Prolonged memory impairment in the absence of hippocampal cell death following traumatic brain injury in the rat

In vivo reprogramming reactive glia into iPSCs to produce new neurons in the cortex following traumatic brain injury

Traumatic brain injury (TBI) results in a significant amount of cell death in the brain. Unfortunately, the adult mammalian brain possesses little regenerative potential following injury and little can be done to reverse the initial brain damage caused by trauma. Reprogramming adult cells to generate induced pluripotent stem cell (iPSCs) has opened new therapeutic opportunities to generate neurons in a non-neurogenic regions in the cortex. In this study we showed that retroviral mediated expression of four transcription factors, Oct4, Sox2, Klf4, and c-Myc, cooperatively reprogrammed reactive glial cells into iPSCs in the adult neocortex following TBI. These iPSCs further differentiated into a large number of neural stem cells, which further differentiated into neurons and glia in situ, and filled up the tissue cavity induced by TBI. The induced neurons showed a typical neuronal morphology with axon and dendrites, and exhibited action potential. Our results report an innovative technology to transform reactive glia into a large number of functional neurons in their natural environment of neocortex without embryo involvement and without the need to grow cells outside the body and then graft them back to the brain. Thus this technology offers hope for personalized regenerative cell therapies for repairing damaged brain.

Minocycline Transiently Reduces Microglia/Macrophage Activation but Exacerbates Cognitive Deficits Following Repetitive Traumatic Brain Injury in the Neonatal Rat

Elevated microglial/macrophage-associated biomarkers in the cerebrospinal fluid of infant victims of abusive head trauma (AHT) suggest that these cells play a role in the pathophysiology of the injury. In a model of AHT in 11-day-old rats, 3 impacts (24 hours apart) resulted in spatial learning and memory deficits and increased brain microglial/macrophage reactivity, traumatic axonal injury, neuronal degeneration, and cortical and white-matter atrophy. The antibiotic minocycline has been effective in decreasing injury-induced microglial/macrophage activation while simultaneously attenuating cellular and functional deficits in models of neonatal hypoxic ischemia, but the potential for this compound to rescue deficits after impact-based trauma to the immature brain remains unexplored. Acute minocycline administration in this model of AHT decreased microglial/macrophage reactivity in the corpus callosum of brain-injured animals at 3 days postinjury, but this effect was lost by 7 days postinjury. Additionally, minocycline treatment had no effect on traumatic axonal injury, neurodegeneration, tissue atrophy, or spatial learning deficits. Interestingly, minocycline-treated animals demonstrated exacerbated injury-induced spatial memory deficits. These results contrast with previous findings in other models of brain injury and suggest that minocycline is ineffective in reducing microglial/macrophage activation and ameliorating injury-induced deficits following repetitive neonatal traumatic brain injury.

Isolated Primary Blast Inhibits Long-Term Potentiation in Organotypic Hippocampal Slice Cultures

Over the last 13 years, traumatic brain injury (TBI) has affected over 230,000 U.S. service members through the conflicts in Iraq and Afghanistan, mostly as a result of exposure to blast events. Blast-induced TBI (bTBI) is multi-phasic, with the penetrating and inertia-driven phases having been extensively studied. The effects of primary blast injury, caused by the shockwave interacting with the brain, remain unclear. Earlier in vivo studies in mice and rats have reported mixed results for primary blast effects on behavior and memory. Using a previously developed shock tube and in vitro sample receiver, we investigated the effect of isolated primary blast on the electrophysiological function of rat organotypic hippocampal slice cultures (OHSC). We found that pure primary blast exposure inhibited long-term potentiation (LTP), the electrophysiological correlate of memory, with a threshold between 9 and 39 kPa·ms impulse. This deficit occurred well below a previously identified threshold for cell death (184 kPa·ms), supporting our previously published finding that primary blast can cause changes in brain function in the absence of cell death. Other functional measures such as spontaneous activity, network synchronization, stimulus-response curves, and paired-pulse ratios (PPRs) were less affected by primary blast exposure, as compared with LTP. This is the first study to identify a tissue-level tolerance threshold for electrophysiological changes in neuronal function to isolated primary blast.

Chronic Histopathological and Behavioral Outcomes of Experimental Traumatic Brain Injury in Adult Male Animals

The purpose of this review is to survey the use of experimental animal models for studying the chronic histopathological and behavioral consequences of traumatic brain injury (TBI). The strategies employed to study the long-term consequences of TBI are described, along with a summary of the evidence available to date from common experimental TBI models: fluid percussion injury; controlled cortical impact; blast TBI; and closed-head injury. For each model, evidence is organized according to outcome. Histopathological outcomes included are gross changes in morphology/histology, ventricular enlargement, gray/white matter shrinkage, axonal injury, cerebrovascular histopathology, inflammation, and neurogenesis. Behavioral outcomes included are overall neurological function, motor function, cognitive function, frontal lobe function, and stress-related outcomes. A brief discussion is provided comparing the most common experimental models of TBI and highlighting the utility of each model in understanding specific aspects of TBI pathology. The majority of experimental TBI studies collect data in the acute postinjury period, but few continue into the chronic period. Available evidence from long-term studies suggests that many of the experimental TBI models can lead to progressive changes in histopathology and behavior. The studies described in this review contribute to our understanding of chronic TBI pathology.

Repetitive Mild Traumatic Brain Injury in the Developing Brain: Effects on Long-Term Functional Outcome and Neuropathology

Although accumulating evidence suggests that repetitive mild TBI (rmTBI) may cause long-term cognitive dysfunction in adults, whether rmTBI causes similar deficits in the immature brain is unknown. Here we used an experimental model of rmTBI in the immature brain to answer this question. Post-natal day (PND) 18 rats were subjected to either one, two, or three mild TBIs (mTBI) or an equivalent number of sham insults 24 h apart. After one or two mTBIs or sham insults, histology was evaluated at 7 days. After three mTBIs or sham insults, motor (d1-5), cognitive (d11-92), and histological (d21-92) outcome was evaluated. At 7 days, silver degeneration staining revealed axonal argyrophilia in the external capsule and corpus callosum after a single mTBI, with a second impact increasing axonal injury. Iba-1 immunohistochemistry showed amoeboid shaped microglia within the amygdalae bilaterally after mTBI. After three mTBI, there were no differences in beam balance, Morris water maze, and elevated plus maze performance versus sham. The rmTBI rats, however, showed impairment in novel object recognition and fear conditioning. Axonal silver staining was observed only in the external capsule on d21. Iba-1 staining did not reveal activated microglia on d21 or d92. In conclusion, mTBI results in traumatic axonal injury and microglial activation in the immature brain with repeated impact exacerbating axonal injury. The rmTBI in the immature brain leads to long-term associative learning deficit in adulthood. Defining the mechanisms damage from rmTBI in the developing brain could be vital for identification of therapies for children.

