Motor and cognitive function evaluation following experimental traumatic brain injury

Impairment of vestibular-mediated cardiovascular response and motor coordination in rats born and reared under hypergravity

It is well known that environmental stimulation is important for the proper development of sensory function. The vestibular system senses gravitational acceleration and then alters cardiovascular and motor functions through reflex pathways. The development of vestibular-mediated cardiovascular and motor functions may depend on the gravitational environment present at birth and during subsequent growth. To examine this hypothesis, arterial pressure (AP) and renal sympathetic nerve activity (RSNA) were monitored during horizontal linear acceleration and performance in a motor coordination task in rats born and reared in 1-G or 2-G environments. Linear acceleration of +/-1 G increased AP and RSNA. These responses were attenuated in rats with a vestibular lesion, suggesting that the vestibular system mediated AP and RSNA responses. These responses were also attenuated in rats born in a 2-G environment. AP and RSNA responses were partially restored in these rats when the hypergravity load was removed, and the rats were maintained in a 1-G environment for 1 wk. The AP response to compressed air, which is mediated independently of the vestibular system, did not change in the 2-G environment. Motor coordination was also impaired in the 2-G environment and remained impaired even after 1 wk of unloading. These results indicate that hypergravity impaired both the vestibulo-cardiovascular reflex and motor coordination. The vestibulo-cardiovascular reflex was only impaired temporarily and partially recovered following 1 wk of unloading. In contrast, motor coordination did not return to normal in response to unloading.

Subacute neural stem cell therapy for traumatic brain injury

INTRODUCTION

Traumatic brain injury (TBI) frequently results in devastating and prolonged morbidity. Cellular therapy is a burgeoning field of experimental treatment that has shown promise in the management of many diseases, including TBI. Previous work suggests that certain stem and progenitor cell populations migrate to sites of inflammation and improve functional outcome in rodents after neural injury. Unfortunately, recent study has revealed potential limitations of acute and intravenous stem cell therapy. We studied subacute, direct intracerebral neural stem and progenitor cell (NSC) therapy for TBI.

MATERIALS AND METHODS

The NSCs were characterized by flow cytometry and placed (400,000 cells in 50 muL 1x phosphate-buffered saline) into and around the direct injury area, using stereotactic guidance, of female Sprague Dawley rats 1 wk after undergoing a controlled cortical impact injury. Immunohistochemistry was used to identify cells located in the brain at 48 h and 2 wk after administration. Motor function was assessed using the neurological severity score, foot fault, rotarod, and beam balance. Cognitive function was assessed using the Morris water maze learning paradigm. Repeated measures analysis of variance with post-hoc analysis were used to determine significance at P < 0.05.

RESULTS

Immunohistochemistry analysis revealed that 1.4-1.9% of infused cells remained in the neural tissue at 48 h and 2 wk post placement. Nearly all cells were located along injection tracks at 48 h. At 2 wk some cell dispersion was apparent. Rotarod motor testing revealed significant increases in maximal speed among NSC-treated rats compared with saline controls at d 4 (36.4 versus 27.1 rpm, P < 0.05) and 5 (35.8 versus 28.9 rpm, P < 0.05). All other motor and cognitive evaluations were not significantly different compared to controls.

CONCLUSIONS

Placement of NSCs led to the cells incorporating and remaining in the tissues 2 wk after placement. Motor function tests revealed improvements in the ability to run on a rotating rod; however, other motor and cognitive functions were not significantly improved by NSC therapy. Further examination of a dose response and optimization of placement strategy may improve long-term cell survival and maximize functional recovery.

Cell therapies for traumatic brain injury

Preliminary discoveries of the efficacy of cell therapy are currently being translated to clinical trials. Whereas a significant amount of work has been focused on cell therapy applications for a wide array of diseases, including cardiac disease, bone disease, hepatic disease, and cancer, there continues to be extraordinary anticipation that stem cells will advance the current therapeutic regimen for acute neurological disease. Traumatic brain injury is a devastating event for which current therapies are limited. In this report the authors discuss the current status of using adult stem cells to treat traumatic brain injury, including the basic cell types and potential mechanisms of action, preclinical data, and the initiation of clinical trials.

