Transient alterations of creatine, creatine phosphate, N-acetylaspartate and high-energy phosphates after mild traumatic brain injury in the rat

Mild traumatic brain injury as a pathological process

Traumatic brain injury (TBI) is defined as dysfunction or other evidence of brain pathology caused by external physical force. More than 69 million new cases of TBI are registered worldwide each year, 80% of them - mild TBI. Based on the physical mechanism of induced trauma, we can separate its pathophysiology into primary and secondary injuries. Many literature sources have confirmed that mechanically induced brain injury initiates ionic, metabolic, inflammatory, and neurovascular changes in the CNS, which can lead to acute, subacute, and chronic neurological consequences. Despite the global nature of the disease, its high heterogeneity, lack of a unified classification system, rapid fluctuation of epidemiological trends, and variability of long-term consequences significantly complicate research and the development of new therapeutic strategies. In this review paper, we systematize current knowledge of biomechanical and molecular mechanisms of mild TBI and provide general information on the classification and epidemiology of this complex disorder.

Acute effects of single and repeated mild traumatic brain injury on levels of neurometabolites, lipids, and mitochondrial function in male rats

Introduction

Mild traumatic brain injuries (mTBIs) are the most common form of acquired brain injury. Symptoms of mTBI are thought to be associated with a neuropathological cascade, potentially involving the dysregulation of neurometabolites, lipids, and mitochondrial bioenergetics. Such alterations may play a role in the period of enhanced vulnerability that occurs after mTBI, such that a second mTBI will exacerbate neuropathology. However, it is unclear whether mTBI-induced alterations in neurometabolites and lipids that are involved in energy metabolism and other important cellular functions are exacerbated by repeat mTBI, and if such alterations are associated with mitochondrial dysfunction.

Methods

In this experiment, using a well-established awake-closed head injury (ACHI) paradigm to model mTBI, male rats were subjected to a single injury, or five injuries delivered 1 day apart, and injuries were confirmed with a beam-walk task and a video observation protocol. Abundance of several neurometabolites was evaluated 24 h post-final injury in the ipsilateral and contralateral hippocampus using in vivo proton magnetic resonance spectroscopy (1H-MRS), and mitochondrial bioenergetics were evaluated 30 h post-final injury, or at 24 h in place of 1H-MRS, in the rostral half of the ipsilateral hippocampus. Lipidomic evaluations were conducted in the ipsilateral hippocampus and cortex.

Results

We found that behavioral deficits in the beam task persisted 1- and 4 h after the final injury in rats that received repetitive mTBIs, and this was paralleled by an increase and decrease in hippocampal glutamine and glucose, respectively, whereas a single mTBI had no effect on sensorimotor and metabolic measurements. No group differences were observed in lipid levels and mitochondrial bioenergetics in the hippocampus, although some lipids were altered in the cortex after repeated mTBI.

Discussion

The decrease in performance in sensorimotor tests and the presence of more neurometabolic and lipidomic abnormalities, after repeated but not singular mTBI, indicates that multiple concussions in short succession can have cumulative effects. Further preclinical research efforts are required to understand the underlying mechanisms that drive these alterations to establish biomarkers and inform treatment strategies to improve patient outcomes.

Functional Connectivity in the Mouse Brainstem Represents Signs of Recovery from Concussion

Mild traumatic brain injury (mTBI) is one of the most frequent neurological disorders. Diagnostic criteria for mTBI are based on cognitive or neurological symptoms without fully understanding the neuropathological basis for explaining behaviors. From the neuropathological perspective of mTBI, recent neuroimaging studies have focused on structural or functional differences in motor-related cortical regions but did not compare topological network properties between the post-concussion days in the brainstem. We investigated temporal changes in functional connectivity and evaluated network properties of functional networks in the mouse brainstem. We observed a significantly decreased functional connectivity and global and local network properties on post-concussion day 7, which normalized on post-concussion day 14. Functional connectivity and local network properties on post-concussion day 2 were also significantly decreased compared with those on post-concussion day 14, but there were no significant group differences in global network properties between days 2 and 14. We also observed that the local efficiency and clustering coefficient of the brainstem network were significantly correlated with anxiety-like behaviors on post-concussion days 7 and 14. This study suggests that functional connectivity in the mouse brainstem provides vital recovery signs from concussion through functional reorganization.

Replicability of proton MR spectroscopic imaging findings in mild traumatic brain injury: Implications for clinical applications

PURPOSE

Proton magnetic resonance spectroscopy (1H MRS) offers biomarkers of metabolic damage after mild traumatic brain injury (mTBI), but a lack of replicability studies hampers clinical translation. In a conceptual replication study design, the results reported in four previous publications were used as the hypotheses (H1-H7), specifically: abnormalities in patients are diffuse (H1), confined to white matter (WM) (H2), comprise low N-acetyl-aspartate (NAA) levels and normal choline (Cho), creatine (Cr) and myo-inositol (mI) (H3), and correlate with clinical outcome (H4); additionally, a lack of findings in regional subcortical WM (H5) and deep gray matter (GM) structures (H6), except for higher mI in patients' putamen (H7).

METHODS

26 mTBI patients (20 female, age 36.5 ± 12.5 [mean ± standard deviation] years), within two months from injury and 21 age-, sex-, and education-matched healthy controls were scanned at 3 Tesla with 3D echo-planar spectroscopic imaging. To test H1-H3, global analysis using linear regression was used to obtain metabolite levels of GM and WM in each brain lobe. For H4, patients were stratified into non-recovered and recovered subgroups using the Glasgow Outcome Scale Extended. To test H5-H7, regional analysis using spectral averaging estimated metabolite levels in four GM and six WM structures segmented from T1-weighted MRI. The Mann-Whitney U test and weighted least squares analysis of covariance were used to examine mean group differences in metabolite levels between all patients and all controls (H1-H3, H5-H7), and between recovered and non-recovered patients and their respectively matched controls (H4). Replicability was defined as the support or failure to support the null hypotheses in accordance with the content of H1-H7, and was further evaluated using percent differences, coefficients of variation, and effect size (Cohen's d).

RESULTS

Patients' occipital lobe WM Cho and Cr levels were 6.0% and 4.6% higher than controls', respectively (Cho, d = 0.37, p = 0.04; Cr, d = 0.63, p = 0.03). The same findings, i.e., higher patients' occipital lobe WM Cho and Cr (both p = 0.01), but with larger percent differences (Cho, 8.6%; Cr, 6.3%) and effect sizes (Cho, d = 0.52; Cr, d = 0.88) were found in the comparison of non-recovered patients to their matched controls. For the lobar WM Cho and Cr comparisons without statistical significance (frontal, parietal, temporal), unidirectional effect sizes were observed (Cho, d = 0.07 - 0.37; Cr, d = 0.27 - 0.63). No differences were found in any metabolite in any lobe in the comparison between recovered patients and their matched controls. In the regional analyses, no differences in metabolite levels were found in any GM or WM region, but all WM regions (posterior, frontal, corona radiata, and the genu, body, and splenium of the corpus callosum) exhibited unidirectional effect sizes for Cho and Cr (Cho, d = 0.03 - 0.34; Cr, d = 0.16 - 0.51).

