Changes in microtubule-associated protein 2 and amyloid precursor protein immunoreactivity following traumatic brain injury in rat: influence of MK-801 treatment

Altered amyloid precursor protein, tau-regulatory proteins, neuronal numbers and behaviour, but no tau pathology, synaptic and inflammatory changes or memory deficits, at 1 month following repetitive mild traumatic brain injury

Repetitive mild traumatic brain injury, commonly experienced following sports injuries, results in various secondary injury processes and is increasingly recognised as a risk factor for the development of neurodegenerative conditions such as chronic traumatic encephalopathy, which is characterised by tau pathology. We aimed to characterise the underlying pathological mechanisms that might contribute to the onset of neurodegeneration and behavioural changes in the less-explored subacute (1-month) period following single or repetitive controlled cortical impact injury (five impacts, 48 h apart) in 12-week-old male and female C57Bl6 mice. We conducted motor and cognitive testing, extensively characterised the status of tau and its regulatory proteins via western blot and quantified neuronal populations using stereology. We report that r-mTBI resulted in neurobehavioural deficits, gait impairments and anxiety-like behaviour at 1 month post-injury, effects not seen following a single injury. R-mTBI caused a significant increase in amyloid precursor protein, an increased trend towards tau phosphorylation and significant changes in kinase/phosphatase proteins that may promote a downstream increase in tau phosphorylation, but no changes in synaptic or neuroinflammatory markers. Lastly, we report neuronal loss in various brain regions following both single and repeat injuries. We demonstrate herein that repeated impacts are required to promote the initiation of a cascade of biochemical events that are consistent with the onset of neurodegeneration subacutely post-injury. Identifying the timeframe in which these changes occur and the pathological mechanisms involved will be crucial for the development of future therapeutics to prevent the onset or mitigate the progression of neurodegeneration following r-mTBI.

Modelling traumatic brain injury and posttraumatic epilepsy in rodents

Posttraumatic epilepsy (PTE) is one of the most debilitating and understudied consequences of traumatic brain injury (TBI). It is challenging to study the effects, underlying pathophysiology, biomarkers, and treatment of TBI and PTE purely in human patients for a number of reasons. Rodent models can complement human PTE studies as they allow for the rigorous investigation into the causal relationship between TBI and PTE, the pathophysiological mechanisms of PTE, the validation and implementation of PTE biomarkers, and the assessment of PTE treatments, in a tightly controlled, time- and cost-efficient manner in experimental subjects known to be experiencing epileptogenic processes. This article will review several common rodent models of TBI and/or PTE, including their use in previous studies and discuss their relative strengths, limitations, and avenues for future research to advance our understanding and treatment of PTE.

Targeting neurodegeneration to prevent post-traumatic epilepsy

In the quest for developing new therapeutic targets for post-traumatic epilepsies (PTE), identifying mechanisms relevant to development and progression of disease is critical. A growing body of literature suggests involvement of neurodegenerative mechanisms in the pathophysiology of acquired epilepsies, including following traumatic brain injury (TBI). In this review, we discuss the potential of some of these mechanisms to be targets for the development of a therapy against PTE.

The Inflammatory Continuum of Traumatic Brain Injury and Alzheimer's Disease

The post-injury inflammatory response is a key mediator in long-term recovery from traumatic brain injury (TBI). Moreover, the immune response to TBI, mediated by microglia and macrophages, is influenced by existing brain pathology and by secondary immune challenges. For example, recent evidence shows that the presence of beta-amyloid and phosphorylated tau protein, two hallmark features of AD that increase during normal aging, substantially alter the macrophage response to TBI. Additional data demonstrate that post-injury microglia are “primed” and become hyper-reactive following a subsequent acute immune challenge thereby worsening recovery. These alterations may increase the incidence of neuropsychiatric complications after TBI and may also increase the frequency of neurodegenerative pathology. Therefore, the purpose of this review is to summarize experimental studies examining the relationship between TBI and development of AD-like pathology with an emphasis on the acute and chronic microglial and macrophage response following injury. Furthermore, studies will be highlighted that examine the degree to which beta-amyloid and tau accumulation as well as pre- and post-injury immune stressors influence outcome after TBI. Collectively, the studies described in this review suggest that the brain’s immune response to injury is a key mediator in recovery, and if compromised by previous, coincident, or subsequent immune stressors, post-injury pathology and behavioral recovery will be altered.

Extent of impaired axoplasmic transport and neurofilament compaction in traumatically injured axon at various strains and strain rates

PRIMARY OBJECTIVE

Secondary axotomy is more prevalent than the primary axotomy and involves subtle intraaxonal changes in response to the injury leading to cytoskeletal disruptions including neurofilament (NF) misalignment and compaction, which is associated with the genesis of impaired axoplasmic transport (IAT). Recent studies have reported two differential axonal responses to injury, one associated with the cytoskeletal collapse and another with the IAT. The objective of this study was to determine the extent of IAT and early NF changes in axons that were subjected to a stretch of various degrees at different strain rates.

RESEARCH DESIGN AND METHODS

Fifty-six L5 dorsal spinal nerve roots were subjected to a predetermined strain at a specified displacement rate (0.01 and 15 mm/second) only once. The histological changes were determined by performing standard immunohistochemical procedures using beta amyloid precursor protein (β APP) and NF-68 kDa antibodies.

RESULTS AND CONCLUSIONS

No significant differences in the occurrence rate of either of the staining in the axons were observed when subjected to similar loading conditions, and the occurrence rate of both β APP and NF68 staining was strain and rate-dependent.

APP as a Protective Factor in Acute Neuronal Insults

Despite its key role in the molecular pathology of Alzheimer’s disease (AD), the physiological function of amyloid precursor protein (APP) is unknown. Increasing evidence, however, points towards a neuroprotective role of this membrane protein in situations of metabolic stress. A key observation is the up-regulation of APP following acute (stroke, cardiac arrest) or chronic (cerebrovascular disease) hypoxic-ischemic conditions. While this mechanism may increase the risk or severity of AD, APP by itself or its soluble extracellular fragment APPsα can promote neuronal survival. Indeed, different animal models of acute hypoxia-ischemia, traumatic brain injury (TBI) and excitotoxicity have revealed protective effects of APP or APPsα. The underlying mechanisms involve APP-mediated regulation of calcium homeostasis via NMDA receptors (NMDAR), voltage-gated calcium channels (VGCC) or internal calcium stores. In addition, APP affects the expression of survival- or apoptosis-related genes as well as neurotrophic factors. In this review, we summarize the current understanding of the neuroprotective role of APP and APPsα and possible implications for future research and new therapeutic strategies.

The potential for animal models to provide insight into mild traumatic brain injury: Translational challenges and strategies

Mild traumatic brain injury (mTBI) is a common health problem. There is tremendous variability and heterogeneity in human mTBI, including mechanisms of injury, biomechanical forces, injury severity, spatial and temporal pathophysiology, genetic factors, pre-injury vulnerability and resilience factors, and clinical outcomes. Animal models greatly reduce this variability and heterogeneity, and provide a means to study mTBI in a rigorous, controlled, and efficient manner. Rodent models, in particular, are time- and cost-efficient, and they allow researchers to measure morphological, cellular, molecular, and behavioral variables in a single study. However, inter-species differences in anatomy, morphology, metabolism, neurobiology, and lifespan create translational challenges. Although the term "mild" TBI is used often in the pre-clinical literature, clearly defined criteria for mild, moderate, and severe TBI in animal models have not been agreed upon. In this review, we introduce current issues facing the mTBI field, summarize the available research methodologies and previous studies in mTBI animal models, and discuss how a translational research approach may be useful in advancing our understanding and management of mTBI.

Dendritic changes in rat visual pathway associated with experimental ocular hypertension

PURPOSE

Increasing evidence shows that structural changes in dendrites play an important role in neuronal degenerative processes. The aims of this study were to characterize and delineate morphological changes of dendrites in retinal ganglion cells (RGCs) and their central target neurons in the superior colliculus (SC) and lateral geniculate nucleus (LGN) in experimental rat glaucoma.

