Administration of excitatory amino acid antagonists via microdialysis attenuates the increase in glucose utilization seen following concussive brain injury

Relationship between systemic glucose and cerebral glucose is preserved in patients with severe traumatic brain injury, but glucose delivery to the brain may become limited when oxidative metabolism is impaired: implications for glycemic control

OBJECTIVE

To clarify the dynamics of glucose delivery to the brain and the effects of changes in blood glucose after severe traumatic brain injury.

DESIGN

Retrospective analysis of a prospective observational cohort study.

SETTING

Neurosurgical intensive care unit of a university hospital.

PATIENTS

Seventeen patients with acute traumatic brain injury monitored with cerebral and subcutaneous microdialysis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

For continuous, accurate systemic monitoring, glucose was measured in the interstitial space of subcutaneous adipose tissue using microdialysis, and 39 specific episodes of spontaneous rises in glucose were identified. During these episodes, there was a significant positive linear relationship between systemic glucose levels and brain glucose concentrations measured by microdialysis (p < .0001). The basal lactate/pyruvate ratio, with a threshold of 25, was adopted to distinguish between disturbed and presumably preserved cerebral oxidative metabolism. Using normal vs. elevated lactate/pyruvate ratio as variable factor, the relationship between brain and systemic glucose during the episodes could be described by two significantly distinct parallel lines (p = .0001), which indicates a strong additive effect of subcutaneous glucose and lactate/pyruvate ratio in determining brain glucose. The line describing the relationship under disturbed metabolic conditions was lower than in presumably intact metabolic conditions, with a significant difference of 0.648 ± 0.192 mM (p = .002). This let us to accurately predict that in this situation systemic glucose concentrations in the lower range of normality would result in critical brain glucose levels.

CONCLUSIONS

The linear relationship between systemic and brain glucose in healthy subjects is preserved in traumatic brain-injured patients. As a consequence, in brain tissue where oxidative metabolism is disturbed, brain glucose concentrations might possibly drop below the critical threshold of 0.8 mM to 1.0 mM when there is a reduction in systemic glucose toward the lower limits of the "normal" range.

The pathophysiology of concussion

Concussion is defined as a biomechanically induced brain injury characterized by the absence of gross anatomic lesions. Early and late clinical symptoms, including impairments of memory and attention, headache, and alteration of mental status, are the result of neuronal dysfunction mostly caused by functional rather than structural abnormalities. The mechanical insult initiates a complex cascade of metabolic events leading to perturbation of delicate neuronal homeostatic balances. Starting from neurotoxicity, energetic metabolism disturbance caused by the initial mitochondrial dysfunction seems to be the main biochemical explanation for most postconcussive signs and symptoms. Furthermore, concussed cells enter a peculiar state of vulnerability, and if a second concussion is sustained while they are in this state, they may be irreversibly damaged by the occurrence of swelling. This condition of concussion-induced brain vulnerability is the basic pathophysiology of the second impact syndrome. N-acetylaspartate, a brain-specific compound representative of neuronal metabolic wellness, is proving a valid surrogate marker of the post-traumatic biochemical damage, and its utility in monitoring the recovery of the aforementioned "functional" disturbance as a concussion marker is emerging, because it is easily detectable through proton magnetic resonance spectroscopy.

Rehabilitation of Concussion and Post-concussion Syndrome

CONTEXT

Prolonged symptoms after concussion are called post-concussion syndrome (PCS), which is a controversial disorder with a wide differential diagnosis.

EVIDENCE ACQUISITION

MEDLINE and PubMed searches were conducted for the years 1966 to 2011 using the search terms brain concussion/complications OR brain concussion/diagnosis OR brain concussion/therapy AND sports OR athletic injuries. Secondary search terms included post-concussion syndrome, trauma, symptoms, metabolic, sports medicine, cognitive behavioral therapy, treatment and rehabilitation. Additional articles were identified from the bibliographies of recent reviews.

RESULTS

Of 564 studies that fulfilled preliminary search criteria, 119 focused on the diagnosis, pathophysiology, and treatment/rehabilitation of concussion and PCS and formed the basis of this review. Rest is the primary treatment for the acute symptoms of concussion. Ongoing symptoms are either a prolonged version of the concussion pathophysiology or a manifestation of other processes, such as cervical injury, migraine headaches, depression, chronic pain, vestibular dysfunction, visual dysfunction, or some combination of conditions. The pathophysiology of ongoing symptoms from the original concussion injury may reflect multiple causes: anatomic, neurometabolic, and physiologic.

CONCLUSIONS

Treatment approaches depend on the clinician's ability to differentiate among the various conditions associated with PCS. Early education, cognitive behavioral therapy, and aerobic exercise therapy have shown efficacy in certain patients but have limitations of study design. An algorithm is presented to aid clinicians in the evaluation and treatment of concussion and PCS and in the return-to-activity decision.

Alcohol and the head-injured patient

Alcohol intoxication is a major predisposing factor for trauma in general and head injury in particular. The management of the head-injured patient is highly contingent on the accurate assessment of this patient’s consciousness, which is invariably impaired if the patient is intoxicated. This complicates the decision-making process and impedes the promptness needed in management when the head injury is severe. Furthermore, the prognosis of the head injury can depend on the patient’s degree and pattern of intoxication. This article presents some of the latest epidemiological data about the association of alcohol and head injury. It also highlights some of the challenges posed by alcohol intoxication in the management of head-injured patients, and examines the importance of documenting intoxication in head-injured patients.

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.

Post-injury administration of NAAG peptidase inhibitor prodrug, PGI-02776, in experimental TBI

Traumatic brain injury (TBI) leads to a rapid and excessive increase in glutamate concentration in the extracellular milieu, which is strongly associated with excitotoxicity and neuronal degeneration. N-acetylaspartylglutamate (NAAG), a prevalent peptide neurotransmitter in the vertebrate nervous system, is released along with glutamate and suppresses glutamate release by actions at pre-synaptic metabotropic glutamate autoreceptors. Extracellular NAAG is hydrolyzed to N-acetylaspartate and glutamate by peptidase activity. In the present study PGI-02776, a newly designed di-ester prodrug of the urea-based NAAG peptidase inhibitor ZJ-43, was tested for neuroprotective potential when administered intraperitoneally 30 min after lateral fluid percussion TBI in the rat. Stereological quantification of hippocampal CA2-3 degenerating neurons at 24 h post injury revealed that 10 mg/kg PGI-02776 significantly decreased the number of degenerating neurons (p<0.05). Both average latency analysis of Morris water maze performance and assessment of 24-hour memory retention revealed significant differences between sham-TBI and TBI-saline. In contrast, no significant difference was found between sham-TBI and PGI-02776 treated groups in either analysis indicating an improvement in cognitive performance with PGI-02776 treatment. Histological analysis on day 16 post-injury revealed significant cell death in injured animals regardless of treatment. In vitro NAAG peptidase inhibition studies demonstrated that the parent compound (ZJ-43) exhibited potent inhibitory activity while the mono-ester (PGI-02749) and di-ester (PGI-02776) prodrug compounds exhibited moderate and weak levels of inhibitory activity, respectively. Pharmacokinetic assays in uninjured animals found that the di-ester (PGI-02776) crossed the blood-brain barrier. PGI-02776 was also readily hydrolyzed to both the mono-ester (PGI-02749) and the parent compound (ZJ-43) in both blood and brain. Overall, these findings suggest that post-injury treatment with the ZJ-43 prodrug PGI-02776 reduces both acute neuronal pathology and longer term cognitive deficits associated with TBI.

