Neuroanatomical correlation of behavioral deficits in the CCI model of TBI

Degradable Poly(amino acid) Vesicles Modulate DNA-Induced Inflammation after Traumatic Brain Injury

Following brain trauma, secondary injury from molecular and cellular changes causes progressive cerebral tissue damage. Acute/chronic neuroinflammation following traumatic brain injury (TBI) is a key player in the development of secondary injury. Rapidly elevated cell-free DNAs (cfDNAs) due to cell death could lead to production of inflammatory cytokines that aggravate TBI. Herein, we designed poly(amino acid)-based cationic nanoparticles (cNPs) and applied them intravenously in a TBI mice model with the purpose of scavenging cfDNA in the brain and suppressing the acute inflammation. In turn, these cNPs could effectively eliminate endogenous cfDNA, inhibit excessive activation of inflammation, and promote neural functional recovery.

Measuring Anxiety-Like Behaviors in Rodent Models of Traumatic Brain Injury

Anxiety is a common complaint following acquired traumatic brain injury (TBI). However, the measurement of dysfunctional anxiety behavioral states following experimental TBI in rodents is complex. Some studies report increased anxiety after TBI, whereas others find a decreased anxiety-like state, often described as increased risk-taking behavior or impulsivity. These inconsistencies may reflect a lack of standardization of experimental injury models or of behavioral testing techniques. Here, we review the most commonly employed unconditioned tests of anxiety and discuss them in a context of experimental TBI. Special attention is given to the effects of repeated testing, and consideration of potential sensory and motor confounds in injured rodents. The use of multiple tests and alternative data analysis methods are discussed, as well as the potential for the application of common data elements (CDEs) as a means of providing a format for documentation of experimental details and procedures of each published research report. CDEs may improve the rigor, reproducibility, as well as endpoint for better relating findings with clinical TBI phenotypes and the final goal of translation. While this may not resolve all incongruities in findings across laboratories, it is seen as a way forward for standardized and universal data collection for improvement of data quality and sharing, and advance therapies for neuropsychiatric symptoms that often present for decades following TBI.

HIF-1α aggravated traumatic brain injury by NLRP3 inflammasome-mediated pyroptosis and activation of microglia

Hypoxia inducible factor 1 alpha (HIF-1α) is involved in regulating the biological functions of neuronal death after traumatic brain injury (TBI), and attaches importance in the inflammatory response, but its potential mechanism is still unknown. Our study aimed to explore the regulatory mechanism between HIF-1α and NLRP3 inflammasome after TBI. Male mice underwent controlled cortical impact (CCI) or sham-operated procedures. Brain water content and blood-brain barrier permeability were measured at the indicated time after TBI. The behavioral performance, ELISA, immunofluorescence, and western blot analysis were used to determine whether HIF-1α specifically targeted TBI-induced pyroptosis. We discovered that TBI-induced brain injury caused by external mechanical forces is characterized by edema and blood-brain barrier disorder, and the release of IL-1β, IL-18, and LDH and upregulation of HIF-1α expression, reaching the peak on the third day post-TBI. In addition, HIF-1α accumulated NLRP3 inflammasome-mediated pyroptosis and activation of microglia. The protein expressions of NLRP3, GSDMD, GSDMD-N, pro-caspase 1, and cleaved caspase 1 were markedly increased in the injured cortex, which were restored to normal levels by the interference of HIF-1α. The inactivation of HIF-1α conferred neuroprotection and alleviated brain injury after TBI. HIF-1α was implicated in TBI-induced brain injury, aggravated NLRP3 inflammasome -mediated pyroptosis, and the activation of microglia, which provided a potential target for treating TBI.