METHODS

Chronic ocular hypertension (OHT) was surgically induced in rats and animals were sacrificed at 1, 4, 8, 16 and 32 weeks following IOP elevation. Animals without IOP elevation served as normal control. Dendritic morphology of neurons was visualized by ex vivo DiI labelling using confocal microscopy and dendritic length and number was quantified using Image J.

RESULTS

We found significant dendritic shrinkage (p < 0.001) and loss (p < 0.001) in RGCs and neurons in the SC and LGN in OHT animals compared to age-matched controls. Analysis of the temporal morphological profiles among them revealed the RGCs to have the earliest changes compared to the SC and LGN although the most prominent changes occurred in the SC.

CONCLUSION

Our study has demonstrated that OHT results in dendritic changes of the neurons throughout the visual pathways, from RGCs to SC cells and LGN cells, suggesting that both the retina and the brain should be targeted when considering diagnosis and therapeutic strategies for glaucoma.

Experimental traumatic brain injury induces rapid aggregation and oligomerization of amyloid-beta in an Alzheimer's disease mouse model

Soluble amyloid-beta (Aβ) oligomers are hypothesized to be the pathogenic species in Alzheimer's disease (AD), and increased levels of oligomers in the brain subsequent to traumatic brain injury (TBI) may exacerbate secondary injury pathways and underlie increased risk of developing AD in later life. To determine whether TBI causes Aβ aggregation and oligomerization in the brain, we exposed triple transgenic AD model mice to controlled cortical impact injury and measured levels of soluble, insoluble, and oligomeric Aβ by enzyme-linked immunosorbent assay (ELISA) at 1, 3, and 7 days postinjury. TBI rapidly increased levels of both soluble and insoluble Aβ40 and Aβ42 in the injured cortex at 1 day postinjury. We confirmed previous findings that identified damaged axons as a major site of Aβ accumulation using both immunohistochemistry and biochemistry. We also report that soluble Aβ oligomers were significantly increased in the injured cortex, as demonstrated by both ELISA and Western blot. Interestingly, the mouse brain is able to rapidly clear trauma-induced Aβ, with both soluble and insoluble Aβ species returning to sham levels by 7 days postinjury. In conclusion, we demonstrate that TBI causes acute accumulation and aggregation of Aβ in the brain, including the formation of low- and high-molecular-weight Aβ oligomers. The formation and aggregation of Aβ into toxic species acutely after injury may play a role in secondary injury cascades after trauma and, chronically, may contribute to increased risk of developing AD in later life.

Detection of β-amyloid oligomers as a predictor of neurological outcome after brain injury

OBJECT

Traumatic brain injury (TBI) is known to be a risk factor for Alzheimer-like dementia. In previous studies, an increase in β-amyloid (Aβ) monomers, such as β-amyloid 42 (Aβ42), in the CSF of patients with TBI has been shown to correlate with a decrease in amyloid plaques in the brain and improved neurological outcomes. In this study, the authors hypothesized that the levels of toxic high-molecular-weight β-amyloid oligomers are increased in the brain and are detectable within the CSF of TBI patients with poor neurological outcomes.

METHODS

Samples of CSF were collected from 18 patients with severe TBI (Glasgow Coma Scale Scores 3-8) and a ventriculostomy. In all cases the CSF was collected within 72 hours of injury. The CSF levels of neuron-specific enolase (NSE) and Aβ42 were measured using enzyme-linked immunosorbent assay. The levels of high-molecular-weight β-amyloid oligomers were measured using Western blot analysis.

RESULTS

Patients with good outcomes showed an increase in the levels of CSF Aβ42 (p = 0.003). Those with bad outcomes exhibited an increase in CSF levels of β-amyloid oligomers (p = 0.009) and NSE (p = 0.001). In addition, the CSF oligomer levels correlated with the scores on the extended Glasgow Outcome Scale (r = -0.89, p = 0.0001), disability rating scale scores (r = 0.77, p = 0.005), CSF Aβ42 levels (r = -0.42, p = 0.12), and CSF NSE levels (r = 0.70, p = 0.004). Additionally, the receiver operating characteristic curve yielded an area under the curve for β-amyloid oligomers of 0.8750 ± 0.09.

CONCLUSIONS

Detection of β-amyloid oligomers may someday become a useful clinical tool for determining injury severity and neurological outcomes in patients with TBI.

sAPPα rescues deficits in amyloid precursor protein knockout mice following focal traumatic brain injury

The amyloid precursor protein (APP) is thought to be neuroprotective following traumatic brain injury (TBI), although definitive evidence at moderate to severe levels of injury is lacking. In the current study, we investigated histological and functional outcomes in APP-/- mice compared with APP+/+ mice following a moderate focal injury, and whether administration of sAPPα restored the outcomes in knockout animals back to the wildtype state. Following moderate controlled cortical impact injury, APP-/- mice demonstrated greater impairment in motor and cognitive outcome as determined by the ledged beam and Barnes Maze tests respectively (p < 0.05). This corresponded with the degree of neuronal damage, with APP-/- mice having significantly greater lesion volume (25.0 ± 1.6 vs. 20.3 ± 1.6%, p < 0.01) and hippocampal damage, with less remaining CA neurons (839 ± 245 vs. 1353 ± 142 and 1401 ± 263). This was also associated with an impaired neuroreparative response, with decreased GAP-43 immunoreactivity within the cortex around the lesion edge compared with APP+/+ mice. The deficits observed in the APP-/- mice related to a lack of sAPPα, as treatment with exogenously added sAPPα post-injury improved APP-/- mice histological and functional outcome to the point that they were no longer significantly different to APP+/+ mice (p < 0.05). This study shows that endogenous APP is potentially protective at moderate levels of TBI, and that this neuroprotective activity is related to the presence of sAPPα. Importantly, it indicates that the mechanism of action of exogenously added sAPPα is independent of the presence of endogenous APP.

Estrone is neuroprotective in rats after traumatic brain injury

In various animal and human studies, early administration of 17β-estradiol, a strong antioxidant, anti-inflammatory, and anti-apoptotic agent, significantly decreases the severity of injury in the brain associated with cell death. Estrone, the predominant estrogen in postmenopausal women, has been shown to be a promising neuroprotective agent. The overall goal of this project was to determine if estrone mitigates secondary injury following traumatic brain injury (TBI) in rats. Male rats were given either placebo (corn oil) or estrone (0.5 mg/kg) at 30 min after severe TBI. Using a controlled cortical impact device in rats that underwent a craniotomy, the right parietal cortex was injured using the impactor tip. Non-injured control and sham animals were also included. At 72 h following injury, the animals were perfused intracardially with 0.9% saline followed by 10% phosphate-buffered formalin. The whole brain was removed, sliced, and stained for TUNEL-positive cells. Estrone decreased cortical lesion volume (p<0.01) and neuronal injury (p<0.001), and it reduced cerebral cortical levels of TUNEL-positive staining (p<0.0001), and decreased numbers of TUNEL-positive cells in the corpus callosum (p<0.03). We assessed the levels of β-amyloid in the injured animals and found that estrone significantly decreased the cortical levels of β-amyloid after brain injury. Cortical levels of phospho-ERK1/2 were significantly (p<0.01) increased by estrone. This increase was associated with an increase in phospho-CREB levels (p<0.021), and brain-derived neurotrophic factor (BDNF) expression (p<0.0006). In conclusion, estrone given acutely after injury increases the signaling of protective pathways such as the ERK1/2 and BDNF pathways, decreases ischemic secondary injury, and decreases apoptotic-mediated cell death. These results suggest that estrone may afford protection to those suffering from TBI.

Animal modelling of traumatic brain injury in preclinical drug development: where do we go from here?