The molecular pathophysiology of concussive brain injury

Concussion or mild traumatic brain injury (mTBI) is a condition that affects hundreds of thousands of patients worldwide. Understanding the pathophysiology of this disorder can help manage its acute and chronic repercussions. Immediately following mTBI, there are several metabolic, hemodynamic, structural, and electric changes that alter normal cerebral function. These alterations can increase the brain's vulnerability to repeat injury and long-term disability. This review evaluates current studies from the bench to the bedside of mTBI. Acute and chronic effects of concussion are measured in both animal and clinical studies. Also, the effect of repeat concussions is analyzed. Concussion-induced pathophysiology with regards to glucose metabolism changes, mitochondrial dysfunction, axonal injury, and structural damage are evaluated. Translational studies such as functional magnetic resonance imaging, magnetic resonance spectroscopy and diffusion tensor imaging prove to be effective clinical tools for both prognostic and treatment parameters. Understanding the neurobiology of concussion will lead to development and validation of physiological biomarkers of this common injury. These biomarkers (eg, laboratory tests, imaging, electrophysiology) will then allow for improved detection, better functional assessment and evidence-based return to play recommendations.

Influence of alcohol on early Glasgow Coma Scale in head-injured patients

BACKGROUND

To assess the depressant effects of alcohol on the level of consciousness of patients admitted with head injuries, this study examined the changes that occur in the Glasgow Coma Scale (GCS) of traumatic brain injury patients over time.

METHODS

The records of 269 head trauma patients consecutively admitted to the neurosurgery intensive care unit were examined retrospectively. Eighty-one patients were excluded because of incomplete data. The remaining 188 patients were further divided into an intoxicated group (blood alcohol concentration [BAC] ≥ 0.08%, n = 100 [53%]) and a nonintoxicated group (BAC <0.08%, n = 88 [47%]). The GCS in the prehospital setting, in the emergency department, and the highest GCS achieved during the first 24 hours postinjury were compared.

RESULTS

The change between emergency department-GCS and the best day 1 GCS in the intoxicated group was greater than the nonintoxicated group and deemed clinically and statistically significant; median change (3 vs. 0) p < 0.001. To assess whether these results were directly related to the BAC%, piecewise regression using a general linear model was used to assess the intercept and slope of alcohol on the changes of GCS with cutting point at BAC% = 0.08. The analysis showed that, in the nonintoxicated range, the effect of alcohol was not significantly related to the changes of GCS. But in the intoxicated range, BAC% was significantly positively related to the changes of GCS.

CONCLUSION

This study concludes that the GCS increases significantly over time in alcohol intoxicated patients with traumatic brain injury.

Pathophysiology of sports-related concussion: an update on basic science and translational research

CONTEXT

Concussions that occur during participation in athletic events affect millions of individuals each year. Although our understanding of the pathophysiology of concussion has grown considerably in recent years, much remains to be elucidated. This article reviews basic science and relevant translational clinical research regarding several aspects of concussion.

EVIDENCE ACQUISITION

A literature search was conducted using PubMed from 1966 to 2010, with an emphasis on work published within the past 10 years. Additional articles were identified from the bibliography of recent reviews.

RESULTS

Basic science and clinical data both indicate that there is a period of increased vulnerability to repeated injury following a concussion and that its duration is variable. Growing evidence indicates that postinjury activity is likely to affect recovery from brain injury. Data suggest that long-term sequelae may result from prior concussion-particularly, repeated injuries. The unique aspects of cerebral development may account for differences in the effects of concussion in children and adolescents when compared with adults.

CONCLUSIONS

The available pathophysiologic data from basic science and clinical studies have increased the evidence base for concussion management strategies-the approaches to which may differ between young athletes and adults.

Molecular and physiological responses to juvenile traumatic brain injury: focus on growth and metabolism

Traumatic brain injury (TBI), one of the most frequent causes of neurologic and neurobehavioral morbidity in the pediatric population, can result in lifelong challenges not only for patients, but also for their families. Survivors of a brain injury experienced during childhood - when the brain is undergoing a period of rapid development - frequently experience unique challenges as the consequences of their injuries are overlaid on normal developmental changes. Experimental studies have significantly advanced our understanding of the mechanisms and underlying molecular underpinnings of the injury response and recovery process following a TBI in the developing brain. In this paper, normal and TBI-related alterations in growth, development and metabolism are comprehensively reviewed in the postweanling/juvenile age range in the rat (postnatal days 21-60). As part of this review, TBI-related changes in gene expression are presented, with a focus on the injury-induced alterations related to cerebral growth and metabolism, and discussed in the context of existing literature related to physiological and behavioral responses to experimental TBI. Increasing evidence from the existing literature and from our own gene microarray data indicates that molecular responses related to growth, development and metabolism may play a particularly important role in the injury response and the recovery trajectory following developmental TBI. While gene expression analysis shows many of these changes occur at the level of transcription, a comprehensive review of other studies suggests that the control of metabolic substrates may preferentially be regulated through changes in transporters and enzymatic activity. The interrelation between cellular metabolism and activity-dependent neuroplasticity shows great promise as an area for future study for an optimal translation of experimental data to clinical TBI, with the ultimate goal of guiding therapeutic interventions.

The effects of age and ketogenic diet on local cerebral metabolic rates of glucose after controlled cortical impact injury in rats

Previous studies from our laboratory have shown the neuroprotective potential of ketones after TBI in the juvenile brain. It is our premise that acutely after TBI, glucose may not be the optimum fuel and decreasing metabolism of glucose in the presence of an alternative substrate will improve cellular metabolism and recovery. The current study addresses whether TBI will induce age-related differences in the cerebral metabolic rates for glucose (CMRglc) after cortical controlled impact (CCI) and whether ketone metabolism will further decrease CMRglc after injury. Postnatal day 35 (PND35; n = 48) and PND70 (n = 42) rats were given either sham or CCI injury and placed on either a standard or a ketogenic (KG) diet. CMRglc studies using (14)C-2 deoxy-D-glucose autoradiography were conducted on days 1, 3, or 7 post-injury. PND35 and PND70 standard-fed CCI-injured rats exhibited no significant neocortical differences in CMRglc magnitude or time course compared to controls. Measurement of contusion volume also indicated no age differences in response to TBI. However, PND35 subcortical structures showed earlier metabolic recovery compared to controls than PND70. Ketosis induced by the KG diet was shown to affect CMRglc in an age-dependent manner after TBI. The presence of ketones after injury further reduced CMRglc in PND35 and normalized CMRglc in PND70 rats at 7 days bilaterally after injury. The changes in CMRglc seen in PND35 TBI rats on the KG diet were associated with decreased contusion volume. These results suggest that conditions of reduced glucose utilization and increased alternative substrate metabolism may be preferable acutely after TBI in the younger rat.

Metabolic and histologic effects of sodium pyruvate treatment in the rat after cortical contusion injury

This study determined the effects of intraperitoneal sodium pyruvate (SP) treatment on the levels of circulating fuels and on cerebral microdialysis levels of glucose (MD(glc)), lactate (MD(lac)), and pyruvate (MD(pyr)), and the effects of SP treatment on neuropathology after left cortical contusion injury (CCI) in rats. SP injection (1000 mg/kg) 5 min after sham injury (Sham-SP) or CCI (CCI-SP) significantly increased arterial pyruvate (p < 0.005) and lactate (p < 0.001) compared to that of saline-treated rats with CCI (CCI-Sal). Serum glucose also increased significantly in CCI-SP compared to that in CCI-Sal rats (p < 0.05), but not in Sham-SP rats. MD(pyr) was not altered after CCI-Sal, whereas MD(lac) levels within the cerebral cortex significantly increased bilaterally (p < 0.05) and those for MD(glc) decreased bilaterally (p < 0.05). MD(pyr) levels increased significantly in both Sham-SP and CCI-SP rats (p < 0.05 vs. CCI-Sal) and were higher in left/injured cortex of the CCI-SP group (p < 0.05 vs. sham-SP). In CCI-SP rats the contralateral MD(lac) decreased below CCI-Sal levels (p < 0.05) and the ipsilateral MD(glc) levels exceeded those of CCI-Sal rats (p < 0.05). Rats with a single low (500 mg/kg) or high dose (1000 mg/kg) SP treatment had fewer damaged cortical cells 6 h post-CCI than did saline-treated rats (p < 0.05), but three hourly injections of SP (1000 mg/kg) were needed to significantly reduce contusion volume 2 weeks after CCI. Thus, a single intraperitoneal SP treatment increases circulating levels of three potential brain fuels, attenuates a CCI-induced reduction in extracellular glucose while increasing extracellular levels of pyruvate, but not lactate, and can attenuate cortical cell damage occurring within 6 h of injury. Enduring (2 week) neuronal protection was achieved only with multiple SP treatments within the first 2 h post-CCI, perhaps reflecting the need for additional fuel throughout the acute period of increased metabolic demands induced by CCI.