Moderate Intensity Treadmill Exercise Increases Survival of Newborn Hippocampal Neurons and Improves Neurobehavioral Outcomes after Traumatic Brain Injury

Physician-prescribed rest after traumatic brain injury (TBI) is both commonplace and an increasingly scrutinized approach to TBI treatment. Although this practice remains a standard of patient care for TBI, research of patient outcomes reveals little to no benefit of prescribed rest after TBI, and in some cases prolonged rest has been shown to interfere with patient well-being. In direct contrast to the clinical advice regarding physical activity after TBI, animal models of brain injury consistently indicate that exercise is neuroprotective and promotes recovery. Here, we assessed the effect of low and moderate intensity treadmill exercise on functional outcome and hippocampal neural proliferation after brain injury. Using the controlled cortical impact (CCI) mouse model of TBI, we show that 10 days of moderate intensity treadmill exercise initiated after CCI reduces anxiety-like behavior, improves hippocampus-dependent spatial memory, and promotes hippocampal proliferation and newborn neuronal survival. Pathophysiological measures including lesion volume and axon degeneration were not altered by exercise. Taken together, these data reveal that carefully titrated physical activity may be a safe and effective approach to promoting recovery after brain injury.

The closed-head impact model of engineered rotational acceleration (CHIMERA) as an application for traumatic brain injury pre-clinical research: A status report

Closed-head traumatic brain injury (TBI) is a worldwide concern with increasing prevalence and cost to society. Rotational acceleration is a primary mechanism in TBI that results from tissue strains that give rise to diffuse axonal injury. The Closed-Head Impact Model of Engineered Rotational Acceleration (CHIMERA) was recently introduced as a method for the study of impact acceleration effects in pre-clinical TBI research. This review provides a survey of the published literature implementing the CHIMERA device and describes pathological, imaging, neurophysiological, and behavioral findings. Findings show CHIMERA inflicts damage in white matter tracts as a key area of injury. Behaviorally, repeated studies have shown motor deficits and more chronic cognitive effects after CHIMERA injury. Good progress with model application has been accomplished by investigators attending to what is required for model validation. However, the majority of CHIMERA studies only utilize adult male mice. To further establish this model, more work with female animals and various age groups need to be performed, as well as studies to further establish and standardize methodologies for validation of the models for clinical relevance. Common data elements to standardize the reporting methodology for the CHIMERA literature are suggested.

Therapeutic Effect of a Novel Fatty Acid Amide Hydrolase Inhibitor PF04457845 in the Repetitive Closed Head Injury Mouse Model

Concussive traumatic brain injury (TBI) is the predominant type of brain injury in young adults and is a risk factor for the development of chronic traumatic encephalopathy and other neurodegenerative diseases late in life. Using a repetitive closed head injury mouse model, we found that treatment with PF04457845, a novel fatty acid amide hydrolase (FAAH) inhibitor that selectively elevated the brain levels of anandamide, improved locomotor function, learning, and memory in TBI mice examined by beam walk, Y-maze, and Morris water maze tests. The accumulation of microglia and astrocytes and the expression of proinflammatory cytokines, including interleukin (IL)-1β, IL-6, and tumor necrosis factor alpha (TNF-α), in the ipsilateral TBI mouse cortex and hippocampus were significantly reduced by drug treatment. The increased expression of amyloid precursor protein (APP), phosphorylated Tau (p-Tau), phosphorylated glycogen synthase kinase 3 beta (pGSK3β) and p35/p25 subunits and the decreased expression of the pre-synaptic proteins, synaptophysin, synaptosome-associated protein of 25 kDa (SNAP25), and cysteine string protein alpha (α-CSP), in TBI mouse brain were also normalized by PF04458745 treatment. The improved locomotor function and working memory were partially mediated by activation of both cannabinoid (CB)1 and CB2 receptors, whereas the improvement on spatial learning and memory seemed to be CB1 receptor dependent. Interestingly, the blockage of PF04457845 on the reduced expression of synaptophysin, but not SNAP25 and α-CSP, was reversed by coadministration of the CB1 receptor antagonist. These results suggest that the therapeutic effect of PF04457845 is mediated by both cannabinoid receptor dependent and independent mechanisms, and selective inhibition of FAAH possesses a great potential for the treatment of TBI.

Dysregulated bile acid signaling contributes to the neurological impairment in murine models of acute and chronic liver failure

BACKGROUND

Hepatic encephalopathy (HE), a severe neuropsychiatric complication, is associated with increased blood levels of ammonia and bile acids (BAs). We sought to determine (1) whether abnormally increased blood BAs in liver cirrhotic patients with HE is caused by elevation of apical sodium-dependent BA transporter (ASBT)-mediated BA reabsorption; and (2) whether increased BA reabsorption would exacerbate ammonia-induced brain injuries.