Brain Injury Impairs Working Memory and Prefrontal Circuit Function

More than 2.5 million Americans suffer a traumatic brain injury (TBI) each year. Even mild to moderate TBI causes long-lasting neurological effects. Despite its prevalence, no therapy currently exists to treat the underlying cause of cognitive impairment suffered by TBI patients. Following lateral fluid percussion injury (LFPI), the most widely used experimental model of TBI, we investigated alterations in working memory and excitatory/inhibitory synaptic balance in the prefrontal cortex. LFPI impaired working memory as assessed with a T-maze behavioral task. Field excitatory postsynaptic potentials recorded in the prefrontal cortex were reduced in slices derived from brain-injured mice. Spontaneous and miniature excitatory postsynaptic currents onto layer 2/3 neurons were more frequent in slices derived from LFPI mice, while inhibitory currents onto layer 2/3 neurons were smaller after LFPI. Additionally, an increase in action potential threshold and concomitant decrease in firing rate was observed in layer 2/3 neurons in slices from injured animals. Conversely, no differences in excitatory or inhibitory synaptic transmission onto layer 5 neurons were observed; however, layer 5 neurons demonstrated a decrease in input resistance and action potential duration after LFPI. These results demonstrate synaptic and intrinsic alterations in prefrontal circuitry that may underlie working memory impairment caused by TBI.

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

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

Inhibition of Eukaryotic Initiation Factor 2 Alpha Phosphatase Reduces Tissue Damage and Improves Learning and Memory after Experimental Traumatic Brain Injury

Patients who survive traumatic brain injury (TBI) are often faced with persistent memory deficits. The hippocampus, a structure critical for learning and memory, is vulnerable to TBI and its dysfunction has been linked to memory impairments. Protein kinase RNA-like ER kinase regulates protein synthesis (by phosphorylation of eukaryotic initiation factor 2 alpha [eIF2α]) in response to endoplasmic reticulum (ER) stressors, such as increases in calcium levels, oxidative damage, and energy/glucose depletion, all of which have been implicated in TBI pathophysiology. Exposure of cells to guanabenz has been shown to increase eIF2α phosphorylation and reduce ER stress. Using a rodent model of TBI, we present experimental results that indicate that postinjury administration of 5.0 mg/kg of guanabenz reduced cortical contusion volume and decreased hippocampal cell damage. Moreover, guanabenz treatment attenuated TBI-associated motor, vestibulomotor, recognition memory, and spatial learning and memory dysfunction. Interestingly, when the initiation of treatment was delayed by 24 h, or the dose reduced to 0.5 mg/kg, some of these beneficial effects were still observed. Taken together, these findings further support the involvement of ER stress signaling in TBI pathophysiology and indicate that guanabenz may have translational utility.

Social interaction attenuates the extent of secondary neuronal damage following closed head injury in mice

Recovery following Traumatic Brain Injury (TBI) can vary tremendously among individuals. Lifestyle following injury, including differential social interactions, may modulate the extent of secondary injury following TBI. To examine this possibility under controlled conditions, closed head injury (CHI) was induced in C57Bl6 mice using a standardized weight drop device after which mice were either housed in isolation or with their original cagemates (“socially-housed”) for 4 weeks. CHI transiently impaired novel object recognition (NOR) in both isolated and social mice, confirming physical and functional injury. By contrast, Y maze navigation was impaired in isolated but not social mice at 1–4 weeks post CHI. CHI increased excitotoxic signaling in hippocampal slices from all mice, which was transiently exacerbated by isolation at 2 weeks post CHI. CHI slightly increased reactive oxygen species and did not alter levels of amyloid beta (Abeta), total or phospho-tau, total or phosphorylated neurofilaments. CHI increased serum corticosterone in both groups, which was exacerbated by isolation. These findings support the hypothesis that socialization may attenuate secondary damage following TBI. In addition, a dominance hierarchy was noted among socially-housed mice, in which the most submissive mouse displayed indices of stress in the above analyses that were statistically identical to those observed for isolated mice. This latter finding underscores that the nature and extent of social interaction may need to vary among individuals to provide therapeutic benefit.

Longitudinal changes in the DTI measures, anti-GFAP expression and levels of serum inflammatory cytokines following mild traumatic brain injury

The majority of human mild traumatic brain injuries (mTBI; 70%) lack radiological evidence of injury, yet may present long term cognitive, and behavioral dysfunctions. With the hypothesis of evident damaged neural tissue and immunological consequences during acute phase of mTBI, we used closed skull weight-drop TBI model to address human mTBI condition. Serum cytokines (TNF-α, IL-10) and glial fibrillary acidic protein (GFAP) expression were examined at day 0 (control, pre-injury), 4h, day 1, day 3 and day 5 post injury (PI). Diffusion tensor imaging (DTI) was performed at similar timepoints to identify neuroinflammation translation into imaging abnormalities and monitor injury progression. DTI indices including mean diffusivity (MD), radial diffusivity (RD), fractional anisotropy and axial diffusivity values were quantified from cortex (CTX), hippocampus and corpus callosum regions. One way ANOVA showed significant increase in TNF-α at 4h and IL-10 at day 1 PI as compared to control. GFAP(+) cells were significantly increased at day 3 and day 5 as compared to control in CTX. Repeated measures ANOVA revealed significant decreases in MD, RD values in CTX at day 3 and day 5 as compared to day 0. A significant, inverse correlation was observed between cortical MD (r=-0.74, p=0.01), AD (r=-0.60, p=0.03) and RD (r=-0.72, p=0.01) values with mean GFAP(+) cells in the cortical region. These findings suggest that mTBI leads to elevated cytokine expression and subsequent hypertrophy of astrocytic processes. The increased numbers of reactive glial cells contribute diffusion restrictions in the CNS leading to reduced MD and RD values. These findings are in line with the deficits and pathologies associated with clinical mTBI, and support the use of mTBI model to address pathology and therapeutic options.

The new neurometabolic cascade of concussion

Since the original descriptions of postconcussive pathophysiology, there has been a significant increase in interest and ongoing research to study the biological underpinnings of concussion. The initial ionic flux and glutamate release result in significant energy demands and a period of metabolic crisis for the injured brain. These physiological perturbations can now be linked to clinical characteristics of concussion, including migrainous symptoms, vulnerability to repeat injury, and cognitive impairment. Furthermore, advanced neuroimaging now allows a research window to monitor postconcussion pathophysiology in humans noninvasively. There is also increasing concern about the risk for chronic or even progressive neurobehavioral impairment after concussion/mild traumatic brain injury. Critical studies are underway to better link the acute pathobiology of concussion with potential mechanisms of chronic cell death, dysfunction, and neurodegeneration. This "new and improved" article summarizes in a translational fashion and updates what is known about the acute neurometabolic changes after concussive brain injury. Furthermore, new connections are proposed between this neurobiology and early clinical symptoms as well as to cellular processes that may underlie long-term impairment.