Transient focal increase in perihematomal glucose metabolism after acute human intracerebral hemorrhage

BACKGROUND AND PURPOSE

Progressive perihematomal cell death over 3 to 4 days has been described after experimental intracerebral hemorrhage (ICH). We investigated whether progressive perihematomal damage occurs in human subjects by measuring relative changes in regional cerebral glucose metabolism with (18)F-fluorordeoxyglucose (FDG) positron emission tomography at multiple time points during the first week after ICH.

METHODS

Thirteen subjects with a median hematoma volume of 22 cm(3) were studied 1.0+/-0.3, 2.9+/-0.8, and 6.7+/-1.6 days after ICH. Normalized mean counts in 5 concentric annular 2-mm-thick perihematomal volumes-of-interest (VOIs) were compared to the initial study. Next, automated searches with 0.5 to 5.0 mL spherical VOIs identified maximum focal changes in normalized counts compared to the initial study.

RESULTS

No annular or focal decrease in perihematomal FDG uptake developed. Instead, FDG uptake significantly increased at session #2 in the first 3 2-mm annular VOIs (9.2%+/-14.2, 7.8%+/-11.3, 5.9%+/-9.0), returning to baseline at session #3. The VOI search identified focal regions of increased perihematomal FDG uptake relative to the contralateral control hemispheres in 6 subjects, which accounted for the annular increase.

CONCLUSIONS

Perihematomal glucose metabolism increased transiently in a subset of patients 2 to 4 days after acute ICH. These transient focal increases in glucose metabolism occurring in the brain after acute ICH demonstrate that there are ongoing processes in response to injury that last for days. Although further studies are needed to elucidate their pathophysiology, these processes may be indicative of a prolonged window for intervention to improve neurological outcome.

Duration of ATP reduction affects extent of CA1 cell death in rat models of fluid percussion injury combined with secondary ischemia

Secondary ischemia (SI) following traumatic brain injury (TBI) increases damage to the brain in both animals and humans. The current study determined if SI after TBI alters the extent or duration of reduced energy production within the first 24 h post-injury and hippocampal cell loss at one week post-injury. Adult male rats were subjected to sham injury, lateral (LFPI) or central fluid percussion injury (CFPI) only, or to combined LFPI or CFPI with SI. The SI was 8 min of bilateral forebrain ischemia combined with hemorrhagic hypotension, applied at 1 h following FPI. After LFPI alone adenosine triphosphate (ATP) levels within the ipsilateral CA1 were reduced at 2 h (p < 0.05) and subsequently recovered. After LFPI+SI the ATP reductions in CA1 ipsilateral to FPI persisted for 24 h (p < 0.01). ATP levels in the contralateral CA1 were not affected by LFPI alone or LFPI+SI. After CFPI alone CA1 ATP levels were depressed bilaterally only at 2 h (p < 0.05). Similar to the LFPI paradigm, CFPI+SI reduced ATP levels for 24 h (p < 0.01), with bilateral ATP reductions seen after CFPI+SI. Cell counts in the CA1 region at 7 days post-injury revealed no significant neuronal cell loss after LFPI or CFPI alone. Significant neuronal cell loss was present only within the ipsilateral (p < 0.001) CA1 after LFPI+SI, but cell loss was bilateral (p < 0.001) after CFPI+SI. Thus, SI prolongs ATP reductions induced by LFPI and CFPI within the CA1 region and this SI-induced energy reduction appears to adversely affect regional neuronal viability.

Glucose control after severe brain injury

PURPOSE OF REVIEW

A substantial body of evidence supports the use of intensive insulin therapy in general critical care practice, particularly in surgical intensive care unit patients. The impact of intensive insulin therapy on the outcome of critically ill neurological patients, however, is still controversial. While avoidance of hyperglycemia is recommended in neurointensive care, no recommendations exist regarding the optimal target for systemic glucose control after severe brain injury.

RECENT FINDINGS

An increase in brain metabolic demand leading to a deficiency in cerebral extracellular glucose has been observed in critically ill neurological patients and correlates with poor outcome. In this setting, a reduction of systemic glucose below 6 mmol/l with exogenous insulin has been found to exacerbate brain metabolic distress. Recent studies have confirmed these findings while showing intensive insulin therapy to have no substantial benefit on the outcome of critically ill neurological patients.

SUMMARY

Questions persist regarding the optimal target for glucose control after severe brain injury. Further studies are needed to analyze the impact of intensive insulin therapy on brain glucose metabolism and outcome of critically ill neurological patients. According to the available evidence, a less restrictive target for systemic glucose control (6-10 mmol/l) may be more appropriate.

Heterogeneous regional and temporal energetic impairment following controlled cortical impact injury in rats

OBJECTIVES

Following traumatic brain injury metabolic stability is impaired. Duration and reversibility of these changes might be important to guide specific interventions.

METHODS

To characterize temporal and regional changes in cerebral metabolism, 68 male Sprague-Dawley rats were subjected to a focal cortical contusion. Lesion progression and mitochondrial impairment were determined by magnetic resonance imaging (MRI) and triphenyl tetrazolium chloride (TTC) staining, respectively. Metabolic alterations were determined at hours 6 and 24 and day 7 by measuring extracellular glucose, lactate and hypoxanthine levels with microdialysis catheters placed adjacent and distant to the contusion and by quantifying changes in tissue ATP, lactate and glucose using bioluminescence imaging.

RESULTS

The cortical lesion reached its maximal extent at hour 24 and remained confined to the ipsilateral hemisphere. In microdialysate, at hour 6, extracellular hypoxanthine and lactate reached maximal values, thereafter hypoxanthine normalized while lactate remained increased. Extracellular glucose reached the highest values at hour 24 and remained elevated. Bioluminescence imaging revealed heterogeneous changes in areas distant to the contusion. No significant changes were found in ATP content. Slightly elevated tissue glucose until 24 hours in the ipsilateral hemisphere was observed. Following a continuous increase, lactate levels were the highest by 6 hours in the ipsilateral cortex and hippocampus.

DISCUSSION

CCI is associated with disturbances in energetic metabolism. Metabolic perturbation is not restricted to the early phase and the contusional region following focal cortical contusion, but also involves hippocampus and primarily uninjured parts of the hemisphere.

Cerebral metabolic adaptation and ketone metabolism after brain injury

The developing central nervous system has the capacity to metabolize ketone bodies. It was once accepted that on weaning, the 'post-weaned/adult' brain was limited solely to glucose metabolism. However, increasing evidence from conditions of inadequate glucose availability or increased energy demands has shown that the adult brain is not static in its fuel options. The objective of this review is to summarize the body of literature specifically regarding cerebral ketone metabolism at different ages, under conditions of starvation and after various pathologic conditions. The evidence presented supports the following findings: (1) there is an inverse relationship between age and the brain's capacity for ketone metabolism that continues well after weaning; (2) neuroprotective potentials of ketone administration have been shown for neurodegenerative conditions, epilepsy, hypoxia/ischemia, and traumatic brain injury; and (3) there is an age-related therapeutic potential for ketone as an alternative substrate. The concept of cerebral metabolic adaptation under various physiologic and pathologic conditions is not new, but it has taken the contribution of numerous studies over many years to break the previously accepted dogma of cerebral metabolism. Our emerging understanding of cerebral metabolism is far more complex than could have been imagined. It is clear that in addition to glucose, other substrates must be considered along with fuel interactions, metabolic challenges, and cerebral maturation.