Traumatic brain injury (TBI) is the leading cause of death and disability in young adults. Survivors of TBI frequently suffer from long-term personality changes and deficits in cognitive and motor performance, urgently calling for novel pharmacological treatment options. To date, all clinical trials evaluating neuroprotective compounds have failed in demonstrating clinical efficacy in cohorts of severely injured TBI patients. The purpose of the present review is to describe the utility of animal models of TBI for preclinical evaluation of pharmacological compounds. No single animal model can adequately mimic all aspects of human TBI owing to the heterogeneity of clinical TBI. To successfully develop compounds for clinical TBI, a thorough evaluation in several TBI models and injury severities is crucial. Additionally, brain pharmacokinetics and the time window must be carefully evaluated. Although the search for a single-compound, 'silver bullet' therapy is ongoing, a combination of drugs targeting various aspects of neuroprotection, neuroinflammation and regeneration may be needed. In summary, finding drugs and prove clinical efficacy in TBI is a major challenge ahead for the research community and the drug industry. For a successful translation of basic science knowledge to the clinic to occur we believe that a further refinement of animal models and functional outcome methods is important. In the clinical setting, improved patient classification, more homogenous patient cohorts in clinical trials, standardized treatment strategies, improved central nervous system drug delivery systems and monitoring of target drug levels and drug effects is warranted.

Morphological alteration and reduction of MAP2-immunoreactivity in pyramidal neurons of cerebral cortex in a rat model of focal cortical compression

Subdural hematoma causes cortical damage including brain tissue disruption, often resulting in neuronal dysfunction and neurological impairment. The aim of the present study was to identify the relationship between cerebral compression and neuronal injury. In this report, we investigated time-dependent morphological alterations within layers II, III, and V pyramidal neurons in the cerebral cortex, using Golgi-Cox staining and immunohistochemistry for microtubule-associated protein 2 (MAP2) in a rat model of focal cortical compression. An acryl pole was used to experimentally induce chronic cerebral compression by continuous pressure on the cortical surface. Changes in cellular morphology were examined at five survival time periods: 12 h and 1, 2, 3, and 4 weeks. The Golgi-Cox method revealed time-dependent alterations in dendritic length of apical and basilar dendrites of pyramidal neurons. The number of dendritic branch segments and spines of basilar dendrites were decreased in cells in layers II, III, and V. Immunohistochemical staining for MAP2 revealed changes in the intracellular distribution of immunoreactive materials. A significant reduction in MAP2 immunostaining was found in nerve cell bodies and apical dendrites of ipsilateral cortical neurons. The number of MAP2-immunoreactive neurons was significantly decreased at 12 h compared with the contralateral cerebral cortex in the same animal. Dendritic changes in layers II, III, and V pyramidal neurons were accompanied by reductions in intracellular MAP2-immunoreactive materials. The present results suggest that cortical compression causes alteration of cellular morphology as a consequence of injury, and that these morphological changes may be related to reductions in MAP2-immunoreactive materials.

Changes in neural dendrites and synapses in rat somatosensory cortex following neonatal post-hemorrhagic hydrocephalus

Neonatal post-hemorrhagic hydrocephalus is associated with cognitive decline and a serious deterioration in the patient's quality of life. The underlying impairments to neurons are not well understood. Here, we used the method described by Cherian et al. to construct a model of hydrocephalus after intra-ventricular hemorrhage and then observed the subsequent pathological changes in the morphology of neurons labeled by enhanced green fluorescent proteins (EGFP) using the in utero electroporation technique. Injection of venous blood into the lateral ventricles of 7-day-old rats in the operation group caused marked enlargement of the ventricles in 60% (9/15) of the rats after 2 weeks and in 53.3% (8/15) of the rats after 3 weeks. Compared with the control group, the length of the neural dendrites in the somatosensory cortex was shortened and the number of both neuron dendrite branches and synapses was significantly decreased. There was no evidence of cerebral cortical neuron death as shown by positive EGFP cell counting which suggest that neurological dysfunction after intra-ventricular hemorrhage-induced hydrocephalus may be related to the shortening of neural dendrites and the decreased number of synapses in somatosensory cortex and thus provides a possible neurological cause for hydrocephalus-induced cognitive decline and motor dysfunction.

Dendritic alterations after dynamic axonal stretch injury in vitro

Traumatic axonal injury (TAI) is the most common and important pathology of traumatic brain injury (TBI). However, little is known about potential indirect effects of TAI on dendrites. In this study, we used a well-established in vitro model of axonal stretch injury to investigate TAI-induced changes in dendrite morphology. Axons bridging two separated rat cortical neuron populations plated on a deformable substrate were used to create a zone of isolated stretch injury to axons. Following injury, we observed the formation of dendritic alterations or beading along the dendrite shaft. Dendritic beading formed within minutes after stretch then subsided over time. Pharmacological experiments revealed a sodium-dependent mechanism, while removing extracellular calcium exacerbated TAI's effect on dendrites. In addition, blocking ionotropic glutamate receptors with the N-methyl-d-aspartate (NMDA) receptor antagonist MK-801 prevented dendritic beading. These results demonstrate that axon mechanical injury directly affects dendrite morphology, highlighting an important bystander effect of TAI. The data also imply that TAI may alter dendrite structure and plasticity in vivo. An understanding of TAI's effect on dendrites is important since proper dendrite function is crucial for normal brain function and recovery after injury.

Role of the proteasome in excitotoxicity-induced cleavage of glutamic acid decarboxylase in cultured hippocampal neurons

Glutamic acid decarboxylase is responsible for synthesizing GABA, the major inhibitory neurotransmitter, and exists in two isoforms—GAD65 and GAD67. The enzyme is cleaved under excitotoxic conditions, but the mechanisms involved and the functional consequences are not fully elucidated. We found that excitotoxic stimulation of cultured hippocampal neurons with glutamate leads to a time-dependent cleavage of GAD65 and GAD67 in the N-terminal region of the proteins, and decrease the corresponding mRNAs. The cleavage of GAD67 was sensitive to the proteasome inhibitors MG132, YU102 and lactacystin, and was also abrogated by the E1 ubiquitin ligase inhibitor UBEI-41. In contrast, MG132 and UBEI-41 were the only inhibitors tested that showed an effect on GAD65 cleavage. Excitotoxic stimulation with glutamate also increased the amount of GAD captured in experiments where ubiquitinated proteins and their binding partners were isolated. However, no evidences were found for direct GADs ubiquitination in cultured hippocampal neurons, and recombinant GAD65 was not cleaved by purified 20S or 26S proteasome preparations. Since calpains, a group of calcium activated proteases, play a key role in GAD65/67 cleavage under excitotoxic conditions the results suggest that GADs are cleaved after ubiquitination and degradation of an unknown binding partner by the proteasome. The characteristic punctate distribution of GAD65 along neurites of differentiated cultured hippocampal neurons was significantly reduced after excitotoxic injury, and the total GAD activity measured in extracts from the cerebellum or cerebral cortex at 24h postmortem (when there is a partial cleavage of GADs) was also decreased. The results show a role of the UPS in the cleavage of GAD65/67 and point out the deregulation of GADs under excitotoxic conditions, which is likely to affect GABAergic neurotransmission. This is the first time that the UPS has been implicated in the events triggered during excitotoxicity and the first molecular target of the UPS affected in this cell death process.

Monitoring of brain interstitial total tau and beta amyloid proteins by microdialysis in patients with traumatic brain injury

OBJECT

Damage to axons contributes to postinjury disabilities and is commonly observed following traumatic brain injury (TBI). Traumatic brain injury is an important environmental risk factor for the development of Alzheimer disease (AD). In the present feasibility study, the aim was to use intracerebral microdialysis catheters with a high molecular cutoff membrane (100 kD) to harvest interstitial total tau (T-tau) and amyloid beta 1-42 (Abeta42) proteins, which are important biomarkers for axonal injury and for AD, following moderate-to-severe TBI.

METHODS

Eight patients (5 men and 3 women) were included in the study; 5 of the patients had a focal/mixed TBI and 3 had a diffuse axonal injury (DAI). Following the bedside analysis of the routinely measured energy metabolic markers (that is, glucose, lactate/pyruvate ratio, glycerol, and glutamate), the remaining dialysate was pooled and two 12-hour samples per day were used to analyze T-tau and Abeta42 by enzyme-linked immunosorbent assay from Day 1 up to 8 days postinjury.

RESULTS

The results show high levels of interstitial T-tau and Abeta42 postinjury. Patients with a predominantly focal lesion had higher interstitial T-tau levels than in the DAI group from Days 1 to 3 postinjury (p < 0.05). In contrast, patients with DAI had consistently higher Abeta42 levels when compared with patients with focal injury.