METHODS

We quantitatively measured blood BA and ammonia levels in liver cirrhosis patients with or without HE and healthy controls. We characterized ASBT expression, BA profiles, and ammonia concentrations in a chronic liver disease (CLD) mouse model induced by streptozotocin-high fat diet (STZ-HFD) and an azoxymethane (AOM) - induced acute liver failure (ALF) mouse model. These two mouse models were treated with SC-435 (ASBT inhibitor) and budesonide (ASBT activator), respectively.

FINDINGS

Blood concentrations of ammonia and conjugated BAs were substantially increased in cirrhotic patients with HE (n = 75) compared to cirrhotic patients without HE (n = 126). Pharmacological inhibition of the enterohepatic BA circulation using a luminal- restricted ASBT inhibitor, SC-435, in mice with AOM-induced ALF and STZ-HFD -induced CLD effectively reduced BA and ammonia concentrations in the blood and brain, and alleviated liver and brain damages. Budesonide treatment induced liver and brain damages in normal mice, and exacerbated these damages in AOM-treated mice.

INTERPRETATION

ASBT mediated BA reabsorption increases intestinal luminal pH and facilitates conversion of intestinal ammonium to ammonia, leading to abnormally high levels of neurotoxic ammonia and cytotoxic BAs in the blood and brain. Inhibition of intestinal ASBT with SC-435 can effectively remove neurotoxic BAs and ammonia from the bloodstream and thus, mitigate liver and brain injuries resulting from liver failure.

Dysregulated Glucose Metabolism as a Therapeutic Target to Reduce Post-traumatic Epilepsy

Traumatic brain injury (TBI) is a significant cause of disability worldwide and can lead to post-traumatic epilepsy. Multiple molecular, cellular, and network pathologies occur following injury which may contribute to epileptogenesis. Efforts to identify mechanisms of disease progression and biomarkers which predict clinical outcomes have focused heavily on metabolic changes. Advances in imaging approaches, combined with well-established biochemical methodologies, have revealed a complex landscape of metabolic changes that occur acutely after TBI and then evolve in the days to weeks after. Based on this rich clinical and preclinical data, combined with the success of metabolic therapies like the ketogenic diet in treating epilepsy, interest has grown in determining whether manipulating metabolic activity following TBI may have therapeutic value to prevent post-traumatic epileptogenesis. Here, we focus on changes in glucose utilization and glycolytic activity in the brain following TBI and during seizures. We review relevant literature and outline potential paths forward to utilize glycolytic inhibitors as a disease-modifying therapy for post-traumatic epilepsy.

Large animal models of traumatic brain injury

Purpose/Aim: Animal models of traumatic brain injury (TBI) provide powerful tools to study TBI in a controlled, rigorous and cost-efficient manner. The mostly used animals in TBI studies so far are rodents. However, compared with rodents, large animals (e.g. swine, rabbit, sheep, ferret, etc.) show great advantages in modeling TBI due to the similarity of their brains to human brain. The aim of our review was to summarize the development and progress of common large animal TBI models in past 30 years.

MATERIALS AND METHODS

Mixed published articles and books associated with large animal models of TBI were researched and summarized.

RESULTS

We majorly sumed up current common large animal models of TBI, including discussion on the available research methodologies in previous studies, several potential therapies in large animal trials of TBI as well as advantages and disadvantages of these models.

CONCLUSIONS

Large animal models of TBI play crucial role in determining the underlying mechanisms and screening putative therapeutic targets of TBI.

Anti-edema effects of rhEpo in experimental traumatic brain injury

PURPOSE

Traumatic brain injury (TBI) is one of the leading causes of disability and death which begins with the formation of edema as the persistent primary causative factor in TBI. Although medical management of cerebral edema by hypothermia, ventriculostomy, mannitol or hypertonic saline have been effective in treating edema, many of these therapies end up with some neurologic deficits, necessitating novel treatment options for treating post-TBI edema. This study investigated edema reducing effects of recombinant human Erythropoietin (rhEPO) in reducing acute brain edema in the CCI mouse model of TBI.