The fate of glucose during the period of decreased metabolism after fluid percussion injury: a 13C NMR study

The present study determined the metabolic fate of [1, 2 13C2] glucose in male control rats and in rats with moderate lateral fluid percussion injured (FPI) at 3.5 h and 24 h post-surgery. After a 3-h infusion, the amount of 13C-labeled glucose increased bilaterally (26% in left/injured cerebral cortex and 45% in right cerebral cortex) at 3.5 h after FPI and in injured cortex (45%) at 24 h after injury, indicating an accumulation of unmetabolised glucose not seen in controls. No evidence of an increase in anaerobic glycolysis above control levels was found after FPI, as 13C-labeled lactate tended to decrease at both time points and was significantly reduced (33%) in the injured cortex at 24 h post-FPI. A bilateral decrease in the 13C-labeling of both glutamate and glutamine was observed in the FPI rats at 3.5 h and the glutamine pool remained significantly decreased in the injured cortex at 24 h, suggesting reduced oxidative metabolism in both neuronal and astrocyte compartments after injury. The percentage of glucose metabolism through the pentose phosphate pathway (PPP) increased in the injured (13%) and contralateral (11%) cortex at 3.5 h post-FPI and in the injured cortex (9%) at 24 h post-injury. Based upon the changes in metabolite pools, our results show an injury-induced decrease in glucose utilization and oxidation within the first 24 h after FPI. Increased metabolism through the PPP would result in increased NADPH synthesis, suggesting a need for reducing equivalents after FPI to help restore the intracellular redox state and/or in response to free radical stress.

Rhythmic synaptic activity induced by mechanical injury of rat CA3 hippocampal area

Mechanical injury of the CNS frequently results from accidents but also occurs in the course of neurosurgical interventions. A great variety of anatomical and physiological changes have been described to evolve after a brain trauma yet only little is known about processes that occur during a trauma. In the present study, I obtained whole-cell patch clamp recordings from pyramidal cells in hippocampal slice cultures while mechanically lesioning the CA3 area. Electrophysiological analysis revealed that traumatic injury massively increased excitatory and inhibitory synaptic activity in the entire CA3 region. Cutting the CA3 region induced highly rhythmic excitatory postsynaptic currents (EPSCs) that reached frequencies of around 70 Hz. Blocking voltage-dependent sodium channels with tetrodotoxin prevented the increase in synaptic activity and injury-induced neurotransmitter release in CA3 remote from the lesion site. With fast synaptic transmission blocked only neurons in the immediate vicinity of a lesion depolarized and fired action potentials upon mechanical damage. I hence suggest that mechanical injury damages the membrane and induces action potential firing in only a small population of neurons. This activity is then propagated throughout the undamaged CA3 network inducing highly rhythmic discharges. Thus mechanical brain injury initiates immediate functional changes that exceed the lesion site.

Glucose metabolism after traumatic brain injury: estimation of pyruvate carboxylase and pyruvate dehydrogenase flux by mass isotopomer analysis

The metabolism of [1, 2 (13)C(2)] glucose via the tricarboxylic acid (TCA) cycle yields a number of key glutamate mass isotopomers whose formation is a function of pyruvate carboxylase (PC) and pyruvate dehydrogenase (PDH). Analysis of the isotopomer distribution patterns was used to determine the relative flux of glucose entry into the TCA cycle through anaplerotic and oxidative pathways in the cerebral cortex of both uninjured and traumatically injured adult male rats. In the cerebral cortex of uninjured animals the PC/PDH ratio showed greater metabolism of glucose via pyruvate carboxylase, which is consistent with the notion that the majority of glucose taken up at rest is used as a substrate for anaplerotic processes and not as an energy source. While traumatic brain injury did not change the overall (13)C enrichment of glutamate indicating a continued oxidation of glucose, the PC/PDH ratio was reduced in the injured cortex at 3.5 h after injury. This suggests that glucose metabolism is primarily directed through pathways associated with energy production in the early postinjury period. By 24 h, the anaplerotic flux decreased and the PC/PDH ratio increased in both the injured and non-injured cortex indicating a switch away from energy production to pathways associated with anabolic and/or regenerative processes.

Minor traumatic brain injury in sports: a review in order to prevent neurological sequelae

Minor traumatic brain injury (mTBI) is caused by inertial effects, which induce sudden rotation and acceleration forces to and within the brain. At less severe levels of injury, for example in mTBI, there is probably only transient disturbance of ionic homeostasis with short-term, temporary disturbance of brain function. With increased levels of severity, however, studies in animal models of TBI and in humans have demonstrated focal intra-axonal alterations within the subaxolemmal, neurofilament and microtubular cytoskeletal network together with impairment of axoplasmic transport. These changes have, until very recently, been thought to lead to progressive axonal swelling, axonal detachment or even cell death over a period of hours or days, the so-called process of "secondary axotomy". However, recent evidence has suggested that there may be two discrete pathologies that may develop in injured nerve fibers. In the TBI scenario, disturbances of ionic homeostasis, acute metabolic changes and alterations in cerebral blood flow compromise the ability of neurons to function and render cells of the brain increasingly vulnerable to the development of pathology. In ice hockey, current return-to-play guidelines do not take into account these new findings appropriately, for example allow returning to play in the same game. It has recently been hypothesized that the processes summarized above may predispose brain cells to assume a vulnerable state for an unknown period after mild injury (mTBI). Therefore, we recommend that any confused player with or without amnesia should be taken off the ice and not be permitted to play again for at least 72h.

Astroglia: important mediators of traumatic brain injury

Traumatic brain injury (TBI) research to date has focused almost exclusively on the pathophysiology of injured neurons with very little attention paid to non-neuronal cells. However in the past decade, exciting discoveries have challenged this century-old view of passive glial cells and have led to a reinterpretation of the role of glial cells in central nervous system (CNS) biology and pathology. In this chapter we review several lines of evidence, indicating that glial cells, particularly astrocytes, are active partners to neurons in the brain, and summarize recent findings that detail the significance of astrocyte pathology in traumatic brain injury.

Is being plastic fantastic? Mechanisms of altered plasticity after developmental traumatic brain injury

Traumatic brain injury (TBI) is predominantly a clinical problem of young persons, resulting in chronic cognitive and behavioral deficits. Specifically, the physiological response to a diffuse biomechanical injury in a maturing brain can clearly alter normal neuroplasticity. To properly evaluate and investigate developmental TBI requires an understanding of normal principles of cerebral maturation, as well as a consideration of experience-dependent changes. Changes in neuroplasticity may occur through many age-specific processes, and our understanding of these responses at a basic neuroscience level is only beginning. In this article, we will particularly discuss mechanisms of TBI-induced altered developmental plasticity such as altered neurotransmission, distinct molecular responses, cell death, perturbations in neuronal connectivity, experience-dependent 'good plasticity' enhancements and chronic 'bad plasticity' sequelae. From this summary, we can conclude that 'young is not always better' and that the developing brain manifests several crucial vulnerabilities to TBI.

