Augmented neuronal death in CA3 hippocampus following hyperventilation early after controlled cortical impact

Selective vulnerability of hippocampal CA1 and CA3 pyramidal cells: What are possible pathomechanisms and should more attention be paid to the CA3 region in future studies?

Transient ischemia and reperfusion selectively damage neurons in brain, with hippocampal pyramidal cells being particularly vulnerable. Even within hippocampus, heterogeneous susceptibility is evident, with higher vulnerability of CA1 versus CA3 neurons described for several decades. Therefore, numerous studies have focused exclusively on CA1. Pediatric cardiac surgery is increasingly focusing on studies of hippocampal structures, and a negative impact of cardiopulmonary bypass on the hippocampus cannot be denied. Recent studies show a shift in selective vulnerability from neurons of CA1 to CA3. This review shows that cell damage is increased in CA3, sometimes stronger than in CA1, depending on several factors (method, species, age, observation period). Despite a highly variable pattern, several markers illustrate greater damage to CA3 neurons than previously assumed. Nevertheless, the underlying cellular mechanisms have not been fully deciphered to date. The complexity is reflected in possible pathomechanisms discussed here, with numerous factors (NMDA, kainate and AMPA receptors, intrinsic oxidative stress potential and various radicals, AKT isoforms, differences in vascular architecture, ratio of pro- and anti-apoptotic Bcl-2 factors, vulnerability of interneurons, mitochondrial dysregulation) contributing to either enhanced CA1 or CA3 vulnerability. Furthermore, differences in expressed genome, proteome, metabolome, and transcriptome in CA1 and CA3 appear to influence differential behavior after damaging stimuli, thus metabolomics-, transcriptomics-, and proteomics-based analyses represent a viable option to identify pathways of selective vulnerability in hippocampal neurons. These results emphasize that future studies should focus on the CA3 field in addition to CA1, especially with regard to improving therapeutic strategies after ischemic/hypoxic brain injury.

mNSCs overexpressing Rimkla transplantation facilitates cognitive recovery in a mouse model of traumatic brain injury

N-acetyl aspartyl-glutamate (NAAG) is easily inactivated for the hydrolysis of NAAG peptidase on the surface of glial cells, thereby losing its endogenous neuroprotective effect after traumatic brain injury. In this study, lentiviral vectors were used to over express/knock out NAAG synthetase II (Rimkla) in mouse embryonic neural stem cells (mNSCs) in vitro and these mNSCs were transplanted at the lesion site in a mouse model of controlled cortical impact (CCI). In vivo experiments showed that transplantation of mNSCs overexpressing Rimkla regulated glutamate-glutamine cycling between adjacent astrocytes and neurons in the subacute phase of CCI, thereby enhancing support for neuronal metabolism and promoting neuronal synaptic repair in the hippocampal CA3 region. Taken together, these findings demonstrate that transplantation of neural stem cells overexpressing Rimkla can effectively increase the NAAG concentration in local brain regions, which opens up new ideas for the maintenance of NAAG neuroprotective effects after TBI.

Optimal Targets of the First 24-h Partial Pressure of Carbon Dioxide in Patients with Cerebral Injury: Data from the MIMIC-III and IV Database

BACKGROUND

It is generally believed that hypercapnia and hypocapnia will cause secondary injury to patients with craniocerebral diseases, but a small number of studies have shown that they may have potential benefits. We assessed the impact of partial pressure of arterial carbon dioxide (PaCO₂) on in-hospital mortality of patients with craniocerebral diseases. The hypothesis of this research was that there is a nonlinear correlation between PaCO₂ and in-hospital mortality in patients with craniocerebral diseases and that mortality rate is the lowest when PaCO₂ is in a normal range.

METHODS

We identified patients with craniocerebral diseases from Medical Information Mart for Intensive Care third and fourth edition databases. Cox regression analysis and restricted cubic splines were used to examine the association between PaCO₂ and in-hospital mortality.

RESULTS

Nine thousand six hundred and sixty patients were identified. A U-shaped association was found between the first 24-h PaCO₂ and in-hospital mortality in all participants. The nadir for in-hospital mortality risk was estimated to be at 39.5 mm Hg (p for nonlinearity < 0.001). In the subsequent subgroup analysis, similar results were found in patients with traumatic brain injury, metabolic or toxic encephalopathy, subarachnoid hemorrhage, cerebral infarction, and other encephalopathies. Besides, the mortality risk reached a nadir at PaCO₂ in the range of 35-45 mm Hg. The restricted cubic splines showed a U-shaped association between the first 24-h PaCO₂ and in-hospital mortality in patients with other intracerebral hemorrhage and cerebral tumor. Nonetheless, nonlinearity tests were not statistically significant. In addition, Cox regression analysis showed that PaCO₂ ranging 35-45 mm Hg had the lowest death risk in most patients. For patients with hypoxic-ischemic encephalopathy and intracranial infections, the first 24-h PaCO₂ and in-hospital mortality did not seem to be correlated.

