactive astrocytes were visible in the deep cortical layers below the impact site after two impacts, and through all cortical layers after three impacts. Swellings were observed in intact axons in multiple white matter tracts at 1 day following single impact and progressed to axonal disconnections by 3 days. In contrast, double or triple impacts resulted in axonal disconnections by 1 day postinjury; in addition, three impacts led to extensive axonal injury in the dorsolateral thalamus by 3 days. Calpain activation was observed in axons in subcortical white matter tracts in all brain-injured animals at 1 day and increased with the number of impacts. Despite these pathologic alterations, neither one nor two impacts led to acquisition deficits on the Morris water maze. While indicative of the graded nature of the pathologic response, these data suggest that repetitive mild brain injury in the immature rat results in pathologic features similar to those following inflicted brain injuries in infants.

Therapeutic effect of hypothermia and dizocilpine maleate on traumatic brain injury in neonatal rats

This study was undertaken to evaluate the therapeutic effect of hypothermia and dizocilpine maleate in traumatic brain injury (TBI) on newborn rats. After induction of TBI, physiologic and histopathological assessments were performed on both the control and therapeutic groups to evaluate the effects of both agents. Rats were assigned into four groups as follows: normothermic (n = 23), hypothermic (n = 18), normothermia plus dizocilpine maleate (n = 18) and hypothermia plus dizocilpine maleate (n = 18). All the rats were injured using a weight-drop head injury model, artificially ventilated with a 33% O(2) and 66% NO(2) mixture, and physiological parameters, intracranial pressure, and brain and rectal temperatures were recorded. Mortality, physiological, neurological parameters, and histopathological changes were assessed after 24 h. As a result, intracranial pressure, cerebral perfusion pressure, morbidity, weight loss, and microscopic changes were significantly worse in the normothermic group (p <0.05). There was no statistical difference between other groups (p > 0.05). Hypothermia and dizocilpine maleate displayed similar neuroprotective effects in TBI on newborn rats, but no additive effect was observed.

Pediatric traumatic brain injury: quo vadis?

In this review, five questions serve as the framework to discuss the importance of age-related differences in the pathophysiology and therapy of traumatic brain injury (TBI). The following questions are included: (1) Is diffuse cerebral swelling an important feature of pediatric TBI and what is its etiology? (2) Is the developing brain more vulnerable than the adult brain to apoptotic neuronal death after TBI and, if so, what are the clinical implications? (3) If the developing brain has enhanced plasticity versus the adult brain, why are outcomes so poor in infants and young children with severe TBI? (4) What contributes to the poor outcomes in the special case of inflicted childhood neurotrauma and how do we limit it? (5) Should both therapeutic targets and treatments of pediatric TBI be unique? Strong support is presented for the existence of unique biochemical, molecular, cellular and physiological facets of TBI in infants and children versus adults. Unique therapeutic targets and enhanced therapeutic opportunities, both in the acute phase after injury and in rehabilitation and regeneration, are suggested.

Phase II clinical trial of moderate hypothermia after severe traumatic brain injury in children

OBJECTIVE

To determine whether moderate hypothermia (HYPO) (32-33 degrees C) begun in the early period after severe traumatic brain injury (TBI) and maintained for 48 hours is safe compared with normothermia (NORM) (36.5-37.5 degrees C).

METHODS

After severe (Glasgow Coma Scale score < or =8) nonpenetrating TBI, 48 children less than 13 years of age admitted within 6 hours of injury were randomized after stratification by age to moderate HYPO (32-33 degrees C) treatment in conjunction with standardized head injury management versus NORM in a multicenter trial. An additional 27 patients were entered into a parallel single-institution trial of excluded patients because of late transfer or consent (delayed in transfer >6 h but within 24 h of admission), unknown time of injury (e.g., child abuse), and adolescence (e.g., aged 13-18 yr). Assessments of safety included mortality, infection, coagulopathy, arrhythmias, and hemorrhage as well as ability to maintain target temperature, mean intracranial pressure (ICP), and percent time of ICP less than 20 mm Hg during the cooling and subsequent rewarming phases. Additionally, assessments of neurocognitive outcomes were obtained at 3 and 6 months of follow-up.

RESULTS

Moderate HYPO after severe TBI in children was found to be safe relative to standard management and NORM in children of all ages and in children with delay of initiation of treatment up to 24 hours. Although there was decreased mortality in HYPO in both studies, there was an increased potential for arrhythmias with HYPO, although they were manageable with fluid administration or rewarming. Additionally, there was a reduction in mean ICP during the first 72 hours after injury in both studies, although rebound ICP elevations in HYPO compared with those in NORM were noted for up to 10 to 12 hours after rewarming. Although functional outcome at 3 or 6 months did not differ between treatment groups, functional outcome tended to improve from the 3- to 6-month cognitive assessment in HYPO compared with NORM, although the sample size was too small for any definitive conclusions.

