The immunophilin ligand FK506 attenuates the axonal damage associated with rapid rewarming following posttraumatic hypothermia

Rapid rewarming rate associated with favorable neurological outcomes in patients with post-cardiac arrest syndrome patients treated with targeted temperature management

Aim

To determine whether the rewarming rate is associated with neurological outcomes in patients with post-cardiac arrest syndrome treated with targeted temperature management (TTM) at 34°C.

Methods

We conducted a retrospective analysis of a nationwide cohort study of out-of-hospital cardiac arrest in Japan. Adult patients who experienced a return of spontaneous circulation and completed TTM at 34°C between June 2014 and December 2019 were divided equally into three groups (slow, moderate, and rapid) according to their rewarming rates from 34°C to 36°C. The rates of favorable neurological outcomes (Cerebral Performance Category of 1-2 after 30 days) were compared among the groups, and the adjusted odds ratios for a favorable neurological outcome were calculated for the groups.

Results

We analyzed 348, 357, and 358 patients in the slow, moderate, and rapid groups, respectively. The periods of rewarming from 34°C to 36°C were 41.9 ± 10.5, 22.4 ± 1.8, and 12.2 ± 3.6 h, respectively. The number of favorable neurological outcomes after 30 days was 121 (34.8%), 125 (35.0%), and 147 (41.1%), respectively, with no significant differences among the three groups (p = 0.145). Rapid rewarming was independently associated with a favorable neurological outcome compared with slow rewarming (adjusted odds ratio 1.57 [95% confidence interval 1.04-2.37]; p = 0.031).

Conclusions

Rapid rewarming after TTM at 34°C was associated with a more favorable neurological outcome than slow rewarming.

Traumatic axonal injury (TAI): definitions, pathophysiology and imaging-a narrative review

Introduction

Traumatic axonal injury (TAI) is a condition defined as multiple, scattered, small hemorrhagic, and/or non-hemorrhagic lesions, alongside brain swelling, in a more confined white matter distribution on imaging studies, together with impaired axoplasmic transport, axonal swelling, and disconnection after traumatic brain injury (TBI). Ever since its description in the 1980s and the grading system by Adams et al., our understanding of the processes behind this entity has increased.

Methods

We performed a scoping systematic, narrative review by interrogating Ovid MEDLINE, Embase, and Google Scholar on the pathophysiology, biomarkers, and diagnostic tools of TAI patients until July 2020.

Results

We underline the misuse of the Adams classification on MRI without proper validation studies, and highlight the hiatus in the scientific literature and areas needing more research. In the past, the theory behind the pathophysiology relied on the inertial force exerted on the brain matter after severe TBI inducing a primary axotomy. This theory has now been partially abandoned in favor of a more refined theory involving biochemical processes such as protein cleavage and DNA breakdown, ultimately leading to an inflammation cascade and cell apoptosis, a process now described as secondary axotomy.

Conclusion

The difference in TAI definitions makes the comparison of studies that report outcomes, treatments, and prognostic factors a daunting task. An even more difficult task is isolating the outcomes of isolated TAI from the outcomes of severe TBI in general. Targeted bench-to-bedside studies are required in order to uncover further pathways involved in the pathophysiology of TAI and, ideally, new treatments.

State-of-the-art considerations in post-arrest care

Cardiac arrest has a high rate of morbidity and mortality. Several advances in post-cardiac arrest management can improve outcome, but are time-dependent, placing the emergency physician in a critical role to both recognize the need for and initiate therapy. We present a novel perspective of both the workup and therapeutic interventions geared toward the emergency physician during the first few hours of care. We describe how the immediate care of a post-cardiac arrest patient is resource intensive and requires simultaneous evaluation for the underlying cause and intensive management to prevent further end organ damage, particularly of the central nervous system. The goal of the initial focused assessment is to rapidly determine if any reversible causes of cardiac arrest are present and to intervene when possible. Interventions performed in this acute period are aimed at preventing additional brain injury through optimizing hemodynamics, providing ventilatory support, and by using therapeutic hypothermia when indicated. After the initial phase of care, disposition is guided by available resources and the clinician's judgment. Transfer to a specialized cardiac arrest center is prudent in centers that do not have significant support or experience in the care of these patients.