Detrimental effects of aging on outcome from traumatic brain injury: a behavioral, magnetic resonance imaging, and histological study in mice

Considerable evidence indicates that outcomes from traumatic brain injury (TBI) are worse in the elderly, but there has been little preclinical research to explore potential mechanisms. In this study, we examined the age-related effects on outcome in a mouse model of controlled cortical impact (CCI) injury. We compared the responses of adult (5-6 months old) and aged (21-24 months old) male mice following a moderate lateral CCI injury to the sensorimotor cortex. Sensorimotor function was evaluated with the rotarod, gridwalk and spontaneous forelimb behavioral tests. Acute edema was assessed from hyperintensity on T2-weighted magnetic resonance images. Blood-brain barrier opening was measured using anti-mouse immunoglobulin G (IgG) immunohistochemistry. Neurodegeneration was assessed by amino-cupric silver staining, and lesion cavity volumes were measured from histological images. Indicators of injury were generally worse in the aged than the adult mice. Acute edema, measured at 24 and 48 h post-injury, resolved more slowly in the aged mice (p < 0.01). Rotarod recovery (p < 0.05) and gridwalk deficits (p < 0.01) were significantly worse in aged mice. There was greater (p < 0.01 at 3 days) and more prolonged post-acute opening of the blood-brain barrier in the aged mice. Neurodegeneration was greater in the aged mice (p < 0.01 at 3 days). In contrast, lesion cavity volumes, measured at 3 days post-injury, were not different between injured groups. These results suggest that following moderate controlled cortical impact injury, the aged brain is more vulnerable than the adult brain to neurodegeneration, resulting in greater loss of function. Tissue loss at the impact site does not explain the increased functional deficits seen in the aged animals. Prolonged acute edema, increased opening of the blood-brain barrier and increased neurodegeneration found in the aged animals implicate secondary processes in age-related differences in outcome.

In vitro neural injury model for optimization of tissue-engineered constructs

Stem cell transplantation is a promising approach for the treatment of traumatic brain injury, although the therapeutic benefits are limited by a high degree of donor cell death. Tissue engineering is a strategy to improve donor cell survival by providing structural and adhesive support. However, optimization prior to clinical implementation requires expensive and time-consuming in vivo studies. Accordingly, we have developed a three-dimensional (3-D) in vitro model of the injured host-transplant interface that can be used as a test bed for high-throughput evaluation of tissue-engineered strategies. The neuronal-astrocytic cocultures in 3-D were subjected to mechanical loading (inducing cell death and specific astrogliotic alterations) or to treatment with transforming growth factor-beta1 (TGF-beta1), inducing astrogliosis without affecting viability. Neural stem cells (NSCs) were then delivered to the cocultures. A sharp increase in the number of TUNEL(+) donor cells was observed in the injured cocultures compared to that in the TGF-beta1-treated and control cocultures, suggesting that factors related to mechanical injury, but not strictly astrogliosis, were detrimental to donor cell survival. We then utilized the mechanically injured cocultures to evaluate a methylcellulose-laminin (MC-LN) scaffold designed to reduce apoptosis. When NSCs were co-delivered with MC alone or MC-LN to the injured cocultures, the number of caspase(+) donor cells significantly decreased compared to that with vehicle delivery (medium). Collectively, these results demonstrate the utility of an in vitro model as a pre-animal test bed and support further investigation of a tissue-engineering approach for chaperoned NSC delivery targeted to improve donor cell survival in neural transplantation.

Statins increase neurogenesis in the dentate gyrus, reduce delayed neuronal death in the hippocampal CA3 region, and improve spatial learning in rat after traumatic brain injury