CONCLUSION

HYPO is likely a safe therapeutic intervention for children after severe TBI up to 24 hours after injury. Further studies are necessary and warranted to determine its effect on functional outcome and intracranial hypertension.

Plastic reorganization of hippocampal and neocortical circuitry in experimental traumatic brain injury in the immature rat

The reorganization of circuitry in the immature forebrain resulting from controlled cortical impact was examined with viral transneuronal tracing. Animals injured on postnatal day (PND) 17 and sham controls from the same litters received an intracerebral injection of a recombinant strain of pseudorabies virus (PRV) into the entorhinal cortex on PND 45. Fifty hours following injection of virus the animals were perfused and infected neurons were localized immunohistochemically with antisera specific for PRV. Prior studies have demonstrated that the PRV recombinant used in this analysis moves exclusively in the retrograde direction through synaptically linked neurons. CCI induced a necrotic loss of cortex at the site of impact and variable damage to the underlying corpus callosum and rostral (dorsal) hippocampus that was not present in sham controls. Analysis of viral transport in sham controls revealed retrograde transport of virus through hippocampal and neocortical circuitry in a pattern consistent with established patterns of connectivity and topography. Injured animals exhibited preservation of topographically organized connections in both the hippocampus and neocortex. However, the magnitude of labeling in the injured hemisphere was significantly increased relative to control animals and correlated with the magnitude of the injury. The distribution of infected neurons in the contralateral uninjured hemisphere also conformed to known connections. However differences in the involvement of the corpus callosum in the injury resulted in greater variability in the number of infected neurons among cases. These data provide novel insights into trauma induced reorganization of the developing brain and add to the experimental tools that can be used to assess the basis for functional recovery in animal models of developmental traumatic brain injury.

A new device for experimental modeling of central nervous system injuries

This article introduces a new device for inducing central nerve system injuries in experimental studies with animal models. The construction of the device is based on a commercially available servo-drive system incorporating the latest instrumentation technology and software developed in house to control the motion profile of the injury bit. The software, which is available upon request from the author, was designed such that the user can set the mechanical properties of the motion. For the purpose of quality control, tests were described and performed to assess the ability of the device to reproduce the prescribed motion when operated repetitively under the same set of parameters. Experiments were then conducted on animals to injure mouse brain and rat spinal cord. Following the injuries, in vivo magnetic resonance imaging was performed on the animals to depict the pathologies of the resulting injuries in the corresponding neuronal tissues. Rat spinal cords injured mildly and severely were followed longitudinally for up to 28 days postinjury. The neurobehaviors of the animals evaluated using locomotor rating scores indicated the ability of the device to produce repeatable graded injuries.

Experience-dependent behavioral plasticity is disturbed following traumatic injury to the immature brain

Traumatic brain injury (TBI) is most prevalent in children and young adults. The long-term effects of pediatric TBI include cognitive and behavioral impairments; however, over time, it is difficult to distinguish individual variability in intellect and behavior from sequelae of early injury. Postnatal day (PND) 19 rats underwent lateral fluid percussion (FP) injury, followed by rearing in either standard (STD) or enriched environment (EE) conditions. The hypothesis was that the traditional enhancement of cognitive functioning following EE rearing would be attenuated when this rearing is preceded by TBI at PND19. Thirty days after injury, Morris water maze (MWM) acquisition and subsequent probe trial retention were used to assess the behavioral effects of injury on experience-dependent plasticity induced by housing in EE at two different time windows. MWM acquisition demonstrated improvements following early EE rearing in both sham and injured animals; however, the degree of improvement was greater for uninjured animals. When EE rearing was delayed for 2 weeks after injury, the injury effect was absent and the effect of rearing even stronger. Memory testing in the early EE groups using a delayed probe trial showed an effect of injury and housing, with the sham EE animals benefiting the most. After the delayed EE, sham EE animals again showed more probe target hits, while FPEE animals did not, demonstrating an enduring memory deficit. These data confirm that early TBI has effects on experience-dependent plasticity resulting in long-term neurobehavioral deficits. In addition, the ability to benefit from environmental stimulation following TBI is dependent upon time after injury.

