Hypothermia blunts acetylcholine increase in CSF of traumatically brain injured rats

Investigating the Safety and Efficacy of Therapeutic Hypothermia in Pediatric Severe Traumatic Brain Injury: A Systematic Review and Meta-Analysis

BACKGROUND

Prior guidelines recommended maintaining normothermia following traumatic brain injury (TBI), but recent studies suggest therapeutic hypothermia as a viable option in pediatric cases. However, some others demonstrated a higher mortality rate. Hence, the impact of hypothermia on neurological symptoms and overall survival remains contentious.

METHODS

We conducted a systematic review and meta-analysis to evaluate the effects of hypothermia on neurological outcomes in pediatric TBI patients. The PubMed/Medline, Scopus, and Web of Science databases were searched until 1 January 2024 and data were analyzed using appropriate statistical methods.

RESULTS

A total of eight studies, comprising nine reports, were included in this analysis. Our meta-analysis did not reveal significant differences in mortality (RR = 1.58; 95% CI = 0.89-2.82, p = 0.055), infection (RR = 0.95: 95% CI = 0.79-1.1, p = 0.6), arrhythmia (RR = 2.85: 95% CI = 0.88-9.2, p = 0.08), hypotension (RR = 1.54: 95% CI = 0.91-2.6, p = 0.10), intracranial pressure (SMD = 5.07: 95% CI = -4.6-14.8, p = 0.30), hospital length of stay (SMD = 0.10; 95% CI = -0.13-0.3, p = 0.39), pediatric intensive care unit length of stay (SMD = 0.04; 95% CI = -0.19-0.28, p = 0.71), hemorrhage (RR = 0.86; 95% CI = 0.34-2.13, p = 0.75), cerebral perfusion pressure (SMD = 0.158: 95% CI = 0.11-0.13, p = 0.172), prothrombin time (SMD = 0.425; 95% CI = -0.037-0.886, p = 0.07), and partial thromboplastin time (SMD = 0.386; 95% CI = -0.074-0.847, p = 0.10) between the hypothermic and non-hypothermic groups. However, the heart rate was significantly lower in the hypothermic group (-1.523 SMD = -1.523: 95% CI = -1.81--1.22 p < 0.001).

CONCLUSIONS

Our findings challenge the effectiveness of therapeutic hypothermia in pediatric TBI cases. Despite expectations, it did not significantly improve key clinical outcomes. This prompts a critical re-evaluation of hypothermia's role as a standard intervention in pediatric TBI treatment.

Drosophila melanogaster as a model to study age and sex differences in brain injury and neurodegeneration after mild head trauma

Repetitive physical insults to the head, including those that elicit mild traumatic brain injury (mTBI), are a known risk factor for a variety of neurodegenerative conditions including Alzheimer's disease (AD), Parkinson's disease (PD), and chronic traumatic encephalopathy (CTE). Although most individuals who sustain mTBI typically achieve a seemingly full recovery within a few weeks, a subset experience delayed-onset symptoms later in life. As most mTBI research has focused on the acute phase of injury, there is an incomplete understanding of mechanisms related to the late-life emergence of neurodegeneration after early exposure to mild head trauma. The recent adoption of Drosophila-based brain injury models provides several unique advantages over existing preclinical animal models, including a tractable framework amenable to high-throughput assays and short relative lifespan conducive to lifelong mechanistic investigation. The use of flies also provides an opportunity to investigate important risk factors associated with neurodegenerative conditions, specifically age and sex. In this review, we survey current literature that examines age and sex as contributing factors to head trauma-mediated neurodegeneration in humans and preclinical models, including mammalian and Drosophila models. We discuss similarities and disparities between human and fly in aging, sex differences, and pathophysiology. Finally, we highlight Drosophila as an effective tool for investigating mechanisms underlying head trauma-induced neurodegeneration and for identifying therapeutic targets for treatment and recovery.

Association between intraoperative body temperature and postoperative delirium: A retrospective observational study

STUDY OBJECTIVE

The effect of perioperative body temperature derangement on postoperative delirium remains unclear. This study aimed to evaluate the association between intraoperative body temperature and postoperative delirium in patients having noncardiac surgery.

DESIGN

Single-center retrospective observational study.

SETTING

Tertiary university hospital.

PATIENT

Adult patients who had major noncardiac surgery under general anesthesia for at least two hours between 2019 and 2021.

INTERVENTIONS

Patients were classified into three groups according to their intraoperative time-weighted average body temperature: severe hypothermia (<35.0 °C), mild hypothermia (35.0 °C-36.0 °C), and normothermia (≥36.0 °C) groups.

MEASUREMENTS

The primary outcome was the risk of delirium occurring within seven days after surgery, which was compared using logistic regression analysis. A multivariable procedure was performed adjusting for potential confounders including demographics, history of hypertension, diabetes, atrial fibrillation or flutter, myocardial infarction, congestive heart failure, and stroke or transient ischemic attack, preoperative use of antidepressants and statins, preoperative sodium imbalance, high-risk surgery, emergency surgery, duration of surgery, and red blood cell transfusion. Cox regression analysis was also performed using the same covariates.

MAIN RESULTS

Among 27,674 patients analyzed, 5.5% experienced postoperative delirium. The incidence rates of delirium were 6.2% (63/388) in the severe hypothermia group, 6.4% (756/11779) in the mild hypothermia group, and 4.6% (712/15507) in the normothermia group. Compared with the normothermia group, the risk of delirium was significantly higher in the severe hypothermia (adjusted odds ratio, 1.43; 95% confidence interval, 1.04-1.97) and mild hypothermia (1.15; 1.02-1.28) groups. The mild hypothermia group also had a significantly increased risk of cumulative development of delirium than the normothermia group (adjusted hazard ratio 1.14; 95% confidence interval, 1.03-1.26).

CONCLUSIONS

Intraoperative hypothermia (even mild hypothermia) was significantly associated with an increased risk of postoperative delirium.

Repetitive mild head trauma induces activity mediated lifelong brain deficits in a novel Drosophila model

Mild head trauma, including concussion, can lead to chronic brain dysfunction and degeneration but the underlying mechanisms remain poorly understood. Here, we developed a novel head impact system to investigate the long-term effects of mild head trauma on brain structure and function, as well as the underlying mechanisms in Drosophila melanogaster. We find that Drosophila subjected to repetitive head impacts develop long-term deficits, including impaired startle-induced climbing, progressive brain degeneration, and shortened lifespan, all of which are substantially exacerbated in female flies. Interestingly, head impacts elicit an elevation in neuronal activity and its acute suppression abrogates the detrimental effects in female flies. Together, our findings validate Drosophila as a suitable model system for investigating the long-term effects of mild head trauma, suggest an increased vulnerability to brain injury in female flies, and indicate that early altered neuronal excitability may be a key mechanism linking mild brain trauma to chronic degeneration.

Role of innate inflammation in traumatic brain injury

Traumatic brain injury is one of the leading causes of morbidity and mortality throughout the world. Its increasing incidence, in addition to its fundamental role in the development of neurodegenerative disease, proves especially concerning. Despite extensive preclinical and clinical studies, researchers have yet to identify a safe and effective neuroprotective strategy. Following brain trauma, secondary injury from molecular, metabolic, and cellular changes causes progressive cerebral tissue damage. Chronic neuroinflammation following traumatic brain injuries is a key player in the development of secondary injury. Targeting this phenomenon for development of effective neuroprotective therapies holds promise. This strategy warrants a concrete understanding of complex neuroinflammatory mechanisms. In this review, we discuss pathophysiological mechanisms such as the innate immune response, glial activation, blood-brain barrier disruption, activation of immune mediators, as well as biological markers of traumatic brain injury. We then review existing and emerging pharmacological therapies that target neuroinflammation to improve functional outcome.

Approaches to Monitor Circuit Disruption after Traumatic Brain Injury: Frontiers in Preclinical Research

Mild traumatic brain injury (TBI) often results in pathophysiological damage that can manifest as both acute and chronic neurological deficits. In an attempt to repair and reconnect disrupted circuits to compensate for loss of afferent and efferent connections, maladaptive circuitry is created and contributes to neurological deficits, including post-concussive symptoms. The TBI-induced pathology physically and metabolically changes the structure and function of neurons associated with behaviorally relevant circuit function. Complex neurological processing is governed, in part, by circuitry mediated by primary and modulatory neurotransmitter systems, where signaling is disrupted acutely and chronically after injury, and therefore serves as a primary target for treatment. Monitoring of neurotransmitter signaling in experimental models with technology empowered with improved temporal and spatial resolution is capable of recording in vivo extracellular neurotransmitter signaling in behaviorally relevant circuits. Here, we review preclinical evidence in TBI literature that implicates the role of neurotransmitter changes mediating circuit function that contributes to neurological deficits in the post-acute and chronic phases and methods developed for in vivo neurochemical monitoring. Coupling TBI models demonstrating chronic behavioral deficits with in vivo technologies capable of real-time monitoring of neurotransmitters provides an innovative approach to directly quantify and characterize neurotransmitter signaling as a universal consequence of TBI and the direct influence of pharmacological approaches on both behavior and signaling.