CONCLUSIONS

These results suggest that monitoring of interstitial T-tau and Abeta42 by using microdialysis may be an important tool when evaluating the presence and role of axonal injury following TBI.

Cerebral transplantation of encapsulated mesenchymal stem cells improves cellular pathology after experimental traumatic brain injury

PURPOSE

"Naked" human mesenchymal stem cells (MSC) are neuro-protective in experimental brain injury (TBI). In a controlled cortical impact (CCI) rat model, we investigated whether encapsulated MSC (eMSC) act similarly, and whether efficacy is augmented using cells transfected to produce the neuro-protective substance glucagon-like peptide-1 (GLP-1).

METHODS

Thirty two Sprague-Dawley rats were randomized to five groups: controls (no CCI), CCI-only, CCI+eMSC, CCI+GLP-1 eMSC, and CCI+empty capsules. On day 14, cisternal cerebro-spinal fluid (CSF) was sampled for measurement of GLP-1 concentration. Brains were immuno-histochemically assessed using specific antibody staining for NeuN, MAP-2 and GFAP. In another nine healthy rats, in vitro.

RESULTS

GLP-1 production rates were measured from cells explanted after 2, 7 and 14 days. GLP-1 production rate in transfected cells, before implantation, was 7.03 fmol/capsule/h. Cells were still secreting GLP-1 at a rate of 3.68+/-0.49, 2.85+/-0.45 and 3.53+/-0.55 after 2, 7 and 14 days, respectively. In both of the stem cell treated CCI groups, hippocampal cell loss was reduced, along with an attenuation of cortical neuronal and glial abnormalities, as measured by MAP-2 and GFAP expression. The effects were more pronounced in animals treated with GLP-1 secreting eMSC. This group displayed an increased CSF level of GLP-1 (17.3+/-3.4pM).

CONCLUSIONS

Hippocampal neuronal cell loss, and cortical glial and neuronal cyto-skeletal abnormalities, after CCI are reduced following transplantation of encapsulated eMSC. These effects were augmented by GLP-1 transfected eMSC.

Expression of amyloid precursor protein after rat traumatic brain injury

OBJECTIVE

Previous reports have demonstrated that some focal brain injuries increase amyloid precursor protein (APP) immunoreactivity in the region surrounding the injury in the cerebral cortex. However, the chronologic changes in APP expression have not been evaluated after traumatic brain injury (TBI).

METHODS

In this study, we immunohistochemically and biologically investigated chronologic changes in cellular sources and levels of APP production after rat TBI.

RESULTS

In the present report, we show that traumatic brain injury increased the expression of APP in the neuronal perikarya and in damaged dystrophic neurites from 1 to 90 days after injury. Moreover, 7 days after injury, some macrophages/microglia also were co-localized with APP, which was overproduced by the neuronal perikarya and APP-positive dystrophic neurites after injury and then APP were phagocytosed by macrophages/microglia during this phase. However, astroglia did not express APP immunopositivity after brain injury.

DISCUSSION

These results suggested that long-term overexpression of APP was confirmed by immunohistochemical and biologic technique after TBI. This may be related to the induction of Alzheimer type dementia and it is a very important risk factor for this disease.

The autophagy-related protein beclin 1 shows reduced expression in early Alzheimer disease and regulates amyloid beta accumulation in mice

Autophagy is the principal cellular pathway for degradation of long-lived proteins and organelles and regulates cell fate in response to stress. Recently, autophagy has been implicated in neurodegeneration, but whether it is detrimental or protective remains unclear. Here we report that beclin 1, a protein with a key role in autophagy, was decreased in affected brain regions of patients with Alzheimer disease (AD) early in the disease process. Heterozygous deletion of beclin 1 (Becn1) in mice decreased neuronal autophagy and resulted in neurodegeneration and disruption of lysosomes. In transgenic mice that express human amyloid precursor protein (APP), a model for AD, genetic reduction of Becn1 expression increased intraneuronal amyloid beta (Abeta) accumulation, extracellular Abeta deposition, and neurodegeneration and caused microglial changes and profound neuronal ultrastructural abnormalities. Administration of a lentiviral vector expressing beclin 1 reduced both intracellular and extracellular amyloid pathology in APP transgenic mice. We conclude that beclin 1 deficiency disrupts neuronal autophagy, modulates APP metabolism, and promotes neurodegeneration in mice and that increasing beclin 1 levels may have therapeutic potential in AD.

Attenuation of microtubule associated protein-2 degradation after mild head injury by mexiletine and calpain-2 inhibitor

The objective of the study was to address the early effects of mild, closed, head injuries on neuronal stability and the prevention of microtubule-associated protein-2 (MAP-2) degradation by mexiletine and calpain-2 inhibitor. Twenty-four rats were divided into four groups: control group (1); trauma group without treatment (2); mexiletine-pretreated and subjected to trauma group (3); trauma subjected and then calpain-2 inhibitor received group (4). All animals were subjected to mild, closed, head trauma. Frontal lobes were removed and processed for staining and immunofluorescent labelling of MAP-2 cytoskeletal proteins, which were evaluated by confocal microscopy in serial optical sections showing the three dimensional cytoarchitecture of affected areas. MAP-2 decoration in almost all neurons obtained from traumatized brain regions drastically diminished, while minute filamentous and granular profiles in axons and/or dendrites were retained together implying a massive degradation/depolymerization of microtubules. In contrast, in mexiletine-pretreated animals, MAP-2 positivity in axonal and perikaryonal profiles was fairly retained, which clearly depicts the protective role of mexiletine after trauma. Compared with mexiletine-pretreated group, calpain-2 inhibitor treated group displayed a less well-preserved MAP-2 expression. Mexiletine can prevent cytoskeletal structure and protein degradation after mild head trauma. Calpain-2 inhibitor prevents protein degradation, but cytoskeletal organization is better preserved with mexiletine.

Extent of nerve cell injury in Marmarou's model compared to other brain trauma models

OBJECTIVES

We sought to determine the extent of nerve cell injury in the Marmarou's acceleration impact model of diffuse brain injury.

METHODS

Sensitive markers for cell injury including immunostaining for beta-amyloid precursor protein (beta-APP, a marker for diffuse axonal injury, DAI), Fluoro-Jade (FJ) histochemistry and electron microscopy (EM) were used in sham-operated and traumatized brains.

RESULTS

APP immunostaining confirmed and extended previous findings of DAI in association and subcortical fiber systems in the white matter after injury. Increasing FJ labeling of neurons in layers II-III of sensorimotor cortex (smCx) from 4 to 48 hours after trauma and scattered labeled cells were found in the lower cortical layers. EM confirmed the presence of dystrophic pyramidal neurons in layers II-III of smCx 24 and 48 hours post-trauma.

DISCUSSION

Taken together, the data revealed significant nerve cell injury without apparent cell death in this model.

Apoptotic and behavioral sequelae of mild brain trauma in mice

Mild traumatic brain injury (mTBI) is a not uncommon event in adolescents and young adults. Although it does not result in clear morphological brain defects, it is associated with long-term cognitive, emotional, and behavioral problems. Herein, we characterized the biochemical and behavioral changes associated with experimental mTBI in mice that may act as either targets or surrogate markers for interventional therapy. Specifically, mTBI was induced by 30-g and 50-g weight drop, and at 8 and 72 hr thereafter markers of cellular apoptosis-caspase-3, Bax, apoptosis-inducing factor (AIF), and cytochrome-c (Cyt-c)-were quantified by Western blot analysis in hippocampus ipsilateral to the impact. Levels of amyloid-beta precursor protein (APP) were also measured, and specific behavioral tests-passive avoidance, open field, and forced swimming (Porsolt) paradigms-were undertaken to assess learning, emotionality, and emotional memory. In the absence of hemorrhage or infarcts, as assessed by triphenyltetrazolium chloride staining, procaspase-3 and Bax levels were markedly altered following mTBI at both times. No cleaved caspase-3 was detected, and levels of AIF and Cyt-c, but not APP, were significantly changed at 72 hr. Mice subjected to mTBI were indistinguishable from controls by neurological examination at 1 and 24 hr, and by passive avoidance/open field at 72 hr, but could be differentiated in the forced swimming paradigm. In general, this model mimics the diffuse effects of mTBI on brain function associated with the human condition and highlights specific apoptotic proteins and a behavioral paradigm as potential markers for prospective interventional strategies.