CONCLUSIONS

Both hypercapnia and hypocapnia are harmful to most patients with craniocerebral diseases. Keeping the first 24-h PaCO₂ in the normal range (35-45 mm Hg) is associated with lower death risk.

Temporal lobe contusions on computed tomography are associated with impaired 6-month functional recovery after mild traumatic brain injury: a TRACK-TBI study

INTRODUCTION

Mild traumatic brain injury (MTBI) can cause persistent functional deficits and healthcare burden. Understanding the association between intracranial contusions and outcome may aid in MTBI treatment and prognosis.

METHODS

MTBI patients with Glasgow Coma Scale 13-15 and 6-month outcomes [Glasgow Outcome Scale-Extended (GOSE)], without polytrauma from the prospective TRACK-TBI Pilot study were analyzed. Intracranial contusions on computed tomography (CT) were coded by location. Multivariable regression evaluated associations between intracranial injury type (temporal contusion [TC], frontal contusion, extraaxial [epidural/subdural/subarachnoid], other-intraaxial [intracerebral/intraventricular hemorrhage, axonal injury]) and GOSE. Odds ratios (OR) are reported.

RESULTS

Overall, 260 MTBI subjects were aged 44.4 ± 18.1-years; 67.7% were male. Ninety-seven subjects were CT-positive and 46 had contusions (41.3%-frontal, 30.4%-temporal, 21.7%-frontal + temporal, 2.2% each-parietal/occipital/brainstem); 95.7% had concurrent extraaxial hemorrhage. Mortality was 0% at discharge and 2.3% by 6-months. GOSE distribution was 2.3%-death, 1.5%-severe disability, 27.7%-moderate disability, 68.5%-good recovery. Forty-six percent of TC-positive subjects suffered moderate disability or worse (GOSE ≤6) and 41.7% were unable to return to baseline work capacity (RTBWC), compared to 29.1%/20.4% for CT-negative and 26.1%/20.9% for CT-positive subjects without TC. On multivariable regression, TC associated with OR = 3.33 (95% CI [1.16-9.60], p = 0.026) for GOSE ≤6, and OR = 4.48 ([1.49-13.51], p = 0.008) for inability to RTBWC.

CONCLUSIONS

Parenchymal contusions in MTBI are often accompanied by extraaxial hemorrhage. TCs may be associated with 6-month functional impairment. Their presence on imaging should alert the clinician to the need for heightened surveillance of sequelae complicating RTBWC, with low threshold for referral to services.

Divergent Induction of Branched-Chain Aminotransferases and Phosphorylation of Branched Chain Keto-Acid Dehydrogenase Is a Potential Mechanism Coupling Branched-Chain Keto-Acid-Mediated-Astrocyte Activation to Branched-Chain Amino Acid Depletion-Mediated Cognitive Deficit after Traumatic Brain Injury

Deficient branched-chain amino acids (BCAAs) are implicated in cognitive dysfunction after traumatic brain injury (TBI). The mechanism remains unknown. BCAAs are catabolized by neuron-specific cytosolic and astrocyte-specific mitochondrial branched-chain aminotransferases (BCATc, BCATm) to generate glutamate and branched-chain keto-acids (BCKAs) that are metabolized by the mitochondrial branched-chain keto-acid dehydrogenase (BCKD) whose activity is regulated by its phosphorylation state. BCKD phosphorylation by BCKD kinase (BCKDK) inactivates BCKD and cause neurocognitive dysfunction, whereas dephosphorylation by specific phosphatase restores BCKD activity. Real-time polymerase chain reaction showed rapidly and significantly decreased BCATc messenger RNA (mRNA) levels, but significantly increased BCATm mRNA level post-CCI (controlled cortical impact). BCKD and BCKDK mRNA decreased significantly immediately after CCI-induced TBI (CCI) in the rat. Phosphorylated BCKD proteins (pBCKD) increased significantly in the ipsilateral-CCI hemisphere. Immunohistochemistry revealed significantly increased pBCKD proteins in ipsilateral astrocytes post-CCI. BCKD protein expression is higher in primarily cultured cortical neurons than in astrocytes, whereas pBCKD protein level is higher in astrocytes than in cortical neurons. Transforming growth factor beta treatment (10 μg/mL for 48 h) significantly increased pBCKD protein expression in astrocytes, whereas glutamate treatment (25 μM for 24 h) significantly decreased pBCKD protein in neurons. Because increased pBCKD would lead to increased BCKA accumulation, BCKA-mediated astrocyte activation, cell death, and cognitive dysfunction as found in maple syrup urine disease; thus, TBI may potentially induce cognitive deficit through diverting BCAA from glutamate production in neurons to BCKA production in astrocytes through the pBCKD-dependent mechanism.