Traumatic brain injury (TBI) remains a major public health problem globally. Presently, there is no way to restore cognitive deficits caused by TBI. In this study, we seek to evaluate the effect of statins (simvastatin and atorvastatin) on the spatial learning and neurogenesis in rats subjected to controlled cortical impact. Rats were treated with atorvastatin and simvastatin 1 day after TBI and daily for 14 days. Morris water maze tests were performed during weeks 2 and 5 after TBI. Bromodeoxyuridine (BrdU; 50 mg/kg) was intraperitoneally injected 1 day after TBI and daily for 14 days. Brain tissue was processed for immunohistochemical staining to identify newly generated cells and vessels. Our data show that (1) treatment of TBI with statins improves spatial learning on days 31-35 after onset of TBI; (2) in the non-neurogenic region of the hippocampal CA3 region, statin treatment reduces the neuronal loss after TBI, demonstrating the neuroprotective effect of statins; (3) in the neurogenic region of the dentate gyrus, treatment of TBI with statins enhances neurogenesis; (4) statin treatment augments TBI-induced angiogenesis; and (5) treatment with simvastatin at the same dose provides a therapeutic effect superior to treatment with atorvastatin. These results suggest that statins may be candidates for treatment of TBI.

COG1410, a novel apolipoprotein E-based peptide, improves functional recovery in a murine model of traumatic brain injury

Traumatic brain injury (TBI) is a silent epidemic affecting approximately 1.4 million Americans annually, at an estimated annual cost of $60 billion in the United States alone. Despite an increased understanding of the pathophysiology of closed head injury, there remains no pharmacological intervention proven to improve functional outcomes in this setting. Currently, the existing standard of care for TBI consists primarily of supportive measures. Apolipoprotein E (apoE) is the primary apolipoprotein synthesized in the brain in response to injury, where it modulates several components of the neuroinflammatory cascade associated with TBI. We have previously demonstrated that COG133, an apoE mimetic peptide, improved functional outcomes and attenuated neuronal death when administered as a single intravenous injection at 30 min post-TBI in mice. Using the principles of rational drug design, we developed a more potent analog, COG1410, which expands the therapeutic window for the treatment of TBI by a factor of four, from 30 min to 2 h. Mice that received a single intravenous injection of COG1410 at 120 min post-TBI exhibited significant improvement on a short term test of vestibulomotor function and on a long term test of spatial learning and memory. This was associated with a significant attenuation of microglial activation and neuronal death in the hippocampus, the neuroanatomical substrate for learning and memory. Rationally derived apoE mimetic peptides have been demonstrated to exert neuroprotective and anti-inflammatory effects in vitro and in clinically relevant models of brain injury. This represents a novel therapeutic strategy in the treatment of TBI.

A simple, efficient tool for assessment of mice after unilateral cortex injury

A refined battery of neurological tests, SNAP (Simple Neuroassessment of Asymmetric Impairment), was developed and validated to efficiently assess neurological deficits induced in a mouse model of traumatic brain injury. Four to 7-month old mice were subjected to unilateral controlled cortical impact or sham injury (craniectomy only). Several behavioral tests (SNAP, beam walk, foot fault, and water maze) were used to assess functional deficits. SNAP was unique among these in that it required no expensive equipment and was performed in less than 5 min per mouse. SNAP demonstrated a high level of sensitivity and specificity as determined by receiver-operator characteristics curve analysis. Interrater reliability was good, as determined by Cohen's Kappa method and by comparing the sensitivity and specificity across various raters. SNAP detected deficits in proprioception, visual fields, and motor strength in brain-injured mice at 3 days, and was sensitive enough to detect magnitude and recovery of injury. The contribution of individual battery components changed as a function of time after injury, however, each was important to the overall SNAP score. SNAP provided a sensitive, reliable, time-efficient and cost-effective means of assessing neurological deficits in mice after unilateral brain injury.

Aldolase C-positive cerebellar Purkinje cells are resistant to delayed death after cerebral trauma and AMPA-mediated excitotoxicity

The cerebellum has been shown to be vulnerable to global ischemic damage in tightly controlled zones of Purkinje cells (PCs) that lack aldolase C, an enzyme critical for glycolysis. Here, we investigated whether aldolase C-negative PCs were more likely to die after cerebral trauma in vivo, and whether this death was mediated by excitotoxic [alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-mediated] means in vitro. Mice were subjected to controlled cortical impact, or remained uninjured, and were killed at 6 h, 24 h or 7 days after injury. Cerebellar sections (both ipsilateral and contralateral to the site of cerebral injury) were stained against aldolase C and calbindin (a marker of PCs). The number of viable, calbindin-positive PCs decreased significantly at 24 h and 7 days after injury, and the percentage of surviving, aldolase C-positive PCs significantly increased at those time-points. In addition, we subjected murine cerebellar cultures to AMPA (30 microm, 20 min), which killed a significant number of PCs at 24 h post-treatment. A similar number of PCs was lost after transfection with aldolase C siRNA, and this effect was exacerbated in transfected cultures treated with AMPA. The results from the present study indicate that aldolase C provides marked neuroprotection to PCs after trauma and excitotoxicity.