Sex differences in traumatic brain injury: a multi-dimensional exploration in genes, hormones, cells, individuals, and society

Traumatic brain injury (TBI) is exceptionally prevalent in society and often imposes a massive burden on patients' families and poor prognosis. The evidence reviewed here suggests that gender can influence clinical outcomes of TBI in many aspects, ranges from patients' mortality and short-term outcome to their long-term outcome, as well as the incidence of cognitive impairment. We mainly focused on the causes and mechanisms underlying the differences between male and female after TBI, from both biological and sociological views. As it turns out that multiple factors contribute to the gender differences after TBI, not merely the perspective of gender and sex hormones. Centered on this, we discussed how female steroid hormones exert neuroprotective effects through the anti-inflammatory and antioxidant mechanism, along with the cognitive impairment and the social integration problems it caused. As to the treatment, both instant and long-term treatment of TBI requires adjustments according to gender. A further study with more focus on this topic is therefore suggested to provide better treatment options for these patients.

(-)-Phenserine Ameliorates Contusion Volume, Neuroinflammation, and Behavioral Impairments Induced by Traumatic Brain Injury in Mice

Traumatic brain injury (TBI), a major cause of mortality and morbidity, affects 10 million people worldwide, with limited treatment options. We have previously shown that (-)-phenserine (Phen), an acetylcholinesterase inhibitor originally designed and tested in clinical phase III trials for Alzheimer's disease, can reduce neurodegeneration after TBI and reduce cognitive impairments induced by mild TBI. In this study, we used a mouse model of moderate to severe TBI by controlled cortical impact to assess the effects of Phen on post-trauma histochemical and behavioral changes. Animals were treated with Phen (2.5 mg/kg, IP, BID) for 5 days started on the day of injury and the effects were evaluated by behavioral and histological examinations at 1 and 2 weeks after injury. Phen significantly attenuated TBI-induced contusion volume, enlargement of the lateral ventricle, and behavioral impairments in motor asymmetry, sensorimotor functions, motor coordination, and balance functions. The morphology of microglia was shifted to an active from a resting form after TBI, and Phen dramatically reduced the ratio of activated to resting microglia, suggesting that Phen also mitigates neuroinflammation after TBI. While Phen has potent anti-acetylcholinesterase activity, its (+) isomer Posiphen shares many neuroprotective properties but is almost completely devoid of anti-acetylcholinesterase activity. We evaluated Posiphen at a similar dose to Phen and found similar mitigation in lateral ventricular size increase, motor asymmetry, motor coordination, and balance function, suggesting the improvement of these histological and behavioral tests by Phen treatment occur via pathways other than anti-acetylcholinesterase inhibition. However, the reduction of lesion size and improvement of sensorimotor function by Posiphen were much smaller than with equivalent doses of Phen. Taken together, these results show that post-injury treatment with Phen over 5 days significantly ameliorates severity of TBI. These data suggest a potential development of this compound for clinical use in TBI therapy.

Therapeutic hypothermia to reduce intracranial pressure after traumatic brain injury: the Eurotherm3235 RCT

BACKGROUND

Traumatic brain injury (TBI) is a major cause of disability and death in young adults worldwide. It results in around 1 million hospital admissions annually in the European Union (EU), causes a majority of the 50,000 deaths from road traffic accidents and leaves a further ≈10,000 people severely disabled.

OBJECTIVE

The Eurotherm3235 Trial was a pragmatic trial examining the effectiveness of hypothermia (32-35 °C) to reduce raised intracranial pressure (ICP) following severe TBI and reduce morbidity and mortality 6 months after TBI.

DESIGN

An international, multicentre, randomised controlled trial.

SETTING

Specialist neurological critical care units.

PARTICIPANTS

We included adult participants following TBI. Eligible patients had ICP monitoring in place with an ICP of > 20 mmHg despite first-line treatments. Participants were randomised to receive standard care with the addition of hypothermia (32-35 °C) or standard care alone. Online randomisation and the use of an electronic case report form (CRF) ensured concealment of random treatment allocation. It was not possible to blind local investigators to allocation as it was obvious which participants were receiving hypothermia. We collected information on how well the participant had recovered 6 months after injury. This information was provided either by the participant themself (if they were able) and/or a person close to them by completing the Glasgow Outcome Scale - Extended (GOSE) questionnaire. Telephone follow-up was carried out by a blinded independent clinician.

INTERVENTIONS

The primary intervention to reduce ICP in the hypothermia group after randomisation was induction of hypothermia. Core temperature was initially reduced to 35 °C and decreased incrementally to a lower limit of 32 °C if necessary to maintain ICP at < 20 mmHg. Rewarming began after 48 hours if ICP remained controlled. Participants in the standard-care group received usual care at that centre, but without hypothermia.

MAIN OUTCOME MEASURES

The primary outcome measure was the GOSE [range 1 (dead) to 8 (upper good recovery)] at 6 months after the injury as assessed by an independent collaborator, blind to the intervention. A priori subgroup analysis tested the relationship between minimisation factors including being aged < 45 years, having a post-resuscitation Glasgow Coma Scale (GCS) motor score of < 2 on admission, having a time from injury of < 12 hours and patient outcome.

RESULTS

We enrolled 387 patients from 47 centres in 18 countries. The trial was closed to recruitment following concerns raised by the Data and Safety Monitoring Committee in October 2014. On an intention-to-treat basis, 195 participants were randomised to hypothermia treatment and 192 to standard care. Regarding participant outcome, there was a higher mortality rate and poorer functional recovery at 6 months in the hypothermia group. The adjusted common odds ratio (OR) for the primary statistical analysis of the GOSE was 1.54 [95% confidence interval (CI) 1.03 to 2.31]; when the GOSE was dichotomised the OR was 1.74 (95% CI 1.09 to 2.77). Both results favoured standard care alone. In this pragmatic study, we did not collect data on adverse events. Data on serious adverse events (SAEs) were collected but were subject to reporting bias, with most SAEs being reported in the hypothermia group.

CONCLUSIONS

In participants following TBI and with an ICP of > 20 mmHg, titrated therapeutic hypothermia successfully reduced ICP but led to a higher mortality rate and worse functional outcome.

LIMITATIONS

Inability to blind treatment allocation as it was obvious which participants were randomised to the hypothermia group; there was biased recording of SAEs in the hypothermia group. We now believe that more adequately powered clinical trials of common therapies used to reduce ICP, such as hypertonic therapy, barbiturates and hyperventilation, are required to assess their potential benefits and risks to patients.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN34555414.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 22, No. 45. See the NIHR Journals Library website for further project information. The European Society of Intensive Care Medicine supported the pilot phase of this trial.

Moderate hypothermia protects increased neuronal autophagy via activation of extracellular signal-regulated kinase signaling pathway in a rat model of early brain injury in subarachnoid hemorrhage

Moderate hypothermia (MH) used as treatment for neurological diseases has a protective effect; however, its mechanism remains unclear. Neuronal autophagy is a fundamental pathological process of early brain injury in subarachnoid hemorrhage (SAH). We found that moderate activation of autophagy can reduce nerve cells damage. In this study, We found that MH can moderately increase the level of autophagy in nerve cells and improve the neurological function in rats. This type of autophagy activation is dependent on extracellular signal-regulated kinase (ERK) signaling pathways. The level of neuronal autophagy was down-regulated significantly by using U0126, an ERK signaling pathway inhibitor. In summary, these results suggest that MH can moderately activate neuronal autophagy through ERK signaling pathway, reduce nerve cell death, and produce neuroprotective effects.

Repositioning drugs for traumatic brain injury - N-acetyl cysteine and Phenserine

Traumatic brain injury (TBI) is one of the most common causes of morbidity and mortality of both young adults of less than 45 years of age and the elderly, and contributes to about 30% of all injury deaths in the United States of America. Whereas there has been a significant improvement in our understanding of the mechanism that underpin the primary and secondary stages of damage associated with a TBI incident, to date however, this knowledge has not translated into the development of effective new pharmacological TBI treatment strategies. Prior experimental and clinical studies of drugs working via a single mechanism only may have failed to address the full range of pathologies that lead to the neuronal loss and cognitive impairment evident in TBI and other disorders. The present review focuses on two drugs with the potential to benefit multiple pathways considered important in TBI. Notably, both agents have already been developed into human studies for other conditions, and thus have the potential to be rapidly repositioned as TBI therapies. The first is N-acetyl cysteine (NAC) that is currently used in over the counter medications for its anti-inflammatory properties. The second is (-)-phenserine ((-)-Phen) that was originally developed as an experimental Alzheimer's disease (AD) drug. We briefly review background information about TBI and subsequently review literature suggesting that NAC and (-)-Phen may be useful therapeutic approaches for TBI, for which there are no currently approved drugs.