Environmental Hyperthermia in Prehospital Patients with Major Traumatic Brain Injury

BACKGROUND

Traumatic brain injury (TBI) results in an estimated 1.7 million emergency department visits each year in the United States. These injuries frequently occur outside, leaving injured individuals exposed to environmental temperature extremes before they are transported to a hospital.

OBJECTIVE

Evaluate the existing literature for evidence that exposure to high temperatures immediately after TBI could result in elevated body temperatures (EBTs), and whether or not EBTs affect patient outcomes.

DISCUSSION

It has been clear since the early 1980s that after brain injury, exposure to environmental temperatures can cause hypothermia, and that this represents a significant contributor to increased morbidity and mortality. Less is known about elevated body temperature. Early evidence from the Iraq and Afghanistan wars indicated that exposure to elevated environmental temperatures in the prehospital setting may result in significant EBTs, however, it is unclear what impact these EBTs might have on outcomes in TBI patients. In the hospital, EBT, or neurogenic fever, is thought to be due to the acute-phase reaction that follows critical injury, and these high body temperatures are associated with poor outcomes after TBI.

CONCLUSION

Hospital data suggest that EBTs are associated with poor outcomes, and some preliminary reports suggest that early EBTs are common after TBI in the prehospital setting. However, it remains unclear whether patients with TBI have an increased risk of EBTs after exposure to high environmental temperatures, or if this very early "hyperthermia" might cause secondary injury after TBI.

Evaluation of the impact of implementing the emergency medical services traumatic brain injury guidelines in Arizona: the Excellence in Prehospital Injury Care (EPIC) study methodology

Traumatic brain injury (TBI) exacts a great toll on society. Fortunately, there is growing evidence that the management of TBI in the early minutes after injury may significantly reduce morbidity and mortality. In response, evidence-based prehospital and in-hospital TBI treatment guidelines have been established by authoritative bodies. However, no large studies have yet evaluated the effectiveness of implementing these guidelines in the prehospital setting. This article describes the background, design, implementation, emergency medical services (EMS) treatment protocols, and statistical analysis of a prospective, controlled (before/after), statewide study designed to evaluate the effect of implementing the EMS TBI guidelines-the Excellence in Prehospital Injury Care (EPIC) study (NIH/NINDS R01NS071049, "EPIC"; and 3R01NS071049-S1, "EPIC4Kids"). The specific aim of the study is to test the hypothesis that statewide implementation of the international adult and pediatric EMS TBI guidelines will significantly reduce mortality and improve nonmortality outcomes in patients with moderate or severe TBI. Furthermore, it will specifically evaluate the effect of guideline implementation on outcomes in the subgroup of patients who are intubated in the field. Over the course of the entire study (~9 years), it is estimated that approximately 25,000 patients will be enrolled.

Traumatic brain injury precipitates cognitive impairment and extracellular Aβ aggregation in Alzheimer's disease transgenic mice

Traumatic brain injury (TBI) has become a signature wound of the wars in Iraq and Afghanistan. Many American soldiers, even those undiagnosed but likely suffering from mild TBI, display Alzheimer's disease (AD)-like cognitive impairments, suggesting a pathological overlap between TBI and AD. This study examined the cognitive and neurohistological effects of TBI in presymptomatic APP/PS1 AD-transgenic mice. AD mice and non-transgenic (NT) mice received an experimental TBI on the right parietal cortex using the controlled cortical impact model. Animals were trained in a water maze task for spatial memory before TBI, and then reevaluated in the same task at two and six weeks post-TBI. The results showed that AD mice with TBI made significantly more errors in the task than AD mice without TBI and NT mice regardless of TBI. A separate group of AD mice and NT mice were evaluated neurohistologically at six weeks after TBI. The number of extracellular beta-amyloid (Aβ)-deposits significantly increased by at least one fold in the cortex of AD mice that received TBI compared to the NT mice that received TBI or the AD and NT mice that underwent sham surgery. A significant decrease in MAP2 positive cells, indicating neuronal loss, was observed in the cortex of both the AD and NT mice that received TBI compared to the AD and NT mice subjected to sham surgery. Similar changes in extracellular Aβ deposits and MAP2 positive cells were also seen in the hippocampus. These results demonstrate for the first time that TBI precipitates cognitive impairment in presymptomatic AD mice, while also confirming extracellular Aβ deposits following TBI. The recognition of this pathological link between TBI and AD should aid in developing novel treatments directed at abrogating cellular injury and extracellular Aβ deposition in the brain.