METHODS

Anti-edema effects of rhEpo in reducing acute brain edema after injury in the CCI mouse model of TBI were assessed by T2 weighted magnetic resonance imaging (T2wMRI) as the accurate detector of brain edema in correlation with Western blot analysis of cerebral aquaporin 4 (AQP4) index as the critical marker of edema.

RESULTS

Results show that rhEpo treatment significantly reduced brain edema with concomitant reduction in AQP4 immunoexpression in the CCI mouse model of TBI.

CONCLUSION

Current results emphasize clinical utility of rhEpo in treating post-TBI edema.

Neuropsychiatric Symptom Modeling in Male and Female C57BL/6J Mice after Experimental Traumatic Brain Injury

Psychiatric symptoms such as anxiety and depression are frequent and persistent complaints following traumatic brain injury (TBI). Modeling these symptoms in animal models of TBI affords the opportunity to determine mechanisms underlying behavioral pathologies and to test potential therapeutic agents. However, testing these symptoms in animal models of TBI has yielded inconsistent results. The goal of the current study was to employ a battery of tests to measure multiple anxiety- and depressive-like symptoms following TBI in C57BL/6J mice, and to determine if male and female mice are differentially affected by the injury. Following controlled cortical impact (CCI) at a parietal location, neither male nor female mice showed depressive-like symptoms as measured by the Porsolt forced-swim test and sucrose preference test. Conclusions regarding anxiety-like behaviors were dependent upon the assay employed; CCI-induced thigmotaxis in the open field suggested an anxiogenic effect of the injury; however, results from the elevated zero maze, light-dark box, and marble-burying tests indicated that CCI reduced anxiety-like behaviors. Fewer anxiety-like behaviors were also associated with the female sex. Increased levels of activity were also measured in female mice and injured mice in these tests, and conclusions regarding anxiety should be taken with caution when experimental manipulations induce changes in baseline activity. These results underscore the irreconcilability of results from studies attempting to model TBI-induced neuropsychiatric symptoms. Changes in injury models or better attempts to replicate the clinical syndrome may improve the translational applicability of rodent models of TBI-induced anxiety and depression.

Automated monitoring of early neurobehavioral changes in mice following traumatic brain injury

Traumatic brain injury often causes a variety of behavioral and emotional impairments that can develop into chronic disorders. Therefore, there is a need to shift towards identifying early symptoms that can aid in the prediction of traumatic brain injury outcomes and behavioral endpoints in patients with traumatic brain injury after early interventions. In this study, we used the SmartCage system, an automated quantitative approach to assess behavior alterations in mice during an early phase of traumatic brain injury in their home cages. Female C57BL/6 adult mice were subjected to moderate controlled cortical impact (CCI) injury. The mice then received a battery of behavioral assessments including neurological score, locomotor activity, sleep/wake states, and anxiety-like behaviors on days 1, 2, and 7 after CCI. Histological analysis was performed on day 7 after the last assessment. Spontaneous activities on days 1 and 2 after injury were significantly decreased in the CCI group. The average percentage of sleep time spent in both dark and light cycles were significantly higher in the CCI group than in the sham group. For anxiety-like behaviors, the time spent in a light compartment and the number of transitions between the dark/light compartments were all significantly reduced in the CCI group than in the sham group. In addition, the mice suffering from CCI exhibited a preference of staying in the dark compartment of a dark/light cage. The CCI mice showed reduced neurological score and histological abnormalities, which are well correlated to the automated behavioral assessments. Our findings demonstrate that the automated SmartCage system provides sensitive and objective measures for early behavior changes in mice following traumatic brain injury.

A Novel Closed-Head Model of Mild Traumatic Brain Injury Using Focal Primary Overpressure Blast to the Cranium in Mice