Long-lasting suppression of acoustic startle response after mild traumatic brain injury

Acoustic startle response (ASR) is a defensive reflex that is largely ignored unless greatly exaggerated. ASR is suppressed after moderate and severe traumatic brain injury (TBI), but the effect of mild TBI (mTBI) on ASR has not been investigated. Because the neural circuitry for ASR resides in the pons in all mammals, ASR may be a good measure of brainstem function after mTBI. The present study assessed ASR in Sprague-Dawley rats after mTBI using lateral fluid percussion and compared these effects to those on spatial working memory. mTBI caused a profound, long-lasting suppression of ASR. Both probability of emitting a startle and startle amplitude were diminished. ASR suppression was observed as soon as 1 day after injury and remained suppressed for the duration of the study (21 days after injury). No indication of recovery was observed. mTBI also impaired spatial working memory. In contrast to the suppression of ASR, working memory impairment was transient; memory was impaired 1 and 7 days after injury, but recovered by 21 days. The long-lasting suppression of ASR suggests long-term dysfunction of brainstem neural circuits at a time when forebrain neural circuits responsible for spatial working memory have recovered. These results have important implications for return-to-activity decisions because recovery of cognitive impairments plays an important role in these decisions.

Predicting changes in cortical electrophysiological function after in vitro traumatic brain injury

Finite element (FE) models of traumatic brain injury (TBI) are capable of predicting injury-induced brain tissue deformation. However, current FE models are not equipped to predict the biological consequences of tissue deformation, which requires the determination of tolerance criteria relating the effects of mechanical stimuli to biologically relevant functional responses. To address this deficiency, we present functional tolerance criteria for the cortex for alterations in neuronal network electrophysiological function in response to controlled mechanical stimuli. Organotypic cortical slice cultures were mechanically injured via equibiaxial stretch with a well-characterized in vitro model of TBI at tissue strains and strain rates relevant to TBI (up to Lagrangian strain of 0.59 and strain rates up to 29 [Formula: see text]. At 4-6 days post-injury, electrophysiological function was assessed simultaneously throughout the cortex using microelectrode arrays. Electrophysiological parameters associated with unstimulated spontaneous network activity (neural event rate, duration, and magnitude), stimulated evoked responses (the maximum response [Formula: see text], the stimulus current necessary for a half-maximal response [Formula: see text], and the electrophysiological parameter [Formula: see text] that is representative of firing uniformity), and evoked paired-pulse ratios at varying interstimulus intervals were quantified for each cortical slice culture. Nonlinear regression was performed between mechanical injury parameters as independent variables (tissue strain and strain rate) and each electrophysiological parameter as output. Parsimonious best-fit equations were determined from a large pool of candidate equations with tenfold cross-validation. Changes in electrophysiological parameters were dependent on strain and strain rate in a complex manner. Compared to the hippocampus, the cortex was less spontaneously active, less excitable, and less prone to significant changes in electrophysiological function in response to controlled deformation (strain or strain rate). Our study provides functional data that can be incorporated into FE models to improve their predictive capabilities of the in vivo consequences of TBI.

Altered regulation of protein kinase a activity in the medial prefrontal cortex of normal and brain-injured animals actively engaged in a working memory task

Cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) signaling is required for short- and long-term memory. In contrast, enhanced PKA activity has been shown to impair working memory, a prefrontal cortex (PFC)-dependent, transient form of memory critical for cognition and goal-directed behaviors. Working memory can be impaired after traumatic brain injury (TBI) in the absence of overt damage to the PFC. The cellular and molecular mechanisms that contribute to this deficit are largely unknown. In the present study, we examined whether altered PKA signaling in the PFC as a result of TBI is a contributing mechanism. We measured PKA activity in medial PFC (mPFC) tissue homogenates prepared from sham and 14-day postinjury rats. PKA activity was measured both when animals were inactive and when actively engaged in a spatial working memory task. Our results demonstrate, for the first time, that PKA activity in the mPFC is actively suppressed in uninjured animals performing a working memory task. By comparison, both basal and working memory-related PKA activity was elevated in TBI animals. Inhibition of PKA activity by intra-mPFC administration of Rp-cAMPS into TBI animals had no influence on working memory performance 30 min postinfusion, but significantly improved working memory when tested 24 h later. This improvement was associated with reduced glutamic acid decarboxylase 67 messenger RNA levels. Taken together, these results suggest that TBI-associated working memory dysfunction may result, in part, from enhanced PKA activity, possibly leading to altered expression of plasticity-related genes in the mPFC.

Experimental traumatic brain injury alters ethanol consumption and sensitivity

Altered alcohol consumption patterns after traumatic brain injury (TBI) can lead to significant impairments in TBI recovery. Few preclinical models have been used to examine alcohol use across distinct phases of the post-injury period, leaving mechanistic questions unanswered. To address this, the aim of this study was to describe the histological and behavioral outcomes of a noncontusive closed-head TBI in the mouse, after which sensitivity to and consumption of alcohol were quantified, in addition to dopaminergic signaling markers. We hypothesized that TBI would alter alcohol consumption patterns and related signal transduction pathways that were congruent to clinical observations. After midline impact to the skull, latency to right after injury, motor deficits, traumatic axonal injury, and reactive astrogliosis were evaluated in C57BL/6J mice. Amyloid precursor protein (APP) accumulation was observed in white matter tracts at 6, 24, and 72 h post-TBI. Increased intensity of glial fibrillary acidic protein (GFAP) immunoreactivity was observed by 24 h, primarily under the impact site and in the nucleus accumbens, a striatal subregion, as early as 72 h, persisting to 7 days, after TBI. At 14 days post-TBI, when mice were tested for ethanol sensitivity after acute high-dose ethanol (4 g/kg, intraperitoneally), brain-injured mice exhibited increased sedation time compared with uninjured mice, which was accompanied by deficits in striatal dopamine- and cAMP-regulated neuronal phosphoprotein, 32 kDa (DARPP-32) phosphorylation. At 17 days post-TBI, ethanol intake was assessed using the Drinking-in-the-Dark paradigm. Intake across 7 days of consumption was significantly reduced in TBI mice compared with sham controls, paralleling the reduction in alcohol consumption observed clinically in the initial post-injury period. These data demonstrate that TBI increases sensitivity to ethanol-induced sedation and affects downstream signaling mediators of striatal dopaminergic neurotransmission while altering ethanol consumption. Examining TBI effects on ethanol responsitivity will improve our understanding of alcohol use post-TBI in humans.

Centella asiatica Attenuates Diabetes Induced Hippocampal Changes in Experimental Diabetic Rats

Diabetes mellitus has been reported to affect functions of the hippocampus. We hypothesized that Centella asiatica, a herb traditionally being used to improve memory, prevents diabetes-related hippocampal dysfunction. Therefore, the aim of this study was to investigate the protective role of C. asiatica on the hippocampus in diabetes. Methods. Streptozotocin- (STZ-) induced adult male diabetic rats received 100 and 200 mg/kg/day body weight (b.w) C. asiatica leaf aqueous extract for four consecutive weeks. Following sacrifice, hippocampus was removed and hippocampal tissue homogenates were analyzed for Na(+)/K(+)-, Ca(2+)- and Mg(2+)-ATPases activity levels. Levels of the markers of inflammation (tumor necrosis factor, TNF-α; interleukin, IL-6; and interleukin, IL-1β) and oxidative stress (lipid peroxidation product: LPO, superoxide dismutase: SOD, catalase: CAT, and glutathione peroxidase: GPx) were determined. The hippocampal sections were visualized for histopathological changes. Results. Administration of C. asiatica leaf aqueous extract to diabetic rats maintained near normal ATPases activity levels and prevents the increase in the levels of inflammatory and oxidative stress markers in the hippocampus. Lesser signs of histopathological changes were observed in the hippocampus of C. asiatica leaf aqueous extract treated diabetic rats. Conclusions. C. asiatica leaf protects the hippocampus against diabetes-induced dysfunction which could help to preserve memory in this condition.