Changes in cerebral energy metabolites induced by impact-acceleration brain trauma and hypoxic-hypotensive injury in rats

The aim of this study was to describe, in rats, brain energy metabolites changes after different levels of head trauma (T) complicated by hypoxia-hypotension (HH). Male Sprague Dawley rats (n = 7 per groups) were subjected to T by impact-acceleration with 450-g weight drop from 1.50 or 1.80 m (T 1.50 or T 1.80), or to a 15-min period of HH (controlled hemorrhage to mean arterial pressure [MAP] of 40 mm Hg, and mechanical ventilation with N(2) 90%/O(2) 10%), or to their association (T followed by HH). Invasive MAP, intraparenchymental intracranial pressure (ICP), and cerebral blood flow (CBF using Laser Doppler flowmetry) were recorded during the 5 post-traumatic hours. Cerebral microdialysis was used to measure each hour interstitial brain glucose, lactate, pyruvate, and glutamate. For the entire period, the levels of cerebral glucose, pyruvate, and glutamate were not statistically different between groups. In addition, there were no differences associated with the lactate-glucose ratio. Lactate was significantly higher overtime only in T 1.80 + HH group (p < 0.001 vs. every other groups). The lactate-pyruvate ratio increased with trauma level, and was significantly different vs. sham for the entire study period in T 1.50 + HH, in T 1.80, and in T 1.80 + HH. There was no correlation between CBF variations and the lactate-pyruvate ratio (r(2) = 0.00001). The cerebral perfusion pressure was greater than 70 mm Hg in all groups. The prolonged post-traumatic impairment in brain energy metabolism may be related to traumatic brain injury (TBI) severity. It became worse when T was complicated by HH, but was not related to changes in CBF.

N-methyl-D-aspartate receptor subunit changes after traumatic injury to the developing brain

Traumatic brain injury (TBI) is a major cause of disability in the pediatric population and can result in abnormal development. Experimental studies conducted in animals have revealed impaired plasticity following developmental TBI, even in the absence of significant anatomical damage. The N-methyl-D-aspartate receptor (NMDAR) is clearly involved in both normal development and in the pathophysiology of TBI. Following lateral fluid percussion injury in postnatal day (PND) 19 rats, we tested the hypothesis that TBI sustained at an early age would result in impaired NMDAR expression. Using immunoblotting and reverse transcriptase-polymerase chain reaction (RT-PCR), protein and RNA levels of NMDAR subunits were measured in the cerebral cortex and hippocampus on post-injury days (PID) 1, 2, 4, and 7 (though the PID7 analysis was only for protein) and compared with age-matched shams. Significant effects of hemisphere (analysis of variance [ANOVA], p<0.01), and interactions between hemisphere and injury (ANOVA, p<0.05) and hemisphere and PID (ANOVA, p<0.05) were found for synaptic protein levels of the NR2A subunit in hippocampus. Specifically, within the ipsilateral hippocampus, NR2A was reduced by 9.9%, 47.9%, 40.8%, and 6.3% on PID1, PID2, PID4, and PID7, respectively. Within the cortex, there was a significant effect of injury (ANOVA, p<0.05) without any hemispheric differences. These bilateral cortical reductions measured 30.5%, 3.2%, 5.7%, and 13.4% at the same timepoints after injury. Injury had no significant main effect on NR1 or NR2B protein levels. RT-PCR analysis showed no significant changes in NR1, NR2A, or NR2B gene expression; however, as a positive control, hsp70 was induced more than twofold in ipsilateral cortex and hippocampus on PID1. It is known that NR2A expression levels increase during normal development, and in response to environmental stimuli. Our data suggest that injury-induced reduction in the expression of NR2A is one likely mechanism for the impaired experience-dependent neuroplasticity seen following traumatic injury to the immature brain.

NAAG peptidase inhibitor increases dialysate NAAG and reduces glutamate, aspartate and GABA levels in the dorsal hippocampus following fluid percussion injury in the rat

Traumatic brain injury (TBI) produces a rapid and excessive elevation in extracellular glutamate that induces excitotoxic brain cell death. The peptide neurotransmitter N-acetylaspartylglutamate (NAAG) is reported to suppress neurotransmitter release through selective activation of presynaptic group II metabotropic glutamate receptors. Therefore, strategies to elevate levels of NAAG following brain injury could reduce excessive glutamate release associated with TBI. We hypothesized that the NAAG peptidase inhibitor, ZJ-43 would elevate extracellular NAAG levels and reduce extracellular levels of amino acid neurotransmitters following TBI by a group II metabotropic glutamate receptor (mGluR)-mediated mechanism. Dialysate levels of NAAG, glutamate, aspartate and GABA from the dorsal hippocampus were elevated after TBI as measured by in vivo microdialysis. Dialysate levels of NAAG were higher and remained elevated in the ZJ-43 treated group (50 mg/kg, i.p.) compared with control. ZJ-43 treatment also reduced the rise of dialysate glutamate, aspartate, and GABA levels. Co-administration of the group II mGluR antagonist, LY341495 (1 mg/kg, i.p.) partially blocked the effects of ZJ-43 on dialysate glutamate and GABA, suggesting that NAAG effects are mediated through mGluR activation. The results are consistent with the hypothesis that inhibition of NAAG peptidase may reduce excitotoxic events associated with TBI.

Excitotoxic mechanisms and the role of astrocytic glutamate transporters in traumatic brain injury

Glutamate excitotoxicity plays an important role in the development of secondary injuries that occur following traumatic brain injury (TBI), and contributes significantly to expansion of the total volume of injury. Acute increases in extracellular glutamate levels have been detected in both experimental brain trauma models and in human patients, and can lead to over-stimulation of glutamate receptors, resulting in a cascade of excitotoxic-related mechanisms culminating in neuronal damage. These elevated levels of glutamate can be effectively controlled by the astrocytic glutamate transporters GLAST (EAAT1) and GLT-1 (EAAT2). However, evidence indicate these transporters and splice variant are downregulated shortly following the insult, which then precipitates glutamate-mediated excitotoxic conditions. Lack of success with glutamate receptor antagonists as a potential source of clinical intervention treatment following TBI has resulted in the necessity for a better understanding of the mechanisms that underlie the process of excitotoxicity, including the function and regulation of glutamate transporters. Such new insight should improve the likelihood of development of novel avenues for therapeutic intervention following TBI.

Lateral fluid percussion injury in the developing rat causes an acute, mild behavioral dysfunction in the absence of significant cell death

Lateral fluid percussion injury (LFP), a model of mild-moderate concussion, leads to the temporary loss of the capacity for experience-dependent plasticity in developing rats. To determine if this injury-induced loss in capacity for plasticity is due to cell death, we conducted stereological measurements within the cerebral cortex and CA3 of the hippocampus 2 weeks following mild, moderate or severe LFP in the post-natal day 19 (P19) rat. Results indicated that there was no significant change in the absolute number of neurons, regardless of injury severity, in either the ipsilateral cortex (sham = 10.6 +/- 1.7, mild = 11.5 +/- 2.1, moderate = 10.0 +/- 1.0, severe = 10.9 +/- 1.3 million neurons) or CA3 region of the hippocampus (sham = 251 +/- 38, mild = 289 +/- 2, moderate = 245 +/- 48, severe = 255 +/- 62 thousand neurons). Even though there was no evidence of a significant degree of injury-induced cell death, animals exhibited cognitive deficits as revealed in a Morris water maze task (MWM). The MWM results indicated that regardless of injury severity, P19-injured rats exhibited a significant increase in escape latency compared to age-matched shams (injury by day; P < 0.001) and a significant increase in the number of trials needed to reach criterion (P < 0.05). Analysis of a probe trial one week post-MWM training, however, indicated that there was no deficit in storage or recall of the learned behavior as analyzed by platform hits (sham = 2.9 +/- 0.37, mild = 2.0 +/- 0.40, moderate = 1 +/- 0, severe = 2.8 +/- 0.62) or percent time spent in, or immediately surrounding, the platform area (sham = 13.5 +/- 1.71, mild = 10.8 +/- 2.32, moderate = 12.7 +/- 0, severe = 13.5 +/- 1.69). Taken together, these results indicate that while LFP in P19-injured animals does not lead to significant cell death, it does generate acute, mild deficits in MWM performance.