Mild traumatic brain injury (TBI) from focal head impact is the most common form of TBI in humans. Animal models, however, typically use direct impact to the exposed dura or skull, or blast to the entire head. We present a detailed characterization of a novel overpressure blast system to create focal closed-head mild TBI in mice. A high-pressure air pulse limited to a 7.5 mm diameter area on the left side of the head overlying the forebrain is delivered to anesthetized mice. The mouse eyes and ears are shielded, and its head and body are cushioned to minimize movement. This approach creates mild TBI by a pressure wave that acts on the brain, with minimal accompanying head acceleration-deceleration. A single 20-psi blast yields no functional deficits or brain injury, while a single 25-40 psi blast yields only slight motor deficits and brain damage. By contrast, a single 50-60 psi blast produces significant visual, motor, and neuropsychiatric impairments and axonal damage and microglial activation in major fiber tracts, but no contusive brain injury. This model thus reproduces the widespread axonal injury and functional impairments characteristic of closed-head mild TBI, without the complications of systemic or ocular blast effects or head acceleration that typically occur in other blast or impact models of closed-skull mild TBI. Accordingly, our model provides a simple way to examine the biomechanics, pathophysiology, and functional deficits that result from TBI and can serve as a reliable platform for testing therapies that reduce brain pathology and deficits.

Mild Concussion, but Not Moderate Traumatic Brain Injury, Is Associated with Long-Term Depression-Like Phenotype in Mice

Mild traumatic brain injuries can lead to long-lasting cognitive and motor deficits, increasing the risk of future behavioral, neurological, and affective disorders. Our study focused on long-term behavioral deficits after repeated injury in which mice received either a single mild CHI (mCHI), a repeated mild CHI (rmCHI) consisting of one impact to each hemisphere separated by 3 days, or a moderate controlled cortical impact injury (CCI). Shams received only anesthesia. Behavioral tests were administered at 1, 3, 5, 7, and 90 days post-injury (dpi). CCI animals showed significant motor and sensory deficits in the early (1-7 dpi) and long-term (90 dpi) stages of testing. Interestingly, sensory and subtle motor deficits in rmCHI animals were found at 90 dpi. Most importantly, depression-like behaviors and social passiveness were observed in rmCHI animals at 90 dpi. These data suggest that mild concussive injuries lead to motor and sensory deficits and affective disorders that are not observed after moderate TBI.

Performance of Male and Female C57BL/6J Mice on Motor and Cognitive Tasks Commonly Used in Pre-Clinical Traumatic Brain Injury Research

To date, clinical trials have failed to find an effective therapy for victims of traumatic brain injury (TBI) who live with motor, cognitive, and psychiatric complaints. Pre-clinical investigators are now encouraged to include male and female subjects in all translational research, which is of particular interest in the field of neurotrauma given that circulating female hormones (progesterone and estrogen) have been demonstrated to exert neuroprotective effects. To determine whether behavior of male and female C57BL6/J mice is differentially impaired by TBI, male and cycling female mice were injured by controlled cortical impact and tested for several weeks with functional assessments commonly employed in pre-clinical research. We found that cognitive and motor impairments post-TBI, as measured by the Morris water maze (MWM) and rotarod, respectively, were largely equivalent in male and female animals. However, spatial working memory, assessed by the y-maze, was poorer in female mice. Female mice were generally more active, as evidenced by greater distance traveled in the first exposure to the open field, greater distance in the y-maze, and faster swimming speeds in the MWM. Statistical analysis showed that variability in all behavioral data was no greater in cycling female mice than it was in male mice. These data all suggest that with careful selection of tests, procedures, and measurements, both sexes can be included in translational TBI research without concern for effect of hormones on functional impairments or behavioral variability.

Experimental induction of type 2 diabetes in aging-accelerated mice triggered Alzheimer-like pathology and memory deficits

Alzheimer's disease (AD) is an age-dependent neurodegenerative disease constituting ~95% of late-onset non-familial/sporadic AD, and only ~5% accounting for early-onset familial AD. Availability of a pertinent model representing sporadic AD is essential for testing candidate therapies. Emerging evidence indicates a causal link between diabetes and AD. People with diabetes are >1.5-fold more likely to develop AD. Senescence-accelerated mouse model (SAMP8) of accelerated aging displays many features occurring early in AD. Given the role played by diabetes in the pre-disposition of AD, and the utility of SAMP8 non-transgenic mouse model of accelerated aging, we examined if high fat diet-induced experimental type 2 diabetes in SAMP8 mice will trigger pathological aging of the brain. Results showed that compared to non-diabetic SAMP8 mice, diabetic SAMP8 mice exhibited increased cerebral amyloid-β, dysregulated tau-phosphorylating glycogen synthase kinase 3β, reduced synaptophysin immunoreactivity, and displayed memory deficits, indicating Alzheimer-like changes. High fat diet-induced type 2 diabetic SAMP8 mice may represent the metabolic model of AD.