The relationship between out-of-hospital airway management and outcome among trauma patients with Glasgow Coma Scale Scores of 8 or less

BACKGROUND

Airway management remains a fundamental component of optimal care of the severely injured patient, with endotracheal intubation representing the definitive strategy for airway control. However, multiple studies document an association between out-of-hospital intubation and increased mortality for severe traumatic brain injury.

OBJECTIVES

To explore the relationship between out-of-hospital intubation attempts and outcome among trauma patients with Glasgow Coma Scale (GCS) scores ≤ 8 across sites participating in the Resuscitation Outcomes Consortium (ROC).

METHODS

The ROC Epistry-Trauma, an epidemiologic database of prehospital encounters with critically injured trauma victims, was used to identify emergency medical services (EMS)-treated patients with GCS scores ≤ 8. Multiple logistic regression was used to explore the association between intubation attempts and vital status at discharge, adjusting for the following covariates: age, gender, GCS score, hypotension, mechanism of injury, and ROC site. Sites were then stratified by frequency of intubation attempts and chi-square test for trend was used to associate the frequency of intubation attempts with outcome.

RESULTS

A total of 1,555 patients were included in this analysis; intubation was attempted in 758 of these. Patients in whom intubation was attempted had higher mortality (adjusted odds ratio [OR] 2.91, 95% confidence interval [CI] 2.13-3.98, p < 0.01). However, sites with higher rates of attempted intubation had lower mortality across all trauma victims with GCS scores ≤ 8 (OR 1.40, 95% CI 1.15-1.72, p < 0.01).

CONCLUSIONS

Patients in whom intubation is attempted have higher adjusted mortality. However, sites with a higher rate of attempted intubation have lower adjusted mortality across the entire cohort of trauma patients with GCS scores ≤ 8. Coma Scale score.

Pediatric neurointensive care: 2008 update for the Rogers' Textbook of Pediatric Intensive Care

OBJECTIVE

To review important articles, in the field of pediatric neurointensive care, that were published subsequent to the fourth edition of the Rogers' Textbook of Pediatric Intensive Care.

DATA SOURCES

The U.S. National Library of Medicine (http://www.ncbi.nlm.nih.gov/sites/entrezPubMed) was searched for the term pediatric and the following individual terms, cardiac arrest, asphyxia, traumatic brain injury, status epilepticus, stroke, cerebral ischemia, and cerebral hemorrhage, to generate abstracts of additional citations that were then screened for potential inclusion. The authors were also aware of a number of key recent articles in both pediatric and adult neurointensive care and these were also screened.

STUDY SELECTION AND DATA EXTRACTION

Promising articles were reviewed and the decision as to whether they were included was made at the discretion of the section editors.

DATA SYNTHESIS

Articles in four categories were included based on selected chapters in the neurointensive care section of the textbook, using the specific chapter heading in the textbook, namely, head and spinal cord trauma, hypoxic-ischemic encephalopathy, status epilepticus, and cerebrovascular disease and stroke.

CONCLUSION

Developments in the field and practice of pediatric neurocritical care continue with significant additions to the literature and practice recommendations concerning care following traumatic brain injury, cardiac arrest, status epilepticus, and cerebrovascular events. Importantly, the continued progression in knowledge raises the health services issue of whether, in certain settings of high clinical volume, it is time for specialized pediatric neurointensive care services or units.

Early ventilation in traumatic brain injury

While airway and ventilatory compromise are significant concerns following traumatic brain injury (TBI), there is little data supporting an aggressive approach to airway management by prehospital personnel, and a growing number of reports suggesting an association between early intubation and increased mortality. Recent clinical and experimental data suggest that hyperventilation is an important contributor to these adverse outcomes in TBI patients. Various mechanisms appear to be responsible for the worsened outcomes, including hemodynamic, cerebrovascular, immunologic and cellular effects. Here, relevant experimental and clinical data regarding the impact of ventilation on TBI are reviewed. In addition, experimental data regarding potential mechanisms for the adverse effects of hyperventilation and hypocapnia on the injured brain are presented. Finally, the limited data regarding the impact of hypoventilation and hypercapnia on outcome from TBI are discussed.