Characterization of an immunodeficient mouse model of mucopolysaccharidosis type I suitable for preclinical testing of human stem cell and gene therapy

Mucopolysaccharidosis type I (MPS-I or Hurler syndrome) is an inherited deficiency of the lysosomal glycosaminoglycan (GAG)-degrading enzyme alpha-l-iduronidase (IDUA) in which GAG accumulation causes progressive multi-system dysfunction and death. Early allogeneic hematopoietic stem cell transplantation (HSCT) ameliorates clinical features and extends life but is not available to all patients, and inadequately corrects its most devastating features including mental retardation and skeletal deformities. To test novel therapies, we characterized an immunodeficient MPS-I mouse model less likely to develop immune reactions to transplanted human or gene-corrected cells or secreted IDUA. In the liver, spleen, heart, lung, kidney and brain of NOD/SCID/MPS-I mice IDUA was undetectable, and reduced to half in heterozygotes. MPS-I mice developed marked GAG accumulation (3-38-fold) in these organs. Neuropathological examination showed GM(3) ganglioside accumulation in the striatum, cerebral peduncles, cerebellum and ventral brainstem of MPS-I mice. Urinary GAG excretion (6.5-fold higher in MPS-I mice) provided a non-invasive and reliable method suitable for serially following the biochemical efficacy of therapeutic interventions. We identified and validated using rigorous biostatistical methods, a highly reproducible method for evaluating sensorimotor function and motor skills development. This Rotarod test revealed marked abnormalities in sensorimotor integration involving the cerebellum, striatum, proprioceptive pathways, motor cortex, and in acquisition of motor coordination. NOD/SCID/MPS-I mice exhibit many of the clinical, skeletal, pathological and behavioral abnormalities of human MPS-I, and provide an extremely suitable animal model for assessing the systemic and neurological effects of human stem cell transplantation and gene therapeutic approaches, using the above techniques to measure efficacy.

Neurotrophin-mediated neuroprotection of hippocampal neurons following traumatic brain injury is not associated with acute recovery of hippocampal function

Traumatic brain injury (TBI) causes selective hippocampal cell death which is believed to be associated with the cognitive impairment observed in both clinical and experimental settings. The endogenous neurotrophin-4/5 (NT-4/5), a TrkB ligand, has been shown to be neuroprotective for vulnerable CA3 pyramidal neurons after experimental brain injury. In this study, infusion of recombinant NT-4/5 increased survival of CA2/3 pyramidal neurons to 71% after lateral fluid percussion brain injury in rats, compared with 55% in vehicle-treated controls. The functional outcome of this NT-4/5-mediated neuroprotection was examined using three hippocampal-dependent behavioral tests. Injury-induced impairment was evident in all three tests, but interestingly, there was no treatment-related improvement in any of these measures. Similarly, injury-induced decreased excitability in the Schaffer collaterals was not affected by NT-4/5 treatment. We propose that a deeper understanding of the factors that link neuronal survival to recovery of function will be important for future studies of potentially therapeutic agents.

Mild in vitro trauma induces rapid Glur2 endocytosis, robustly augments calcium permeability and enhances susceptibility to secondary excitotoxic insult in cultured Purkinje cells