Traumatic brain injury alters long-term hippocampal neuron morphology in juvenile, but not immature, rats

PURPOSE

Pediatric traumatic brain injury (TBI) represents a prominent yet understudied medical condition that can profoundly impact brain development. As the juvenile injured brain matures in the wake of neuropathological cascades during potentially critical periods, circuit alterations may explain neurological consequences, including cognitive deficits. We hypothesize that experimental brain injury in juvenile rats, with behavioral deficits that resolve, will lead to quantifiable structural changes in hippocampal neurons at chronic time points post-injury.

METHODS

Controlled cortical impact (CCI), a model of focal TBI with contusion, was used to induce brain injury on post-natal day (PND) 17 juvenile rats. The histological consequence of TBI was quantified in regions of the hippocampus at post-injury day 28 (PID28) on sections stained using a variation of the Golgi-Cox staining method. Individual neuronal morphologies were digitized from the dentate gyrus (DG), CA3, and CA1 regions.

RESULTS

Soma area in the ipsilateral injured DG and CA3 regions of the hippocampus increased significantly at PID28 in comparison to controls. In CA1, dendritic length and dendritic branching decreased significantly in comparison to controls and the contralateral hemisphere, without change in soma area. To extend the study, we examined neuronal morphology in rats with CCI at PND7. On PID28 after CCI on PND7 rats, CA1 neurons showed no injury-induced change in morphology, potentially indicating an age-dependent morphological response to injury.

CONCLUSIONS

Long-lasting structural alterations in hippocampal neurons of brain-injured PND17 juvenile animals, but not PND7 immature animals, suggest differential plasticity depending on age-at-injury, with potential consequences for later function.

A semicircular controlled cortical impact produces long-term motor and cognitive dysfunction that correlates well with damage to both the sensorimotor cortex and hippocampus

Animal models of traumatic brain injury (TBI) are essential for testing novel hypotheses and therapeutic interventions. Unfortunately, due to the broad heterogeneity of TBI in humans, no single model has been able to reproduce the entire spectrum of these injuries. The controlled cortical impact (CCI) model is one of the most commonly used models of contusion TBI. However, behavioral evaluations have revealed transient impairment in motor function after CCI in rats and mice. Here we report a new semicircular CCI (S-CCI) model by increasing the impact tip area to cover both the motor cortex and hippocampal regions in adult mice. Mice were subjected to S-CCI or CCI using an electromagnetic impactor (Impactor One, MyNeuroLab; semicircular tip: 3mm radius; CCI tip diameter: 3mm). We showed that S-CCI, at two injury severities, significantly decreased the neuroscore and produced deficits in performance on a rotarod device for the entire duration of the study. In contrast, the CCI induced motor deficits only at early stages after the injury, suggesting that the S-CCI model produces long-lasting motor deficits. Morris water maze test showed that both CCI and S-CCI produced persisting memory deficits. Furthermore, adhesive removal test showed significant somatosensory and motor deficits only in the S-CCI groups. Histological analysis showed a large extent of cortical contusion lesions, including both the sensory and motor cortex, and hippocampal damage in the S-CCI. These findings collectively suggest that the current model may offer sensitive, reliable, and clinically relevant outcomes for assessments of therapeutic strategies for TBI.

Progesterone treatment shows benefit in a pediatric model of moderate to severe bilateral brain injury

PURPOSE

Controlled cortical impact (CCI) models in adult and aged Sprague-Dawley (SD) rats have been used extensively to study medial prefrontal cortex (mPFC) injury and the effects of post-injury progesterone treatment, but the hormone's effects after traumatic brain injury (TBI) in juvenile animals have not been determined. In the present proof-of-concept study we investigated whether progesterone had neuroprotective effects in a pediatric model of moderate to severe bilateral brain injury.