CONCLUSIONS

We replicated findings of diffuse WM injury, which correlated with clinical outcome (supporting H1-H2, H4). These findings, however, were among the glial markers Cho and Cr, not the neuronal marker NAA (not supporting H3). No differences were found in regional GM and WM metabolite levels (supporting H5-H6), nor in putaminal mI (not supporting H7). Unidirectional effect sizes of higher patients' Cho and Cr within all WM analyses suggest widespread injury, and are in line with the conclusion from the previous publications, i.e., that detection of WM injury may be more dependent upon sensitivity of the 1H MRS technique than on the selection of specific regions. The findings lend further support to the corollary that clinic-ready 1H MRS biomarkers for mTBI may best be achieved by using high signal-to-noise-ratio single-voxels placed anywhere within WM. The biochemical signature of the injury, however, may differ and therefore absolute levels, rather than ratios may be preferred. Future replication efforts should further test the generalizability of these findings.

Effects of Creatine Supplementation on Brain Function and Health

While the vast majority of research involving creatine supplementation has focused on skeletal muscle, there is a small body of accumulating research that has focused on creatine and the brain. Preliminary studies indicate that creatine supplementation (and guanidinoacetic acid; GAA) has the ability to increase brain creatine content in humans. Furthermore, creatine has shown some promise for attenuating symptoms of concussion, mild traumatic brain injury and depression but its effect on neurodegenerative diseases appears to be lacking. The purpose of this narrative review is to summarize the current body of research pertaining to creatine supplementation on total creatine and phophorylcreatine (PCr) content, explore GAA as an alternative or adjunct to creatine supplementation on brain creatine uptake, assess the impact of creatine on cognition with a focus on sleep deprivation, discuss the effects of creatine supplementation on a variety of neurological and mental health conditions, and outline recent advances on creatine supplementation as a neuroprotective supplement following traumatic brain injury or concussion.

Microenvironmental Variations After Blood-Brain Barrier Breakdown in Traumatic Brain Injury

Traumatic brain injury (TBI) is linked to several pathologies. The blood-brain barrier (BBB) breakdown is considered to be one of the initial changes. Further, the microenvironmental alteration following TBI-induced BBB breakdown can be multi-scaled, constant, and dramatic. The microenvironmental variations after disruption of BBB includes several pathological changes, such as cerebral blood flow (CBF) alteration, brain edema, cerebral metabolism imbalances, and accumulation of inflammatory molecules. The modulation of the microenvironment presents attractive targets for TBI recovery, such as reducing toxic substances, inhibiting inflammation, and promoting neurogenesis. Herein, we briefly review the pathological alterations of the microenvironmental changes following BBB breakdown and outline potential interventions for TBI recovery based on microenvironmental modulation.

Repeated 31P-MRS in severe traumatic brain injury: Insights into cerebral energy status and altered metabolism

Phosphorous magnetic resonance spectroscopy (31P-MRS) is suited to non-invasively investigate energy metabolism and to detect molecules containing phosphorus in the human brain. The aim of this longitudinal study was to perform 31P-MRS at two different time points (within 72 hours and between day 10-14) after severe traumatic brain injury (sTBI) to reveal alterations in cerebral energy metabolism. Twenty-six ventilated sTBI patients, aged between 20 to 75 years, with a median initial GCS of 5 were prospectively analyzed. 31P-MRS data of the structurally more affected side were compared to data from contralateral normal appearing areas and to data of age- and gender-matched healthy controls. There were no significant intraindividual differences between the lesioned and the less affected side at either of time points. In the acute phase, PCr/ATP and PCr/Pi were significantly elevated whereas PME/PDE and Pi/ATP were significantly decreased in contrast to healthy controls. In the subacute phase these differences gradually dissipated, remaining lower Pi/ATP ratio, and only partly altered levels of PCr/Pi and PME/PDE. Our data affirm that cerebral metabolism is globally altered after sTBI, demonstrating the diffuse impairment of brain bioenergetics at multiple levels, with resultant developments in terms of time.

Translational neuroimaging in mild traumatic brain injury

Traumatic brain injuries (TBIs) are common with an estimated 27.1 million cases per year. Approximately 80% of TBIs are categorized as mild TBI (mTBI) based on initial symptom presentation. While in most individuals, symptoms resolve within days to weeks, in some, symptoms become chronic. Advanced neuroimaging has the potential to characterize brain morphometric, microstructural, biochemical, and metabolic abnormalities following mTBI. However, translational studies are needed for the interpretation of neuroimaging findings in humans with respect to the underlying pathophysiological processes, and, ultimately, for developing novel and more targeted treatment options. In this review, we introduce the most commonly used animal models for the study of mTBI. We then summarize the neuroimaging findings in humans and animals after mTBI and, wherever applicable, the translational aspects of studies available today. Finally, we highlight the importance of translational approaches and outline future perspectives in the field of translational neuroimaging in mTBI.

Cerebral Energy Status and Altered Metabolism in Early Severe TBI: First Results of a Prospective 31P-MRS Feasibility Study

OBJECTIVE

Severe traumatic brain injury (sTBI) represents a serious public health issue with high morbidity and mortality. Neuroimaging plays a crucial role in the evaluation of sTBI patients. Phosphorous magnetic resonance spectroscopy (³¹P-MRS) is an imaging technique for evaluation of energy metabolites. The aim of this study is to evaluate the feasibility and the diagnostic potential of ultra-early ³¹P-MRS to detect changes in cerebral energy metabolism in sTBI.

METHODS

Adult patients with sTBI presenting with GCS ≤ 8 being eligible for MRI were prospectively included in the study and MRI was performed within 72 h after trauma. Imaging was performed using a 3 Tesla MRI. ³¹P-MRS data from the structurally affected side were compared to data from normal appearing contralateral areas symmetrically to the location of the traumatic lesions, and to data of matched healthy controls.

RESULTS

Ten sTBI patients (3 female, 7 male), aged between 20 and 75 years, with a mean initial GCS of 6 were analyzed. MRI was performed 61 h (mean, range 37-71 h) after trauma. Statistical analysis revealed no significant differences between the lesioned side and contralaterally. An increased PCr/ATP ratio and a decreased PME/PDE ratio were present in structurally normal appearing, but traumatized tissue when compared to the healthy population, thus indicating significant differences in ATP resynthesis and membrane turnover (F (2,33), P = 0.005 and, P = 0.027, respectively).

CONCLUSION

³¹P-MRS could provide a better understanding of pertinent global changes in cerebral energy metabolism in sTBI patients under general anesthesia.

Lithium and the Interplay Between Telomeres and Mitochondria in Bipolar Disorder

Bipolar disorder is a severe psychiatric disorder which affects more than 1% of the world's population and is a leading cause of disability among young people. For the past 50 years, lithium has been the drug of choice for maintenance treatment of bipolar disorder due to its potent ability to prevent both manic and depressive episodes as well as suicide. However, though lithium has been associated with a multitude of effects within different cellular pathways and biological systems, its specific mechanism of action in stabilizing mood remains largely elusive. Mitochondrial dysfunction and telomere shortening have been implicated in both the pathophysiology of bipolar disorder and as targets of lithium treatment. Interestingly, it has in recent years become clear that these phenomena are intimately linked, partly through reactive oxygen species signaling and the subcellular translocation and non-canonical actions of telomerase reverse transcriptase. In this review, we integrate the current understanding of mitochondrial dysfunction, oxidative stress and telomere shortening in bipolar disorder with documented effects of lithium. Moreover, we propose that lithium's mechanism of action is intimately connected with the interdependent regulation of mitochondrial bioenergetics and telomere maintenance.