Meta-Analysis of Therapeutic Hypothermia for Traumatic Brain Injury in Adult and Pediatric Patients

OBJECTIVE

Therapeutic hypothermia has been used to attenuate the effects of traumatic brain injuries. However, the required degree of hypothermia, length of its use, and its timing are uncertain. We undertook a comprehensive meta-analysis to quantify benefits of hypothermia therapy for traumatic brain injuries in adults and children by analyzing mortality rates, neurologic outcomes, and adverse effects.

DATA SOURCES

Electronic databases PubMed, Google Scholar, Web of Science, Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov and manual searches of studies were conducted for relevant publications up until February 2016.

STUDY SELECTION

Forty-one studies in adults (n = 3,109; age range, 18-81 yr) and eight studies in children (n = 454; age range, 3 mo to 18 yr) met eligibility criteria.

DATA EXTRACTION

Baseline patient characteristics, enrollment time, methodology of cooling, target temperature, duration of hypothermia, and rewarming protocols were extracted.

DATA SYNTHESIS

Risk ratios with 95% CIs were calculated. Compared with adults who were kept normothermic, those who underwent therapeutic hypothermia were associated with 18% reduction in mortality (risk ratio, 0.82; 95% CI, 0.70-0.96; p = 0.01) and a 35% improvement in neurologic outcome (risk ratio, 1.35; 95% CI, 1.18-1.54; p < 0.00001). The optimal management strategy for adult patients included cooling patients to a minimum of 33°C for 72 hours, followed by spontaneous, natural rewarming. In contrast, adverse outcomes were observed in children who underwent hypothermic treatment with a 66% increase in mortality (risk ratio, 1.66; 95% CI, 1.06-2.59; p = 0.03) and a marginal deterioration of neurologic outcome (risk ratio, 0.90; 95% CI, 0.80-1.01; p = 0.06).

CONCLUSIONS

Therapeutic hypothermia is likely a beneficial treatment following traumatic brain injuries in adults but cannot be recommended in children.

Cognitive Impairments Induced by Concussive Mild Traumatic Brain Injury in Mouse Are Ameliorated by Treatment with Phenserine via Multiple Non-Cholinergic and Cholinergic Mechanisms

Traumatic brain injury (TBI), often caused by a concussive impact to the head, affects an estimated 1.7 million Americans annually. With no approved drugs, its pharmacological treatment represents a significant and currently unmet medical need. In our prior development of the anti-cholinesterase compound phenserine for the treatment of neurodegenerative disorders, we recognized that it also possesses non-cholinergic actions with clinical potential. Here, we demonstrate neuroprotective actions of phenserine in neuronal cultures challenged with oxidative stress and glutamate excitotoxicity, two insults of relevance to TBI. These actions translated into amelioration of spatial and visual memory impairments in a mouse model of closed head mild TBI (mTBI) two days following cessation of clinically translatable dosing with phenserine (2.5 and 5.0 mg/kg BID x 5 days initiated post mTBI) in the absence of anti-cholinesterase activity. mTBI elevated levels of thiobarbituric acid reactive substances (TBARS), a marker of oxidative stress. Phenserine counteracted this by augmenting homeostatic mechanisms to mitigate oxidative stress, including superoxide dismutase [SOD] 1 and 2, and glutathione peroxidase [GPx], the activity and protein levels of which were measured by specific assays. Microarray analysis of hippocampal gene expression established that large numbers of genes were exclusively regulated by each individual treatment with a substantial number of them co-regulated between groups. Molecular pathways associated with lipid peroxidation were found to be regulated by mTBI, and treatment of mTBI animals with phenserine effectively reversed injury-induced regulations in the ‘Blalock Alzheimer’s Disease Up’ pathway. Together these data suggest that multiple phenserine-associated actions underpin this compound’s ability to ameliorate cognitive deficits caused by mTBI, and support the further evaluation of the compound as a therapeutic for TBI.

Making Waves in the Brain: What Are Oscillations, and Why Modulating Them Makes Sense for Brain Injury

Traumatic brain injury (TBI) can result in persistent cognitive, behavioral and emotional deficits. However, the vast majority of patients are not chronically hospitalized; rather they have to manage their disabilities once they are discharged to home. Promoting recovery to pre-injury level is important from a patient care as well as a societal perspective. Electrical neuromodulation is one approach that has shown promise in alleviating symptoms associated with neurological disorders such as in Parkinson’s disease (PD) and epilepsy. Consistent with this perspective, both animal and clinical studies have revealed that TBI alters physiological oscillatory rhythms. More recently several studies demonstrated that low frequency stimulation improves cognitive outcome in models of TBI. Specifically, stimulation of the septohippocampal circuit in the theta frequency entrained oscillations and improved spatial learning following TBI. In order to evaluate the potential of electrical deep brain stimulation for clinical translation we review the basic neurophysiology of oscillations, their role in cognition and how they are changed post-TBI. Furthermore, we highlight several factors for future pre-clinical and clinical studies to consider, with the hope that it will promote a hypothesis driven approach to subsequent experimental designs and ultimately successful translation to improve outcome in patients with TBI.

Alterations in Cholinergic Pathways and Therapeutic Strategies Targeting Cholinergic System after Traumatic Brain Injury

Traumatic brain injury (TBI) results in varying degrees of disability in a significant number of persons annually. The mechanisms of cognitive dysfunction after TBI have been explored in both animal models and human clinical studies for decades. Dopaminergic, serotonergic, and noradrenergic dysfunction has been described in many previous reports. In addition, cholinergic dysfunction has also been a familiar topic among TBI researchers for many years. Although pharmacological agents that modulate cholinergic neurotransmission have been used with varying degrees of success in previous studies, improving their function and maximizing cognitive recovery is an ongoing process. In this article, we review the previous findings on the biological mechanism of cholinergic dysfunction after TBI. In addition, we describe studies that use both older agents and newly developed agents as candidates for targeting cholinergic neurotransmission in future studies.

Progress in Clinical Neurosciences: Therapeutic Hypothermia in Severe Traumatic Brain Injury

Severe traumatic brain injury (sTBI) is a relatively common problem with few therapies proven effective. Despite its use for over 50 years, therapeutic hypothermia has not gained widespread acceptance in the treatment of sTBI due to conflicting results from clinical trials. This review will summarize the current evidence from animal, mechanistic and clinical studies supporting the use of therapeutic hypothermia. In addition, issues of rewarming and optimal temperature will be discussed. Finally, the future of hypothermia in sTBI will be addressed.

Therapeutic hypothermia: benefits, mechanisms and potential clinical applications in neurological, cardiac and kidney injury

Therapeutic hypothermia involves the controlled reduction of core temperature to attenuate the secondary organ damage which occurs following a primary injury. Clinicians have been increasingly using therapeutic hypothermia to prevent or ameliorate various types of neurological injury and more recently for some forms of cardiac injury. In addition, some recent evidence suggests that therapeutic hypothermia may also provide benefit following acute kidney injury. In this review we will examine the potential mechanisms of action and current clinical evidence surrounding the use of therapeutic hypothermia. We will discuss the ideal methodological attributes of future studies using hypothermia to optimise outcomes following organ injury, in particular neurological injury. We will assess the importance of target hypothermic temperature, time to achieve target temperature, duration of cooling, and re-warming rate on outcomes following neurological injury to gain insights into important factors which may also influence the success of hypothermia in other organ injuries, such as the heart and the kidney. Finally, we will examine the potential of therapeutic hypothermia as a future kidney protective therapy.

Pre-hospital hypothermia is not associated with increased survival after traumatic brain injury

BACKGROUND

Conclusions from in vivo and in vitro studies suggest hypothermia may be protective in traumatic brain injury (TBI). Few studies evaluated the effect of admission temperature on outcomes. The purpose of this study is to examine the relationship between admission hypothermia and mortality in patients with isolated, blunt, moderate to severe TBI.

METHODS

The Los Angeles Trauma Database was queried for all patients ≥ 14 y of age with isolated, blunt, moderate to severe TBI (head abbreviated injury score (AIS) ≥ 3, all other <3), admitted between 2005 and 2009. The study population was then stratified into two groups by admission temperature: hypothermic (≤ 35°C) and normothermic (>35°C). Demographic characteristics and outcomes were compared between groups. Logistic regression analysis was used to determine the relationship between admission hypothermia and mortality.

RESULTS

A total of 1834 patients were analyzed and then stratified into two groups: hypothermic (n = 44) and normothermic (n = 1790). There was a significant difference noted in overall mortality (25% versus 7%), with the hypothermic group being four times more likely to succumb to their injuries. After adjusting for confounding factors, admission hypothermia was independently associated with increased mortality (AOR 2.5; 95% CI 1.1-6.3; P = 0.04).