METHODS

Twenty-eight-day old (PND 28) male Sprague Dawley rats received sham (n = 24) or CCI (n = 47) injury and were given progesterone (4, 8, or 16 mg/kg per 100 g body weight) or vehicle injections on post-injury days (PID) 1-7, subjected to behavioral testing from PID 9-27, and analyzed for lesion size at PID 28.

RESULTS

The 8 and 16 mg/kg doses of progesterone were observed to be most beneficial in reducing the effect of CCI on lesion size and behavior in PND 28 male SD rats.

CONCLUSION

Our findings suggest that a midline CCI injury to the frontal cortex will reliably produce a moderate TBI comparable to what is seen in the adult male rat and that progesterone can ameliorate the injury-induced deficits.

Non-spatial pre-training in the water maze as a clinically relevant model for evaluating learning and memory in experimental TBI

Explicit and implicit learning and memory networks exist where each network can facilitate or inhibit cognition. Clinical evidence suggests that implicit networks are relatively preserved after traumatic brain injury (TBI). Non-spatial pre-training (NSPT) in the Morris Water Maze (MWM) provides the necessary behavioral components to complete the task, while limiting the formation of spatial maps. Our study utilized NSPT in the MWM to assess implicit and explicit learning and memory system deficits in the controlled cortical impact (CCI) model of TBI. 76 adult male Sprague-Dawley rats were divided: CCI vs. sham surgery, NSPT vs. No-NSPT, and cued vs. non-cued groups. NSPT occurred for 4d prior to surgery (dynamic hidden platform location, extra-maze cues covered, static pool entry point). Acquisition (d14-18), Probe/Visible Platform (d19), and Reversal (d20-21) trials were conducted with or without extra-maze cues. Novel time allocation and search strategy selection metrics were utilized. Results indicated implicit and explicit learning/memory networks are distinguishable in the MWM. In the cued condition, NSPT reduced thigmotaxis, improved place learning, and largely eliminated the apparent injury-induced deficits typically observed between untrained CCI and sham rats. However, among NSPT groups, incorporation of cues into search strategy selection for CCI rats was relatively impaired compared to shams. Non-cued condition performance showed sham/NSPT and CCI/NSPT rats perform similarly, suggesting implicit memory networks are largely intact 2weeks after CCI. Place learning differences between CCI/NSPT and sham/NSPT rats more accurately reflect spatial deficits in our CCI model compared to untrained controls. These data suggest NSPT as a clinically relevant construct for evaluating potential neurorestorative and neuroprotective therapies. These findings also support development of non-spatial cognitive training paradigms for evaluating rehabilitation relevant combination therapies.

Selective inhibition of alpha/beta-hydrolase domain 6 attenuates neurodegeneration, alleviates blood brain barrier breakdown, and improves functional recovery in a mouse model of traumatic brain injury

2-arachidonylglycerol (2-AG) is the most abundant endocannabinoid in the central nervous system and is elevated after brain injury. Because of its rapid hydrolysis, however, the compensatory and neuroprotective effect of 2-AG is short-lived. Although inhibition of monoacylglycerol lipase, a principal enzyme for 2-AG degradation, causes a robust increase of brain levels of 2-AG, it also leads to cannabinoid receptor desensitization and behavioral tolerance. Alpha/beta hydrolase domain 6 (ABHD6) is a novel 2-AG hydrolytic enzyme that accounts for a small portion of 2-AG hydrolysis, but its inhibition is believed to elevate the levels of 2-AG within the therapeutic window without causing side effect. Using a mouse model of traumatic brain injury (TBI), we found that post-insult chronic treatment with a selective ABHD6 inhibitor WWL70 improved motor coordination and working memory performance. WWL70 treatment reduced lesion volume in the cortex and neurodegeneration in the dendate gyrus. It also suppressed the expression of inducible nitric oxide synthase and cyclooxygenase-2 and enhanced the expression of arginase-1 in the ipsilateral cortex at 3 and 7 days post-TBI, suggesting microglia/macrophages shifted from M1 to M2 phenotypes after treatment. The blood-brain barrier dysfunction at 3 and 7 days post-TBI was dramatically reduced. Furthermore, the beneficial effects of WWL70 involved up-regulation and activation of cannabinoid type 1 and type 2 receptors and were attributable to the phosphorylation of the extracellular signal regulated kinase and the serine/threonine protein kinase AKT. This study indicates that the fine-tuning of 2-AG signaling by modulating ABHD6 activity can exert anti-inflammatory and neuroprotective effects in TBI.