Age-dependent reduction of cortical contusion volume by ketones after traumatic brain injury

Although the adult brain primarily metabolizes glucose, the evidence from the starvation literature has demonstrated that the adult brain retains some potential to revert to ketone metabolism. This attribute has been exploited recently to shift the adult brain toward ketone metabolism after traumatic brain injury (TBI), resulting in increased cerebral uptake and oxidation of exogenously administered ketones and improved cerebral energy. The ability to utilize ketones as an alternative substrate decreases with cerebral maturation, suggesting that the younger brain has a greater ability to metabolize this substrate and may be more receptive to this therapy. It was hypothesized that the administration of ketones after TBI in the developing brain will decrease lesion size in an age-dependent manner. Postnatal day (PND) 17, 35, 45, and 65 rats were placed on either a standard or ketogenic (KG) diet after controlled cortical impact (CCI) injury. PND35 and PND45 KG-fed animals showed a 58% and 39% reduction in cortical contusion volume, respectively, at 7 days post-injury. The KG diet had no effect on contusion volume in PND17 and PND65 injured rats. Both PND35 and PND45 KG-fed groups revealed fewer Fluoro-Jade-positive cells in the cortex and hippocampus at 6 hr and showed earlier decreases in plasma lactate compared to standard-fed animals. The age-dependent ketogenic neuroprotection is likely related to age-related differences in cerebral metabolism of ketones and suggests that alternative substrate therapy has potential applications for younger head-injured patients.

Upregulation of pentose phosphate pathway and preservation of tricarboxylic acid cycle flux after experimental brain injury

The metabolic fate of [1,2 13C]-labeled glucose was determined in male control and unilateral controlled cortical impact (CCI) injured rats at 3.5 and 24 h after surgery. The concentration of 13C-labeled glucose, lactate, glutamate and glutamine were measured in the injured and contralateral cortex. CCI animals showed a 145% increase in 13C lactate in the injured cortex at 3.5 h, but not at 24 h after injury, indicating increased glycolysis in neurons and/or astrocytes ipsilateral to CCI. Total levels of 13C glutamate in cortical tissue extracts did not differ between groups. However, 13C glutamine increased by 40% in the left and 98% in the right cortex at 3.5 h after injury, most likely resulting from an increase in astrocytic metabolism of glutamate. Levels of 13C incorporation into the glutamine isotopomers had returned to control levels by 24 h after CCI. The singlet to doublet ratio of the lactate C3 resonances was calculated to estimate the flux of glucose through the pentose phosphate pathway (PPP). CCI resulted in bilateral increases (9-12%) in the oxidation of glucose via the PPP, with the largest increase occurring at 24 h. Since an increase in PPP activity is associated with NADPH generation, the data suggest that there was an increasing need for reducing equivalents after CCI. Furthermore, 13C was incorporated into glutamate and glutamine isotopomers associated with multiple turns of the tricarboxylic acid (TCA) cycle, indicating that oxidative phosphorylation of glucose was maintained in the injured cortex at 3.5 and 24 h after a moderate to severe CCI injury.

Routine and quantitative EEG in mild traumatic brain injury

This article reviews the pathophysiology of mild traumatic brain injury, and the findings from EEG and quantitative EEG (QEEG) testing after such an injury. Research on the clinical presentation and pathophysiology of mild traumatic brain injury is reviewed with an emphasis on details that may pertain to EEG or QEEG and their interpretation. Research reports on EEG and QEEG in mild traumatic brain injury are reviewed in this setting, and conclusions are drawn about general diagnostic results that can be determined using these tests. QEEG strengths and weaknesses are reviewed in the context of factors used to determine the clinical usefulness of proposed diagnostic tests. Clinical signs, symptoms, and the pathophysiologic axonal injury and cytotoxicity tend to clear over weeks or months after a mild head injury. Loss of consciousness might be similar to a non-convulsive seizure and accompanied subsequently by postictal-like symptoms. EEG shows slowing of the posterior dominant rhythm and increased diffuse theta slowing, which may revert to normal within hours or may clear more slowly over many weeks. There are no clear EEG or QEEG features unique to mild traumatic brain injury. Late after head injury, the correspondence is poor between electrophysiologic findings and clinical symptoms. Complicating factors are reviewed for the proposed commercial uses of QEEG as a diagnostic test for brain injury after concussion or mild traumatic brain injury. The pathophysiology, clinical symptoms and electrophysiological features tend to clear over time after mild traumatic brain injury. There are no proven pathognomonic signatures useful for identifying head injury as the cause of signs and symptoms, especially late after the injury.

Restoration of Cerebral Vasoreactivity by an L-Type Calcium Channel Blocker following Fluid Percussion Brain Injury

Traumatic brain injury (TBI) results in significant acute reductions in regional cerebral blood flow (rCBF). However, the mechanisms by which TBI impairs CBF and cerebral vascular reactivity have remained elusive. In the present study, the effect of verapamil, an L-type calcium (Ca(2+)) channel blocker, on post-traumatic vascular reactivity was evaluated following a lateral fluid percussion injury (FPI) in rats. rCBF was measured by [(14)C]-iodoantipyrine autoradiography 1 h after FPI. Following FPI, significant rCBF reductions were documented in all examined cortical areas. These reductions were the most prominent (72.0%) at the primary injury site. Intravenous infusion of verapamil (VE; 200 microg/kg/min), and norepinephrine (NE; 20 microg/mL/min) to maintain normal blood pressure, increased rCBF by 141.5% at the primary injury site when compared to untreated, FPinjured animals. Under stimulated conditions, both the ipsilateral and contralateral hemispheres failed to show any increases in rCBF at 1 h following FPI. In direct contrast, following VE+NE treatment all cortical areas measured showed near normal vascular reactivity to direct cortical stimulation (normal reactivity = 45% increase in rCBF vs. 47% increase in FPI+VE+NE cases). These findings suggest that the majority of post-traumatic hemodynamic depressions are closely related to mechanisms involving vasoconstriction. Furthermore, Ca(2+) may play a causative role in this vasoconstriction and the loss of vasoreactivity.

Lateral fluid percussion brain injury: a 15-year review and evaluation

This article comprehensively reviews the lateral fluid percussion (LFP) model of traumatic brain injury (TBI) in small animal species with particular emphasis on its validity, clinical relevance and reliability. The LFP model, initially described in 1989, has become the most extensively utilized animal model of TBI (to date, 232 PubMed citations), producing both focal and diffuse (mixed) brain injury. Despite subtle variations in injury parameters between laboratories, universal findings are evident across studies, including histological, physiological, metabolic, and behavioral changes that serve to increase the reliability of the model. Moreover, demonstrable histological damage and severity-dependent behavioral deficits, which partially recover over time, validate LFP as a clinically-relevant model of human TBI. The LFP model, also has been used extensively to evaluate potential therapeutic interventions, including resuscitation, pharmacologic therapies, transplantation, and other neuroprotective and neuroregenerative strategies. Although a number of positive studies have identified promising therapies for moderate TBI, the predictive validity of the model may be compromised when findings are translated to severely injured patients. Recently, the clinical relevance of LFP has been enhanced by combining the injury with secondary insults, as well as broadening studies to incorporate issues of gender and age to better approximate the range of human TBI within study design. We conclude that the LFP brain injury model is an appropriate tool to study the cellular and mechanistic aspects of human TBI that cannot be addressed in the clinical setting, as well as for the development and characterization of novel therapeutic interventions. Continued translation of pre-clinical findings to human TBI will enhance the predictive validity of the LFP model, and allow novel neuroprotective and neuroregenerative treatment strategies developed in the laboratory to reach the appropriate TBI patients.