Investigate the Variations of the Head and Brain Response in a Rodent Head Impact Acceleration Model by Finite Element Modeling

Diffuse axonal injury (DAI) is a severe form of traumatic brain injury and often induced by blunt trauma. The closed head impact acceleration (IA) model is the most widely used rodent DAI model. However, this model results in large variations of injury severity. Recently, the impact device/system was modified to improve the consistency of the impact energy, but variations of the head kinematics and subsequent brain injuries were still observed. This study was aimed to utilize a Finite Element (FE) model of a rat head/body and simulation to investigate the potential biomechanical factors influencing the impact energy transfer to the head. A detailed FE rat head model containing detailed skull and brain anatomy was developed based on the MRI, microCT and atlas data. The model consists of over 722,000 elements, of which 310,000 are in the brain. The white matter structures consisting of highly aligned axonal fibers were simulated with transversely isotropic material. The rat body was modeled to provide a realistic boundary at the spine-medulla junction. Rodent experiments including dynamic cortical deformation, brain-skull displacement, and IA kinematics were simulated to validate the FE model. The model was then applied to simulate the rat IA experiments. Parametric studies were conducted to investigate the effect of the helmet inclination angles (0°-5°) and skull stiffness (varied 20%) on the resulting head kinematics and maximum principal strain in the brain. The inclination angle of the helmet at 5° could vary head linear acceleration by 8-31%. The change in head rotational velocity was inversely related to the change in linear acceleration. Varying skull stiffness resulted in changes in head linear acceleration by 3% but with no effect on rotational velocity. The brain strain in the corpus callosum was only affected by head rotation while the strain in the brainstem was influenced by the combined head kinematics, local skull deformation, and head-neck position. Validated FE models of rat impact head injury can assist in exploring various biomechanical factors influencing the head impact response and internal brain response. Identification of these variables may help explain the variability of injury severity observed among experiments and across different labs.

Association between rewarming duration and neurological outcome in out-of-hospital cardiac arrest patients receiving therapeutic hypothermia

AIM

The European Resuscitation Council guidelines recommend a slow rate of rewarming of 0.25 °C/h-0.5 °C/h for out-of-hospital cardiac arrest (OHCA) patients receiving therapeutic hypothermia (TH). Conversely, a very slow rewarming of 1 °C/day is generally applied in Japan. The rewarming duration ranged from less than 24 h up to more than 50 h. No randomized control trials have examined the optimal rewarming speed for TH in OHCA patients. Therefore, we examined the association between the rewarming duration and neurological outcomes in OHCA patients who received TH.

METHODS

This study was a secondary analysis of the Japanese Population-based Utstein-style study with defibrillation and basic/advanced Life Support Education and implementation-Hypothermia (J-PULSE-HYPO) study registry, a multicenter prospective cohort study. Patients suffering from OHCA who received TH (target temperature, 34 °C) after the return of spontaneous circulation from 2005 to 2011 in 14 hospitals throughout Japan were enrolled. The rewarming duration was defined as the time from the beginning of rewarming at a target temperature of 34 °C until reaching 36 °C. The primary outcome was an unfavorable neurological outcome at hospital discharge, i.e., a cerebral performance category of 3-5.

RESULTS

The J-PULSE-HYPO study enrolled 452 OHCA patients. Of these, 328 were analyzed; 79.9% survived to hospital discharge, of which 56.4% had a favorable neurological outcome. Multivariable logistic regression analysis revealed that the rewarming duration was independently associated with unfavorable neurological outcomes [odds ratio (per 5 h), 0.89; 95% confidence interval, 0.79-0.99; p =  0.032].

CONCLUSION

A longer rewarming duration was significantly associated with and was an independent predictor of favorable neurological outcomes in OHCA patients who received TH.

Successful Therapeutic Hypothermia in a Propofol-Related Cardiac Arrest Case: A Case Report and Literature Review

Targeted temperature management (therapeutic hypothermia) is a treatment method used to prevent potential complications that can develop in relation to the increased temperature in the brain as a result of cardiac arrest. Due to costs and various health policies there is no comprehensive study in the world that has been able to guide the relevant literature on therapeutic hypothermia. We have presented a 25-year-old female patient in our study who developed cardiac arrest after the administration of propofol for sedation before undergoing a diagnostic upper gastroscopy procedure and received a successful therapeutic hypothermia therapy following a resuscitation of 19 minutes.

Variation in PPP3CC Genotype Is Associated with Long-Term Recovery after Severe Brain Injury

After experimental traumatic brain injury (TBI), calcineurin is upregulated; blocking calcineurin is associated with improved outcomes. In humans, variation in the calcineurin A-gamma gene (PPP3CC) has been associated with neuropsychiatric disorders, though any role in TBI recovery remains unknown. This study examines associations between PPP3CC genotype and mortality, as well as gross functional status assessed at admission using the Glasgow Coma Scale (GCS) and at 3, 6, and 12 months after severe TBI using the Glasgow Outcome Score (GOS). The following tagging single nucleotide polymorphisms (tSNPs) in PPP3CC were genotyped: rs2443504, rs2461491, rs2469749, and rs10108011. The rs2443504 AA genotype was univariately associated with GCS (p = 0.022), GOS at 3, 6, and 12 months (p = 0.002, p = 0.034, and p = 0.004, respectively), and mortality (p = 0.007). In multivariate analysis controlling for age, sex, and GCS, the AA genotype of rs2443504 was associated with GOS at 3 (p = 0.02), and 12 months (p = 0.01), with a trend toward significance at 6 months (p = 0.05); the AA genotype also was associated with mortality in the multivariate model (p = 0.04). Further work is warranted to better understand the role of calcineurin, as well as the genes encoding it and their relevance to outcomes after brain injury.