The effect of injury severity on behavior: a phenotypic study of cognitive and emotional deficits after mild, moderate, and severe controlled cortical impact injury in mice

Traumatic brain injury (TBI) can cause a broad array of behavioral problems including cognitive and emotional deficits. Human studies comparing neurobehavioral outcomes after TBI suggest that cognitive impairments increase with injury severity, but emotional problems such as anxiety and depression do not. To determine whether cognitive and emotional impairments increase as a function of injury severity we exposed mice to sham, mild, moderate, or severe controlled cortical impact (CCI) and evaluated performance on a variety of neurobehavioral tests in the same animals before assessing lesion volume as a histological measure of injury severity. Increasing cortical impact depth successfully produced lesions of increasing severity in our model. We found that cognitive impairments in the Morris water maze increased with injury severity, as did the degree of contralateral torso flexion, a measure of unilateral striatal damage. TBI also caused deficits in emotional behavior as quantified in the forced swim test, elevated-plus maze, and prepulse inhibition of acoustic startle, but these deficits were not dependent on injury severity. Stepwise regression analyses revealed that Morris water maze performance and torso flexion predicted the majority of the variability in lesion volume. In summary, we find that cognitive deficits increase in relation to injury severity, but emotional deficits do not. Our data suggest that the threshold for emotional changes after experimental TBI is low, with no variation in behavioral deficits seen between mild and severe brain injury.

Long-term intrathecal infusion of outer surface protein C from Borrelia burgdorferi causes axonal damage

Lyme neuroborreliosis (LNB) is the most frequent tick-borne infectious disease of the central nervous system. In acute LNB and the rare chronic state of infection, patients can experience cognitive deficits such as attention and memory disturbances. During LNB, single compounds of Borrelia burgdorferi sensu lato are released into the subarachnoid space.To investigate the pathogenesis of neurologic dysfunction in LNB, we determined that the outer surface protein C (OspC), a major virulence factor of B. burgdorferi, stimulated mouse microglial cells in a dose-dependent manner to release nitric oxide (EC50 = 0.24 mg/L) in vitro. To mimic pathophysiologic conditions of long-term release of this bacterial component in vivo, we treated C57BL/6 mice with recombinant OspC from Borrelia garinii or buffer by intraventricular infusion and tested them for behavioral deficits. After 4weeks, brains were examined by routine histology and immunohistochemistry. Assessment of spatial learning and memory of treated mice during OspC exposure did not reveal significant differences from controls. Continuous exposure to intrathecal B. burgdorferi OspC led to activation of microglia and axonal damage without demonstrable cognitive impairment in experimental mice. These results suggest that long-term intrathecal exposure to OspC resulted in axonal damage that may underlie the neurologic manifestations in chronic LNB.

Synergistic benefits of erythropoietin and simvastatin after traumatic brain injury

Simvastatin and recombinant human erythropoietin (rhEpo) are implicated as potential therapeutic candidates for traumatic brain injury (TBI). Prominent effects of simvastatin include its anti-inflammatory, neurotrophic and neuroregenerative actions studied in various models of neuronal injury. On the other hand, rhEpo has been shown to promote cell survival mechanisms by producing anti-apoptotic and cell proliferative actions. Beneficial effects of rhEpo and statin monotherapies have been well studied. However, there are no reports showing combined use of rhEpo and statins after TBI. This investigation examined if combined efficacy of cell proliferative ability of rhEpo along with the neuroregenerative ability of simvastatin will render maximum recovery in a controlled cortical impact (CCI) mouse model of TBI. Results showed that compared to baseline TBI, rhEpo was more effective than simvastatin in promoting cell proliferation while simvastatin was more effective than rhEpo in restoring axonal damage following TBI. Combined treatment with simvastatin and rhEpo maximally restored axonal integrity while simultaneously inducing greater proliferation of newly formed cells resulting in better functional recovery after TBI than either alone. This is the first study showing the efficacy of erythropoietin-simvastatin combinational therapeutic approach in achieving greater structural and cognitive recovery after TBI.