NMDA and age dependent cerebral hemodynamics after traumatic brain injury

Activation of N-methyl-D-aspartate (NMDA) glutamatergic receptors elicits cerebrovascular dilation, may couple local cerebral metabolism to blood flow but contribute to excitotoxic neuronal cell death. While cerebral hemodynamics following traumatic brain injury may correlate with neurologic status, the role of NMDA vascular activity is uncertain in the sequelae of brain injury. NMDA dilation was impaired following fluid percussion brain injury (FPI) in an age dependent manner in the pig and the newly described opioid nociceptin/orphanin FQ (NOC/ oFQ) contributes to such impairment via the cyclooxygenase dependent generation of superoxide. Further, hypotensive pial artery dilation (PAD) was blunted after FPI but partially protected by pretreatment with the NMDA antagonist MK801. Cerebral blood flow (CBF) was reduced during normotension by FPI, further reduced by hypotension, but both were partially protected by MK801 in the newborn. In contrast, blunted hypotensive PAD was protected significantly less by MK801 in the juvenile pig. Similarly, MK801 had less protective effect on normotensive and hypotensive CBF values post FPI in the juvenile. These data indicate that NMDA receptor activation contributes to impaired hypotensive cerebral hemodynamics following FPI in an age dependent manner. Further, these data suggest that NMDA receptor activation, NOC/oFQ, and prostaglandins dynamically interact to impair cerebral hemodynamics following FPI.

Relationship between flow-metabolism uncoupling and evolving axonal injury after experimental traumatic brain injury

Blood flow-metabolism uncoupling is a well-documented phenomenon after traumatic brain injury, but little is known about the direct consequences for white matter. The aim of this study was to quantitatively assess the topographic interrelationship between local cerebral blood flow (LCBF) and glucose metabolism (LCMRglc) after controlled cortical impact injury and to determine the degree of correspondence with the evolving axonal injury. LCMRglc and LCBF measurements were obtained at 3 hours in the same rat from 18F-fluorodeoxyglucose and 14C-iodoantipyrine coregistered autoradiographic images, and compared to the density of damaged axonal profiles in adjacent sections and in an additional group at 24 hours using beta-amyloid precursor protein (beta-APP) immunohistochemistry. LCBF was significantly reduced over the ipsilateral hemisphere by 48 +/- 15% compared with sham-controls, whereas LCMRglc was unaffected, apart from foci of elevated LCMRglc in the contusion margin. Flow-metabolism was uncoupled, indicated by a significant 2-fold elevation in the LCMRglc/LCBF ratio within most ipsilateral structures. There was a significant increase in beta-APP-stained axons from 3 to 24 hours, which was negatively correlated with LCBF and positively correlated with the LCMRglc/LCBF ratio at 3 hours in the cingulum and corpus callosum. Our study indicates a possible dependence of axonal outcome on flow-metabolism in the acute injury stage.

Effect of mild hypothermia on brain dialysate lactate after fluid percussion brain injury in rodents

OBJECTIVE

To investigate the effects of mild hypothermia on brain microdialysate lactate after fluid percussion traumatic brain injury (TBI) in rats.

METHODS

Brain dialysate lactate before and after fluid percussion brain injury (2.1 +/- 0.2 atm) was measured in rats with preinjury mild hypothermia (32 degrees C), postinjury mild hypothermia (32 degrees C), injury normothermia (37 degrees C), and the sham control group. Mild hypothermia (32 degrees C) was induced by partial immersion in a water bath (0 degrees C) under general anesthesia and maintained for 2 hours.

RESULTS

In the normothermia TBI group, brain extracellular fluid lactate increased from 0.311 +/- 0.03 to 1.275 +/- 0.08 mmol/L within 30 minutes after TBI (P < 0.01) and remained at a high level (0.546 +/- 0.05 mmol/L) (P < 0.01) at 2 hours after injury. In the postinjury mild hypothermic group, brain extracellular fluid lactate increased from 0.303 +/- 0.03 to 0.875 +/- 0.05 mmol/L at 15 minutes after TBI (P < 0.01) and then gradually decreased to 0.316 +/- 0.04 mmol/L at 2 hours after TBI (P > 0.05). In the preinjury mild hypothermic group, brain extracellular fluid lactate remained at normal levels after injury (P > 0.05).

CONCLUSION

The cerebral extracellular fluid lactate level increases significantly after fluid percussion brain injury. Preinjury mild hypothermia completely inhibits the cerebral lactate accumulation, and early postinjury mild hypothermia significantly blunts the increase of cerebral lactate level after fluid percussion injury.

Nitric oxide in traumatic brain injury

Nitric oxide (NO) is a gaseous chemical messenger which has functions in the brain in a variety of broad physiological processes, including control of cerebral blood flow, interneuronal communications, synaptic plasticity, memory formation, receptor functions, intracellular signal transmission, and release of neurotransmitters. As might be expected from the numerous and complex roles that NO normally has, it can have both beneficial and detrimental effects in disease states, including traumatic brain injury. There are two periods of time after injury when NO accumulates in the brain, immediately after injury and then again several hours-days later. The initial immediate peak in NO after injury is probably due to the activity of endothelial NOS and neuronal NOS. Pre-injury treatment with 7-nitroindazole, which probably inhibits this immediate increase in NO by neuronal NOS, is effective in improving neurological outcome in some models of traumatic brain injury (TBI). After the initial peak in NO, there can be a period of relative deficiency in NO. This period of low NO levels is associated with a low cerebral blood flow (CBF). Administration of L-arginine at this early time improves CBF, and outcome in many models. The late peak in NO after traumatic injury is probably due primarily to the activity of inducible NOS. Inhibition of inducible NOS has neuroprotective effects in most models.

Acute ethanol intoxication in a model of traumatic brain injury: the protective role of moderate doses demonstrated by immunoreactivity of synaptophysin in hippocampal neurons

Although ethanol intoxication is reported to be a complicating factor in traumatic brain injury, some recent studies are indicating its possible protective role especially at lower doses. Ethanol inhibition of NMDA-mediated excitotoxicity which predominates at lower doses is believed to be responsible for this protection. The aim of this study was to demonstrate this neuroprotective role of alcohol using immunoreactivity for synaptophysin as an indirect marker for severity of injury. Acute ethanol intoxication at moderate doses was performed 2 h prior to trauma. Severe traumatic brain injury was administrated using an impact acceleration model in Sprague-Dawley rats. At post-traumatic 48th hour, immunorectivity for synapthophysin in the rat hippocampi was evaluated under light microscopy. According to our results there were slight increases in immunoreactivity for synaptophysin in the stratum oriens and striatum radiatum of CA1 subfield of hippocampus when ethanol was administered prior to trauma comparing to moderate increase in the trauma-only group. On the other hand vacuolar degeneration and red neuron formation was more prominent in the pyramidal cell layer of CA1 and CA3 when ethanol was not administered. Ethanol may have a neuroprotective role when administered at moderate doses prior to traumatic brain injury. This effect of ethanol may primarily be due to inhibition of NMDA receptors.

Neuronal activity and cortical perfusion determined by quantitative EEG analysis and laser doppler flowmetry are uncoupled in brain injured rats

Following traumatic brain injury uncoupling of metabolism from perfusion, reflected by an increase in cellular activity in face of reduced perfusion contributes to secondary tissue damage. Standard autoradiographic techniques employed to study metabolism and perfusion are limited by the inability to perform longitudinal investigations. Therefore, the aims of this study were to investigate if metabolic uncoupling can be studied by applying noninvasive and non-radioactive methods. For this, quantitative EEG analysis and laser Doppler flowmetry were employed to determine changes in EEG activity as a global measure of neuronal activity and pericontusional cortical perfusion during the early phase following controlled cortical impact injury (CCII). In eight rats changes in neuronal activity and pericontusional cortical perfusion were determined before, at 4 and 24 hours after CCII. Neuronal activity was significantly increased by 40% at 4 hours after CCII followed by a significant decrease by 60% at 24 hours compared to pre-trauma levels. Pericontusional cortical perfusion was significantly reduced by 45% and 18% at 4 and 24 hours after CCII. respectively. Non-radioactive methods like quantitative EEG analysis and laser Doppler flowmetry can be used to reveal underlying uncoupling of EEG activity from cortical perfusion which is mostly sustained in the early phase following CCII.