Reduced dendrite growth and altered glutamic acid decarboxylase (GAD) 65- and 67-kDa isoform protein expression from mouse cortical GABAergic neurons following excitotoxic injury in vitro

The vulnerability of brain cells to neurologic insults varies greatly, depending on their neuronal subpopulation. However, cells surviving pathological insults such as ischemia or brain trauma may undergo structural changes, e.g., altered process growth, that could compromise brain function. In this study, we examined the effect of glutamate excitotoxicity on dendrite growth from surviving cortical GABAergic neurons in vitro. Glutamate exposure did not affect GABAergic neuron viability, however, it significantly reduced dendrite growth from GABAergic neurons. This effect was blocked by the AMPA receptor antagonists NBQX and CFM-2, and mimicked by AMPA, but not NMDA. Glutamate excitotoxicity also caused an NMDA receptor-mediated decrease in the GABA synthesizing enzyme glutamic acid decarboxylase (GAD65/67) immunoreactivity from GABAergic neurons, measured using immunocytochemical and Western blot techniques. GAD is necessary for GABA synthesis; however, reduction of GABA by 3-mercaptopropionic acid (3-MPA), which inhibits GABA synthesis, did not alter dendrite growth. These results suggest that GABAergic cortical neurons are relatively resistant to excitotoxic-induced cell death, but they can display morphological and biochemical alterations which may impair their function.

Stretch-induced injury in organotypic hippocampal slice cultures reproduces in vivo post-traumatic neurodegeneration: role of glutamate receptors and voltage-dependent calcium channels

The relationship between an initial mechanical event causing brain tissue deformation and delayed neurodegeneration in vivo is complex because of the multiplicity of factors involved. We have used a simplified brain surrogate based on rat hippocampal slices grown on deformable silicone membranes to study stretch-induced traumatic brain injury. Traumatic injury was induced by stretching the culture substrate, and the biological response characterized after 4 days. Morphological abnormalities consistent with traumatic injury in humans were widely observed in injured cultures. Synaptic function was significantly reduced after a severe injury. The N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 attenuated neuronal damage, prevented loss of microtubule-associated protein 2 immunoreactivity and attenuated reduction of synaptic function. In contrast, the NMDA receptor antagonists 3-[(R)-2-carboxypiperazin-4-yl]-propyl-1-phosphonic acid (CPP) and GYKI53655, were neuroprotective in a moderate but not a severe injury paradigm. Nifedipine, an L-type voltage-dependent calcium channel antagonist was protective only after a moderate injury, whereas omega-conotoxin attenuated damage following severe injury. These results indicate that the mechanism of damage following stretch injury is complex and varies depending on the severity of the insult. In conclusion, the pharmacological, morphological and electrophysiological responses of organotypic hippocampal slice cultures to stretch injury were similar to those observed in vivo. Our model provides an alternative to animal testing for understanding the mechanisms of post-traumatic delayed cell death and could be used as a high-content screen to discover neuroprotective compounds before advancing to in vivo models.

Transient cognitive deficits are associated with the reversible accumulation of amyloid precursor protein after mild traumatic brain injury

Mild traumatic brain injury (MTBI) may frequently cause transient behavioral abnormalities without observable morphological findings. In this study, we investigated neuropathological mechanisms underlying transient cognitive deficits after MTBI. Mongolian gerbils were subjected to experimental MTBI. At various time points after injury, behavioral changes were evaluated by the open-field test and T-maze test, and immunohistochemistry of microtubule-associated protein (MAP2) and amyloid precursor protein (APP) was performed to examine disruptions of the neuronal cytoskeleton and axonal transport, respectively. Transient cognitive deficits were observed after MTBI. Sustained MAP2 loss was found within the cortical impact site, but not the hippocampus. Transient APP accumulation at the same time as transient cognitive deficits occurred in the ipsilateral hemisphere, particularly in the subcortical white matter. These results suggest that the axonal dysfunction indicated by the reversible APP accumulation in the white matter, but not the sustained neuronal cytoskeletal damage reflected by the cortical MAP2 loss confined to the impact site, is responsible for the transient functional deficits after MTBI.

Genetically modified bone morphogenetic protein signalling Alters traumatic brain injury-induced gene expression responses in the adult mouse

Three genetic mouse models were examined to define effects of bone morphogenetic protein (BMP) signalling on gene expression in normal and injured adult brain. CaMKII-Cre eliminated the BMP receptor Acvr1 (Alk2) and the common TGFbeta superfamily signal mediator Smad4 or activated a constitutively active Acvr1 in postnatal forebrain neurons. All mutants followed mendelian ratios, with no overt phenotypic changes. In situ hybridization demonstrated normal patterns of the dendritic marker MAP2 (Mtap2) throughout cortex despite neuron-specific losses of Acvr1 or Smad4. However, strong up-regulation of Mtap2 transcript in these mice was found by quantitative RT-PCR (qRT-PCR), indicating that Mtap2 is normally suppressed by BMP. Traumatic brain injury (TBI) resulted in increases of histone-associated DNA fragments in both control and Smad4-deficient cortex. Several cell-type-specific transcripts known to be involved in injury-related responses were measured by qRT-PCR. Gfap mRNA was strongly up-regulated in controls as well as in the loss-of-BMP-signalling mutants. Notably, activated Acvr1 signalling gave significantly lower TBI-induced up-regulations of Gfap and Phox2a mRNA levels, indicating reductions in astroglial and neuronal reactions to injury. Strong impairment in injury-induced Timp1 transcript up-regulation was also seen in these mice. In contrast, osteopontin (Spp1) transcript levels in activated microglia were not reduced by Acvr1 signalling. Altogether, the data suggest that BMP signalling is dispensable in adult cortical neurons but that augmented BMP signalling affects molecular changes associated with neuronal lesions.

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.

Correlation of Hippocampal Morphological Changes and Morris Water Maze Performance after Cortical Contusion Injury in Rats

OBJECTIVE

The hippocampus is essential to the processing and formation of memory. This study analyzed the relationship among memory dysfunction as revealed by Morris water maze (MWM) trial, cortical lesion volume, and regional hippocampal morphological changes after controlled cortical contusion (CCC). We also analyzed the influence of pretreatment with the nitrone radical scavenger alpha-phenyl-N-tert-butyl-nitrone (PBN).

METHODS

Rats were subjected to CCC. We used two levels of CCC (mild, 1.5 mm and severe, 2.5 mm) and pretreated some severely injured animals with PBN. The animals were killed 15 days postinjury. We evaluated morphological changes to the hippocampus semiquantitatively by scoring sections immunohistochemically stained for microtubule-associated protein 2 with a four-point scale for the cornu ammonis (CA) 1, CA2, CA3, and hilus of the dentate gyrus (HDG). The cortical lesion volume was quantified.

RESULTS

Rats subjected to severe, but not mild, CCC demonstrated impaired spatial learning ability in the MWM, but this impairment was attenuated with pretreatment with the radical scavenger PBN. We documented bilateral morphological changes in CA1, CA3, and HDG and an ipsilateral neocortical cavitation in severely injured rats. PBN treatment attenuated (P < 0.05) the morphological characteristics of abnormality in the ipsilateral CA1, CA2, HDG, and the contralateral HDG and reduced the cortical lesion volume. Mild injury led to minor ipsilateral hippocampal and cortical damage but no MWM deficiency. Hippocampal morphological scores and total mean latencies in the MWM task were strongly correlated (r = 0.69; P < 0.001). The correlation between the cortical lesion volume and MWM latency was weaker (r = 0.48; P = 0.02).

CONCLUSION

Severe CCC causes bilateral morphological changes in the hippocampus and ipsilateral neocortical cavitation, which correlate to impairment in a spatial learning task (MWM). PBN protected the structure of the CA2 ipsilaterally and HDG bilaterally and reduced the cortical lesion volume, correlating to improved functional outcome.