Evidence for the therapeutic efficacy of either mild hypothermia or oxygen radical scavengers after repetitive mild traumatic brain injury

Repetitive brain injury, particularly that occurring with sporting-related injuries, has recently garnered increased attention in both the clinical and public settings. In the laboratory, we have demonstrated the adverse axonal and vascular consequences of repetitive brain injury and have demonstrated that moderate hypothermia and/or FK506 exerted protective effects after repetitive mild traumatic brain injury (mTBI) when administered within a specific time frame, suggesting a range of therapeutic modalities to prevent a dramatic exacerbation. In this communication, we revisit the utility of targeted therapeutic intervention to seek the minimal level of hypothermia needed to achieve protection while probing the role of oxygen radicals and their therapeutic targeting. Male Sprague-Dawley rats were subjected to repetitive mTBI by impact acceleration injury. Mild hypothermia (35 °C, group 2), superoxide dismutase (group 3), and Tempol (group 4) were employed as therapeutic interventions administered 1  h after the repetitive mTBI. To assess vascular function, cerebral vascular reactivity to acetylcholine was evaluated 3 and 4 h after the repetitive mTBI, whereas to detect the burden of axonal damage, amyloid precursor protein (APP) density in the medullospinal junction was measured. Whereas complete impairment of vascular reactivity was observed in group 1 (without intervention), significant preservation of vascular reactivity was found in the other groups. Similarly, whereas remarkable increase in the APP-positive axon was observed in group 1, there were no significant increases in the other groups. Collectively, these findings indicate that even mild hypothermia or the blunting free radical damage, even when performed in a delayed period, is protective in repetitive mTBI.

Therapeutic targeting of the axonal and microvascular change associated with repetitive mild traumatic brain injury

Recent interest in mild traumatic brain injury (mTBI) has increased the recognition that repetitive mTBI occurring within the sports and military settings can exacerbate the adverse consequences of the initial injury. While multiple studies have recently reported the pathological, metabolic, and functional changes associated with repetitive mTBI, no consideration has been given to the development of therapeutic approaches to attenuate these abnormalities. In this study, we used the model of repetitive impact acceleration insult previously reported by our laboratory to cause no initial structural and functional changes, yet evoke dramatic change following second insult of the same intensity. Using this model, we employed established neuroprotective agents including FK506 and hypothermia that were administered 1 h after the second insult. Following either therapeutic intervention, changes of cerebral vascular reactivity to acetylcholine were assessed through a cranial window. Following the completion of the vascular studies, the animals were prepared to access the numbers of amyloid precursor protein (APP) positive axons, a marker of axonal damage. Following repetitive injury, cerebral vascular reactivity was dramatically preserved by either therapeutic intervention or the combination thereof compared to control group in which no intervention was employed. Similarly, APP density was significantly lower in the therapeutic intervention group compared in controls. Although the individual use of FK506 or hypothermia exerted significant protection, no additive benefit was found when both therapies were combined. In sum, the current study demonstrates that the exacerbated pathophysiological changes associated with repetitive mTBI can be therapeutically targeted.

Therapy development for diffuse axonal injury

Diffuse axonal injury (DAI) remains a prominent feature of human traumatic brain injury (TBI) and a major player in its subsequent morbidity. The importance of this widespread axonal damage has been confirmed by multiple approaches including routine postmortem neuropathology as well as advanced imaging, which is now capable of detecting the signatures of traumatically induced axonal injury across a spectrum of traumatically brain-injured persons. Despite the increased interest in DAI and its overall implications for brain-injured patients, many questions remain about this component of TBI and its potential therapeutic targeting. To address these deficiencies and to identify future directions needed to fill critical gaps in our understanding of this component of TBI, the National Institute of Neurological Disorders and Stroke hosted a workshop in May 2011. This workshop sought to determine what is known regarding the pathogenesis of DAI in animal models of injury as well as in the human clinical setting. The workshop also addressed new tools to aid in the identification of this axonal injury while also identifying more rational therapeutic targets linked to DAI for continued preclinical investigation and, ultimately, clinical translation. This report encapsulates the oral and written components of this workshop addressing key features regarding the pathobiology of DAI, the biomechanics implicated in its initiating pathology, and those experimental animal modeling considerations that bear relevance to the biomechanical features of human TBI. Parallel considerations of alternate forms of DAI detection including, but not limited to, advanced neuroimaging, electrophysiological, biomarker, and neurobehavioral evaluations are included, together with recommendations for how these technologies can be better used and integrated for a more comprehensive appreciation of the pathobiology of DAI and its overall structural and functional implications. Lastly, the document closes with a thorough review of the targets linked to the pathogenesis of DAI, while also presenting a detailed report of those target-based therapies that have been used, to date, with a consideration of their overall implications for future preclinical discovery and subsequent translation to the clinic. Although all participants realize that various research gaps remained in our understanding and treatment of this complex component of TBI, this workshop refines these issues providing, for the first time, a comprehensive appreciation of what has been done and what critical needs remain unfulfilled.