Mild brain trauma results in a wide range of neurological symptoms that are not easily explained by the primary pathology. Purkinje neurons of the cerebellum are selectively vulnerable to brain trauma, including indirect remote trauma to the forebrain. This vulnerability manifests itself as a selective and delayed cell loss, for which the underlying mechanisms are poorly understood. Alterations to the surface expression of calcium impermeable AMPA receptors (GluR2-containing) may mediate post-traumatic calcium overload, and initiate biochemical cascades that ultimately cause progressive cell death. Our current study examined this hypothesis using an in vitro model of mild Purkinje trauma, delivered by an elastic stretch at 2.5-2.9 pounds per square inch (psi). This mild trauma alone did not increase cell loss as measured by propidium iodide (PI) uptake (at 20 h) compared to uninjured controls. However, there was a marked increase in cell loss, when cells following mild trauma, were exposed to 10 microM AMPA for 1 h compared to either mild trauma or AMPA exposure alone. Mild injury rendered Purkinje neurons significantly more permeable to AMPA-stimulated (4 microM) calcium influx at 15 min post-injury, including a sustained calcium plateau. This effect was eliminated by inhibiting protein kinase C-dependent GluR2 endocytosis with 2 microM Go6976 or blocking the calcium pore of GluR1/3 containing AMPARs with 500 nM 1-naphthylacetyl spermine (Naspm). Nifedipine (2 microM) eliminated the calcium plateau following mild injury but not the initial spike of Ca2+ increase. These results suggest that mild injuries resulted in a rapid AMPA receptor subtype switch (GluR2 was replaced by GluR1/3), which in turn resulted in an enhanced Ca2+ permeability. We further confirmed this by immunocytochemistry. Dendritic GluR2 co-localization with the pre-synaptic marker synaptophysin was markedly down-regulated at 15 min following mild stretch (P < 0.01), indicative of a rapid decrease in the synaptic expression of receptors containing this subunit. Carboxyfluorescence (CBF) assays revealed that mild stretch did not alter membrane integrity. Finally, we demonstrated that the combination of 500 nM Naspm and 5 nM Go6976 conferred a powerful neuroprotective effect on Purkinje cells by effectively eliminating the effects of mild stretch combined with AMPA in 95% of cells. These results represent a newly described mechanism rendering neurons susceptible to secondary injuries following trauma. Prevention of GluR2 endocytosis may be critical in the development of pharmacotherapies aimed at mild, seemingly inconsequential trauma, to avoid ensuing secondary damage.

Plasticity and remodeling of brain

The injured brain can be stimulated to amplify its intrinsic restorative processes to improve neurological function. Thus, after stroke, both cell and pharmacological neurorestorative treatments, amplify the induction of brain neurogenesis and angiogenesis, and thereby reduce neurological deficits. In this manuscript, we describe the use of bone marrow mesenchymal cells (MSCs) and erythropoietin (EPO) as examples of cell-based and pharmacological neurorestorative treatments, respectively, for both stroke and a mouse model of experimental autoimmune encephalomyelitis (EAE). We demonstrate that these therapies significantly improve neurological function with treatment initiated after the onset of injury and concomitantly promote brain plasticity. The application of MRI to monitor changes in the injured brain associated with reduction of neurological deficit is also described.

Electromagnetic controlled cortical impact device for precise, graded experimental traumatic brain injury

Genetically modified mice represent useful tools for traumatic brain injury (TBI) research and attractive preclinical models for the development of novel therapeutics. Experimental methods that minimize the number of mice needed may increase the pace of discovery. With this in mind, we developed and characterized a prototype electromagnetic (EM) controlled cortical impact device along with refined surgical and behavioral testing techniques. By varying the depth of impact between 1.0 and 3.0 mm, we found that the EM device was capable of producing a broad range of injury severities. Histologically, 2.0-mm impact depth injuries produced by the EM device were similar to 1.0-mm impact depth injuries produced by a commercially available pneumatic device. Behaviorally, 2.0-, 2.5-, and 3.0-mm impacts impaired hidden platform and probe trial water maze performance, whereas 1.5-mm impacts did not. Rotorod and visible platform water maze deficits were also found following 2.5- and 3.0-mm impacts. No impairment of conditioned fear performance was detected. No differences were found between sexes of mice. Inter-operator reliability was very good. Behaviorally, we found that we could statistically distinguish between injury depths differing by 0.5 mm using 12 mice per group and between injury depths differing by 1.0 mm with 7-8 mice per group. Thus, the EM impactor and refined surgical and behavioral testing techniques may offer a reliable and convenient framework for preclinical TBI research involving mice.