Pyruvate Dehydrogenase and Tricarboxylic Acid Cycle Enzymes Are Sensitive Targets of Traumatic Brain Injury Induced Metabolic Derangement

Using a closed-head impact acceleration model of mild or severe traumatic brain injury (mTBI or sTBI, respectively) in rats, we evaluated the effects of graded head impacts on the gene and protein expressions of pyruvate dehydrogenase (PDH), as well as major enzymes of mitochondrial tricarboxylic acid cycle (TCA). TBI was induced in anaesthetized rats by dropping 450 g from 1 (mTBI) or 2 m height (sTBI). After 6 h, 12 h, 24 h, 48 h, and 120 h gene expressions of enzymes and subunits of PDH. PDH kinases and phosphatases (PDK1-4 and PDP1-2, respectively), citrate synthase (CS), isocitrate dehydrogenase (IDH), oxoglutarate dehydrogenase (OGDH), succinate dehydrogenase (SDH), succinyl-CoA synthase (SUCLG), and malate dehydrogenase (MDH) were determined in whole brain extracts (n = 6 rats at each time for both TBI levels). In the same samples, the high performance liquid chromatographic (HPLC) determination of acetyl-coenzyme A (acetyl-CoA) and free coenzyme A (CoA-SH) was performed. Sham-operated animals (n = 6) were used as controls. After mTBI, the results indicated a general transient decrease, followed by significant increases, in PDH and TCA gene expressions. Conversely, permanent PDH and TCA downregulation occurred following sTBI. The inhibitory conditions of PDH (caused by PDP1-2 downregulations and PDK1-4 overexpression) and SDH appeared to operate only after sTBI. This produced almost no change in acetyl-CoA and free CoA-SH following mTBI and a remarkable depletion of both compounds after sTBI. These results again demonstrated temporary or steady mitochondrial malfunctioning, causing minimal or profound modifications to energy-related metabolites, following mTBI or sTBI, respectively. Additionally, PDH and SDH appeared to be highly sensitive to traumatic insults and are deeply involved in mitochondrial-related energy metabolism imbalance.

A Systematic Review of Closed Head Injury Models of Mild Traumatic Brain Injury in Mice and Rats

Mild TBI (mTBI) is a significant health concern. Animal models of mTBI are essential for understanding mechanisms, and pathological outcomes, as well as to test therapeutic interventions. A variety of closed head models of mTBI that incorporate different aspects (i.e., biomechanics) of the mTBI have been reported. The aim of the current review was to compile a comprehensive list of the closed head mTBI rodent models, along with the common data elements, and outcomes, with the goal to summarize the current state of the field. Publications were identified from a search of PubMed and Web of Science and screened for eligibility following PRISMA guidelines. Articles were included that were closed head injuries in which the authors classified the injury as mild in rats or mice. Injury model and animal-specific common data elements, as well as behavioral and histological outcomes, were collected and compiled from a total of 402 articles. Our results outline the wide variety of methods used to model mTBI. We also discovered that female rodents and both young and aged animals are under-represented in experimental mTBI studies. Our findings will aid in providing context comparing the injury models and provide a starting point for the selection of the most appropriate model of mTBI to address a specific hypothesis. We believe this review will be a useful starting place for determining what has been done and what knowledge is missing in the field to reduce the burden of mTBI.

Protection Before Impact: the Potential Neuroprotective Role of Nutritional Supplementation in Sports-Related Head Trauma

Even in the presence of underreporting, sports-related concussions/mild traumatic brain injuries (mTBI) are on the rise. In the absence of proper diagnosis, an athlete may return to play prior to full recovery, increasing the risk of second-impact syndrome or protracted symptoms. Recent evidence has demonstrated that sub-concussive impacts, those sustained routinely in practice and competition, result in a quantifiable pathophysiological response and the accumulation of both concussive and sub-concussive impacts sustained over a lifetime of sports participation may lead to long-term neurological impairments and an increased risk of developing neurodegenerative diseases. The pathophysiological, neurometabolic, and neurochemical cascade that initiates subsequent to the injury is complex and involves multiple mechanisms. While pharmaceutical treatments may target one mechanism, specific nutrients and nutraceuticals have been discovered to impact several pathways, presenting a broader approach. Several studies have demonstrated the neuroprotective effect of nutritional supplementation in the treatment of mTBI. However, given that many concussions go unreported and sub-concussive impacts result in a pathophysiological response that, too, may contribute to long-term brain health, protection prior to impact is warranted. This review discusses the current literature regarding the role of nutritional supplements that, when provided before mTBI and traumatic brain injury, may provide neurological protection.

Assessing Metabolism and Injury in Acute Human Traumatic Brain Injury with Magnetic Resonance Spectroscopy: Current and Future Applications

Traumatic brain injury (TBI) triggers a series of complex pathophysiological processes. These include abnormalities in brain energy metabolism; consequent to reduced tissue pO₂ arising from ischemia or abnormal tissue oxygen diffusion, or due to a failure of mitochondrial function. In vivo magnetic resonance spectroscopy (MRS) allows non-invasive interrogation of brain tissue metabolism in patients with acute brain injury. Nuclei with “spin,” e.g., ¹H, ³¹P, and ¹³C, are detectable using MRS and are found in metabolites at various stages of energy metabolism, possessing unique signatures due to their chemical shift or spin–spin interactions (J-coupling). The most commonly used clinical MRS technique, ¹H MRS, uses the great abundance of hydrogen atoms within molecules in brain tissue. Spectra acquired with longer echo-times include N-acetylaspartate (NAA), creatine, and choline. NAA, a marker of neuronal mitochondrial activity related to adenosine triphosphate (ATP), is reported to be lower in patients with TBI than healthy controls, and the ratio of NAA/creatine at early time points may correlate with clinical outcome. ¹H MRS acquired with shorter echo times produces a more complex spectrum, allowing detection of a wider range of metabolites.³¹ P MRS detects high-energy phosphate species, which are the end products of cellular respiration: ATP and phosphocreatine (PCr). ATP is the principal form of chemical energy in living organisms, and PCr is regarded as a readily mobilized reserve for its replenishment during periods of high utilization. The ratios of high-energy phosphates are thought to represent a balance between energy generation, reserve and use in the brain. In addition, the chemical shift difference between inorganic phosphate and PCr enables calculation of intracellular pH.¹³ C MRS detects the ¹³C isotope of carbon in brain metabolites. As the natural abundance of ¹³C is low (1.1%), ¹³C MRS is typically performed following administration of ¹³C-enriched substrates, which permits tracking of the metabolic fate of the infused ¹³C in the brain over time, and calculation of metabolic rates in a range of biochemical pathways, including glycolysis, the tricarboxylic acid cycle, and glutamate–glutamine cycling. The advent of new hyperpolarization techniques to transiently boost signal in ¹³C-enriched MRS in vivo studies shows promise in this field, and further developments are expected.

Effects of Blast Exposure on Subjective and Objective Sleep Measures in Combat Veterans with and without PTSD

STUDY OBJECTIVES

This study examined the extent to which self-reported exposure to blast during deployment to Iraq and Afghanistan affects subjective and objective sleep measures in service members and veterans with and without posttraumatic stress disorder (PTSD).

METHODS

Seventy-one medication-free service members and veterans (mean age = 29.47 ± 5.76 years old; 85% men) completed self-report sleep measures and overnight polysomnographic studies. Four multivariate analyses of variance (MANOVAs) were conducted to examine the impact of blast exposure and PTSD on subjective sleep measures, measures of sleep continuity, non-rapid eye movement (NREM) sleep parameters, and rapid eye movement (REM) sleep parameters.

RESULTS

There was no significant Blast × PTSD interaction on subjective sleep measures. Rather, PTSD had a main effect on insomnia severity, sleep quality, and disruptive nocturnal behaviors. There was no significant Blast × PTSD interaction, nor were there main effects of PTSD or Blast on measures of sleep continuity and NREM sleep. A significant PTSD × Blast interaction effect was found for REM fragmentation.