Normoxic ventilatory resuscitation following controlled cortical impact reduces peroxynitrite-mediated protein nitration in the hippocampus

OBJECTIVES

Ventilatory resuscitation with 100% O2 after severe traumatic brain injury (TBI) raises concerns about the increased production of reactive oxygen species (ROS). The product of peroxynitrite-meditated tyrosine residue nitration, 3-nitrotyrosine (3-NT), is a marker for oxidative damage to proteins. The authors hypothesized that posttraumatic resuscitation with hyperoxia (100% fraction of inspired oxygen [FiO2] concentration) results in increased ROS-induced damage to proteins compared with resuscitation using normoxia (21% FiO2 concentration).

METHODS

Male Sprague-Dawley rats underwent controlled cortical impact (CCI) injury and resuscitation with either normoxic or hyperoxic ventilation for 1 hour (5 rats per group). Twenty-four hours after injury, rat hippocampi were evaluated using 3-NT immunostaining. In a second experiment, animals similarly underwent CCI injury and normoxic or hyperoxic ventilation for 1 hour (4 rats per group). One week after injury, neuronal counts were performed after neuronal nuclei immunostaining.

RESULTS

The 3-NT staining was significantly increased in the hippocampi of the hyperoxic group. The normoxic group showed a 51.0% reduction of staining in the CA1 region compared with the hyperoxic group and a 50.8% reduction in the CA3 region (p < 0.05, both regions). There was no significant difference in staining between the injured normoxic group and sham-operated control groups. In the delayed analysis of neuronal survival (neuronal counts), there was no significant difference between the hyperoxic and normoxic groups.

CONCLUSIONS

In this clinically relevant model of TBI, normoxic resuscitation significantly reduced oxidative damage to proteins compared with hyperoxic resuscitation. Neuronal counts showed no benefit from hyperoxic resuscitation. These findings indicate that hyperoxic ventilation in the early stages after severe TBI may exacerbate oxidative damage to proteins.

Early ventilation and outcome in patients with moderate to severe traumatic brain injury

OBJECTIVES

An increase in mortality has been reported with early intubation in severe traumatic brain injury, possibly due to suboptimal ventilation. This analysis explores the impact of early ventilation on outcome in moderate to severe traumatic brain injury.

DESIGN

Retrospective, registry-based analysis.

SETTING

This study was conducted in a large county trauma system that includes urban, suburban, and rural jurisdictions.

PATIENTS

Nonarrest trauma victims with a Head Abbreviated Injury Score of > or =3 were identified from our county trauma registry.

INTERVENTIONS

Intubated patients were stratified into 5 mm Hg arrival PCO(2) increments. Logistic regression was used to calculate odds ratios for each increment, adjusting for age, gender, mechanism of injury, year of injury, preadmission Glasgow Coma Scale score, hypotension, Head Abbreviated Injury Score, Injury Severity Score, PO(2), and base deficit. Increments with the highest relative survival were used to define the optimal PCO(2) range. Outcomes for patients with arrival PCO(2) values inside and outside this optimal range were then explored for both intubated and nonintubated patients, adjusting for the same factors as defined previously. In addition, the independent outcome effect of hyperventilation and hypoventilation was assessed.

MEASUREMENTS AND MAIN RESULTS

A total of 890 intubated and 2,914 nonintubated patients were included. Improved survival was observed for the arrival PCO(2) range 30-49 mm Hg. Patients with arrival PCO(2) values inside this optimal range had improved survival and a higher incidence of good outcomes. Conversely, there was no improvement in outcomes for patients within this optimal PCO(2) range for nonintubated patients after adjusting for all of the factors defined previously. Both hyperventilation and hypoventilation were associated with worse outcomes in intubated but not nonintubated patients. The proportion of arrival PCO(2) values within the optimal range was lower for intubated vs. nonintubated patients.

CONCLUSIONS

Arrival hypercapnia and hypocapnia are common and associated with worse outcomes in intubated but not spontaneously breathing patients with traumatic brain injury.

Experimental models of traumatic brain injury: do we really need to build a better mousetrap?