Traumatic brain injury: cause or risk of Alzheimer's disease? A review of experimental studies

Traumatic Brain Injury is the leading cause of death and disability among young individuals in our society. Moreover, according to some epidemiological studies, head trauma is one of the most potent environmental risk factors for subsequent development of Alzheimer's disease. Interestingly, pathological features that are present also in Alzheimer's disease (in particular deposition of beta-amyloid protein) were observed in traumatised brains already a few hours after the initial insult. The primary objective of this review is to present methodology and results of numerous recent human and animal studies dealing with this issue. Special emphasis was placed on head trauma experiments in transgenic mouse models of Alzheimer's disease. We further evaluate the connection between traumatic brain insults and subsequent development of dementia and try to differentiate between primary and secondary pathological mechanisms.

Downregulation of amyloid precursor protein (APP) expression following post-traumatic cyclosporin-A administration

The aim of these studies was to assess and quantitate the effects of cyclosporin-A (CyA) on brain APP messenger RNA and neuronal perikaryal APP antigen expression following controlled focal head impact in sheep. Impact results in a significant increase in both APP mRNA and neuronal perikaryal APP antigen expression. Post-traumatic administration of CyA (intrathecal 10 mg/kg) resulted in a reduction in APP mRNA and neuronal perikaryal antigen expression. At 2 h postinjury, CyA treatment caused a statistically significant (p < 0.05) 1.3 +/- 0.1-fold decrease in APP mRNA in the central gray matter of impacted sheep compared to untreated impacted sheep. A more profound reduction in APP mRNA synthesis (1.6 +/- 0.2 fold) was evident at 6 h (p < 0.05). The mean percentage brain area with APP immunoreactive neuronal perikarya at 6 h post-injury was 94.5% in untreated impacted animals, 10.0% in CyA-treated impacted animals, 5.5% in untreated nonimpacted animals, and 6% in CyA-treated non-impacted controls. These results demonstrate that CyA has a downregulatory effect on increased APP expression caused by TBI.

Effect of systemic LPS injection on cortical NF-κB activity and inflammatory response following traumatic brain injury in rats

The aim of current study is to investigate the effect of systemic administration of lipopolysaccharide (LPS) on the temporal pattern of cortical nuclear factor kappa B (NF-kappaB) binding activity, inflammatory response and secondary damage in the injured brain following traumatic brain injury (TBI). Right parietal cortical contusion in rats was made by using weight-dropping method. The rats were randomly divided into sham, LPS, TBI and TBI-LPS groups, with LPS injected intraperitoneally. NF-kappaB binding activity, cytokines, intercellular adhesion molecule-1 (ICAM-1) and brain damage were detected by electrophoretic mobility shift assay (EMSA), enzyme-linked immunosorbent assay (ELISA), immunohistochemistry and terminal deoxynucleotidyl-transferase-mediated biotin-dUTP nick end labeling (TUNEL) apoptosis, respectively. The results showed that systemic administration of LPS following TBI could induce an immediate, strong and persistent upregulation of NF-kappaB, tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and ICAM-1 in the area surrounding the injured brain. As compared with rats of sham, LPS and TBI groups, NF-kappaB binding activity, TNF-alpha and IL-6 were significantly upregulated in the surrounding cortex of injured site as early as 3 h postinjury when challenged with LPS, kept at high level up to 7-days postinjury. ICAM-1-positive vessels and apoptotic TUNEL-positive cells in the injured brain were also significantly increased in TBI-LPS rats. It was concluded that inflammatory response and secondary brain damage occurred in the injured brain could be highly exacerbated by endotoxemia.

A model for studies of intracranial volume pressure dynamics in traumatic brain injury

The present study was undertaken to establish an experimental trauma model where it was possible to alter intracranial pressure (ICP) dynamics without raising intracranial pressure to abnormal levels and monitor metabolic disturbances with microdialysis. Thirty rats were intubated and mechanically ventilated before and after trauma. ICP was measured in the left ventricle. A weight-drop technique (21 g from 35 cm) with a brain compression of 1.5 mm was used to produce the injury. Intracranial compensatory volume was decreased 20 or 60 microL by placement of rubber film between the dura mater and bone. A bolus injection technique was used for the pressure volume response. ICP remained within normal limits for 2 h after trauma irrespective of the reduction in compensatory intracranial volume. Pressure-volume index decreased from 0.0825 +/- 0.009 to 0.0779 +/- 0.011 mL in the sham trauma and from 0.0871 +/- 0.018 to 0.0748 +/- 0.017 mL in the trauma groups (p < 0.015) when the intracranial volume was reduced by 60 microL. Intracranial compliance was not affected significantly. The present study shows that it is possible to vary ICP dynamics in a traumatic brain injury model without causing pathological increases in baseline ICP. This model may be used to study the effects of secondary insults (i.e., hypotension, hypoxia, hypercarbia, and hyperthermia) on the injured brain when ICP is normal but intracranial compensatory volume is impaired.

Effect of excess extracellular glutamate on dendrite growth from cerebral cortical neurons at 3 days in vitro: Involvement of NMDA receptors

Glutamate is an important regulator of dendrite development; however, during cerebral ischemia, massive glutamate release can lead to neurodegeneration and death. An early consequence of glutamate excitotoxicity is dendrite injury, which often precedes cell death. We examined the effect of glutamate on dendrite growth from embryonic day 18 (E18) mouse cortical neurons grown for 3 days in vitro (DIV) and immunolabeled with anti-microtubule-associated protein (MAP)2 and anti-neurofilament (NF)-H, to identify dendrites and axons, respectively. Cortical neurons exposed to excess extracellular glutamate (100 microM) displayed reduced dendrite growth, which occurred in the absence of cell death. This effect was mimicked by the ionotropic glutamate receptor agonist N-methyl-D-aspartate (NMDA) and blocked by the ionotropic glutamate receptor antagonist kynurenic acid and the NMDA receptor-specific antagonist MK-801. The non-NMDA receptor agonist AMPA, however, did not affect process growth. Neither NMDA nor AMPA influenced neuron survival. Immunolabeling and Western blot analysis of NMDA receptors using antibodies against the NR1 subunit, demonstrated that immature cortical neurons used in this study, express NMDA receptors. These results suggest that excess glutamate decreases dendrite growth through a mechanism resulting from NMDA receptor subclass activation. Furthermore, these data support the possibility that excess glutamate activation of NMDA receptors mediate both cell death in mature neurons and the inhibitory effect of excess glutamate on dendrite growth in immature neurons or in the absence of cell death.

Transient Loss of Microtubule-Associated Protein 2 Immunoreactivity after Moderate Brain Injury in Mice

Microtubule-associated protein 2 (MAP2) is important for microtubule stability and neural plasticity and appears to be among the most vulnerable of the cytoskeletal proteins under conditions of neuronal injury. To evaluate the acute effects of moderate severity traumatic brain injury on MAP2, anesthetized, adult male C57BL/6 mice were subjected to controlled cortical impact brain injury. At 5 min, 15 min, 90 min, 4 h, and 24 h following brain injury (n = 4 injured and n = 1 sham-injured per time point), mice were sacrificed and immunohistochemistry was performed on coronal brain sections. Profound decreases in MAP2 immunolabeling were observed in the ipsilateral cortex and hippocampal dentate hilus at 5 min postinjury and in the ipsilateral hippocampal CA3 area by 4 h postinjury. Decreases in MAP2 labeling occurred prior to notable neuronal cell loss. Interestingly, cortical MAP2 immunoreactivity returned by 90 min postinjury, but the recovery was short-lived within the core in comparison to the periphery of the impact site. Partial restoration of MAP2 immunoreactivity was also observed in the ipsilateral CA3 and dentate hilus by 24 h postinjury. Our data corroborate that MAP2 is an early and sensitive marker for neuronal damage following traumatic brain injury. Acute MAP2 loss, however, may not necessarily presage neuronal death, even following moderate severity traumatic brain injury. Rather, to the best of our knowledge, our data are the first to suggest an intrinsic ability of the traumatized brain for MAP2 recovery after injury of moderate severity.