CONCLUSIONS

The results suggest that, although persistent concussive symptoms following blast exposure are associated with sleep disturbances, self-reported blast exposure without concurrent symptoms does not appear to contribute to poor sleep quality, insomnia, and disruptive nocturnal disturbances beyond the effects of PTSD. Reduced REM sleep fragmentation may be a sensitive index of the synergetic effects of both psychological and physical insults.

Study of neurometabolic and behavioral alterations in rodent model of mild traumatic brain injury: a pilot study

Mild traumatic brain injury (mTBI) is the most common form of TBI (70-90%) with consequences of anxiety-like behavioral alterations in approximately 23% of mTBI cases. This study aimed to assess whether mTBI-induced anxiety-like behavior is a consequence of neurometabolic alterations. mTBI was induced using a weight drop model to simulate mild human brain injury in rodents. Based on injury induction and dosage of anesthesia, four animal groups were included in this study: (i) injury with anesthesia (IA); (ii) sham1 (injury only, IO); (iii) sham2 (only anesthesia, OA); and (iv) control rats. After mTBI, proton magnetic resonance spectroscopy (¹ H-MRS) and neurobehavioral analysis were performed in these groups. At day 5, reduced taurine (Tau)/total creatine (tCr, creatine and phosphocreatine) levels in cortex were observed in the IA and IO groups relative to the control. These groups showed mTBI-induced anxiety-like behavior with normal cognition at day 5 post-injury. An anxiogenic effect of repeated dosage of anesthesia in OA rats was observed with normal Tau/tCr levels in rat cortex, which requires further examination. In conclusion, this mTBI model closely mimics human concussion injury with anxiety-like behavior and normal cognition. Reduced cortical Tau levels may provide a putative neurometabolic basis of anxiety-like behavior following mTBI.

Metabolic, enzymatic and gene involvement in cerebral glucose dysmetabolism after traumatic brain injury

In this study, the metabolic, enzymatic and gene changes causing cerebral glucose dysmetabolism following graded diffuse traumatic brain injury (TBI) were evaluated. TBI was induced in rats by dropping 450g from 1 (mild TBI; mTBI) or 2m height (severe TBI; sTBI). After 6, 12, 24, 48, and 120h gene expressions and enzymatic activities of glycolysis and pentose phosphate pathway (PPP) enzymes, and levels of lactate, ATP, ADP, ATP/ADP (indexing mitochondrial phosphorylating capacity), NADP(+), NADPH and GSH were determined in whole brain extracts (n=9 rats at each time for both TBI levels). Sham-operated animals (n=9) were used as controls. Results demonstrated that mTBI caused a late increase (48-120h post injury) of glycolytic gene expression and enzymatic activities, concomitantly with mitochondrial functional recovery (ATP and ATP/ADP normalization). No changes in lactate and PPP genes and enzymes, were accompanied by transient decrease in GSH, NADP(+), NADPH and NADPH/NADP(+). Animals following sTBI showed early increase (6-24h post injury) of glycolytic gene expression and enzymatic activities, occurring during mitochondrial malfunctioning (50% decrease in ATP and ATP/ADP). Higher lactate and lower GSH, NADP(+), NADPH, NADPH/NADP(+) than controls were recorded at anytime post injury (p<0.01). Both TBI levels caused metabolic and gene changes affecting glucose metabolism. Following mTBI, increased glucose flux through glycolysis is coupled to mitochondrial glucose oxidation. "True" hyperglycolysis occurs only after sTBI, where metabolic changes, caused by depressed mitochondrial phosphorylating capacity, act on genes causing net glycolytic flux increase uncoupled from mitochondrial glucose oxidation.

Impact Acceleration Model of Diffuse Traumatic Brain Injury

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

Diffusion tensor imaging and magnetic resonance spectroscopy in traumatic brain injury: a review of recent literature

Concussion is the most common form of traumatic brain injury (TBI), but diagnosis remains controversial because the brain appears quite normal in conventional computed tomography and magnetic resonance imaging (MRI). These conventional tools are not sensitive enough to detect diffuse traumatic axonal injury, and cannot depict aberrations in mild TBIs. Advanced MRI modalities including diffusion tensor imaging (DTI), and magnetic resonance spectroscopy (MRS), make it possible to detect brain injuries in TBI. The purpose of this review is to provide the latest information regarding the visualization and quantification of important abnormalities in TBI and new insights into their clinical significance. Advanced imaging modalities allow the discovery of biomarkers of injury and the detection of changes in brain injury over time. Such tools will likely be used to evaluate treatment efficacy in research. Combining multiple imaging modalities would not only provide greater insight into the underlying physiological changes in TBI, but also improve diagnostic accuracy in predicting outcomes. In this review we present evidence of brain abnormalities in TBI based on investigations using MRI, including DTI and MRS. Our review provides a summary of some of the important studies published from 2002 to 2012 on the topic of MRI findings in head trauma. With the growing realization that even mild head injury can lead to neurocognitive deficits, medical imaging has assumed preeminence for detecting abnormalities associated with TBI. Advanced MRI modalities such as DTI and MRS have an important role in the diagnosis of lesions for TBI patients.

Blast Overpressure Waves Induce Transient Anxiety and Regional Changes in Cerebral Glucose Metabolism and Delayed Hyperarousal in Rats

Physiological alterations, anxiety, and cognitive disorders are strongly associated with blast-induced traumatic brain injury (blast TBI), and are common symptoms in service personnel exposed to blasts. Since 2006, 25,000–30,000 new TBI cases are diagnosed annually in U.S. Service members; increasing evidence confirms that primary blast exposure causes diffuse axonal injury and is often accompanied by altered behavioral outcomes. Behavioral and acute metabolic effects resulting from blast to the head in the absence of thoracic contributions from the periphery were examined, following a single blast wave directed to the head of male Sprague-Dawley rats protected by a lead shield over the torso. An 80 psi head blast produced cognitive deficits that were detected in working memory. Blast TBI rats displayed increased anxiety as determined by elevated plus maze at day 9 post-blast compared to sham rats; blast TBI rats spent significantly more time than the sham controls in the closed arms (p < 0.05; n = 8–11). Interestingly, anxiety symptoms were absent at days 22 and 48 post-blast. Instead, blast TBI rats displayed increased rearing behavior at day 48 post-blast compared to sham rats. Blast TBI rats also exhibited suppressed acoustic startle responses, but similar pre-pulse inhibition at day 15 post-blast compared to sham rats. Acute physiological alterations in cerebral glucose metabolism were determined by positron emission tomography 1 and 9 days post-blast using ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG). Global glucose uptake in blast TBI rat brains increased at day 1 post-blast (p < 0.05; n = 4–6) and returned to sham levels by day 9. Our results indicate a transient increase in cerebral metabolism following a blast injury. Markers for reactive astrogliosis and neuronal damage were noted by immunoblotting motor cortex tissue from day 10 post-blast in blast TBI rats compared to sham controls (p < 0.05; n = 5–6).

Prognostic factor from MR spectroscopy in rat with astrocytic tumour during radiation therapy

OBJECTIVE

To investigate the relationship between the tumour volume and metabolic rates of astrocytic tumours using MR spectroscopy (MRS) during radiation therapy (RT).

METHODS

12 healthy male Sprague-Dawley® rats (Sprague-Dawley Animal Company, Madison, WI) were used, and a tumour model was created through injecting C6 tumour cells into the right caudate nuclei of the rats. Tumours grew for 18 days after the injection and before the imaging study and radiation treatment. MRS was performed with two-dimensional multivoxel point-resolved spectroscopy sequence using a GE Signa VH/i 3.0-T MR scanner (GE Healthcare, Milwaukee, WI) equipped with rat-special coil. RT was given on the 19th day with a dose of 4 Gy in one single fraction. The image examinations were performed before RT, and on the 4th, 10th, 14th and 20th days after treatment, respectively. GE FuncTool software package (GE Healthcare) was used for post-processing of spectrum.