Hyperglycolysis is exacerbated after traumatic brain injury with fentanyl vs. isoflurane anesthesia in rats

Despite common use of narcotics in the clinical management of severe traumatic brain injury (TBI), in experimental models rats treated with fentanyl have exhibited worse functional outcome and more CA1 hippocampal death than rats treated with standard isoflurane anesthesia. We hypothesized that greater post-traumatic excitotoxicity, reflected by cerebral glucose utilization (CMRglu), may account for detrimental effects of fentanyl vs. isoflurane. Rats were anesthetized with either isoflurane (1% by inhalation) or fentanyl (10 mcg/kg iv bolus then 50 mcg/kg/h infusion). 14C-deoxyglucose autoradiography was performed 45 min after controlled cortical impact (CCI) to left parietal cortex (n=4 per anesthetic group) or in uninjured rats after 45 min of anesthesia (n=3 per anesthetic group). Uninjured rats treated with fentanyl vs. isoflurane showed 35-45% higher CMRglu in all brain structures (p<0.05) except CA3. After TBI in rats treated with isoflurane, CMRglu increased significantly only in ipsilateral CA1 and ipsilateral parietal cortex (p<0.05 vs. isoflurane uninjured). Conversely, after TBI in rats treated with fentanyl, CMRglu increased markedly and bilaterally in CA1 and CA3 (p<0.05 vs. fentanyl uninjured), but not ipsilateral parietal cortex. In contralateral CA1, CMRglu was nearly two times greater after TBI in fentanyl vs. isoflurane treated rats (p<0.05). Hyperglycolysis was exacerbated in CA1 and CA3 hippocampus after TBI in rats treated with fentanyl vs. isoflurane anesthesia. This post-traumatic hyperglycolysis suggests greater excitotoxicity and concurs with reports of worse functional outcome and more CA1 hippocampal death after TBI with fentanyl vs. isoflurane anesthesia.

Energy dysfunction as a predictor of outcome after moderate or severe head injury: indices of oxygen, glucose, and lactate metabolism

The purpose of this study was to determine if the relationship between abnormalities in glucose, lactate, and oxygen metabolism were predictive of neurologic outcome after moderate or severe head injury, relative to other known prognostic factors. Serial assessments of the cerebral metabolic rates for glucose, lactate, and oxygen were performed using a modified Kety-Schmidt method. In total, 31 normal control subjects were studied once, and 49 TBI patients (mean age 36+/-16 years, median GCS 7) were studied five times median per patient from postinjury days 0 to 9. Univariate and multivariate analyses were performed. Univariate analysis showed that the 6-month postinjury Glasgow Outcome Scale (GOS) was most strongly associated with the mean cerebral metabolic rate of oxygen (CMRO2) (P = 0.0001), mean arterial lactate level (P = 0.0001), mean arterial glucose (P = 0.0008), mean cerebral blood flow (CBF), (P = 0.002), postresuscitation GCS (P = 0.003), and pupillary status (P = 0.004). Brain lactate uptake was observed in 44% of all metabolic studies, and 76% of patients had at least one episode of brain lactate uptake. By dichotomized GOS, patients achieving a favorable outcome (GOS 4-5) were distinguished from those with an unfavorable outcome (GOS1-3) by having a higher CMRO2 (P = 0.003), a higher rate of abnormal brain lactate uptake relative to arterial lactate levels (P = 0.04), and lesser degrees of blood-brain barrier damage based on CT findings (P = 0.03).

CONCLUSIONS

During the first 6 days after moderate or severe TBI, CMRO2 and arterial lactate levels are the strongest predictors of neurologic outcome. However, the frequent occurrence of abnormal brain lactate uptake despite only moderate elevations in arterial lactate levels in the favorable outcome patients suggests the brain's ability to use lactate as a fuel may be another key outcome predictor. Future studies are needed to determine to what degree nonglycolytic energy production from alternative fuels such as lactate occurs after TBI and whether alternative fuel administration is a viable therapy for TBI patients.

Metabolic changes in the vicinity of brain contusions: a proton magnetic resonance spectroscopy and histology study

Proton MR spectroscopy (1H-MRS) has been previously used to monitor metabolic changes in areas of diffuse brain injury. We studied metabolism in the close vicinity of experimental traumatic brain contusions and remote on the contralateral side from 1h to 28d post-injury. Changes of creatine and phosphocreatine (Cr&PCr), N-acetylaspartate (NAA), choline (Cho), inositol (Ino), taurine (Tau), glutamate (Glu), and lactate (Lac) were assessed and compared to neuronal, glial and inflammatory changes in histology. In the pericontusional zone Cr&PCr, NAA, and Glu decreased immediately after trauma by -35%, -60%, and -37%, respectively, related to primary cell disintegration and secondary perturbations as reflected in histology. These metabolites partially recovered at 7d (-15%, -37%, and -21% respectively), in parallel to indicators of repair in immunhistochemistry. Control levels were not regained at 28d, in correlation to a decrease of viable neurons. Cho and Ino, initially lowered by -26% and -31% respectively, increased at 7d by +74% and 31%, reflecting glial activation and proliferation. The signal including the lactate resonance increased by >1000% with a maximum at 7d, possibly related to energy failure, inflammation and glial activation. A partial contribution of lipids to this signal cannot be fully excluded. The contralateral side showed mild astroglial activation in histology, but no changes in 1H-MRS. The study demonstrates the feasibility of volume selective 1H-MRS using the LCModel (Linear Combination of Model in vitro spectra of metabolites solutions) to monitor metabolic changes close to focal traumatic lesions and suggests how metabolic alterations can be differentiated in cause.

Persistently low extracellular glucose correlates with poor outcome 6 months after human traumatic brain injury despite a lack of increased lactate: a microdialysis study

Disturbed glucose brain metabolism after brain trauma is reflected by changes in extracellular glucose levels. The authors hypothesized that posttraumatic reductions in extracellular glucose levels are not due to ischemia and are associated with poor outcome. Intracerebral microdialysis, electroencephalography, and measurements of brain tissue oxygen levels and jugular venous oxygen saturation were performed in 30 patients with traumatic brain injury. Levels of glucose, lactate, pyruvate, glutamate, and urea were analyzed hourly. The 6-month Glasgow Outcome Scale extended (GOSe6) score was assessed for each patient. In regions of increased glucose utilization defined by positron emission tomography, the extracellular glucose concentration was less than 0.2 mmol/l. Extracellular glucose values were less than 0.2 mmol during postinjury days 0 to 7 in 19% to 30% of hourly samples on each day. Transient decreases in glucose levels occurred with electrographic seizures and nonischemic reductions in cerebral perfusion pressure and jugular venous oxygen saturation. Glutamate levels were elevated in the majority of low-glucose samples, but the lactate/pyruvate ratio did not indicate focal ischemia. Terminal herniation resulted in reductions in glucose with increases in the lactate/pyruvate ratio but not in lactate concentration alone. GOSe6 scores correlated with persistently low glucose levels, combined early low glucose levels and low lactate/glucose ratio, and with the overall lactate/glucose ratio. These results suggest that the level of extracellular glucose is typically reduced after traumatic brain injury and associated with poor outcome, but is not associated with ischemia.