Apolipoprotein e4 decreases whereas apolipoprotein e3 increases the level of secreted amyloid precursor protein after closed head injury

Apolipoprotein E (apoE4) and head trauma are important genetic and environmental risk factors for Alzheimer's disease. Furthermore, apoE4 increases both the acute and chronic consequences of head trauma. The latter are associated with the deposition of amyloid-beta, which is particularly elevated in apoE4 subjects. The short-term effects of head injury are associated with transiently increased metabolism of amyloid precursor protein (APP) and its secreted fragment, APPs. In the present study, we examined the possibility that the acute, short-term pathological effects of apoE4 following head trauma and the corresponding neuroprotective effects of apoE3 are related to isoform-specific effects of apoE on APP metabolism. Accordingly, male transgenic mice expressing human apoE3 or apoE4 on a null mouse apoE background and apoE-deficient and control mice were subjected to closed head injury (CHI). The resulting effects on brain APP, and on its secreted products, APPs and secreted product of the alpha-cleavage of APP (APPsalpha) were then determined 24 h following injury. Immunoblotting revealed no significant differences between the basal APP, APPs and APPsalpha levels of the hippocampus or the cortex of the control and the apoE3 and ApoE4 transgenic mice. The apoE-deficient mice also had similar cortical basal levels of APP and its metabolites, whereas their corresponding basal hippocampal APP and APPs levels were lower than those of the other groups. CHI lowered the hipppocampal APPs and APPsalpha levels of the apoE4 transgenic mice, whereas those of the apoE3 transgenic mice and of the control and apoE-deficient mice were not affected by this insult. In contrast, CHI raised the cortical APP and APPs levels of the apoE3 transgenic mice but had no significant effect on those of the other mice groups. These animal model findings suggest that the acute, short-term pathological effects of apoE4 following CHI and the corresponding neuroprotective effects of apoE3 may be mediated by their opposing effects on the expression and cleavage of cortical and hippocampal APP. Similar isoform-specific interactions between apoE and APP may play a role in the acute, short-term effects of head trauma in humans.

Changes in expression of amyloid precursor protein and interleukin-1beta after experimental traumatic brain injury in rats

There is increasing evidence linking neurodegenerative mechanisms in Alzheimer's disease (AD) and traumatic brain injury (TBI), including increased production of amyloid precursor protein (APP), and amyloid-beta (Abeta) peptide. In vitro data indicate that expression of APP may be regulated in part by the inflammatory cytokine IL-1beta. To further investigate the mechanisms involved, we measured APP and IL-1beta protein levels and examined immunohistochemical localization of APP in brain tissue from rats subjected to controlled cortical impact (CCI) injury. Animals were examined at time intervals ranging from 3 h to 4 weeks after TBI. The 24-h time point revealed a dramatic increase in APP immunoreactivity, detected with both N- and C-terminal antibodies, in the hippocampus and cortex ipsilateral to injury. This finding was sustained up to 3 days post-injury. At these early time points, APP increase was particularly robust in the white matter axonal tracts. By 14 days after injury, APP immunoreactivity was not significantly different from sham controls in cortex, but remained slightly elevated in hippocampus. Western blot data corroborated early increases in hippocampal and cortical APP in injured versus control animals. Despite profound APP changes, no Abeta deposits were observed at any time after injury. Hippocampal and cortical IL-1beta increases were even more robust, with IL-1beta levels peaking by 6 h post-injury and returning to baseline by 24-72 h. Our results demonstrate that both APP and IL-1beta are rapidly elevated after injury. Because of the rapidity in the IL-1beta peak increase, it may serve a role in regulation of APP expression after TBI.

Both MK801 and NBQX reduce the neuronal damage after impact-acceleration brain injury

To understand the pathogenesis of diffuse axonal injury, we investigated the temporal and spatial profiles of neuronal degeneration in impact-acceleration injury in rats using Fluoro-Jade (FJ) staining. Impact-acceleration injury was produced in Wistar rats by the method described by Marmarou et al. with some modifications. Animals were sacrificed 1, 2, 7, 14, or 28 days after injury. Paraffin-embedded coronal sections were stained with HE or FJ, or analyzed immunohistochemically for GFAP or amyloid precursor protein (APP). FJ-positive degenerative neurons were found primarily in the dorsal brainstem and thalamus from 1 to 2 days following injury and these were associated with GFAP expression. However, FJ-positive cells were rarely found after 7 days. In all rats, significant expression of APP was observed primarily in the cingulum, cerebral peduncle and pontomedullary junction. FJ also stained these injured axons. Intrathecal administration of both NMDA and AMPA/kinate glutamate receptor antagonists MK-801 and NBQX, respectively, reduced the neuronal injury. NBQX showed more significant effects on axonal injury than MK-801. These observations indicate that not only axonal damage, but also primary neuronal damage occurs in this impact-acceleration injury model. It is also suggested that NBQX can act both directly on neuronal cells and white matter and that NMDA could have a significant protective effect against not only neuronal, but also axonal injury.

Mild traumatic brain injury induces apoptotic cell death in the cortex that is preceded by decreases in cellular Bcl-2 immunoreactivity

Although mild traumatic brain injury is associated with behavioral dysfunction and histopathological alterations, few studies have assessed the temporal pattern of regional apoptosis following mild brain injury. Anesthetized rats were subjected to mild lateral fluid-percussion brain injury (1.1-1.3 atm), and brains were evaluated for the presence of in situ DNA fragmentation (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling, TUNEL) and morphologic characteristics of apoptotic cell death (nuclear and cytoplasmic condensation, presence of apoptotic bodies). Significant numbers of apoptotic TUNEL(+) cells were observed in the injured parietal cortex and underlying white matter up to 72 h post-injury (P<0.05 compared to sham-injured-injured), with maximal numbers present at 24 h. Apoptosis was confirmed by the presence of 180-200 bp nuclear DNA fragments in tissue homogenates. The appearance of apoptotic TUNEL(+) cells in the injured cortex was preceded by a marked decrease in immunoreactivity for the anti-cell death protein, Bcl-2, as early as 2 h post-injury. This decrease in cellular Bcl-2 staining was not accompanied by a concomitant loss of staining for the pro-cell death Bax protein, suggesting that post-traumatic neuronal death in the cortex may be dependent on altered cellular ratios of Bcl-2:Bax. In the hippocampus, no significant increase in apoptotic TUNEL(+) cells was observed compared to sham-injured-injured animals. However, selective neuronal loss was evident in the CA3 region at 24 h post-injury, that was preceded by an overt loss of neuronal Bcl-2 immunoreactivity at 6 h. No changes in either cellular Bcl-2 or Bax expression were observed in the thalamus or white matter at any time post-injury. Taken together from these data, we suggest that apoptosis contributes to cell death in both gray and white matter, and that decreases in cellular Bcl-2 may, in part, be associated with both apoptotic and non-apoptotic cell death following mild brain trauma.

Rapid loss and partial recovery of neurofilament immunostaining following focal brain injury in mice

Neurofilaments (NF), the intermediate filaments of the neuronal cytoskeleton, provide mechanical stability to the cell. High-molecular-weight NF (NFH) comprises a heavily phosphorylated carboxyl terminal ("sidearm") domain which helps determine interfilament spacing distances. Experimental evidence suggests that dephosphorylation greatly increases the rate and extent of proteolysis of NFH. Because NF proteolysis has been implicated as one pathogenic mechanism underlying cell death following traumatic brain injury (TBI), we analyzed the patterns of acute NFH damage in relation to phosphorylation state following focal, concussive, controlled cortical impact (CCI) brain injury in mice. Brains from C57BL/6 male mice (n = 4 injured and n = 1 sham per time point) were evaluated 5 min, 15 min, 90 min, 4 h, and 24 h following CCI injury (1 mm depth, 5 m/s). Immunohistochemistry was performed using antibodies that recognize epitopes on either dephosphorylated (d-NFH) or phosphorylated (p-NFH) sidearms or on the core (c-NFH) domain. As early as 5-15 min postinjury, immunoreactivity for d-, p-, and c-NFH decreased in the ipsilateral cortex, and hippocampal CA3, CA1, and dentate areas. This marked decrease of NFH labeling occurred in the absence of notable cell loss. Furthermore, partial recovery of NFH labeling was observed as early as 90 min postinjury in the cortex and by 24 h postinjury in hippocampal CA3 and dentate. The results of this study suggest that both phosphorylated and dephosphorylated NFH are vulnerable almost immediately following focal brain injury in mice, but that injured neurons may have an adaptive capability to partially restore this important cytoskeletal protein.