Diffuse traumatic brain injury and the sensory brain

In this review we discuss the consequences to the brain's cortex, specifically to the sensory cortex, of traumatic brain injury. The thesis underlying this approach is that long-term deficits in cognition seen after brain damage in humans are likely underpinned by an impaired cortical processing of the sensory information needed to drive cognition or to be used by cognitive processes to produce a response. We take it here that the impairment to sensory processing does not arise from damage to peripheral sensory systems, but from disordered brain processing of sensory input.

Elucidating the severity of preclinical traumatic brain injury models: a role for functional assessment?

BACKGROUND

Concussion remains a symptom-based diagnosis clinically, yet preclinical studies investigating traumatic brain injury, of which concussion is believed to represent a "mild" form, emphasize histological end points with functional assessments often minimized or ignored all together. Recently, clinical studies have identified the importance of cognitive and neuropsychiatric symptoms, in addition to somatic concerns, following concussion. How these findings may translate to preclinical studies is unclear at present.

OBJECTIVE

To address the contrasting end points used clinically compared with those in preclinical studies and the potential role of functional assessments in a commonly used model of diffuse axonal injury (DAI).

METHODS

Animals were subjected to DAI by the use of the impact-acceleration model. Functional and behavioral assessments were conducted during 1 week following DAI before the completion of the histological assessment at 1 week post-DAI.

RESULTS

We show, despite the suggestion that this model represents concussive injury, no functional impairments as determined by using the common measures of motor, sensorimotor, cognitive, and neuropsychiatric function following injury over the course of 1 week. The lack of functional deficits is in sharp contrast to neuropathological findings indicating neural degeneration, astrocyte reactivity, and microglial activation.

CONCLUSION

Future studies are needed to identify functional assessments, neurophysiologic techniques, and imaging assessments more apt to distinguish differences following so-called "mild" traumatic brain injury in preclinical models and determine whether these models are truly studying concussive or subconcussive injury. These studies are needed not only to understand the mechanism of injury and production of subsequent deficits, but also to rigorously evaluate potential therapeutic agents.

Incretin mimetics as pharmacologic tools to elucidate and as a new drug strategy to treat traumatic brain injury

Traumatic brain injury (TBI), either as an isolated injury or in conjunction with other injuries, is an increasingly common event. An estimated 1.7 million injuries occur within the USA each year and 10 million people are affected annually worldwide. Indeed, nearly one third (30.5%) of all injury-related deaths in the USA are associated with TBI, which will soon outpace many common diseases as the major cause of death and disability. Associated with a high morbidity and mortality and no specific therapeutic treatment, TBI has become a pressing public health and medical problem. The highest incidence of TBI occurs in young adults (15-24 years age) and in the elderly (≥75 years of age). Older individuals are particularly vulnerable to these types of injury, often associated with falls, and have shown increased mortality and worse functional outcome after lower initial injury severity. In addition, a new and growing form of TBI, blast injury, associated with the detonation of improvised explosive devices in the war theaters of Iraq and Afghanistan, are inflicting a wave of unique casualties of immediate impact to both military personnel and civilians, for which long-term consequences remain unknown and may potentially be catastrophic. The neuropathology underpinning head injury is becoming increasingly better understood. Depending on severity, TBI induces immediate neuropathologic effects that, for the mildest form, may be transient; however, with increasing severity, these injuries cause cumulative neural damage and degeneration. Even with mild TBI, which represents the majority of cases, a broad spectrum of neurologic deficits, including cognitive impairments, can manifest that may significantly influence quality of life. Further, TBI can act as a conduit to longer term neurodegenerative disorders. Prior studies of glucagon-like peptide-1 (GLP-1) and long-acting GLP-1 receptor agonists have demonstrated neurotrophic/neuroprotective activities across a broad spectrum of cellular and animal models of chronic neurodegenerative (Alzheimer's and Parkinson's diseases) and acute cerebrovascular (stroke) disorders. In view of the mechanisms underpinning these disorders as well as TBI, we review the literature and recent studies assessing GLP-1 receptor agonists as a potential treatment strategy for mild to moderate TBI.

Molecular alterations in the hippocampus after experimental subarachnoid hemorrhage

Patients with aneurysmal subarachnoid hemorrhage (SAH) frequently have deficits in learning and memory that may or may not be associated with detectable brain lesions. We examined mediators of long-term potentiation after SAH in rats to determine what processes might be involved. There was a reduction in synapses in the dendritic layer of the CA1 region on transmission electron microscopy as well as reduced colocalization of microtubule-associated protein 2 (MAP2) and synaptophysin. Immunohistochemistry showed reduced staining for GluR1 and calmodulin kinase 2 and increased staining for GluR2. Myelin basic protein staining was decreased as well. There was no detectable neuronal injury by Fluoro-Jade B, TUNEL, or activated caspase-3 staining. Vasospasm of the large arteries of the circle of Willis was mild to moderate in severity. Nitric oxide was increased and superoxide anion radical was decreased in hippocampal tissue. Cerebral blood flow, measured by magnetic resonance imaging, and cerebral glucose metabolism, measured by positron emission tomography, were no different in SAH compared with control groups. The results suggest that the etiology of loss of LTP after SAH is not cerebral ischemia but may be mediated by effects of subarachnoid blood such as oxidative stress and inflammation.

Exendin-4 ameliorates traumatic brain injury-induced cognitive impairment in rats

Traumatic brain injury represents a major public health issue that affects 1.7 million Americans each year and is a primary contributing factor (30.5%) of all injury-related deaths in the United States. The occurrence of traumatic brain injury is likely underestimated and thus has been termed "a silent epidemic". Exendin-4 is a long-acting glucagon-like peptide-1 receptor agonist approved for the treatment of type 2 diabetes mellitus that not only effectively induces glucose-dependent insulin secretion to regulate blood glucose levels but also reduces apoptotic cell death of pancreatic β-cells. Accumulating evidence also supports a neurotrophic and neuroprotective role of glucagon-like peptide-1 in an array of cellular and animal neurodegeneration models. In this study, we evaluated the neuroprotective effects of Exendin-4 using a glutamate toxicity model in vitro and fluid percussion injury in vivo. We found neuroprotective effects of Exendin-4 both in vitro, using markers of cell death, and in vivo, using markers of cognitive function, as assessed by Morris Water Maze. In combination with the reported benefits of ex-4 in other TBI models, these data support repositioning of Exendin-4 as a potential treatment for traumatic brain injury.