RESULTS

Metabolic ratios of serial MRS decrease progressively with time after RT. Choline-containing components (Cho)/creatine and creatine phosphate (Cr) ratios immediately prior to RT differed significantly from those on the 10th, 14th and 20th days after RT; both Cho/N-acetyl aspartate (NAA) ratios and NAA/Cr ratios immediately prior to RT differed significantly from those on the 14th and 20th days after RT. A positive correlation between changes of tumour volume and changes of Cho/Cr, lipid and lactate/Cr and glutamate plus glutamine/Cr ratio was observed on the 4th day after RT.

CONCLUSION

MRS provides potential in monitoring tumour response during RT, and the imaging biomarkers predict the response of astrocytic tumours to treatment.

ADVANCES IN KNOWLEDGE

MRS is combined with both tumour size and Ki-67 labelling index to access tumour response to radiation.

S100B and Glial Fibrillary Acidic Protein as Indexes to Monitor Damage Severity in an In Vitro Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading and rising cause of death and disability worldwide. There is great interest in S100B and Glial Fibrillary Acid Protein (GFAP) as candidate biomarkers of TBI for diagnosis, triage, prognostication and drug development. However, conflicting results especially on S100B hamper their routine application in clinical practice. To try to address this question, we mimicked TBI damage utilizing a well-validated, simplified in vitro model of graded stretch injury induced in rat organotypic hippocampal slice cultures (OHSC). Different severities of trauma, from mild to severe, have been tested by using an equi-biaxial stretch of the OHSCs at a specified Lagrangian strain of 0 (controls), 5, 10, 20 and 50 %. OHSC were analysed at 3, 6, 18, 24, 48 and 96 h post-injury. Cell death, gene expressions and release into the culture medium of S100B and GFAP were determined at each time point. Gene expression and release of S100B slightly increased only in 20 and 50 % stretched OHSC. GFAP over-expression occurred in 10, 20 and 50 % and was inversely correlated with time post-injury. GFAP release significantly increased with time at any level of injury (p < 0.01 with respect to controls). Consequently, the total amount of GFAP released showed a strong linear relationship with the severity of injury (R(2) = 0.7662; p < 0.001). Under these experimental conditions, S100B seems to be useful in diagnosing only moderate to severe TBI-like injuries. Differently, GFAP demonstrates adequate biomarker requisites since its cellular release is affected by all grades of injury severity.

Systemic, local, and imaging biomarkers of brain injury: more needed, and better use of those already established?

Much progress has been made over the past two decades in the treatment of severe acute brain injury, including traumatic brain injury and subarachnoid hemorrhage, resulting in a higher proportion of patients surviving with better outcomes. This has arisen from a combination of factors. These include improvements in procedures at the scene (pre-hospital) and in the hospital emergency department, advances in neuromonitoring in the intensive care unit, both continuously at the bedside and intermittently in scans, evolution and refinement of protocol-driven therapy for better management of patients, and advances in surgical procedures and rehabilitation. Nevertheless, many patients still experience varying degrees of long-term disabilities post-injury with consequent demands on carers and resources, and there is room for improvement. Biomarkers are a key aspect of neuromonitoring. A broad definition of a biomarker is any observable feature that can be used to inform on the state of the patient, e.g., a molecular species, a feature on a scan, or a monitoring characteristic, e.g., cerebrovascular pressure reactivity index. Biomarkers are usually quantitative measures, which can be utilized in diagnosis and monitoring of response to treatment. They are thus crucial to the development of therapies and may be utilized as surrogate endpoints in Phase II clinical trials. To date, there is no specific drug treatment for acute brain injury, and many seemingly promising agents emerging from pre-clinical animal models have failed in clinical trials. Large Phase III studies of clinical outcomes are costly, consuming time and resources. It is therefore important that adequate Phase II clinical studies with informative surrogate endpoints are performed employing appropriate biomarkers. In this article, we review some of the available systemic, local, and imaging biomarkers and technologies relevant in acute brain injury patients, and highlight gaps in the current state of knowledge.

Cerebrolysin improves cognitive performance in rats after mild traumatic brain injury

OBJECT

Long-term memory deficits occur after mild traumatic brain injuries (mTBIs), and effective treatment modalities are currently unavailable. Cerebrolysin, a peptide preparation mimicking the action of neurotrophic factors, has beneficial effects on neurodegenerative diseases and brain injuries. The present study investigated the long-term effects of Cerebrolysin treatment on cognitive function in rats after mTBI.

METHODS

Rats subjected to closed-head mTBI were treated with saline (n = 11) or Cerebrolysin (2.5 ml/kg, n = 11) starting 24 hours after injury and then daily for 28 days. Sham animals underwent surgery without injury (n = 8). To evaluate cognitive function, the modified Morris water maze (MWM) test and a social odor-based novelty recognition task were performed after mTBI. All rats were killed on Day 90 after mTBI, and brain sections were immunostained for histological analyses of amyloid precursor protein (APP), astrogliosis, neuroblasts, and neurogenesis.

RESULTS

Mild TBI caused long-lasting cognitive memory deficits in the MWM and social odor recognition tests up to 90 days after injury. Compared with saline treatment, Cerebrolysin treatment significantly improved both long-term spatial learning and memory in the MWM test and nonspatial recognition memory in the social odor recognition task up to 90 days after mTBI (p < 0.05). Cerebrolysin significantly increased the number of neuroblasts and promoted neurogenesis in the dentate gyrus, and it reduced APP levels and astrogliosis in the corpus callosum, cortex, dentate gyrus, CA1, and CA3 regions (p < 0.05).

CONCLUSIONS

These results indicate that Cerebrolysin treatment of mTBI improves long-term cognitive function, and this improvement may be partially related to decreased brain APP accumulation and astrogliosis as well as increased neuroblasts and neurogenesis.

Combat-related blast exposure and traumatic brain injury influence brain glucose metabolism during REM sleep in military veterans

Traumatic brain injury (TBI), a signature wound of Operations Enduring and Iraqi Freedom, can result from blunt head trauma or exposure to a blast/explosion. While TBI affects sleep, the neurobiological underpinnings between TBI and sleep are largely unknown. To examine the neurobiological underpinnings of this relationship in military veterans, [(18)F]-fluorodeoxyglucose positron emission tomography (FDG PET) was used to compare mTBI-related changes in relative cerebral metabolic rate of glucose (rCMRglc) during wakefulness, Rapid Eye Movement (REM) sleep, and non-REM (NREM) sleep, after adjusting for the effects of posttraumatic stress (PTS). Fourteen veterans with a history of blast exposure and/or mTBI (B/mTBI) (age 27.5±3.9) and eleven veterans with no history (No B/mTBI) (age 28.1±4.3) completed FDG PET studies during wakefulness, REM sleep, and NREM sleep. Whole-brain analyses were conducted using Statistical Parametric Mapping (SPM8). Between group comparisons revealed that B/mTBI was associated with significantly lower rCMRglc during wakefulness and REM sleep in the amygdala, hippocampus, parahippocampal gyrus, thalamus, insula, uncus, culmen, visual association cortices, and midline medial frontal cortices. These results suggest that alterations in neurobiological networks during wakefulness and REM sleep subsequent to B/mTBI exposure may contribute to chronic sleep disturbances and differ in individuals with acute symptoms.