CONCLUSIONS

Although in-vivo and in-vitro studies demonstrate induced hypothermia may be protective in TBI, our study demonstrates that admission hypothermia was associated with increased mortality in isolated, blunt, moderate to severe TBI. Further prospective research is needed to elucidate the role of thermoregulation in patients sustaining TBI.

Blood-based diagnostics of traumatic brain injuries

Traumatic brain injury is a major health and socioeconomic problem that affects all societies. However, traditional approaches to the classification of clinical severity are the subject of debate and are being supplemented with structural and functional neuroimaging, as the need for biomarkers that reflect elements of the pathogenetic process is widely recognized. Basic science research and developments in the field of proteomics have greatly advanced our knowledge of the mechanisms involved in damage and have led to the discovery and rapid detection of new biomarkers that were not available previously. However, translating this research for patients' benefits remains a challenge. In this article, we summarize new developments, current knowledge and controversies, focusing on the potential role of these biomarkers as diagnostic, prognostic and monitoring tools of brain-injured patients.

αII-spectrin breakdown products (SBDPs): diagnosis and outcome in severe traumatic brain injury patients

In this study we assessed the clinical utility of quantitative assessments of alphaII-spectrin breakdown products (SBDP145 produced by calpain, and SBDP120 produced by caspase-3) in cerebrospinal fluid (CSF) as markers of brain damage and outcome after severe traumatic brain injury (TBI). We analyzed 40 adult patients with severe TBI (Glasgow Coma Scale [GCS] score 6 ng/mL) and SBDP120 levels (>17.55 ng/mL) strongly predicted death (odds ratio 5.9 for SBDP145, and 18.34 for SBDP120). The time course of SBDPs in nonsurvivors also differed from that of survivors. These results suggest that CSF SBDP levels can predict injury severity and mortality after severe TBI, and can be useful complements to clinical assessment.

Bench-to-bedside review: Hypothermia in traumatic brain injury

Traumatic brain injury remains a major cause of death and severe disability throughout the world. Traumatic brain injury leads to 1,000,000 hospital admissions per annum throughout the European Union. It causes the majority of the 50,000 deaths from road traffic accidents and leaves 10,000 patients severely handicapped: three quarters of these victims are young people. Therapeutic hypothermia has been shown to improve outcome after cardiac arrest, and consequently the European Resuscitation Council and American Heart Association guidelines recommend the use of hypothermia in these patients. Hypothermia is also thought to improve neurological outcome after neonatal birth asphyxia. Cardiac arrest and neonatal asphyxia patient populations present to health care services rapidly and without posing a diagnostic dilemma; therefore, therapeutic systemic hypothermia may be implemented relatively quickly. As a result, hypothermia in these two populations is similar to the laboratory models wherein systemic therapeutic hypothermia is commenced very soon after the injury and has shown so much promise. The need for resuscitation and computerised tomography imaging to confirm the diagnosis in patients with traumatic brain injury is a factor that delays intervention with temperature reduction strategies. Treatments in traumatic brain injury have traditionally focussed on restoring and maintaining adequate brain perfusion, surgically evacuating large haematomas where necessary, and preventing or promptly treating oedema. Brain swelling can be monitored by measuring intracranial pressure (ICP), and in most centres ICP is used to guide treatments and to monitor their success. There is an absence of evidence for the five commonly used treatments for raised ICP and all are potential 'double-edged swords' with significant disadvantages. The use of hypothermia in patients with traumatic brain injury may have beneficial effects in both ICP reduction and possible neuro-protection. This review will focus on the bench-to-bedside evidence that has supported the development of the Eurotherm3235Trial protocol.

The evidence for hypothermia as a neuroprotectant in traumatic brain injury

This article reviews published experimental and clinical evidence for the benefits of modest hypothermia in the treatment of traumatic brain injury (TBI). Therapeutic hypothermia has been reported to improve outcome in several animal models of CNS injury and has been successfully translated to specific patient populations. A PubMed search for hypothermia and TBI was conducted, and important papers were selected for review. The research summarized was conducted at major academic institutions throughout the world. Experimental studies have emphasized that hypothermia can affect multiple pathophysiological mechanisms thought to participate in the detrimental consequences of TBI. Published data from several relevant clinical trials on the use of hypothermia in severely injured TBI patients are also reviewed. The consequences of mild to moderate levels of hypothermia introduced by different strategies to the head-injured patient for variable periods of time are discussed. Both experimental and clinical data support the beneficial effects of modest hypothermia following TBI in specific patient populations. Following on such single-institution studies, positive findings from multicenter TBI trials will be required before this experimental treatment can be considered standard of care.

Protection in animal models of brain and spinal cord injury with mild to moderate hypothermia

For the past 20 years, various laboratories throughout the world have shown that mild to moderate levels of hypothermia lead to neuroprotection and improved functional outcome in various models of brain and spinal cord injury (SCI). Although the potential neuroprotective effects of profound hypothermia during and following central nervous system (CNS) injury have long been recognized, more recent studies have described clinically feasible strategies for protecting the brain and spinal cord using hypothermia following a variety of CNS insults. In some cases, only a one or two degree decrease in brain or core temperature can be effective in protecting the CNS from injury. Alternatively, raising brain temperature only a couple of degrees above normothermia levels worsens outcome in a variety of injury models. Based on these data, resurgence has occurred in the potential use of therapeutic hypothermia in experimental and clinical settings. The study of therapeutic hypothermia is now an international area of investigation with scientists and clinicians from every part of the world contributing to this important, promising therapeutic intervention. This paper reviews the experimental data obtained in animal models of brain and SCI demonstrating the benefits of mild to moderate hypothermia. These studies have provided critical data for the translation of this therapy to the clinical arena. The mechanisms underlying the beneficial effects of mild hypothermia are also summarized.

Therapeutic hypothermia preserves antioxidant defenses after severe traumatic brain injury in infants and children

OBJECTIVE

Oxidative stress contributes to secondary damage after traumatic brain injury (TBI). Hypothermia decreases endogenous antioxidant consumption and lipid peroxidation after experimental cerebral injury. Our objective was to determine the effect of therapeutic hypothermia on oxidative damage after severe TBI in infants and children randomized to moderate hypothermia vs. normothermia.

DESIGN

Prospective randomized controlled study.

SETTING

Pediatric intensive care unit of Pittsburgh Children's Hospital.

PATIENTS

The study included 28 patients.

MEASUREMENTS AND MAIN RESULTS

We compared the effects of hypothermia (32 degrees C-33 degrees C) vs. normothermia in patients treated in a single center involved in a multicentered randomized controlled trial of hypothermia in severe pediatric TBI (Glasgow Coma Scale score <or=8). The patients randomized to hypothermia (n = 13) were cooled to target temperature within approximately 6 to 24 hours for 48 hours and then rewarmed. Antioxidant status was assessed by measurements of total antioxidant reserve and glutathione. Protein oxidation and lipid peroxidation were assessed by measurements of protein thiols and F2-isoprostane, respectively, in ventricular cerebrospinal fluid (CSF) samples (n = 76) obtained on day 1-3 after injury. The association between Glasgow Coma Scale score, age, gender, treatment, temperature, time after injury, and CSF antioxidant reserve, glutathione, protein-thiol, F2-isoprostane levels were assessed by bivariate and multiple regression models. Demographic and clinical characteristics were similar between the two treatment groups. Mechanism of injury included both accidental injury and nonaccidental injury. Multiple regression models revealed preservation of CSF antioxidant reserve by hypothermia (p = 0.001). Similarly, a multiple regression model showed that glutathione levels were inversely associated with patient temperature at the time of sampling (p = 0.002). F2-isoprostane levels peaked on day 1 after injury and were progressively decreased thereafter. Although F2-isoprostane levels were approximately three-fold lower in patients randomized to hypothermia vs. normothermia, this difference was not statistically significant.

CONCLUSION

To our knowledge, this is the first study demonstrating that hypothermia attenuates oxidative stress after severe TBI in infants and children. Our data also support the concept that CSF represents a valuable tool for monitoring treatment effects on oxidative stress after TBI.

Can we improve neurological outcomes in severe traumatic brain injury? Something old (early prophylactic hypothermia) and something new (erythropoietin)

Traumatic brain injury is a leading cause of mortality and long-term morbidity, particularly affecting young people. With our best therapies, one half of the patients with severe traumatic brain injury are never capable of living independently. Two interventions, which have real potential to improve neurological outcomes in patients with traumatic brain injury, are (i) very early induction of prophylactic hypothermia and (ii) exogenous erythropoietin therapy. There is substantial experimental evidence, a plausible biological rationale, and supportive clinical evidence from clinical trials to suggest a possible beneficial effect of prophylactic hypothermia and also for exogenous erythropoietin therapy in severe traumatic brain injury. Despite the recent guidelines and publications recommending these interventions, critical care clinicians should be conservative towards implementing these therapies outside clinical trials due to substantial efficacy and safety concerns. Nevertheless the high morbidity and mortality associated with severe traumatic brain injury (TBI) demands that we investigate the safety and efficacy of these promising potential therapies as a matter of urgency.