Approximately 4000 human beings experience a traumatic brain injury each day in the United States ranging in severity from mild to fatal. Improvements in initial management, surgical treatment, and neurointensive care have resulted in a better prognosis for traumatic brain injury patients but, to date, there is no available pharmaceutical treatment with proven efficacy, and prevention is the major protective strategy. Many patients are left with disabling changes in cognition, motor function, and personality. Over the past two decades, a number of experimental laboratories have attempted to develop novel and innovative ways to replicate, in animal models, the different aspects of this heterogenous clinical paradigm to better understand and treat patients after traumatic brain injury. Although several clinically-relevant but different experimental models have been developed to reproduce specific characteristics of human traumatic brain injury, its heterogeneity does not allow one single model to reproduce the entire spectrum of events that may occur. The use of these models has resulted in an increased understanding of the pathophysiology of traumatic brain injury, including changes in molecular and cellular pathways and neurobehavioral outcomes. This review provides an up-to-date and critical analysis of the existing models of traumatic brain injury with a view toward guiding and improving future research endeavors.

A Follow-Up Analysis of Factors Associated with Head-Injury Mortality After Paramedic Rapid Sequence Intubation

BACKGROUND

The San Diego Paramedic Rapid Sequence Intubation (RSI) Trial documented an increase in mortality after paramedic RSI, with hyperventilation identified as a contributing factor in a small subgroup analysis. Here we explore factors affecting outcome in the entire cohort of patients undergoing paramedic RSI to confirm previous findings. This also represents a synthesis of findings from previous analyses

METHODS

Adult trauma patients with severe head injury (Glasgow Coma Scale score, 3-8) who could not be intubated without RSI were prospectively enrolled in the trial. This analysis excluded patients without traumatic brain injury (head/neck abbreviated injury score <2 or failure to meet Major Trauma Outcome Study criteria) or death in the field or within 30 minutes of arrival. Each remaining trial patient was matched to two nonintubated historical controls from the county trauma registry based on: age, sex, mechanism, abbreviated injury scores for each body system, and Injury Severity Score. Logistic regression, cohort analysis, mean least squares regression, and discordant group analysis were used to explore the impact of various factors on outcome.

RESULTS

Of the 426 trial patients, 352 met inclusion criteria for this analysis and were hand-matched to 704 controls. Trial patients and controls were identical with regard to all matching variables. Mortality was increased in RSI patients versus matched controls (31.8 versus 23.7%; odds ration, 1.5; 95% confidence interval, 1.1-2.0; p < 0.01). Hyperventilation was associated with an increase in mortality, whereas transport by aeromedical crews after paramedic RSI was associated with improved outcomes. The reported incidence of aspiration pneumonia was higher for the RSI patients.

CONCLUSION

Paramedic RSI was associated with an increase in mortality compared with matched historical controls. The association between hyperventilation and mortality was confirmed. In addition, patients transported by helicopter after paramedic RSI had improved outcomes. Paramedic RSI did not seem to prevent aspiration pneumonia.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Differential Concentration-Dependent Effects of Prolonged Norepinephrine Infusion on Intraparenchymal Hemorrhage and Cortical Contusion in Brain-Injured Rats

Under clinical conditions catecholamines are infused to elevate cerebral perfusion pressure and improve impaired posttraumatic cerebral microcirculation. This, however, is associated with the risk of additional hemorrhage in the acute phase following traumatic brain injury. In the present study we investigated the dose-dependent effects of prolonged norepinephrine infusion on arterial blood pressure, blood glucose, and structural damage in brain-injured rats. At 4 h following induction of a focal cortical contusion (CCI), 40 rats were randomized to receive low (0.15), medium (0.3), or high dose (1 microg/kg/min) norepinephrine. Control rats were given equal volume of NaCl. Norepinephrine and NaCl were infused intravenously via Alzet osmotic pumps for 44 h. Mean arterial blood pressure (MABP), blood gases and blood glucose were determined before, at 4, 24, 48 h after CCI in repeatedly anesthetized rats (n = 28). Systolic arterial blood pressure (SABP) was measured using the tail cuff method in awake, restrained rats (n = 12). Cortical contusion and intraparenchymal hemorrhage volume were quantified at 48 h in all rats. MABP determined in anesthetized rats was only marginally increased. SABP was significantly elevated during infusion of medium and high dose norepinephrine in awake rats, exceeding 140 mm Hg. Medium and high dose norepinephrine significantly increased cortical hemorrhage by 157% and 142%, without increasing the cortical contusion volume. Low dose norepinephrine significantly reduced the cortical contusion by 44%. Norepinephrine aggravates the underlying brain damage during the acute posttraumatic phase. Future studies are needed to determine the least deleterious norepinephrine concentration.