Exendin-4 induced glucagon-like peptide-1 receptor activation reverses behavioral impairments of mild traumatic brain injury in mice

Mild traumatic brain injury (mTBI) represents a major and increasing public health concern and is both the most frequent cause of mortality and disability in young adults and a chief cause of morbidity in the elderly. Albeit mTBI patients do not show clear structural brain defects and, generally, do not require hospitalization, they frequently suffer from long-lasting cognitive, behavioral, and emotional problems. No effective pharmaceutical therapy is available, and existing treatment chiefly involves intensive care management after injury. The diffuse neural cell death evident after mTBI is considered mediated by oxidative stress and glutamate-induced excitotoxicity. Prior studies of the long-acting GLP-1 receptor agonist, exendin-4 (Ex-4), an incretin mimetic approved for type 2 diabetes mellitus treatment, demonstrated its neurotrophic/protective activity in cellular and animal models of stroke, Alzheimer's and Parkinson's diseases, and, consequent to commonalities in mechanisms underpinning these disorders, Ex-4 was assessed in a mouse mTBI model. In neuronal cultures in this study, Ex-4 ameliorated H2O2-induced oxidative stress and glutamate toxicity. To evaluate in vivo translation, we administered steady-state Ex-4 (3.5 pM/kg/min) or saline to control and mTBI mice over 7 days starting 48 h prior to or 1 h post-sham or mTBI (30 g weight drop under anesthesia). Ex-4 proved well-tolerated and fully ameliorated mTBI-induced deficits in novel object recognition 7 and 30 days post-trauma. Less mTBI-induced impairment was evident in Y-maze, elevated plus maze, and passive avoidance paradigms, but when impairment was apparent Ex-4 induced amelioration. Together, these results suggest that Ex-4 may act as a neurotrophic/neuroprotective drug to minimize mTBI impairment.

Medial septal nucleus theta frequency deep brain stimulation improves spatial working memory after traumatic brain injury

More than 5,000,000 survivors of traumatic brain injury (TBI) live with persistent cognitive deficits, some of which likely derive from hippocampal dysfunction. Oscillatory activity in the hippocampus is critical for normal learning and memory functions, and can be modulated using deep brain stimulation techniques. In this pre-clinical study, we demonstrate that lateral fluid percussion TBI results in the attenuation of hippocampal theta oscillations in the first 6 days after injury, which correlate with deficits in the Barnes maze spatial working memory task. Theta band stimulation of the medial septal nucleus (MSN) results in a transient increase in hippocampal theta activity, and when delivered 1 min prior to training in the Barnes maze, it significantly improves spatial working memory. These results suggest that MSN theta stimulation may be an effective neuromodulatory technique for treatment of persistent learning and memory deficits after TBI.

Repeated mild traumatic brain injury: mechanisms of cerebral vulnerability

Among the 3.5 million annual new head injury cases is a subpopulation of children and young adults who experience repeated traumatic brain injury (TBI). The duration of vulnerability after a single TBI remains unknown, and biomarkers have yet to be determined. Decreases in glucose metabolism (cerebral metabolic rate of glucose [CMRglc]) are consistently observed after experimental and human TBI. In the current study, it is hypothesized that the duration of vulnerability is related to the duration of decreased CMRglc and that a single mild TBI (mTBI) increases the brain's vulnerability to a second insult for a period, during which a subsequent mTBI will worsen the outcome. Postnatal day 35 rats were given sham, single mTBI, or two mTBI at 24-h or 120-h intervals. (14)C-2-deoxy-D-glucose autoradiography was conducted at 1 or 3 days post-injury to calculate CMRglc. At 24 h after a single mTBI, CMRglc is decreased by 19% in both the parietal cortex and hippocampus, but approached sham levels by 3 days post-injury. When a second mTBI is introduced during the CMRglc depression of the first injury, the consequent CMRglc is depressed (36.5%) at 24 h and remains depressed (25%) at 3 days. In contrast, when the second mTBI is introduced after the metabolic recovery of the first injury, the consequent CMRglc depression is similar to that seen with a single injury. Results suggest that the duration of metabolic depression reflects the time-course of vulnerability to second injury in the juvenile brain and could serve as a valuable biomarker in establishing window of vulnerability guidelines.

Integration of proteomics, bioinformatics, and systems biology in traumatic brain injury biomarker discovery

Traumatic brain injury (TBI) is a major medical crisis without any FDA-approved pharmacological therapies that have been demonstrated to improve functional outcomes. It has been argued that discovery of disease-relevant biomarkers might help to guide successful clinical trials for TBI. Major advances in mass spectrometry (MS) have revolutionized the field of proteomic biomarker discovery and facilitated the identification of several candidate markers that are being further evaluated for their efficacy as TBI biomarkers. However, several hurdles have to be overcome even during the discovery phase which is only the first step in the long process of biomarker development. The high-throughput nature of MS-based proteomic experiments generates a massive amount of mass spectral data presenting great challenges in downstream interpretation. Currently, different bioinformatics platforms are available for functional analysis and data mining of MS-generated proteomic data. These tools provide a way to convert data sets to biologically interpretable results and functional outcomes. A strategy that has promise in advancing biomarker development involves the triad of proteomics, bioinformatics, and systems biology. In this review, a brief overview of how bioinformatics and systems biology tools analyze, transform, and interpret complex MS datasets into biologically relevant results is discussed. In addition, challenges and limitations of proteomics, bioinformatics, and systems biology in TBI biomarker discovery are presented. A brief survey of researches that utilized these three overlapping disciplines in TBI biomarker discovery is also presented. Finally, examples of TBI biomarkers and their applications are discussed.

Robust training attenuates TBI-induced deficits in reference and working memory on the radial 8-arm maze

Globally, it is estimated that nearly 10 million people sustain severe brain injuries leading to hospitalization and/or death every year. Amongst survivors, traumatic brain injury (TBI) results in a wide variety of physical, emotional and cognitive deficits. The most common cognitive deficit associated with TBI is memory loss, involving impairments in spatial reference and working memory. However, the majority of research thus far has characterized the deficits associated with TBI on either reference or working memory systems separately, without investigating how they interact within a single task. Thus, we examined the effects of TBI on short-term working and long-term reference memory using the radial 8-arm maze (RAM) with a sequence of four baited and four unbaited arms. Subjects were given 10 daily trials for 6 days followed by a memory retrieval test 2 weeks after training. Multiple training trials not only provide robust training, but also test the subjects' ability to frequently update short-term memory while learning the reference rules of the task. Our results show that TBI significantly impaired short-term working memory function on previously acquired spatial information but has little effect on long-term reference memory. Additionally, TBI significantly increased working memory errors during acquisition and reference memory errors during retention testing 2 weeks later. With a longer recovery period after TBI, the robust RAM training mitigated the reference memory deficit in retention but not the short-term working memory deficit during acquisition. These results identify the resiliency and vulnerabilities of short-term working and long-term reference memory to TBI in the context of robust training. The data highlight the role of cognitive training and other behavioral remediation strategies implicated in attenuating deficits associated with TBI.