Dicyclomine, an M1 muscarinic antagonist, reduces biomarker levels, but not neuronal degeneration, in fluid percussion brain injury

Recent studies indicate that alphaII-spectrin breakdown products (SBDPs) have utility as biological markers of traumatic brain injury (TBI). However, the utility of SBDP biomarkers for detecting effects of therapeutic interventions has not been explored. Acetylcholine plays a role in pathological neuronal excitation and TBI-induced muscarinic cholinergic receptor activation may contribute to excitotoxic processes. In experiment I, regional and temporal changes in calpain-mediated alpha-spectrin degradation were evaluated at 3, 12, 24, and 48 h using immunostaining for 145-kDa SBDP. Immunostaining of SBDP-145 was only evident in the hemisphere ipsilateral to TBI and was generally limited to the cortex except at 24 h when immunostaining was also prominent in the dentate gyrus and striatum. In Experiment II, cerebral spinal fluid (CSF) samples were analyzed for various SBDPs 24 h after moderate lateral fluid percussion TBI. Rats were administered either dicyclomine (5 mg/kg i.p.) or saline vehicle (n = 8 per group) 5 min prior to injury. Injury produced significant increases (p < 0.001) of 300%, 230%, and >1000% in SBDP-150, -145, and -120, respectively in vehicle-treated rats compared to sham. Dicyclomine treatment produced decreases of 38% (p = 0.077), 37% (p = 0.028), and 63% (p = 0.051) in SBDP-150, -145, and -120, respectively, compared to vehicle-treated injury. Following CSF extraction, coronal brain sections were processed for detecting degenerating neurons using Fluoro-Jade histofluorescence. Stereological techniques were used to quantify neuronal degeneration in the dorsal hippocampus CA2/3 region and in the parietal cortex. No significant differences were detected in numbers of degenerating neurons in the dorsal CA2/3 hippocampus or the parietal cortex between saline and dicyclomine treatment groups. The percent weight loss following TBI was significantly reduced by dicyclomine treatment. These data provide additional evidence that, as TBI biomarkers, SBDPs are able to detect a therapeutic intervention even in the absence of changes in neuronal cell degeneration measured by Fluoro-jade.

Neurotoxic zinc translocation into hippocampal neurons is inhibited by hypothermia and is aggravated by hyperthermia after traumatic brain injury in rats

Hypothermia reduces excitotoxic neuronal damage after seizures, cerebral ischemia and traumatic brain injury (TBI), while hyperthermia exacerbates damage from these insults. Presynaptic release of ionic zinc (Zn2+), translocation and accumulation of Zn2+ ions in postsynaptic neurons are important mechanisms of excitotoxic neuronal injury. We hypothesized that temperature-dependent modulation of excitotoxicity is mediated in part by temperature-dependent changes in the synaptic release and translocation of Zn2+. In the present studies, we used autometallographic (AMG) and fluorescent imaging of N-(6-methoxy-8-quinolyl)-para-toluenesulfonamide (TSQ) staining to quantify the influence of temperature on translocation of Zn2+ into hippocampal neurons in adult rats after weight drop-induced TBI. The central finding was that TBI-induced Zn2+ translocation is strongly influenced by brain temperature. Vesicular Zn2+ release was detected by AMG staining 1 h after TBI. At 30 degrees C, hippocampus showed almost no evidence of vesicular Zn2+ release from presynaptic terminals; at 36.5 degrees C, the hippocampus showed around 20% to 30% presynaptic vesicular Zn2+ release; and at 39 degrees C vesicular Zn2+ release was significantly greater (40% to 60%) than at 36.5 degrees C. At 6 h after TBI, intracellular Zn2+ accumulation was detected by the TSQ staining method, which showed that Zn2+ translocation also paralleled the vesicular Zn2+ release. Neuronal injury, assessed by counting eosinophilic neurons, also paralleled the translocation of Zn2+, being minimal at 30 degrees C and maximal at 39 degrees C. We conclude that pathological Zn2+ translocation in brain after TBI is temperature-dependent and that hypothermic neuronal protection might be mediated in part by reduced Zn2+ translocation.

Accumulation of non-erythroid alpha II-spectrin and calpain-cleaved alpha II-spectrin breakdown products in cerebrospinal fluid after traumatic brain injury in rats

Although a number of increased CSF proteins have been correlated with brain damage and outcome after traumatic brain injury (TBI), a major limitation of currently tested biomarkers is a lack of specificity for defining neuropathological cascades. Identification of surrogate biomarkers that are elevated in CSF in response to brain injury and that offer insight into one or more pathological neurochemical events will provide critical information for appropriate administration of therapeutic compounds for treatment of TBI patients. Non-erythroid alpha II-spectrin is a cytoskeletal protein that is a substrate of both calpain and caspase-3 cysteine proteases. As we have previously demonstrated, cleavage of alpha II-spectrin by calpain and caspase-3 results in accumulation of protease-specific spectrin breakdown products (SBDPs) that can be used to monitor the magnitude and temporal duration of protease activation. However, accumulation of alpha II-spectrin and alpha II-SBDPs in CSF after TBI has never been examined. Following a moderate level (2.0 mm) of controlled cortical impact TBI in rodents, native alpha II-spectrin protein was decreased in brain tissue and increased in CSF from 24 h to 72 h after injury. In addition, calpain-specific SBDPs were observed to increase in both brain and CSF after injury. Increases in the calpain-specific 145 kDa SBDP in CSF were 244%, 530% and 665% of sham-injured control animals at 24 h, 48 h and 72 h after TBI, respectively. The caspase-3-specific SBDP was observed to increase in CSF in some animals but to a lesser degree. Importantly, levels of these proteins were undetectable in CSF of uninjured control rats. These results indicate that detection of alpha II-spectrin and alpha II-SBDPs is a powerful discriminator of outcome and protease activation after TBI. In accord with our previous studies, results also indicate that calpain may be a more important effector of cell death after moderate TBI than caspase-3.

Traumatic brain injury reduces hippocampal alpha7 nicotinic cholinergic receptor binding

Changes in the expression of central nervous system (CNS) neurotransmitter receptors may contribute to behavioral and physiological deficits that occur following traumatic brain injury (TBI). Studies investigating the neurochemical basis for the protracted cognitive dysfunction that follows TBI have focused in part on cholinergic mechanisms. The present study compared the effects of mild and moderate cortical contusion injury (CCI) on the density of cholinergic receptor subtypes, NMDA-type glutamate receptors, and calcium channel expression. Quantitative autoradiography was used to determine the effects of CCI on receptor expression, 48 h following injury. The most robust and consistent change in receptor binding was in the density of alpha7 nicotinic receptors as determined by alpha-[125I]-bungarotoxin (BTX) binding. Bilateral deficits in BTX binding were present following both mild and moderate levels of injury. In contrast, changes in the density of alpha3/alpha4 nAChr's, muscarinic AChr's, NMDA-type glutamate receptors, and L-type calcium channel expression were more regionally restricted and lower in magnitude, as compared to changes in BTX binding. The high calcium permeability of the alpha7 nAChr may be related to the extensive decrease in BTX binding that occurs following TBI.

Dicyclomine, an M1 muscarinic antagonist, reduces infarct volume in a rat subdural hematoma model

The rat subdural hematoma (SDH) model produces a zone of ischemic brain damage within the hemisphere beneath the SDH. Previous studies have measured large increases in extracellular acetylcholine during cerebral ischemia in the rat. We examined infarct volume after selectively blocking muscarinic M1 receptors with dicyclomine during SDH. Rats were anesthetized with isoflurane (2%), intubated, and femoral artery and vein cannulated. Autologous blood (0.375 ml) was injected (0.05 ml/min) under the dura of the right parietal cortex. Dicyclomine (5 mg/kg, i.v.) was injected at 5 min after and again at 2 h after completion of the subdural blood infusion. Blood pressure and intracranial pressure (ICP) were continuously measured. At 4 h after SDH rats were euthanized, brains sectioned, and immunoreacted with glia fibrillary acidic protein. Cortical infarct volume was quantified in coronal brain sections at 0.7-mm intervals from +1.0 mm to -3.9 mm relative to bregma. Infarct volume in drug-treated rats (n = 10) 22.1 +/- 6.99 mm3 was significantly smaller (p < 0.02) than vehicle treated rats (n = 10) 56.7 +/- 9.59 mm3. ICP, blood pressure and cerebral perfusion pressure were not significantly different between groups. These data suggest that activation of M1 muscarinic receptors during an ischemic event may contribute to the development of subsequent pathology.