Injury severity determines Purkinje cell loss and microglial activation in the cerebellum after cortical contusion injury

Clinical evidence suggests that the cerebellum is damaged after traumatic brain injury (TBI) and experimental studies have validated these observations. We have previously shown cerebellar vulnerability, as demonstrated by Purkinje cell loss and microglial activation, after fluid percussion brain injury. In this study, we examine the effect of graded controlled cortical impact (CCI) injury on the cerebellum in the context of physiologic and anatomical parameters that have been shown by others to be sensitive to injury severity. Adult male rats received mild, moderate, or severe CCI and were euthanized 7 days later. We first validated the severity of the initial injury using physiologic criteria, including apnea and blood pressure, during the immediate postinjury period. Increasing injury severity was associated with an increased incidence of apnea and higher mortality. Severe injury also induced transient hypertension followed by hypotension, while lower grade injuries produced an immediate and sustained hypotension. We next evaluated the pattern of subcortical neuronal loss in response to graded injuries. There was significant neuronal loss in the ipsilateral cortex, hippocampal CA2/CA3, and laterodorsal thalamus that was injury severity-dependent and that paralleled microglial activation. Similarly, there was a distinctive pattern of Purkinje cell loss and microglial activation in the cerebellar vermis that varied with injury severity. Together, these findings emphasize the vulnerability of the cerebellum to TBI. That a selective pattern of Purkinje cell loss occurs regardless of the type of injury suggests a generalized response that is a likely determinant of recovery and a target for therapeutic intervention.

Recovery of Function after Vagus Nerve Stimulation Initiated 24 Hours after Fluid Percussion Brain Injury

Recent evidence from our laboratory demonstrated in laboratory rats that stimulation of the vagus nerve (VNS) initiated 2 h after lateral fluid percussion brain injury (FPI) accelerates the rate of recovery on a variety of behavioral and cognitive tests. VNS animals exhibited a level of performance comparable to that of sham-operated uninjured animals by the end of a 2-week testing period. The effectiveness of VNS was further evaluated in the present study in which initiation of stimulation was delayed until 24 h post-injury. Rats were subjected to a moderate FPI and tested on the beam walk, skilled forelimb reaching, locomotor placing, forelimb flexion and Morris water maze tasks for 2 weeks following injury. VNS (30 sec trains of 0.5 mA, 20.0-Hz biphasic pulses) was initiated 24 h post-injury and continued at 30-min intervals for the duration of the study, except for brief periods when the animals were detached for behavioral assessments. Consistent with our previous findings when stimulation was initiated 2 h post-injury, VNS animals showed significantly faster rates of recovery compared to controls. By the last day of testing (day 14 post-injury), the FPI-VNS animals were performing significantly better than the FPI-no-VNS animals and were not significantly different from shams in all motor and sensorimotor tasks. Performance in the Morris water maze indicated that the VNS animals acquired the task more rapidly on days 11-13 post-injury. On day 14, the FPI-VNS animals did not differ in the latency to find the platform from sham controls, whereas the injured controls did; however, the FPI-VNS animals and injured controls were not significantly different. Despite the lack of significant histological differences between the FPI groups, VNS, when initiated 24 h following injury, clearly attenuated the ensuing behavioral deficits and enhanced acquisition of the cognitive task. The results are discussed with respect to the norepinephrine hypothesis.

Hippocampal vulnerability following traumatic brain injury: a potential role for neurotrophin-4/5 in pyramidal cell neuroprotection

Traumatic brain injury (TBI) causes selective hippocampal cell death, which is believed to be associated with cognitive impairment observed both in clinical and experimental settings. Although neurotrophin administration has been tested as a strategy to prevent cell death following TBI, the potential neuroprotective role of neurotrophin-4/5 (NT-4/5) in TBI remains unknown. We hypothesized that NT-4/5 would offer neuroprotection for selectively vulnerable hippocampal neurons following TBI. Measurements of NT-4/5 in rats subjected to lateral fluid percussion (LFP) TBI revealed two-threefold increases in the injured cortex and hippocampus in the acute period (1-3 days) following brain injury. Subsequently, the response of NT-4/5 knockout (NT-4/5(-/-)) mice to controlled-cortical impact TBI was investigated. NT-4/5(-/-) mice were more susceptible to selective pyramidal cell loss in Ahmon's corn (CA) subfields of the hippocampus following TBI, and showed impaired motor recovery when compared with their brain-injured wild-type controls (NT-4/5(wt)). Additionally, we show that acute, prolonged administration of recombinant NT-4/5 (5 microg/kg/day) prevented up to 50% of the hippocampal CA pyramidal cell death following LFP TBI in rats. These results suggest that post-traumatic increases in endogenous NT-4/5 may be part of an adaptive neuroprotective response in the injured brain, and that administration of this neurotrophic factor may be useful as a therapeutic strategy following TBI.