NAAG peptidase inhibitor improves motor function and reduces cognitive dysfunction in a model of TBI with secondary hypoxia

Immediately following traumatic brain injury (TBI) and TBI with hypoxia, there is a rapid and pathophysiological increase in extracellular glutamate, subsequent neuronal damage and ultimately diminished motor and cognitive function. N-acetyl-aspartyl glutamate (NAAG), a prevalent neuropeptide in the CNS, is co-released with glutamate, binds to the presynaptic group II metabotropic glutamate receptor subtype 3 (mGluR3) and suppresses glutamate release. However, the catalytic enzyme glutamate carboxypeptidase II (GCP II) rapidly hydrolyzes NAAG into NAA and glutamate. Inhibition of the GCP II enzyme with NAAG peptidase inhibitors reduces the concentration of glutamate both by increasing the duration of NAAG activity on mGluR3 and by reducing degradation into NAA and glutamate resulting in reduced cell death in models of TBI and TBI with hypoxia. In the following study, rats were administered the NAAG peptidase inhibitor PGI-02776 (10mg/kg) 30 min following TBI combined with a hypoxic second insult. Over the two weeks following injury, PGI-02776-treated rats had significantly improved motor function as measured by increased duration on the rota-rod and a trend toward improved performance on the beam walk. Furthermore, two weeks post-injury, PGI-02776-treated animals had a significant decrease in latency to find the target platform in the Morris water maze as compared to vehicle-treated animals. These findings demonstrate that the application of NAAG peptidase inhibitors can reduce the deleterious motor and cognitive effects of TBI combined with a second hypoxic insult in the weeks following injury.

Reversible behavioral deficits in rats during a cycle of demyelination-remyelination of the fimbria

Traumatic brain injury (TBI) selectively damages white matter. White matter damage does not produce deficits in many behavioral tests used to analyze experimental TBI. Rats were impaired on an active place avoidance task following inactivation of one hippocampal injection of tetrodotoxin. The need for both hippocampi suggests that acquisition of the active place avoidance task may require interhippocampal communication. The controlled cortical impact model of TBI demyelinates midline white matter and impairs rats on the active place avoidance task. One white matter region that is demyelinated is the fimbria that contains hippocampal commissural fibers. We therefore tested whether demyelination of the fimbria produces deficits in active place avoidance. Lysophosphatidylcholine (LPC) was injected stereotaxically to produce a cycle of demyelination-remyelination of the fimbria. At 4 days, myelin loss was observed in the fimbria of LPC-, but not saline-injected rats. Fourteen days after injection, myelin content increased in LPC-, but not saline-injected rats. Three days after injection, both saline- and LPC-injected rats had similar performance on an open field and passive place avoidance task in which the rat avoided a stationary shock zone on a stationary arena. The following day, on the active place avoidance task, LPC-injected rats had a significantly higher number of shock zone entrances suggesting learning was impaired. At 14 days after injection, saline- and LPC-injected rats had similar performance on open field and passive place avoidance. On active place avoidance, however, saline- and LPC-injected rats had a similar number of total entrances suggesting that the impairment seen at 4 days was no longer present at 14 days. These data suggest that active place avoidance is highly sensitive to white matter injury.

A Model for Mild Traumatic Brain Injury that Induces Limited Transient Memory Impairment and Increased Levels of Axon Related Serum Biomarkers

Mild traumatic brain injury (mTBI) is one of the most common neuronal insults and can lead to long-term disabilities. mTBI occurs when the head is exposed to a rapid acceleration-deceleration movement triggering axonal injuries. Our limited understanding of the underlying pathological changes makes it difficult to predict the outcome of mTBI. In this study we used a scalable rat model for rotational acceleration TBI, previously characterized for the threshold of axonal pathology. We have analyzed whether a TBI just above the defined threshold would induce any detectable behavioral changes and/or changes in serum biomarkers. The effect of injury on sensory motor functions, memory and anxiety were assessed by beam walking, radial arms maze and elevated plus maze at 3–7 days following TBI. The only behavioral deficits found were transient impairments in working and reference memory. Blood serum was analyzed at 1, 3, and 14 days after injury for changes in selected protein biomarkers. Serum levels of neurofilament heavy chain and Tau, as well as S100B and myelin basic protein showed significant increases in the injured animals at all time points. No signs of macroscopic injuries such as intracerebral hematomas or contusions were found. Amyloid precursor protein immunostaining indicated axonal injuries at all time points analyzed. In summary, this model mimics some of the key symptoms of mTBI, such as transient memory impairment, which is paralleled by an increase in serum biomarkers. Our findings suggest that serum biomarkers may be used to detect mTBI. The model provides a suitable foundation for further investigation of the underlying pathology of mTBI.

Lateralized response of dynorphin a peptide levels after traumatic brain injury

Traumatic brain injury (TBI) induces a cascade of primary and secondary events resulting in impairment of neuronal networks that eventually determines clinical outcome. The dynorphins, endogenous opioid peptides, have been implicated in secondary injury and neurodegeneration in rodent and human brain. To gain insight into the role of dynorphins in the brain's response to trauma, we analyzed short-term (1-day) and long-term (7-day) changes in dynorphin A (Dyn A) levels in the frontal cortex, hippocampus, and striatum, induced by unilateral left-side or right-side cortical TBI in mice. The effects of TBI were significantly different from those of sham surgery (Sham), while the sham surgery also produced noticeable effects. Both sham and TBI induced short-term changes and long-term changes in all three regions. Two types of responses were generally observed. In the hippocampus, Dyn A levels were predominantly altered ipsilateral to the injury. In the striatum and frontal cortex, injury to the right (R) hemisphere affected Dyn A levels to a greater extent than that seen in the left (L) hemisphere. The R-TBI but not L-TBI produced Dyn A changes in the striatum and frontal cortex at 7 days after injury. Effects of the R-side injury were similar in the two hemispheres. In naive animals, Dyn A was symmetrically distributed between the two hemispheres. Thus, trauma may reveal a lateralization in the mechanism mediating the response of Dyn A-expressing neuronal networks in the brain. These networks may differentially mediate effects of left and right brain injury on lateralized brain functions.

Traumatic brain injury-induced cognitive and histological deficits are attenuated by delayed and chronic treatment with the 5-HT1A-receptor agonist buspirone

The aim of this study was to evaluate the potential efficacy of the serotonin(1A) (5-HT(1A)) receptor agonist buspirone (BUS) on behavioral and histological outcome after traumatic brain injury (TBI). Ninety-six isoflurane-anesthetized adult male rats were randomized to receive either a controlled cortical impact or sham injury, and then assigned to six TBI and six sham groups receiving one of five doses of BUS (0.01, 0.05, 0.1, 0.3, or 0.5 mg/kg) or saline vehicle (VEH, 1.0 mL/kg). Treatments began 24 h after surgery and were administered intraperitoneally once daily for 3 weeks. Motor function (beam-balance/beam-walk tests) and spatial learning/memory (Morris water maze) were assessed on post-operative days 1-5 and 14-19, respectively. Morphologically intact CA1/CA3 cells and cortical lesion volume were quantified at 3 weeks. No differences were observed among the BUS and VEH sham groups in any end-point measure and thus the data were pooled. Regarding the TBI groups, repeated-measures ANOVAs revealed that the 0.3 mg/kg dose of BUS enhanced cognitive performance relative to VEH and the other BUS doses (p<0.05), but did not significantly impact motor function. Moreover, the same dose conferred selective histological protection as evidenced by smaller cortical lesions, but not greater CA1/CA3 cell survival. No significant behavioral or histological differences were observed among the other BUS doses versus VEH. These data indicate that BUS has a narrow therapeutic dose response, and that 0.3 mg/kg is optimal for enhancing spatial learning and memory in this model of TBI. BUS may have potential as a novel pharmacotherapy for clinical TBI.