Experimental brain injury induces expression of amyloid precursor protein, which may be related to neuronal loss in the hippocampus

Previous reports have demonstrated that some focal brain injuries increase amyloid precursor protein (APP) immunoreactivity in the region surrounding the injury where it was localized, in damaged axons and in pre-alpha 2 cells of the entorhinal cortex. However, to date, APP expression in the hippocampus remote from the impact site has not been comprehensively studied. Therefore, we have evaluated APP expression not only in the locally injured cerebral cortex but also in the hippocampus remote from the impact site. In the present paper, diffuse axonal injury was induced in rats in midline fluid percussion injury. APP expression was examined post injury using Western blot analysis and immunohistochemistry. Western blot analysis demonstrated that the expression of 100-kd APP was increased in both the cerebral cortex and hippocampus 24 h after injury. It then decreased in the hippocampus, but did not change in the cerebral cortex, 7 days after injury. Immunohistochemical studies showed increased immunoreactivity of APP in the neuronal perikarya and reactive astrocytes near the region of injury in the cerebral cortex 24 h to 7 days after injury. In the hippocampus, APP accumulated in the CA3 neurons 24 h and 3 days after injury, although no hemorrhagic lesions were seen at that site. The APP positive neurons in CA3 showed shrunken cell bodies and pyknotic nuclei 3 days after injury, and some of the neurons in CA3 had disappeared by 7 days postinjury. The results of present study suggest that traumatic brain injury induces overexpression and accumulation of APP in neuronal perikarya and that these events are followed by degeneration of CA3 neurons. Further, the decline in APP expression in the hippocampus is thought to be due to neuronal loss in CA3 subsector.

Novel pharmacologic strategies in the treatment of experimental traumatic brain injury: 1998

The mechanisms underlying secondary or delayed cell death following traumatic brain injury are poorly understood. Recent evidence from experimental models suggests that widespread neuronal loss is progressive and continues in selectively vulnerable brain regions for months to years after the initial insult. The mechanisms underlying delayed cell death are believed to result, in part, from the release or activation of endogenous "autodestructive" pathways induced by the traumatic injury. The development of sophisticated neurochemical, histopathological and molecular techniques to study animal models of TBI have enabled researchers to begin to explore the cellular and genomic pathways that mediate cell damage and death. This new knowledge has stimulated the development of novel therapeutic agents designed to modify gene expression, synthesis, release, receptor or functional activity of these pathological factors with subsequent attenuation of cellular damage and improvement in behavioral function. This article represents a compendium of recent studies suggesting that modification of post-traumatic neurochemical and cellular events with targeted pharmacotherapy can promote functional recovery following traumatic injury to the central nervous system.

Protective effects of moderate hypothermia on behavioral deficits but not necrotic cavitation following cortical impact injury in the rat

A number of experimental studies have reported that moderate hypothermia can produce significant protection against behavioral deficits and/or morphopathological alterations following traumatic brain injury; a Phase 3 clinical trial is currently examining the therapeutic potential for moderate hypothermia (32 degrees C) to improve outcome following severe traumatic brain injury in humans. The current study examined whether hypothermia (32 degrees C) provided behavioral protection following experimental cortical impact injury. The extent of focal cortical contusion was also examined in the same rats. A total of 30 male Sprague-Dawley rats were trained on beam balance and beam walking tasks prior to injury. Under isoflurane anesthesia, cortical impact was produced on the right parietal cortex of 20 rats. Ten rats underwent all surgical procedures but were not impacted (sham-injured rats). Ten of the injured rats were cooled to 32 degrees C (measured in temporalis muscle) beginning 5 min postinjury, maintained for 2 h and rewarmed slowly for 1 h. In the other 10 injured rats, normothermic temperatures (37.5 degrees C) were maintained for the same duration. Beam balance and beam walking performance was assessed daily for 5 days following injury. At 11 days postinjury, rats were assessed for 5 days on acquisition of the Morris water maze task. Following behavioral assessments, rats were perfused and the brain removed. Coronal sections were cut through the site of cortical impact injury and stained with hematoxylin and eosin. Hypothermic treatment resulted in significantly less beam balance and beam walking deficits than observed in normothermic rats. Hypothermia also significantly attenuated spatial memory performance deficits. Quantitative morphometric analyses failed to detect any significant differences in volumes of necrotic tissue cavitation in cortices of hypothermic and normothermic rats. Hypothermic treatment also had no effect on volumes of dorsal hippocampal tissue or numbers of cells in CA1 or CA3 regions of the hippocampus. These data suggest that hypothermia, consistent with the reports of others, can produce significant behavioral protection following cortical impact injury that is not necessarily correlated with changes in focal cortical necrosis within the first 15 days following injury.

Therapeutic Moderate Hypothermia for Severe Traumatic Brain Injury

Use of therapeutic hypothermia to treat patients with severe traumatic brain injury was described more than 50 years ago. Unexpected improvement in some of these patients was attributed to hypothermia, but none of the early studies systematically evaluated the efficacy of hypothermia, and many patients were thought to have been harmed by the treatment, particularly when cooled below 30°C or when cooled for longer than 48 hours. Recent investigations have found that therapeutic moderate hypothermia (32–34°C) for relatively brief durations can improve histological and behavioral outcome following experimental brain injury. Cooling to this degree and duration has not been implicated as a cause for the cardiac arrhythmias, coagulation abnormalities, or infections attributed to hypothermia in the earlier studies. These laboratory investigations also defined several neurochemical mechanisms through which hypothermia may limit secondary brain injury and brain swelling. Four clinical trials of therapeutic moderate hypothermia were completed during the past three years; each detected a beneficial effect from cooling patients with severe traumatic brain injury to 32 to 34°C for up to 48 hours. In the largest of these studies, therapeutic moderate hypothermia was shown to cause a significant improvement in neurological outcomes 3, 6, and 12 months after injury for those patients with an initial Glasgow Coma Scale score of 5 to 7. The improvement in outcome for these patients was associated with a hypothermia-induced reduction of intracranial pressure and cerebrospinal fluid levels of interleukln-1β and glutamate.

The effect of brain temperature on acute inflammation after traumatic brain injury in rats

The effect of varying brain temperature on neutrophil accumulation in brain and the expression of E-selectin and intercellular adhesion molecule-1 (ICAM-1) on cerebrovascular endothelium after controlled cortical impact (CCI) was studied in rats. Sprague Dawley rats were anesthetized and subjected to CCI to the left parietal cortex. Ten minutes after CCI, brain temperature was modulated and maintained at 32 degrees C, 37 degrees C, or 39 degrees C (n = 8 per group) for 4 h. Rats were then decapitated and immunohistochemistry on brain sections was performed using monoclonal antibodies (MoAb) that recognize neutrophils (RP-3), ICAM-1 (TM-8, Athena Neurosciences), or MoAb that react with E-selectin (La-Roche). Each of these markers was quantified in 100 x fields. Neutrophil accumulation was also quantified with myeloperoxidase (MPO) assay. Absolute neutrophil count (ANC) was measured in blood samples before and 1 h and 4 h after CCI. Neutrophil accumulation in injured brain was decreased in rats maintained at 32 degrees C vs 39 degrees C (4-fold difference as assessed by immunohistochemistry, p < 0.05; 8-fold difference as assessed by MPO assay, p < 0.05). Peripheral blood ANC was not affected by temperature. E-selectin was induced on cerebrovascular endothelium after CCI (p < 0.05), but was only decreased modestly at 32 degrees C versus 39 degrees C (p = 0.11). ICAM-1 was not upregulated on cerebrovascular endothelium at this early time following CCI. Neutrophil accumulation is directly dependent on brain temperature during the initial 4 h after CCI. This appears to be mediated by mechanisms other than effects of temperature on E-selectin or ICAM-1 expression or systemic ANC.

Effects of muscarinic receptor antagonism on the phosphatidylinositol bisphosphate signal transduction pathway after experimental brain injury

Hippocampal levels of fatty acids extracted from phosphatidylinositol 4,5-bisphosphate (PIP2), free fatty acids (FFA), and lactate were measured after central fluid percussion traumatic brain injury (TBI) in rats. At 5 min after injury, there was a decrease in fatty acids extracted from PIP2 suggesting a decrease in PIP2. At the same time point, total FFA increased in saline-treated TBI rats. Levels of arachidonic acid were significantly decreased in PIP2, while at the same time arachidonic and stearic acids increased in FFA in saline-treated TBI rats. No significant alterations in PIP2-derived fatty acids or FFA were observed at 20 min after TBI. Hippocampal concentrations of lactate were significantly elevated at 5 and 20 min after injury in saline-treated rats. In general, these alterations were blunted by preinjury administration of the muscarinic antagonist, scopolamine. These results suggest that the PIP2 signal transduction pathway is activated in the hippocampus at the onset of central fluid percussion TBI and that the enhanced phospholipase C-catalyzed phosphodiestric breakdown of PIP2 is a major mechanism of liberation of FFA in these sites immediately after such injury. The blunting of PIP2 and FFA alterations in animals treated with scopolamine suggests that activation of muscarinic receptors significantly contributes to the phospholipase C (PLC) signal transduction pathophysiology in TBI. The attenuation of lactate accumulation in scopolamine-treated rats suggests that TBI-induced muscarinic receptor activation also contributes to increased glycolytic metabolism and/or ionic imbalances.