Effects of lecithinized superoxide dismutase on neuronal cell loss in CA3 hippocampus after traumatic brain injury in rats

BACKGROUND

The protective effect of excitatory amino acid antagonists for CA3 hippocampal neuronal loss has been well documentated. From a clinical point of view, however, alternative therapies should also be explored because excitatory amino acid antagonists have relatively deleterious side effects. Administration of lecithinized superoxide dismutase (PC-SOD) has recently been demonstrated to reduce brain edema after traumatic brain injury (TBI) in the cerebral cortex. In this study, we investigated the effectiveness of PC-SOD on CA3 hippocampal cell loss by examining hematoxylin and eosin-stained sections.

METHODS

Rats were divided at random into three groups. The first group received 1 mL of saline (contusion + saline group, n = 5). Rats of the second group were treated with 3000 IU/kg of PC-SOD (contusion + SOD 1 group, n = 5), while the third group received 5000 IU/kg of PC-SOD (contusion + SOD 2 group, n = 5). All agents were administered intraperitoneally 1 minute after traumatic insult and every 24 hours until 2 or 3 days post-TBI. Animals were sacrificed 3 or 7 days after contusion injury.

RESULTS

PC-SOD prevented CA3 neuronal loss 3 days after TBI, and increased the number of surviving CA3 neurons 7 days after TBI.

CONCLUSION

Our findings suggest that PC-SOD may serve as a pharmacological agent in the treatment of neuronal loss after TBI.

Protective effects of glial cell line-derived neurotrophic factor on hippocampal neurons after traumatic brain injury in rats

OBJECT

The purpose of this study was to evaluate whether glial cell line-derived neurotrophic factor (GDNF) can protect against hippocampal neuronal death after traumatic brain injury (TBI).

METHODS

Male Sprague-Dawley rats were subjected to moderate TBI with a controlled cortical impact device while in a state of halothane-induced anesthesia. Then, GDNF or artificial cerebrospinal fluid ([aCSF]; vehicle) was infused into the frontal horn of the left lateral ventricle. In eight brain-injured and eight sham-operated rats, GDNF was infused continuously for 7 days (200 ng/day intracerebroventricularly at a rate of 8.35 ng/0.5 microl/hour). An equal volume of vehicle was infused at the same rate into the remaining eight brain-injured and eight sham-operated rats. Seven days post-injury, all rats were killed. Their brains were sectioned and stained with cresyl violet, and the hippocampal neuronal loss was evaluated in the CA2 and CA3 regions with the aid of microscopy. A parallel set of sections from each brain was subjected to immunoreaction with antibodies against glial fibrillary acidic protein (GFAP; astroglia marker). In the aCSF-treated group, TBI resulted in a significant neuronal loss in the CA2 (60%, p < 0.05) and CA3 regions (68%, p < 0.05) compared with the sham-operated control animals. Compared with control rats infused with aCSF, GDNF infusion significantly decreased the TBI-induced neuronal loss in both the CA2 (58%, p < 0.05) and CA3 regions (51%, p < 0.05). There was no difference in the number of GFAP-positive astroglial cells in the GDNF-infused rats in the TBI and sham-operated groups compared with the respective vehicle-treated groups.

CONCLUSIONS

The authors found that GDNF treatment following TBI is neuroprotective.

Cerebral resuscitation after traumatic brain injury and cardiopulmonary arrest in infants and children in the new millennium

As outlined in Figure 1, it is likely that a series of interventions beginning in the field and continuing through the emergency department, ICU, rehabilitation center, and possibly beyond, will be needed to optimize clinical outcome after severe TBI or asphyxial CA in infants and children. Despite the many differences between these two important pediatric insults, it is likely that many of the therapies targeting neuronal death, in either condition, will need to be administered early after the insult, possibly at the injury scene. Even cerebral swelling, a pathophysiologic derangement routinely treated in the PICU, almost certainly is better prevented rather than treated. Finally, this review includes, for one of the first times, a brief discussion of additional horizons in the management of patients with severe brain injury, namely, manipulation of the injured circuitry and stimulation of regeneration. Further research is needed to define better the pathobiology of these two important conditions at the bedside, to understand the optimal application of contemporary therapies, and to develop and apply novel therapies. The tools necessary to carry out these studies are materializing, although the obstacles are great. This difficult but important challenge awaits further investigation by clinician-scientists in pediatric neurointensive care.