Decrease in tonic inhibition contributes to increase in dentate semilunar granule cell excitability after brain injury

Brain injury is an etiological factor for temporal lobe epilepsy and can lead to memory and cognitive impairments. A recently characterized excitatory neuronal class in the dentate molecular layer, semilunar granule cell (SGC), has been proposed to regulate dentate network activity patterns and working memory formation. Although SGCs, like granule cells, project to CA3, their typical sustained firing and associational axon collaterals suggest that they are functionally distinct from granule cells. We find that brain injury results in an enhancement of SGC excitability associated with an increase in input resistance 1 week after trauma. In addition to prolonging miniature and spontaneous IPSC interevent intervals, brain injury significantly reduces the amplitude of tonic GABA currents in SGCs. The postinjury decrease in SGC tonic GABA currents is in direct contrast to the increase observed in granule cells after trauma. Although our observation that SGCs express Prox1 indicates a shared lineage with granule cells, data from control rats show that SGC tonic GABA currents are larger and sIPSC interevent intervals shorter than in granule cells, demonstrating inherent differences in inhibition between these cell types. GABA(A) receptor antagonists selectively augmented SGC input resistance in controls but not in head-injured rats. Moreover, post-traumatic differences in SGC firing were abolished in GABA(A) receptor blockers. Our data show that cell-type-specific post-traumatic decreases in tonic GABA currents boost SGC excitability after brain injury. Hyperexcitable SGCs could augment dentate throughput to CA3 and contribute substantively to the enhanced risk for epilepsy and memory dysfunction after traumatic brain injury.

Mild traumatic brain injury is associated with impaired hippocampal spatiotemporal representation in the absence of histological changes

Mild traumatic brain injury (mTBI) accounts for the majority of head trauma cases. Despite some lasting cognitive, emotional, and behavioral deficits, there are frequently no overt morphological defects, suggesting that changes may result from alterations in the physiology of individual neurons. We investigated hippocampal neural activity in rats during a working memory task to determine the effect of mTBI on cellular physiology. Male Sprague-Dawley rats (300-350 g) underwent mTBI via lateral fluid percussion (1.5 atm), and were compared with sham-operated rats. The rats then underwent bilateral implantation of electrodes into the CA1 and CA3 hippocampal subfields and were trained to perform in a delayed nonmatch-to-place swim T-maze. Single-neuron activity was analyzed during task performance 30-90 days after trauma. There were no histological differences between control and mTBI rats. Stereological analysis demonstrated no neuronal loss. Nevertheless, rats subjected to mTBI demonstrated significantly poorer performance on the task with increasing delay. Examination of single-neuron spiking activity revealed no significant difference in firing rates or spike characteristics, but rats exposed to mTBI were found to have significantly fewer cells with activity spatiotemporally correlated with location in the maze ("task-specific cells," p<0.05 by Fisher's exact test). Memory deficits, including disorganized patterns of hippocampal neural activity after mTBI, were seen in rats. Because it is seen in the absence of clear morphological defects, these data suggest that functional impairment after mTBI may result from alterations in the activity of individual neurons.

Unmyelinated axons show selective rostrocaudal pathology in the corpus callosum after traumatic brain injury

Axonal injury is consistently observed after traumatic brain injury (TBI). Prior research has extensively characterized the post-TBI response in myelinated axons. Despite evidence that unmyelinated axons comprise a numerical majority of cerebral axons, pathologic changes in unmyelinated axons after TBI have not been systematically studied. To identify morphologic correlates of functional impairment of unmyelinated fibers after TBI, we assessed ultrastructural changes in corpus callosum axons. Adult rats received moderate fluid percussion TBI, which produced diffuse injury with no contusion. Cross-sectional areas of 13,797 unmyelinated and 3,278 intact myelinated axons were stereologically measured at survival intervals from 3 hours to 15 days after injury. The mean caliber of unmyelinated axons was significantly reduced at 3 to 7 days and recovered by 15 days, but the time course of this shrinkage varied among the genu, mid callosum, and splenium. Relatively large unmyelinated axons seemed to be particularly vulnerable. Injury-induced decreases in unmyelinated fiber density were also observed, but they were more variable than caliber reductions. By contrast, no significant morphometric changes were observed in myelinated axons. The finding of a preferential vulnerability in unmyelinated axons has implications for current concepts of axonal responses after TBI and for development of specifically targeted therapies.

Characterization of a novel rat model of penetrating traumatic brain injury

A penetrating traumatic brain injury (pTBI) occurs when an object impacts the head with sufficient force to penetrate the skin, skull, and meninges, and inflict injury directly to the brain parenchyma. This type of injury has been notoriously difficult to model in small laboratory animals such as rats or mice. To this end, we have established a novel non-fatal model for pTBI based on a modified air rifle that accelerates a pellet, which in turn impacts a small probe that then causes the injury to the experimental animal's brain. In the present study, we have focused on the acute phase and characterized the tissue destruction, including increasing cavity formation, white matter degeneration, hemorrhage, edema, and gliosis. We also used a battery of behavioral models to examine the neurological outcome, with the most noteworthy finding being impairment of reference memory function. In conclusion, we have described a number of events taking place after pTBI in our model. We expect this model will prove useful in our efforts to unravel the biological events underlying injury and regeneration after pTBI and possibly serve as a useful animal model in the development of novel therapeutic and diagnostic approaches.

Caffeic Acid phenethyl ester protects blood-brain barrier integrity and reduces contusion volume in rodent models of traumatic brain injury

A number of studies have established a deleterious role for inflammatory molecules and reactive oxygen species (ROS) in the pathology of traumatic brain injury (TBI). Caffeic acid phenethyl ester (CAPE) has been shown to exert both antioxidant and anti-inflammatory effects. The primary objective of the present study was to examine if CAPE could be used to reduce some of the pathological consequences of TBI using rodent models. Male Sprague-Dawley rats and C57BL/6 mice were subjected to controlled cortical impact (CCI) injury. Blood-brain barrier (BBB) integrity was assessed by examining claudin-5 expression and the extravasation of Evans blue dye. The effect of post-injury CAPE administration on neurobehavioral function was assessed using vestibulomotor, motor, and two hippocampus-dependent learning and memory tasks. We report that post-TBI administration of CAPE reduces Evans blue extravasation both in rats and mice. This improvement was associated with preservation of the levels of the tight junction protein claudin-5. CAPE treatment did not improve performance in either vestibulomotor/motor function (tested using beam balance and foot-fault tests), or in learning and memory function (tested using the Morris water maze and associative fear memory tasks). However, animals treated with CAPE were found to have significantly less cortical tissue loss than vehicle-treated controls. These findings suggest that CAPE may provide benefit in the treatment of vascular compromise following central nervous system injury.