Neurochemical mechanisms in brain injury and treatment: a review

This article reviews cellular energy transformation processes and neurochemical events that take place at the time of brain injury and shortly thereafter emphasizing hypoxia-ischemia, cerebrovascular accident, and traumatic brain injury. New interpretations of established concepts, such as diffuse axonal injury, are discussed; specific events, such as free radical production, excess production of excitatory amino acids, and disruption of calcium homeostasis, are reviewed. Neurochemically-based interventions are also presented: calcium channel blockers, excitatory amino acid antagonists, free radical scavengers, and hypothermia treatment. Concluding remarks focus on the role of clinical neuropsychologists in validation of treatment interventions.

Moderate hypothermia in patients with severe head injury: cerebral and extracerebral effects

Cerebral and extracerebral effects of moderate hypothermia (core temperature 32.5 degrees C-33.0 degrees C) were prospectively studied in 10 patients with severe closed head injury (Glasgow Coma Scale score < 7) in the intensive care unit of a university hospital. Hypothermia was induced by cooling the patient's body surface with water-circulating blankets. Before cooling, a conventional intracranial pressure (ICP) reduction therapy was applied, which remained unchanged throughout the study. Cerebral blood flow (CBF), cerebral metabolic rates for oxygen (CMRO2) and lactate (CMRL), and ICP were simultaneously measured prior to inducing hypothermia, after obtaining hypothermia, after 24 hours of hypothermia, and after rewarming. With respect to extracerebral effects, supplemental investigations were conducted 24 and 72 hours after rewarming. The median delay between injury and induction of hypothermia was 16 hours. Hypothermia reduced CMRO2 by 45% (p < 0.01), whereas CBF did not change significantly. Before cooling, six patients had elevated CMRL indicating cerebral ischemia. Cooling normalized CMRL in all patients (p < 0.01). The intracranial hypertension present prior to cooling declined markedly during hypothermia (p < 0.01) without significant rebound effects after rewarming. Cardiac index decreased by 18% after hypothermia was reached (p < 0.05), recovered at 24 hours of hypothermia, and surpassed baseline values after rewarming. Platelet counts dropped continuously up to 24 hours after rewarming (p < 0.01). Plasma coagulation tests did not show significant worsening. Creatinine clearance decreased during cooling (p < 0.01) and recovered by 24 hours after rewarming. Twenty-four hours after cooling had begun, eight patients had elevated serum lipase activity (p < 0.01) and four of them acquired pancreatitis. Rewarming normalized both pancreatic alterations. Seven patients made a good recovery; one survived severely disabled; and two patients died. Moderate hypothermia is effective in preventing secondary brain damage while reducing cerebral ischemia. However, there are potentially hazardous side effects that require additional monitoring.

Mild posttraumatic hypothermia reduces mortality after severe controlled cortical impact in rats

The effect of posttraumatic hypothermia (brain temperature controlled at 32 degrees C for 4 h) on mortality after severe controlled cortical impact (CCI) was studied in rats. Four posttraumatic brain temperatures were compared: 37 degrees C (n = 10), 36 degrees C (n = 4), 32 degrees C (n = 10), and uncontrolled (UC; n = 6). Rats were anesthetized and subjected to severe CCI (4.0-m/s velocity, 3.0-mm depth) to the exposed left parietal cortex. At 10 min posttrauma the rats were cooled or maintained at their target brain temperature, using external cooling or warming. Brain temperature in the UC group was recorded but not regulated, and rectal temperature was maintained at 37 +/- 0.5 degrees C. After 4 h, rats were rewarmed over a 1-h period to 37 degrees C, extubated, and observed for 24 h. In the 37 and 36 degree C groups, 24-h mortality was 50% (37 degrees C = 5/10, 36 degrees C = 2/4). In the 32 degree C group, 24-h mortality was 10% (1/10). In the UC group, brain temperature was 35.4 +/- 0.6 degrees C during the 4-h treatment period and 24-h mortality was 0% (0/6). Mortality was higher in groups with brain temperatures > or = 36 degrees C versus those with brain temperatures < 36 degrees C (50 vs. 6%, respectively; p < 0.05). Additionally, electroencephalograms (EEG) were recorded in subsets of each temperature group and the percentage of time that the EEG was suppressed (isoelectric) was determined. Percentage of EEG suppression was greater in the hypothermic (32 degrees C, n = 6; UC, n = 4) groups than in the normothermic (36 degrees C, n = 3; 37 degrees C, n = 6) groups (23.3 +/- 14.3 vs. 1.2 +/- 3.1%, respectively; p < 0.05). Posttraumatic hypothermia suppressed EEG during treatment and reduced mortality after severe CCI. The threshold for this protective effect appears to be a brain temperature < 36 degrees C. Thus, even mild hypothermia may be beneficial after severe brain trauma.

Treatment of experimental brain injury with moderate hypothermia and 21-aminosteroids

Studies of experimental traumatic brain injury have found that histologic injury is significantly reduced and behavioral outcome improved in animals treated with moderate hypothermia (32-33 degrees C) or a 21-aminosteroid. Because these treatments are thought to work through different neurochemical mechanisms, their combined use might be expected to be more efficacious than either treatment alone. To test this hypothesis, we studied each treatment separately and in combination in a rodent model of controlled cortical contusion. Treatment with moderate hypothermia (32 degrees C for 4 h), a 21-aminosteroid (U-74389G, Upjohn, 10 mg/kg intravenously, repeated 3 h after the first dose), or both, was initiated 10, 25, or 40 min after injury. The brains were perfused 24 h after injury, and sagittal sections were stained for the 68-kDa "core" neurofilament subunit, a marker of axonal injury. The total number of positively stained axons in the ipsilateral internal capsule were counted under light microscopy. Compared with the control group (injury but no treatment), treatment with each therapy alone or combined, initiated 10 min after injury, caused significant reductions in the number of stained axons (21-aminosteroid alone-35% reduction; hypothermia alone-55% reduction; combination-48% reduction). The number of positively stained axons was significantly reduced in the aminosteroid and combination therapy groups at all three postinjury times (p = 0.01) and in the hypothermia groups treated at 10 or 25 min (p = 0.01) but not at 40 min after injury. We concluded that combination therapy with hypothermia and 21-aminosteroids was no more efficacious than either therapy alone, and that 21-aminosteroid therapy was more efficacious than hypothermia when treatment was initiated 40 min after injury.

Differential consequences of lateral and central fluid percussion brain injury on receptor coupling in rat hippocampus

We have identified alterations in the responses of muscarinic and metabotropic receptors in rat hippocampus that persist for at least 15 days after central fluid percussion injury. This study compares the effect of lateral fluid percussion and central fluid percussion on these responses. Moderate injury was obtained by displacement and deformation of the brain within the closed cranial cavity using a fluid percussion device positioned either centrally or laterally. Carbachol and (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD)-stimulated polyphosphoinositide (PPI) hydrolysis was assayed in hippocampus from injured and sham-injured controls at 15 days following injury. At 15 days after central fluid percussion traumatic brain injury (TBI), the response to carbachol was enhanced by 30% and the response to trans-ACPD was enhanced by 75% compared to sham-injured animals. At 15 days after lateral fluid percussion TBI the response to trans-ACPD was enhanced by 40% both ipsilateral and contralateral to the side of injury. In contrast, the response to carbachol was enhanced by 29% contralateral to the side of injury but was diminished by 12% ipsilateral to the side of injury. Cresyl violet staining shows no hippocampal cell death after central fluid percussion injury or on the side contralateral to lateral fluid percussion injury but on the ipsilateral side cell death was identified in hippocampal area CA3. Thus, abnormal hippocampal cell signaling through the phosphoinositide pathway occurs in the absence of cell death and may contribute to cognitive impairment.

Differential modulation of carbachol and trans-ACPD-stimulated phosphoinositide turnover following traumatic brain injury

In the fluid percussion model of traumatic brain injury (TBI), we examined muscarinic and metabotropic glutamate receptor-stimulated polyphosphoinositide (PPI) turnover in rat hippocampus. Moderate injury was obtained by displacement and deformation of the brain within the closed cranial cavity using a fluid percussion device. Carbachol and (+/-)-1-Aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD)-stimulated PPI hydrolysis was assayed in hippocampus from injured and sham-injured controls at both 1 hour and 15 days following injury. At 1 hour after TBI, the response to carbachol was enhanced in injured rats by up to 200% but the response to trans-ACPD was diminished by as much as 28%. By contrast, at 15 days after TBI, the response to carbachol was enhanced by 25% and the response to trans-ACPD was enhanced by 73%. The ionotropic glutamate agonists N-methyl-D-aspartate (NMDA), and alpha-amino-3 hydroxy-5-methyl-4-isoxazolepropionate (AMPA), did not increase PPI hydrolysis in either sham or injured rats and injury did not alter basal hydrolysis. Thus, hippocampal muscarinic and metabotropic receptors linked to phospholipase C are differentially altered by TBI.