Apoptotic neurodegeneration in the context of traumatic injury to the developing brain

Head trauma is the leading cause of death and disability in the pediatric population. Some recent studies on neuropathological and biochemical features of traumatic injury to the developing brain revealed interesting aspects and potential targets for future research. Trauma triggers both excitotoxic and apoptotic neurodegeneration in the developing rat brain. Apoptotic neurodegeneration occurs in a delayed fashion over several days and contributes in an age-dependent fashion to neuropathologic outcome following head trauma, with the immature brain being exceedingly sensitive. Biochemical studies indicate that both the extrinsic and the intrinsic apoptotic pathways are involved in pathogenesis of apoptotic cell death following trauma in the developing brain and that caspase inhibition ameliorates apoptotic neurodegeneration in an infant head trauma model. Given the major contribution of apoptotic neurodegeneration to neuropathologic outcome following trauma to the developing brain, interference with apoptotic pathways may comprise a potential therapeutic target in pediatric traumatic brain injury.

Traumatic axonal injury is exacerbated following repetitive closed head injury in the neonatal pig

Inflicted brain injury is associated with widespread traumatic axonal injury (TAI) and subdural hematoma and is the leading cause of death in infants and children. Anesthetized 3-5-day-old piglets were subjected to either a single (n = 5) or double (n = 6, 15 min apart) rapid (<15 msec), non-impact, axial rotations of the head. Peak rotational velocities (averaging 172 rad/sec for single and 138 rad/sec for double loads) were lower than those utilized to induce severe injuries (240-260 rad/sec; Raghupathi and Margulies, 2002). At 6 h post-injury, brains were evaluated for the presence TAI using immunohistochemistry for the 200-kDa neurofilament protein (NF200). Accumulation of NF200 was observed in both contiguous (swellings) and in disconnected axons (axon bulbs) predominantly in central deep and peripheral subcortical white matter regions in the frontal, temporal, and parietal lobes of all injured piglets. Although the density of injured axons did not significantly increase after two rotational loads, the distribution of injured axons shifted from a few foci (2.2 +/- 2.3 per animal) with 1-2 swellings/bulbs following a single rotation to significantly more foci (14.7 +/- 11.9), and additional foci (2.5 +/- 1.9) containing 3 or more axon swellings/bulbs following two rotational loads. The density and distribution of injured axons following a single mild rotation were significantly reduced compared with those obtained previously following a single more severe rotational load. Collectively, these data are indicative of the graded response of the immature brain to rotational load magnitude, and importantly, the vulnerability to repeated, mild, non-impact loading conditions.

Age-Dependent Changes in Material Properties of the Brain and Braincase of the Rat

Clinical and biomechanical evidence indicates that mechanisms and pathology of head injury in infants and young children may be different from those in adults. Biomechanical computer-based modeling, which can be used to provide insight into the thresholds for traumatic tissue injury, requires data on material properties of the brain, skull, and sutures that are specific for the pediatric population. In this study, brain material properties were determined for rats at postnatal days (PND) 13, 17, 43, and 90, and skull/suture composite (braincase) properties were determined at PND 13, 17, and 43. Controlled 1 mm indentation of a force probe into the brain was used to measure naive, non-preconditioned (NPC) and preconditioned (PC) instantaneous (G(i)) and long-term (G( infinity )) shear moduli of brain tissue both in situ and in vitro. Brains at 13 and 17 PND exhibited statistically indistinguishable shear moduli, as did brains at 43 and 90 PND. However, the immature (average of 13 and 17 PND) rat brain (G(i) = 3336 Pa NPC, 1754 Pa PC; G( infinity )= 786 Pa NPC, 626 Pa PC) was significantly stiffer (p < 0.05) than the mature (average of 43 and 90 PND) brains (G(i) = 1721 Pa NPC, 1232 Pa PC; G( infinity ) = 508 Pa NPC, 398 Pa PC). A "reverse engineering" finite element model approach, which simulated the indentation of the force probe into the intact braincase, was used to estimate the effective elastic moduli of the braincase. Although the skull of older rats was significantly thicker than that of the younger rats, there was no significant age-dependent change in the effective elastic modulus of the braincase (average value = 6.3 MPa). Thus, the increase in structural rigidity of the braincase with age (up to 43 PND) was due to an increase in skull thickness rather than stiffening of the tissue. These observations of a stiffer brain and more compliant braincase in the immature rat compared with the adult rat will aid in the development of age-specific experimental models and in computational head injury simulations. Specifically, these results will assist in the selection of forces to induce comparable mechanical stresses, strains and consequent injury profiles in brain tissues of immature and adult animals.

Experimental models of head trauma

Traumatic brain injury is one of the most common causes for chronic disability in young people. Despite this there are currently no widely available modes of therapy that would limit the extent of brain damage secondary to trauma. Therefore, new insights into the pathological mechanisms involved in head trauma possibly leading to the identification of new therapeutic targets are urgently needed. In order to attain these goals adequate animal models for traumatic brain injury are needed. In the following paper the authors will review the various animal models for head trauma and emphasize their potential strengths and weaknesses.