Microenvironment changes in mild traumatic brain injury

Traumatic brain injury (TBI) is a major public-health problem for which mild TBI (MTBI) makes up majority of the cases. MTBI is a poorly-understood health problem and can persist for years manifesting into neurological and non-neurological problems that can affect functional outcome. Presently, diagnosis of MTBI is based on symptoms reporting with poor understanding of ongoing pathophysiology, hence precluding prognosis and intervention. Other than rehabilitation, there is still no pharmacological treatment for the treatment of secondary injury and prevention of the development of cognitive and behavioural problems. The lack of external injuries and absence of detectable brain abnormalities lend support to MTBI developing at the cellular and biochemical level. However, the paucity of suitable and validated non-invasive methods for accurate diagnosis of MTBI poses as a substantial challenge. Hence, it is crucial that a clinically useful evaluation and management procedure be instituted for MTBI that encompasses both molecular pathophysiology and functional outcome. The acute microenvironment changes post-MTBI presents an attractive target for modulation of MTBI symptoms and the development of cognitive changes later in life.

Effects of chronic guanosine treatment on hippocampal damage and cognitive impairment of rats submitted to chronic cerebral hypoperfusion

Chronic cerebral hypoperfusion contributes to a cognitive decline related to brain disorders. Its experimental model in rats is a permanent bilateral common carotid artery occlusion (2VO). Overstimulation of the glutamatergic system excitotoxicity due to brain energetic disturbance in 2VO animals seems to play a pivotal role as a mechanism of cerebral damage. The nucleoside guanosine (GUO) exerts extracellular effects including antagonism of glutamatergic activity. Accordingly, our group demonstrated several neuroprotective effects of GUO against glutamatergic excitotoxicity. Therefore, in this study, we evaluated a chronic GUO treatment effects in rats submitted to 2VO. We evaluated the animals performance in the Morris water maze and hippocampal damage by neurons and astrocytes immunohistochemistry. In addition, we investigated the cerebrospinal fluid (CSF) brain derived neurotrophic factor (BDNF) and serum S100B levels. Additionally, the purine CSF and plasma levels were determined. GUO treatment did not prevent the cognitive impairment promoted by 2VO. However, none of the 2VO animals treated with GUO showed differences in the hippocampal regions compared to control, while 20% of 2VO rats not treated with GUO presented loss of pyramidal neurons and increased glial labeling cells in CA1 hippocampal region. In addition, we did not observe differences in CSF BDNF nor serum S100B levels among the groups. Of note, both the 2VO surgery and GUO treatment changed the purine CSF and plasma profile. In conclusion, GUO treatment did not prevent the cognitive impairment observed in 2VO animals, but our data suggest that GUO could be neuroprotective against hippocampal damage induced by 2VO.

Impaired myelination of the human hippocampal formation in Down syndrome

Myelination is considered as one of the last steps of neuronal development and is essential to the physiologically matured function of afferent and efferent pathways. In the present study, myelin formation was examined in the human fetal, postnatal and adult hippocampal formation in Down syndrome and in age-matched controls with immunohistochemistry detecting a protein component of the myelin sheath, the myelin basic protein synthesized by oligodendroglial cells. Myelination is mainly a postnatal event in the hippocampal formation of both healthy controls and in patients with Down syndrome. In patients with Down syndrome the sequence of myelination of the hippocampal formation followed a similar developmental pattern to that in controls. However, myelin formation was generally delayed in Down syndrome compared to age-matched controls. In addition, in the hilus of the dentate gyrus a decreased density of myelinated axons was detected from the start of myelination until adulthood. The majority of local axons (mossy fibers) are not myelinated in the hilar region and myelinated fibers arriving in the hilus come mainly from the subcortical septal nuclei. Since intact septo-hippocampal connections are necessary for memory formation, we hypothesize that decreased myelination in the hilus may contribute to the mental retardation of Down syndrome patients.

Severity profile of penetrating ballistic-like brain injury on neurofunctional outcome, blood-brain barrier permeability, and brain edema formation

This study evaluated the injury severity profile of unilateral, frontal penetrating ballistic-like brain injury (PBBI) on neurofunctional outcome, blood-brain barrier (BBB) permeability, and brain edema formation. The degree of injury severity was determined by the delivery of a water-pressure pulse designed to produce a temporary cavity by rapid (<40 ms) expansion of the probe's elastic balloon calibrated to equal 5%, 10%, 12.5%, or 15% of total rat brain volume (control groups consisted of sham surgery or insertion of the probe only). Neurofunctional assessments revealed motor and cognitive deficits related to the degree of injury severity, with the most clear-cut profile of PBBI injury severity depicted by the Morris water maze (MWM) results. A biphasic pattern of BBB leakage was detected in the injured hemisphere at all injury severity levels at 4 h post-injury, and again at 48-72 h post-injury, which remained evident out to 7 days post-PBBI in the 10% and 12.5% PBBI groups. Likewise, significant brain edema was detected in the injured hemisphere by 4 h post-injury and remained elevated out to 7 days post-injury in the 10% and 12.5% PBBI groups. However, following 5% PBBI, significant levels of edema were only detected from 24 h to 48h post-injury. These results identify an injury severity profile of BBB permeability, brain edema, and neurofunctional impairment that provides sensitive and clinically relevant outcome metrics for studying potential therapeutics.

Moderate traumatic brain injury causes acute dendritic and synaptic degeneration in the hippocampal dentate gyrus

Hippocampal injury-associated learning and memory deficits are frequent hallmarks of brain trauma and are the most enduring and devastating consequences following traumatic brain injury (TBI). Several reports, including our recent paper, showed that TBI brought on by a moderate level of controlled cortical impact (CCI) induces immature newborn neuron death in the hippocampal dentate gyrus. In contrast, the majority of mature neurons are spared. Less research has been focused on these spared neurons, which may also be injured or compromised by TBI. Here we examined the dendrite morphologies, dendritic spines, and synaptic structures using a genetic approach in combination with immunohistochemistry and Golgi staining. We found that although most of the mature granular neurons were spared following TBI at a moderate level of impact, they exhibited dramatic dendritic beading and fragmentation, decreased number of dendritic branches, and a lower density of dendritic spines, particularly the mushroom-shaped mature spines. Further studies showed that the density of synapses in the molecular layer of the hippocampal dentate gyrus was significantly reduced. The electrophysiological activity of neurons was impaired as well. These results indicate that TBI not only induces cell death in immature granular neurons, it also causes significant dendritic and synaptic degeneration in pathohistology. TBI also impairs the function of the spared mature granular neurons in the hippocampal dentate gyrus. These observations point to a potential anatomic substrate to explain, in part, the development of posttraumatic memory deficits. They also indicate that dendritic damage in the hippocampal dentate gyrus may serve as a therapeutic target following TBI.