Brain core temperature of patients with mild traumatic brain injury as assessed by DWI-thermometry

Introduction

The aim of this study was to assess the brain core temperature of patients with mild traumatic brain injury (mTBI) using a noninvasive temperature measurement technique based on the diffusion coefficient of the cerebrospinal fluid.

Methods

This retrospective study used the data collected from April 2008 to June 2011. The patient group comprised 20 patients with a Glasgow Coma Scale score of 14 or 15 who underwent magnetic resonance imaging within 30 days after head trauma. The normal control group comprised 14 subjects who volunteered for a brain checkup (known in Japan as “brain dock”). We compared lateral ventricular (LV) temperature between patient and control groups. Follow-up studies were performed for four patients.

Results

LV temperature measurements were successfully performed for both patients and controls. Mean (±standard deviation) measured LV temperature was 36.9 ± 1.5 °C in patients, 38.7 ± 1.8 °C in follow-ups, and 37.9 ± 1.2 °C in controls, showing a significant difference between patients and controls (P = 0.017). However, no significant difference was evident between patients and follow-ups (P = 0.595) or between follow-ups and controls (P = 0.465).

Conclusions

A reduction in brain core temperature was observed in patients with mTBI, possibly due to a global decrease in metabolism.

Relative metabolite concentrations and ratios determined by use of 3-T region-specific proton magnetic resonance spectroscopy of the brain of healthy Beagles

OBJECTIVE

To determine relative concentrations of selected major brain tissue metabolites and their ratios and lobar variations by use of 3-T proton (hydrogen 1 [(1)H]) magnetic resonance spectroscopy (MRS) of the brain of healthy dogs.

ANIMALS

10 healthy Beagles.

PROCEDURES

3-T (1)H MRS at echo times of 144 and 35 milliseconds was performed on 5 transverse slices and 1 sagittal slice of representative brain lobe regions. Intravoxel parenchyma was classified as white matter, gray matter, or mixed (gray and white) and analyzed for relative concentrations (in arbitrary units) of N-acetylaspartate (NAA), choline, and creatine (ie, height at position of peak on MRS graph) as well as their ratios (NAA-to-choline, NAA-to-creatine, and choline-to-creatine ratios). Peak heights for metabolites were compared between echo times. Peak heights for metabolites and their ratios were correlated and evaluated among matter types. Yield was calculated as interpretable voxels divided by available lobar voxels.

RESULTS

Reference ranges of the metabolite concentration ratios were determined at an echo time of 35 milliseconds (NAA-to-choline ratio, 1.055 to 2.224; NAA-to-creatine ratio, 1.103 to 2.161; choline-to-creatine ratio, 0.759 to 1.332) and 144 milliseconds (NAA-to-choline ratio, 0.687 to 1.788; NAA-to-creatine ratio, 0.984 to 2.044; choline-to-creatine ratio, 0.828 to 1.853). Metabolite concentration ratios were greater in white matter than in gray matter. Voxel yields ranged from 43% for the temporal lobe to 100% for the thalamus.

CONCLUSIONS AND CLINICAL RELEVANCE

Metabolite concentrations and concentration ratios determined with 3-T (1)H MRS were not identical to those in humans and were determined for clinical and research investigations of canine brain disease.

Mild traumatic brain injury results in depressed cerebral glucose uptake: An (18)FDG PET study

Moderate to severe traumatic brain injury (TBI) in humans and rats induces measurable metabolic changes, including a sustained depression in cerebral glucose uptake. However, the effect of a mild TBI on brain glucose uptake is unclear, particularly in rodent models. This study aimed to determine the glucose uptake pattern in the brain after a mild lateral fluid percussion (LFP) TBI. Briefly, adult male rats were subjected to a mild LFP and positron emission tomography (PET) imaging with (18)F-fluorodeoxyglucose ((18)FDG), which was performed prior to injury and at 3 and 24 h and 5, 9, and 16 days post-injury. Locomotor function was assessed prior to injury and at 1, 3, 7, 14, and 21 days after injury using modified beam walk tasks to confirm injury severity. Histology was performed at either 10 or 21 days post-injury. Analysis of function revealed a transient impairment in locomotor ability, which corresponds to a mild TBI. Using reference region normalization, PET imaging revealed that mild LFP-induced TBI depresses glucose uptake in both the ipsilateral and contralateral hemispheres in comparison with sham-injured and naïve controls from 3 h to 5 days post-injury. Further, areas of depressed glucose uptake were associated with regions of glial activation and axonal damage, but no measurable change in neuronal loss or gross tissue damage was observed. In conclusion, we show that mild TBI, which is characterized by transient impairments in function, axonal damage, and glial activation, results in an observable depression in overall brain glucose uptake using (18)FDG-PET.

Postconcussion syndrome and mild head injury: the role of early diagnosis using neuropsychological tests and functional magnetic resonance/spectroscopy

OBJECTIVE

Postconcussion syndrome (PCS) is usually underestimated in cases of mild head injury (MHI). It is one of the most common causes of physical, cognitive, and psychomotor disturbances that affect the quality of life, work, and social reintegration of individuals. Until now, we did not have evidence of structural abnormalities shown by traditional imaging methods. We describe a series of instruments that confirm PCS with satisfactory evidence.

METHODS

We conducted a clinical prospective study of 19 adult patients selected from a pool of 320 adults who had MHI. The cognitive, executive, and memory functions of subjects were examined within the first 72 hours using neuropsychological tests. These results were analyzed with neurological examination and functional MR/spectroscopy.

RESULTS

Neurobehavioral alterations were found in 47% of cases, with posttraumatic amnesia. Around 55% of subjects experienced physical disturbances such as headache and postural vertigo due to PCS. The spectroscopy reports revealed neurometabolite disturbances in 54% of cases, particularly N-acetylaspartate (Naa) and the Naa/lactate ratio in the frontal lobe. We observed a relationship between metabolite disturbances in spectroscopy and the digit span backward test (P = .045).

CONCLUSIONS

This first diagnostic strategy supports with scientific evidence the presence of PCS in MHI. We identified physical and neuropsychological abnormalities from this group, affecting the areas of memory and learning. Evidence of neurometabolite disturbances were found specifically in the frontal lobe. It is necessary to complete comparative follow-up for an extended period of time. The neuropsychological and spectroscopy tests allow us to confirm the diagnosis of a syndrome that is usually neglected.

Myalgic encephalomyelitis/chronic fatigue syndrome and encephalomyelitis disseminata/multiple sclerosis show remarkable levels of similarity in phenomenology and neuroimmune characteristics

BACKGROUND

'Encephalomyelitis disseminata' (multiple sclerosis) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) are both classified as diseases of the central nervous system by the World Health Organization. This review aims to compare the phenomenological and neuroimmune characteristics of MS with those of ME/CFS.

DISCUSSION

There are remarkable phenomenological and neuroimmune overlaps between both disorders. Patients with ME/CFS and MS both experience severe levels of disabling fatigue and a worsening of symptoms following exercise and resort to energy conservation strategies in an attempt to meet the energy demands of day-to-day living. Debilitating autonomic symptoms, diminished cardiac responses to exercise, orthostatic intolerance and postural hypotension are experienced by patients with both illnesses. Both disorders show a relapsing-remitting or progressive course, while infections and psychosocial stress play a large part in worsening of fatigue symptoms. Activated immunoinflammatory, oxidative and nitrosative (O+NS) pathways and autoimmunity occur in both illnesses. The consequences of O+NS damage to self-epitopes is evidenced by the almost bewildering and almost identical array of autoantibodies formed against damaged epitopes seen in both illnesses. Mitochondrial dysfunctions, including lowered levels of ATP, decreased phosphocreatine synthesis and impaired oxidative phosphorylation, are heavily involved in the pathophysiology of both MS and ME/CFS. The findings produced by neuroimaging techniques are quite similar in both illnesses and show decreased cerebral blood flow, atrophy, gray matter reduction, white matter hyperintensities, increased cerebral lactate and choline signaling and lowered acetyl-aspartate levels.