Induction of Cu,Zn-superoxide dismutase after cortical contusion injury during hypothermia

To determine the effect of hypothermia on superoxide injury after cerebral contusion, the induction of Cu,Zn-superoxide dismutase was examined 6 h after contusion in rats using Northern blotting. Cu,Zn-superoxide dismutase gene expression increased at the periphery of the contusion, which may indicate the severity of the superoxide stimulus. This increase was preserved after contusion under hypothermia, which may show that superoxide injury is still severe although brain edema is decreased.

Traumatic brain injury causes a decrease in M2 muscarinic cholinergic receptor binding in the rat brain

Numerous studies indicate that an acute, excessive activation of muscarinic acetylcholine receptors (mAChR) contributes to the pathophysiological sequela of TBI. The present study examined the effect of moderate fluid percussion traumatic brain injury (TBI) on binding to M1 and M2 mAChR subtypes in the hippocampal formation and adjacent cortex using quantitative autoradiography. Injured animals along with concurrent controls were sacrificed by in situ freezing at 3 h or 24 h following TBI. Slide-mounted tissue sections were incubated in either [3H]pirenzepine (23 nM) for M1 or [3H]AFDX384 (9 nM) for M2 mAChR subtype labeling. Binding of [3H]pirenzepine to the M1 mAChR subtype was not significantly altered by TBI when compared to sham-injured animals. [3H]AFDX384 binding to the M2 mAChR subtype was significantly decreased at 24 h in hippocampal CA2-3 region and dorsal blade of the dentate gyrus (P < 0.05). The differences observed between M1 and M2 subtypes suggests that these muscarinic subtypes may differentially contribute to the pathophysiology of TBI.

Muscarinic cholinergic receptor binding in rat brain at 15 days following traumatic brain injury

Laboratory studies indicate that activation of muscarinic cholinergic receptors (mAChRs) at or soon after traumatic brain injury (TBI) significantly contributes to behavioral morbidity. Recent research has demonstrated that pre-injury treatment with the muscarinic antagonist scopolamine significantly reduces spatial memory deficits at 11-15 days post-TBI. In the present study, we examined mAChR binding kinetics in brain regions at 15 days after moderate (1.95 atm) fluid percussion TBI in untreated and scopolamine-treated rats. Three groups were examined: untreated TBI (n = 8), TBI with pre-injury scopolamine treatment (1.0 mg/kg, i.p., 15 min prior to injury) (n = 11), and sham-injury (n = 7). The affinity (Kd) and maximum number of binding sites (Bmax) of mAChRs in hippocampus, neocortex, and brainstem were determined by [3H]QNB binding. Bmax values in TBI animals were significantly higher in hippocampus (4061 +/- 494 fmol/mg protein) and neocortex (4272 +/- 640 fmol/mg protein), but not in brainstem (833 +/- 39 fmol/mg protein) compared to sham-injured controls (hipp. 2812 +/- 218 fmol/mg/protein; neoctx. 2850 +/- 129 fmol/mg protein; brainstem 794 +/- 26 fmol/mg protein) (P < 0.05). At 15 days after injury, Bmax values of mAChRs in TBI animals with pre-injury scopolamine treatment (hipp. 2850 +/- 129 fmol/mg protein; neoctx. 2948 +/- 123 fmol/mg protein) did not differ from control. In all brain regions, Kd values did not differ between groups. These results demonstrate that TBI significantly alters the binding sites of mAChRs in hippocampus and neocortex for as long as 15 days after TBI. Furthermore, these results indicate that a pharmacological treatment that improves motor and memory function outcome also normalizes aspects of mAChRs physiology. These data suggest that excessive activation of mAChRs at or soon after TBI impact contributes to long-term pathophysiological processes in TBI.

Hypothermia in acute blunt head injury

Mild to moderate hypothermia has been employed since the 1940s in the treatment of acute blunt head trauma. The utility of hypothermia in ischemic injury has been confirmed, by both animal studies and clinical experience, in cardiovascular and neurological surgery. In blunt injury, though, only one prospective, randomized study has shown a statistically significant improvement in long term outcome. Clinical experience, animal data, proposed mechanisms, technical considerations, and potential risks are reviewed. Hypothermia remains controversial in the setting of blunt head injury but may prove to be a useful treatment modality.

Muscarinic cholinergic receptor binding in rat brain following traumatic brain injury

Recent evidence suggests that excessive activation of muscarinic cholinergic receptors (mAChRs) contributes significantly to the pathophysiological consequences of traumatic brain injury (TBI). To examine possible alterations in mAChRs after TBI, the affinity (Kd) and maximum number of binding sites (Bmax) of mAChRs in hippocampus, neocortex, brain stem and cerebellum were determined by [3H]QNB binding. Three groups of rats were examined: 1 h post-TBI (n = 21), 24 h post-TBI (n = 21) and sham-injured rats (n = 21). Kd values were significantly higher in hippocampus and brain stem at 1 but not 24 h post-TBI compared with sham-injured controls (P < 0.05). Kd values did not significantly differ in neocortex and cerebellum at 1 or 24 h post-TBI compared with sham-injured controls. Bmax values did not significantly differ in any brain areas at 1 or 24 h post-TBI compared with sham-injured controls. These results show that TBI significantly decreases the affinity of mAChRs in hippocampus and brain stem at an early stage post-TBI, which may contribute to desensitization of mAChRs after TBI. The findings of no change in Bmax values are consistent with a transient elevation in ACh concentrations after TBI.

Protective effect of galanin on behavioral deficits in experimental traumatic brain injury

The magnitude of behavioral deficits in traumatic brain injury (TBI) has been shown to be partly related to alterations in the balance between excitatory and inhibitory neurotransmitter release. Previous studies have demonstrated that extracellular excitatory neurotransmitter concentrations dramatically increase following experimental TBI. We examined the effects of a neuromodulatory peptide, galanin (GAL), on behavioral morbidity, as measured by sensory motor and memory performance tasks, associated with experimental TBI in the rat. A single intraventricular injection of GAL (1.0 micrograms, n = 8 or 10.0 micrograms, n = 10) or cerebrospinal fluid (CSF) vehicle (n = 10) was administered 5 minutes prior to central fluid percussion TBI in rats. Performance on sensory motor tasks was assessed prior to injury and for 5 days after TBI with beam-balance, beam-walking, and rotarod tasks. Memory performance was assessed on days 11-15 after TBI with the Morris water maze. TBI produced significant motor and memory deficits in the CSF-treated group. GAL-treated rats had significantly less magnitude of deficits compared to CSF-treated rats on beam-balance, beam-walking, and rotarod performance. The 1.0 micrograms GAL dose produced slightly greater protection than the 10.0 micrograms GAL dose. Neither GAL dose affected body weight loss or Morris water maze performance. These results suggest that the physiologic effects of GAL may reduce certain components of TBI morbidity, possibly by modulating neuronal excitability.

Behavioral protection by moderate hypothermia initiated after experimental traumatic brain injury

The effects of postinjury hypothermia on behavioral outcome following moderate fluid percussion traumatic brain injury (TBI) were examined. In Experiment I, three groups of rats were examined. The first group was normothermic (37.5 degrees C); and hypothermia (30 degrees C) was initiated 15 min and 30 min postinjury in the second and third groups, respectively. Whole body cooling was achieved by ventral ice pack. Cooling of the brain to 30 degrees C was achieved in 25 min and maintained for 60 min. Brain temperature was measured indirectly by a probe in the temporalis muscle. Behavioral outcome was assessed by beam-balance performance, beam-walking performance, and body weight loss measured daily for 5 days after TBI. Both the normothermic group and the 30-min postinjury hypothermic group exhibited significant (p < 0.05) beam-balance and beam-walking deficits on days 1 through 5 after TBI. In contrast, the 15-min postinjury hypothermic group exhibited significant (p < 0.05) beam-walking deficits only on day 1 after TBI and significant (p < 0.05) beam-balance deficits on days 1, 3, and 4 after TBI. In Experiment II, subcortical brain temperature was compared to temporalis muscle temperature in normothermic (37.5 degrees C) and hypothermic (30 degrees C) rats subjected to TBI. In both groups brain temperature tracked within 0.4 degree C of temporalis muscle temperature. These results are similar to post-TBI excitatory receptor antagonist studies and indicate a therapeutic window for moderate hypothermia of less than 30 min after moderate fluid percussion TBI in the rat.