The impact of hypercarbia on the evolution of brain injury in a porcine model of traumatic brain injury and systemic hemorrhage

Carbon dioxide is perhaps the most potent available modulator of cerebrovascular tone and thus cerebral blood flow (CBF). These experiments evaluate the impact of induced hypercarbia on the matching of blood flow and metabolism in the injured brain. We explore the hypothesis that hypercarbia will restore the relationship of CBF to metabolic demand, resulting in improved outcome following traumatic brain injury (TBI) and hemorrhage. A behavioral outcome score, hemodynamic, metabolic, and pathologic parameters were assessed in anesthetized and ventilated juvenile pigs. Animals were assigned to either normocarbia or hypercarbia and subdivided into TBI (via fluid percussion) with or without hemorrhage. The experimental groups were TBI; TBI + 40% hemorrhage (40%H); TBI + hypercarbia (CO2); and TBI + 40%H + CO2. Hemorrhaged animals were resuscitated with blood and crystalloid. Hypercarbia was induced immediately following TBI using 10% FiCO2. The normocarbic group demonstrated disturbance of the matching of CBF to metabolism evidenced by statistically significant increases in cerebral oxygen and glucose extraction. Hypercarbic animals showed falls in the same parameters, demonstrating improvement in the matching of CBF to metabolic demand. Parenchymal injury was significantly decreased in hypercarbic animals: 3/10 hypercarbic versus 6/8 normocarbic animals showed cerebral contusions at the gray/white interface (p = 0.05). The hypercarbic group had significantly better behavioral outcome scores, 10.5, versus 7.3 for the normocarbic groups (p = 0.005). The decreased incidence of cerebral contusion and improved behavioral outcome scores in our experiments appear to be mediated by better matching of cerebral metabolism and blood flow, suggesting that manipulations modulating the balance of blood flow and metabolism in injured brain may improve outcomes from TBI.

Presynaptic excitability changes following traumatic brain injury in the rat

Pathological processes affecting presynaptic terminals may contribute to morbidity following traumatic brain injury (TBI). Posttraumatic widespread neuronal depolarization and elevated extracellular potassium and glutamate are predicted to alter the transduction of action potentials in terminals into reliable synaptic transmission and postsynaptic excitation. Evoked responses to orthodromic single- and paired-pulse stimulation were examined in the CA1 dendritic region of hippocampal slices removed from adult rats following fluid percussion TBI. The mean duration of the extracellularly recorded presynaptic volley (PV) increased from 1.08 msec in controls to 1.54 msec in slices prepared at 1 hr postinjury. There was a time-dependent recovery of this injury effect, and PV durations at 2 and 7 days postinjury were not different from controls. In slices removed at 1 hr postinjury, the initial slopes of field excitatory postsynaptic potentials (fEPSPs) were reduced to 36% of control values, and input/output plots revealed posttraumatic deficits in the transfer of excitation from pre- to postsynaptic elements. Manipulating potassium currents with 1.0 mM tetraethylammonium or elevating potassium ion concentration to 7.5 mM altered evoked responses but did not replicate the injury effects to PV duration. Paired-pulse facilitation of fEPSP slopes was significantly elevated at all postinjury survivals: 1 hr, 2 days, and 7 days. These results suggest two pathological processes with differing time courses: 1) a transient impairment of presynaptic terminal functioning affecting PV durations and the transduction of afferent activity in the terminals to reliable synaptic excitation and 2) a more protracted deficit to the plasticity mechanisms underlying paired-pulse facilitation.

Evidence disputing the importance of excitotoxicity in hippocampal neuron death after experimental traumatic brain injury

The hippocampus is selectively vulnerable to experimental traumatic brain injury (TBI). Beneficial effects of glutamate receptor antagonists and increased extracellular levels of glutamate have suggested that glutamate-mediated excitotoxicity may be responsible for this selective damage. In order to clarify this important issue, we applied a severe parasagittal fluid percussion injury (FPI) to strains of mice shown to be susceptible and resistant to kainic acid (KA)-induced excitotoxic hippocampal damage. Dystrophic neurons were present by 10 min after FPI in the hippocampi of both strains. Damaged hippocampal neurons were absent at 4 days and 7 days. Additionally, there was no significant difference (p = 1.00) in CA3 neuron survival between KA-susceptible and -resistant mice at 4 days. In conclusion, excitotoxicity does not significantly contribute to hippocampal neuron loss after FPI and, in contrast to classic studies of excitotoxicity in vivo, the pattern of hippocampal cell death after TBI is extremely acute.