SUMMARY

This review shows that there are neuroimmune similarities between MS and ME/CFS. This further substantiates the view that ME/CFS is a neuroimmune illness and that patients with MS are immunologically primed to develop symptoms of ME/CFS.

Cortical hypoexcitation defines neuronal responses in the immediate aftermath of traumatic brain injury

Traumatic brain injury (TBI) from a blow to the head is often associated with complex patterns of brain abnormalities that accompany deficits in cognitive and motor function. Previously we reported that a long-term consequence of TBI, induced with a closed-head injury method modelling human car and sporting accidents, is neuronal hyper-excitation in the rat sensory barrel cortex that receives tactile input from the face whiskers. Hyper-excitation occurred only in supra-granular layers and was stronger to complex than simple stimuli. We now examine changes in the immediate aftermath of TBI induced with same injury method. At 24 hours post-trauma significant sensorimotor deficits were observed and characterisation of the cortical population neuronal responses at that time revealed a depth-dependent suppression of neuronal responses, with reduced responses from supragranular layers through to input layer IV, but not in infragranular layers. In addition, increased spontaneous firing rate was recorded in cortical layers IV and V. We postulate that this early post-injury suppression of cortical processing of sensory input accounts for immediate post-trauma sensory morbidity and sets into train events that resolve into long-term cortical hyper-excitability in upper sensory cortex layers that may account for long-term sensory hyper-sensitivity in humans with TBI.

Impact of reduced k-space acquisition on pathologic detectability for volumetric MR spectroscopic imaging

PURPOSE

To assess the impact of accelerated acquisitions on the spectral quality of volumetric magnetic resonance spectroscopic imaging (MRSI) and to evaluate their ability in detecting metabolic changes with mild injury.

MATERIALS AND METHODS

The implementation of a generalized autocalibrating partially parallel acquisition (GRAPPA) method for a high-resolution whole-brain echo planar SI (3D-EPSI) sequence is first described and the spectral accuracy of the GRAPPA-EPSI method is investigated using lobar and voxel-based analyses for normal subjects and patients with mild traumatic brain injuries (mTBI). The performance of GRAPPA was compared with that of fully encoded EPSI for five datasets collected from normal subjects at the same scanning session, as well as on 45 scans (20 normal subjects and 25 mTBI patients) for which the reduced k-space sampling was simulated. For comparison, a central k-space lower-resolution 3D-EPSI acquisition was also simulated. Differences in individual metabolites and metabolite ratio distributions of the mTBI group relative to those of age-matched control subjects were statistically evaluated using analyses divided into hemispheric brain lobes and tissue types.

RESULTS

GRAPPA-EPSI with 16-minute scan time yielded robust and similar results in terms of MRSI quantitation, spectral fitting, and accuracy with that of fully sampled 3D-EPSI acquisitions and was more accurate than central k-space acquisition. Primary findings included high correlations (accuracy of 92.6%) between the GRAPPA and fully sampled results.

CONCLUSION

Although the reduced encoding method is associated with lower signal-to-noise ratio (SNR) that impacts the quality of spectral analysis, the use of the parallel imaging method can lead to the same diagnostic outcomes as the fully sampled data when using the sensitivity-limited volumetric MRSI.

Examining the neural impact of pediatric concussion: a scoping review of multimodal and integrative approaches using functional and structural MRI techniques

PURPOSE OF REVIEW

This study presents the findings from a scoping review of recent, original research investigating changes in brain structure and/or function following pediatric concussion or mild traumatic brain injury (mTBI) using MRI and functional MRI techniques.

RECENT FINDINGS

Our scoping review identified only five studies, two of which were focused specifically on sports-related concussion. A common finding across studies was that traditional structural methods such as anatomical T1, T2, and even susceptibility-weighted MRI failed to reveal abnormalities in brain structure following pediatric concussion/mTBI. Although data suggest alterations in brain function associated with concussion, correlation with changes in performance is inconsistently found, possibly because of the use of compensatory cerebral mechanisms or alternate pathways while the brain is still dysfunctional.

SUMMARY

In conclusion, the literature describing neuroimaging investigations of pediatric concussion is too scarce to allow the formulation of definitive conclusions regarding the impact of concussion on the developing brain. There is a dire need for longitudinal, multisite investigations focused on a wider age range and recovery period.

Concussion in athletics: ongoing clinical and brain imaging research controversies

Concussion, the most common form of traumatic brain injury, proves to be increasingly complex and not mild in nature as its synonymous term mild traumatic brain injury (mTBI) would imply. Despite the increasing occurrence and prevalence of mTBI there is no universally accepted definition and conventional brain imaging techniques lack the sensitivity to detect subtle changes it causes. Moreover, clinical management of sports induced mild traumatic brain injury has not changed much over the past decade. Advances in neuroimaging that include electroencephalography (EEG), functional magnetic resonance imaging (fMRI), resting-state functional connectivity, diffusion tensor imaging (DTI) and magnetic resonance spectroscopy (MRS) offer promise in aiding research into understanding the complexities and nuances of mTBI which may ultimately influence clinical management of the condition. In this paper the authors review the major findings from these advanced neuroimaging methods along with current controversy within this field of research. As mTBI is frequently associated with youth and sports injury this review focuses on sports-related mTBI in the younger population.

A new method for modulating traumatic brain injury with mechanical tissue resuscitation

BACKGROUND

Traumatic brain injuries remain a treatment enigma with devastating late results. As terminally differentiated tissue, the brain retains little capacity to regenerate, making early attempts to preserve brain cells after brain injury essential.

OBJECTIVE

To resuscitate damaged tissue by modulating edema, soluble cytokines, and metabolic products in the "halo" of damaged tissue around the area of central injury that progressively becomes compromised. By re-equilibrating the zone of injury milieu, it is postulated neurons in this area will survive and function.

METHODS

Mechanical tissue resuscitation used localized, controlled, subatmospheric pressure directly to the area of controlled cortical impact injury and was compared with untreated injured controls and with sham surgery in a rat model. Functional outcome, T2 magnetic resonance imaging hyperintense volume, magnetic resonance imaging spectroscopy metabolite measurement, tissue water content, injury cavity area, and cortical volume were compared.

RESULTS

There were significant differences between mechanical tissue resuscitation treated and untreated groups in levels of myoinositol, N-acetylaspartate, and creatine. Treated animals had significantly less tissue swelling and density than the untreated animals. Nonviable brain tissue areas were smaller in treated animals than in untreated animals. Treated animals performed better than untreated animals in functional tests. Histological analysis showed the remaining viable ipsilateral cerebral area was 58% greater for treated animals than for untreated animals, and the cavity for treated animals was 95% smaller than for untreated animals 1 month after injury.

CONCLUSION

Mechanical tissue resuscitation with controlled subatmospheric pressure can significantly modulate levels of excitatory amino acids and lactate in traumatic brain injury, decrease the water content and volume of injured brain, improve neuronal survival, and speed functional recovery.