Purkinje cell vulnerability to mild and severe forebrain head trauma

Pathophysiological changes in the cortex, thalamus, and hippocampus have been implicated as contributors to motor and cognitive deficits in a number of animal models of traumatic brain injury (TBI). Indirect cerebellar injury may contribute to TBI pathophysiology because impairment of motor function and coordination are common consequences of TBI, but are also domains associated with cerebellar function. However, there is a lack of direct evidence to support this claim. Hence, in this study, a dose-response relationship of the cerebellum's susceptibility was determined at four grades of fluid percussion injury (1.5, 2.0, 2.5, and 3.0 atm) applied in the right lateral cerebral cortex of adult male Sprague-Dawley rats. Evidence suggests primary and secondary injury mechanisms resulting in selective cerebellar Purkinje neuron (PN) loss, whereas interneurons of the molecular layer were spared. The posterior region of the cerebellar vermis displayed significant PN loss (p = 0.001) at 1 day postinjury, whereas the gyrus of the horizontal fissure and gyrus of lobules III and IV exhibited delayed PN loss at higher levels of injury severity. Interestingly, neither terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) or cleaved caspase-3 colocalized with PNs at any time point or injury severity. Expression of calbindin-28k increased in regions of greatest PN loss, suggesting that the surviving PNs possess higher calcium-buffering capacities, which may account for their survival.

Impaired long-term habituation is dissociated from increased locomotor activity after sensorimotor cortex compression

Behavioural habituation to a novel environment is a simple form of learning in rodents. We studied the habituation and locomotor activity (LMA) of Wistar rats subjected to unilateral, transient (30min) extradural compression (EC) of the right sensorimotor cortex. One group of rats was tested every 24h during the first 5 days (D1-D5) post-EC. Two other groups were tested for the first time in the LMA boxes on D3 and D6 post-EC and their performance was compared with the group tested on D1 (activity in a novel environment). Total and center locomotion, vertical activity and time spent in the center of the LMA box were reduced on D1 post-EC and normalized by D2. The EC-induced motor paresis was undetectable on the rotarod by D2 and on the beam-walking by D3. Total locomotion, vertical activity and time spent in the center of EC-rats significantly increased from D1 to D3. EC caused neurodegeneration in the cortex, caudate putamen and thalamus as detected by Fluoro-Jade staining. The size of the cortical damage decreased from D2 to D5 in the medial and caudal regions of the compressed hemisphere, in accordance with recovery of motor function. LMA provided additional information in the follow-up of recovery from brain injury and habituation to the environment. Thus, long-term, inter-session habituation was impaired from D1 to D3 but dissociated from increased LMA intra-session on D3, when the motor deficits provoked by EC were already undetectable in the rotarod and beam-walking tests.

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.

Morris water maze search strategy analysis in PDAPP mice before and after experimental traumatic brain injury

Traumatic brain injury (TBI) is a common cause of cognitive dysfunction and a major risk factor for Alzheimer's disease (AD). PDAPP mice, a transgenic line overexpressing a mutant human amyloid precursor protein (APP) implicated in familial AD, have markedly impaired behavioral performance in the Morris water maze relative to wild-type (WT) littermates. Performance further deteriorates following experimental TBI in both PDAPP and WT mice. However, the aspects of cognitive function involved are not well understood. Here, we have analyzed search strategies used in the water maze by 3-4 month old PDAPP and WT C57Bl6 littermates both before and after moderate controlled cortical impact TBI. Prior to TBI, PDAPP mice used less spatial strategies and more nonspatial systematic strategies and strategies involving repetitive looping than WT mice. With training, PDAPP mice used more spatial strategies and less repetitive looping. After TBI, PDAPP mice lost use of spatial strategies and relied more on repetitive looping. TBI in WT mice also reduced their use of spatial strategies but instead caused a switch to nonspatial systematic strategies. We also analyzed changes in the efficiency with which mice used each individual strategy, but found that differences in which strategies were used quantitatively accounted for most of the differences in performance between groups. These results demonstrate that suboptimal search strategy use in addition to effects on spatial learning and memory underlies the impaired performance of PDAPP mice and further deterioration following TBI. Human TBI patients may have analogous poor use of problem solving strategies.