Mild head injury increasing the brain's vulnerability to a second concussive impact

OBJECT

Mild, traumatic repetitive head injury (RHI) leads to neurobehavioral impairment and is associated with the early onset of neurodegenerative disease. The authors developed an animal model to investigate the behavioral and pathological changes associated with RHI.

METHODS

Adult male C57BL/6 mice were subjected to a single injury (43 mice), repetitive injury (two injuries 24 hours apart; 49 mice), or no impact (36 mice). Cognitive function was assessed using the Morris water maze test, and neurological motor function was evaluated using a battery of neuroscore, rotarod, and rotating pole tests. The animals were also evaluated for cardiovascular changes, blood-brain barrier (BBB) breakdown, traumatic axonal injury, and neurodegenerative and histopathological changes between 1 day and 56 days after brain trauma. No cognitive dysfunction was detected in any group. The single-impact group showed mild impairment according to the neuroscore test at only 3 days postinjury, whereas RHI caused pronounced deficits at 3 days and 7 days following the second injury. Moreover, RHI led to functional impairment during the rotarod and rotating pole tests that was not observed in any animal after a single impact. Small areas of cortical BBB breakdown and axonal injury. observed after a single brain injury, were profoundly exacerbated after RHI. Immunohistochemical staining for microtubule-associated protein-2 revealed marked regional loss of immunoreactivity only in animals subjected to RHI. No deposits of beta-amyloid or tau were observed in any brain-injured animal.

CONCLUSIONS

On the basis of their results, the authors suggest that the brain has an increased vulnerability to a second traumatic insult for at least 24 hours following an initial episode of mild brain trauma.

Paradoxical increase in neuronal DNA fragmentation after neuroprotective free radical scavenger treatment in experimental traumatic brain injury

The mechanisms and role of nerve cell death after traumatic brain injury (TBI) are not fully understood. The authors investigated the effect of pretreatment with the oxygen free radical spin trap alpha-phenyl-N-tert-butyl-nitrone (PBN) on the number of neurons undergoing apoptosis after TBI in rats. Apoptotic cells were identified by the TUNEL method combined with the nuclear stain, Hoechst 33258, and immunohistochemistry for the active form of caspase-3. Numerous neurons became positive for activated caspase 3 and TUNEL in the cortex at 24 hours after injury, suggesting ongoing biochemical apoptosis. In PBN-treated rats, a significantly greater number of cells were found to be TUNEL positive at 24 hours compared with controls. However, PBN treatment resulted in a reduced cortical lesion volume and improved behavioral outcome two weeks after injury. The authors conclude that a treatment producing an increase in DNA fragmentation in the early phase may be compatible with an overall beneficial effect on outcome after TBI. This should be considered in the screening process for future neuroprotective remedies.

Acute cytoskeletal alterations and cell death induced by experimental brain injury are attenuated by magnesium treatment and exacerbated by magnesium deficiency

Traumatic brain injury results in a profound decline in intracellular magnesium ion levels that may jeopardize critical cellular functions. We examined the consequences of preinjury magnesium deficiency and post-traumatic magnesium treatment on injury-induced cytoskeletal damage and cell death at 24 h after injury. Adult male rats were fed either a normal (n = 24) or magnesium-deficient diet (n = 16) for 2 wk prior to anesthesia and lateral fluid percussion brain injury (n = 31) or sham injury (n = 9). Normally fed animals were then randomized to receive magnesium chloride (125 micromol, i.v., n = 10) or vehicle solution (n = 11) at 10 min postinjury. Magnesium treatment reduced cortical cell loss (p < 0.05), cortical alterations in microtubule-associated protein-2 (MAP-2) (p < 0.05), and both cortical and hippocampal calpain-mediated spectrin breakdown (p < 0.05 for each region) when compared to vehicle treatment. Conversely, magnesium deficiency prior to brain injury led to a greater area of cortical cell loss (p < 0.05 compared to vehicle treatment). Moreover, brain injury to magnesium-deficient rats resulted in cytoskeletal alterations within the cortex and hippocampus that were not observed in vehicle- or magnesium-treated animals. These data suggest that cortical cell death and cytoskeletal disruptions in cortical and hippocampal neurons may be sensitive to magnesium status after experimental brain injury, and may be mediated in part through modulation of calpains.

Upregulation of neuronal amyloid precursor protein (APP) and APP mRNA following magnesium sulphate (MgSO4) therapy in traumatic brain injury

The aim of this study was to assess and quantitate topographically the effects of posttraumatic intravenous magnesium sulphate (MgSO4) on neuronal perikaryal APP antigen and messenger RNA (mRNA) expression in sheep brains 2 h after a controlled focal head impact. The percentage brain area with APP immunoreactive neuronal perikarya was 71, 56, 27.5 and 5.5%, respectively, in MgSO4-treated head-injured animals, head-injured animals without any treatment, MgSO4 treated nonimpacted animals, and nontreated nonimpacted control sheep. Although there was no statistically significant difference in APP immunoreactive neuronal perikarya in the MgSO4-treated HI group (mean 71%) compared to the HI group without any treatment (mean 56%), northern analysis showed that there was a 2.3-+/-0.2-fold increase in APP mRNA in the thalamus of treated impacted animals compared to untreated impacted animals (p < 0.005). However, MgSO4 treated nonimpacted control animals also showed a 1.6-+/-0.1-fold increase in APP mRNA compared to untreated nonimpacted controls (p < 0.005). MgSO4 therapy results in upregulation of neuronal APP mRNA and APP expression that is quantitatively greater following a focal head impact.

NPS 1506: a novel NMDA receptor antagonist: neuroprotective effects in a model of closed head trauma in rats

We examined whether NPS 1506, a novel uncompetitive N-methyl-D-aspartate receptor antagonist, influences neurological outcome following closed head trauma (CHT) in rats. One hundred ten rats were divided into 11 groups: CHT (yes/no), treatment with NPS 1506 (yes/no), and time of euthanization (24 h/48 h). The dose of NPS 1506 was 1 mg/kg IV at 1 and 4 hours following CHT or sham operation. Closed head trauma induced the following changes in the injured hemisphere: Decreased specific gravity (sg) (1.036 +/- 0.006) and magnesium (Mg) (0.042 +/- 0.005 microg/mg) at 24 hours, and potassium (K) at 24 (1.145 +/- 0.376 microg/mg) and 48 hours, and increased water content (W) (84.9 +/- 2.5%) and sodium (Na) (2.135 +/- 0.699 microg/mg) at 24 hours, and calcium (Ca) at 24 (0.543 +/- 0.157 microg/mg) and 48 hours. These were reversed by NPS 1506; sg of 1.043 +/- 0.004, Mg of 0.077 +/- 0.009 microg/mg, K of 1.930 +/- 0.238 microg/mg, W of 81.5 +/- 1.9%, Ca of 0.043 +/- 0.023 microg/mg, and Na of 0.688 +/- 0.110 microg/mg. In groups not given NPS 1506, a nonsignificant decrease in neurological severity score (NSS) occurred at 24 and 48 hours as compared to NSS at 1 hour after CHT. In groups given NPS 1506, NSS at 24 and 48 hours decreased significantly (improved) compared to NSS at 1 hour, but not compared to NSS at 24 and 48 hours in groups not given NPS 1506. NPS 1506 caused no significant change in ischemic tissue volume or hemorrhagic necrosis volume in the injured hemisphere at 24 hours or 48 hours. These findings indicate that NPS 1506 improved measures of brain tissue edema (at 24 hours but not at 48 hours) and ion homeostasis, and this improvement was not related to other measures of outcome.