The use of magnetic resonance spectroscopy in the subacute evaluation of athletes recovering from single and multiple mild traumatic brain injury

Advanced neuroimaging techniques have shown promise in highlighting the subtle changes and nuances in mild traumatic brain injury (MTBI) even though clinical assessment has shown a return to pre-injury levels. Here we use ¹H-magnetic resonance spectroscopy (¹H-MRS) to evaluate the brain metabolites N-acetyl aspartate (NAA), choline (Cho), and creatine (Cr) in the corpus callosum in MTBI. Specifically, we looked at the NAA/Cho, NAA/Cr, and Cho/Cr ratios in the genu and splenium. We recruited 20 normal volunteers (NV) and 28 student athletes recovering from the subacute phase of MTBI. The MTBI group was categorized based upon the number of MTBIs and time from injury to ¹H-MRS evaluation. Significant reductions in NAA/Cho and NAA/Cr ratios were seen in the genu of the corpus callosum, but not in the splenium, for MTBI subjects, regardless of the number of MTBIs. MTBI subjects recovering from their first MTBI showed the greatest alteration in NAA/Cho and NAA/Cr ratios. Time since injury to ¹H-MRS acquisition was based upon symptom resolution and did not turn out to be a significant factor. We observed that as the number of MTBIs increased, so did the length of time for symptom resolution. Unexpected findings from this study are that MTBI subjects showed a trend of increasing NAA/Cho and NAA/Cr ratios that coincided with increasing number of MTBIs.

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.

MR spectroscopic studies of the brain in psychiatric disorders

The measurement of brain metabolites with magnetic resonance spectroscopy (MRS) provides a unique perspective on the brain bases of neuropsychiatric disorders. As a context for interpreting MRS studies of neuropsychiatric disorders, we review the characteristic MRS signals, the metabolic dynamics,and the neurobiological significance of the major brain metabolites that can be measured using clinical MRS systems. These metabolites include N-acetylaspartate(NAA), creatine, choline-containing compounds, myo-inositol, glutamate and glutamine, lactate, and gamma-amino butyric acid (GABA). For the major adult neuropsychiatric disorders (schizophrenia, bipolar disorder, major depression, and the anxiety disorders), we highlight the most consistent MRS findings, with an emphasis on those with potential clinical or translational significance. Reduced NAA in specific brain regions in schizophrenia, bipolar disorder, post-traumatic stress disorder, and obsessive–compulsive disorder corroborate findings of reduced brain volumes in the same regions. Future MRS studies may help determine the extent to which the neuronal dysfunction suggested by these findings is reversible in these disorders. Elevated glutamate and glutamine (Glx) in patients with bipolar disorder and reduced Glx in patients with unipolar major depression support models of increased and decreased glutamatergic function, respectively, in those conditions. Reduced phosphomonoesters and intracellular pH in bipolar disorder and elevated dynamic lactate responses in panic disorder are consistent with metabolic models of pathogenesis in those disorders. Preliminary findings of an increased glutamine/glutamate ratio and decreased GABA in patients with schizophrenia are consistent with a model of NMDA hypofunction in that disorder. As MRS methods continue to improve, future studies may further advance our understanding of the natural history of psychiatric illnesses, improve our ability to test translational models of pathogenesis, clarify therapeutic mechanisms of action,and allow clinical monitoring of the effects of interventions on brain metabolicmarkers

Determinants of the enzymatic activity and the subcellular localization of aspartate N-acetyltransferase

Aspartate N-acetyltransferase (NAT8L, N-acetyltransferase 8-like), the enzyme that synthesizes N-acetylaspartate, is membrane-bound and is at least partially associated with the ER (endoplasmic reticulum). The aim of the present study was to determine which regions of the protein are important for its catalytic activity and its subcellular localization. Transfection of truncated forms of NAT8L into HEK (human embryonic kidney)-293T cells indicated that the 68 N-terminal residues (regions 1 and 2) have no importance for the catalytic activity and the subcellular localization of this enzyme, which was exclusively associated with the ER. Mutation of conserved residues that precede (Arg81 and Glu101, in region 3) or follow (Asp168 and Arg220, in region 5) the putative membrane region (region 4) markedly affected the kinetic properties, suggesting that regions 3 and 5 form the catalytic domain and that the membrane region has a loop structure. Evidence is provided for the membrane region comprising α-helices and the catalytic site being cytosolic. Transfection of chimaeric proteins in which GFP (green fluorescent protein) was fused to different regions of NAT8L indicated that the membrane region (region 4) is necessary and sufficient to target NAT8L to the ER. Thus NAT8L is targeted to the ER membrane by a hydrophobic loop that connects two regions of the catalytic domain.

Stuck at the bench: Potential natural neuroprotective compounds for concussion

Background:

While numerous laboratory studies have searched for neuroprotective treatment approaches to traumatic brain injury, no therapies have successfully translated from the bench to the bedside. Concussion is a unique form of brain injury, in that the current mainstay of treatment focuses on both physical and cognitive rest. Treatments for concussion are lacking. The concept of neuro-prophylactic compounds or supplements is also an intriguing one, especially as we are learning more about the relationship of numerous sub-concussive blows and/or repetitive concussive impacts and the development of chronic neurodegenerative disease. The use of dietary supplements and herbal remedies has become more common place.

Methods:

A literature search was conducted with the objective of identifying and reviewing the pre-clinical and clinical studies investigating the neuroprotective properties of a few of the more widely known compounds and supplements.

Results:

There are an abundance of pre-clinical studies demonstrating the neuroprotective properties of a variety of these compounds and we review some of those here. While there are an increasing number of well-designed studies investigating the therapeutic potential of these nutraceutical preparations, the clinical evidence is still fairly thin.

Conclusion:

There are encouraging results from laboratory studies demonstrating the multi-mechanistic neuroprotective properties of many naturally occurring compounds. Similarly, there are some intriguing clinical observational studies that potentially suggest both acute and chronic neuroprotective effects. Thus, there is a need for future trials exploring the potential therapeutic benefits of these compounds in the treatment of traumatic brain injury, particularly concussion.

Ketogenic diet prevents alterations in brain metabolism in young but not adult rats after traumatic brain injury

Previous studies have shown that the change of cerebral metabolic rate of glucose (CMRglc) in response to traumatic brain injury (TBI) is different in young (PND35) and adult rats (PND70), and that prolonged ketogenic diet treatment results in histological and behavioral neuroprotection only in younger rat brains. However, the mechanism(s) through which ketones act in the injured brain and the biochemical markers of their action remain unknown. Therefore, the current study was initiated to: 1) determine the effect of injury on the neurochemical profile in PND35 compared to PND70 rats; and 2) test the effect of early post-injury administration of ketogenic diet on brain metabolism in PND35 versus PND70 rats. The data show that alterations in energy metabolites, amino acid, and membrane metabolites were not evident in PND35 rats on standard diet until 24  h after injury, when the concentration of most metabolites was reduced from sham-injured values. In contrast, acute, but transient deficits in energy metabolism were measured at 6  h in PND70 rats, together with deficits in N-acetylaspartate that endured until 24  h. Administration of a ketogenic diet resulted in significant increases in plasma β-hydroxybutyrate (βOHB) levels. Similarly, brain βOHB levels were significantly elevated in all injured rats, but were elevated by 43% more in PND35 rats compared to PND70 rats. As a result, ATP, creatine, and phosphocreatine levels at 24  h after injury were significantly improved in the ketogenic PND35 rats, but not in the PND70 group. The improvement in energy metabolism in the PND35 brains was accompanied by the recovery of NAA and reduction of lactate levels, as well as amelioration of the deficits of other amino acids and membrane metabolites. These results indicate that the PND35 brains are more resistant to the injury, indicated by a delayed deficit in energy metabolism. Moreover, the younger brains revert to ketones metabolism more quickly than do the adult brains, resulting in better neurochemical and cerebral metabolic recovery after injury.