CNS injury research; reviewing the last decade: methodological errors and a proposal for a new strategy

During the last decades the field of Traumatic Brain Injury (TBI) has been characterized by a paucity of new treatments. This is in contrast to the amount of pre-clinical experimental work and the number of clinical trials done. This paper aims to contribute to the ongoing debate on the reasons that have led to this phenomenon. A reasonable suggestion could be the presence of methodological limitations when comparing and integrating experimental results. The first methodological drawback, which is shortly discussed, is the insistence (during the last decades) on the concept of "similarity to the human pathology" as the main criterion to evaluate results, and the constant effort to create a "super model" that would fully replicate human TBI cases. The second methodological limitation examined is the lack of a common way to present and analyze data. It is proposed that the basic neuro-histo-pathology of each injury model should serve as the ground on which hypotheses should be built, as it could constitute the common basis for comparisons between different experimental settings. In this context, 95 papers reporting experimental results from various models of animal CNS injury were reviewed in order to examine the extent to which results were presented and analyzed using a common basis. No such common basis was observed; moreover, the review revealed a remarkable lack of histopathological examination of the animals, especially when biochemical and/or behavioral endpoints were assessed. It is argued that this practice deprives data of an objective common basis. Conclusively, a new theoretical way of organizing experimental work in the field of TBI is briefly presented.

Experimental models of traumatic brain injury: do we really need to build a better mousetrap?

Approximately 4000 human beings experience a traumatic brain injury each day in the United States ranging in severity from mild to fatal. Improvements in initial management, surgical treatment, and neurointensive care have resulted in a better prognosis for traumatic brain injury patients but, to date, there is no available pharmaceutical treatment with proven efficacy, and prevention is the major protective strategy. Many patients are left with disabling changes in cognition, motor function, and personality. Over the past two decades, a number of experimental laboratories have attempted to develop novel and innovative ways to replicate, in animal models, the different aspects of this heterogenous clinical paradigm to better understand and treat patients after traumatic brain injury. Although several clinically-relevant but different experimental models have been developed to reproduce specific characteristics of human traumatic brain injury, its heterogeneity does not allow one single model to reproduce the entire spectrum of events that may occur. The use of these models has resulted in an increased understanding of the pathophysiology of traumatic brain injury, including changes in molecular and cellular pathways and neurobehavioral outcomes. This review provides an up-to-date and critical analysis of the existing models of traumatic brain injury with a view toward guiding and improving future research endeavors.

Use of methylphenidate in traumatic brain injury

OBJECTIVE

To review literature regarding the effectiveness of methylphenidate in the management of the cognitive and behavioral changes observed following traumatic brain injury (TBI).

DATA SOURCES

A literature search was conducted using the following databases: MEDLINE (1966-June 2004); Cochrane Central Register of Controlled Trials, fourth quarter 2004 (1988-June 2004); and International Pharmaceutical Abstracts (1970-June 2004). Methylphenidate and brain injury were the key search terms used. Limits were set to include clinical trial publications, human subjects, and English language.

DATA SYNTHESIS

Ten clinical trials evaluating the efficacy and safety of methylphenidate in pediatric and adult patients with TBI are reviewed. Improvements in different aspects of cognition and behavior were evaluated before, during, and after treatment with methylphenidate. The results demonstrated that methylphenidate is likely to improve memory, attention, concentration, and mental processing, but its effects on behavior have not been determined.

CONCLUSIONS

Larger, double-blind, placebo-controlled studies are needed to determine optimal doses, during which phase of recovery to begin treatment, length of treatment, and long-term effects for patients with mild, moderate, and severe TBI.

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.