Effect of PACAP in central and peripheral nerve injuries

Pituitary adenylate cyclase activating polypeptide (PACAP) is a bioactive peptide with diverse effects in the nervous system. In addition to its more classic role as a neuromodulator, PACAP functions as a neurotrophic factor. Several neurotrophic factors have been shown to play an important role in the endogenous response following both cerebral ischemia and traumatic brain injury and to be effective when given exogenously. A number of studies have shown the neuroprotective effect of PACAP in different models of ischemia, neurodegenerative diseases and retinal degeneration. The aim of this review is to summarize the findings on the neuroprotective potential of PACAP in models of different traumatic nerve injuries. Expression of endogenous PACAP and its specific PAC1 receptor is elevated in different parts of the central and peripheral nervous system after traumatic injuries. Some experiments demonstrate the protective effect of exogenous PACAP treatment in different traumatic brain injury models, in facial nerve and optic nerve trauma. The upregulation of endogenous PACAP and its receptors and the protective effect of exogenous PACAP after different central and peripheral nerve injuries show the important function of PACAP in neuronal regeneration indicating that PACAP may also be a promising therapeutic agent in injuries of the nervous system.

Temporal assessment of traumatic axonal injury in the rat corpus callosum and optic chiasm

Impaired axoplasmic transport (IAT) and neurofilament compaction (NFC), two common axonal pathology processes involved in traumatic axonal injury (TAI), have been well characterized. TAI is found clinically and in animal models in brainstem white matter (WM) tracts and in the corpus callosum (CC), optic chiasm (Och), and internal capsule. Previous published quantitative studies of the time course of TAI expression induced by the Marmarou impact acceleration model have been limited to the brainstem. Accordingly, this study assessed the extent of IAT and NFC in the CC and Och at 8h, 28 h, 3 days and 7 days after traumatic brain injury (TBI) induction by the Marmarou impact acceleration model. IAT peak density was observed at 8h in the CC and 28 h in the Och post-TBI. NFC peak density was observed at 28 h in both structures. The density of IAT and NFC decreased with increasing survival time in both structures. The NFC density time profile followed a similar trend in both the Och and CC, whereas the IAT density time profile was variable between the Och and CC. Furthermore, a strong linear relationship was observed between IAT and NFC in the CC but not in the Och. These findings highlight the heterogeneity of TAI as evidenced by variable IAT and NFC injury time profiles in each anatomical structure. This variability indicates the requirement of multiple markers for a comprehensive TAI evaluation and multiple targeted treatments for TAI polypathology within its therapeutic window time frame.

Impaired axoplasmic transport is the dominant injury induced by an impact acceleration injury device: an analysis of traumatic axonal injury in pyramidal tract and corpus callosum of rats

Traumatic axonal injury (TAI) involves neurofilament compaction (NFC) and impaired axoplasmic transport (IAT) in distinct populations of axons. Previous quantification studies of TAI focused on limited areas of pyramidal tract (Py) but not its entire length. Quantification of TAI in corpus callosum (CC) and its comparison to that in Py is also lacking. This study assessed and compared the extent of TAI in the entire Py and CC of rats following TBI. TBI was induced by a modified Marmarou impact acceleration device in 31 adult male Sprague Dawley rats by dropping a 450 gram impactor from either 1.25 m or 2.25 m. Twenty-four hours after TBI, TAI was assessed by beta amyloid precursor protein (β-APP-IAT) and RMO14 (NFC) immunocytochemistry. TAI density (β-APP and RMO14 axonal swellings, retraction balls and axonal profiles) was counted from panoramic images of CC and Py. Significantly high TAI was observed in 2.25 m impacted rats. β-APP immunoreactive axons were significantly higher in number than RMO14 immunoreactive axons in both the structures. TAI density in Py was significantly higher than in CC. Based on our parallel biomechanical studies, it is inferred that TAI in CC may be related to compressive strains and that in Py may be related to tensile strains. Overall, IAT appears to be the dominant injury type induced by this model and injury in Py predominates that in CC.

THE EFFECTS OF POSTTRAUMATIC HYPOTHERMIA ON DIFFUSE AXONAL INJURY FOLLOWING PARASAGGITAL FLUID PERCUSSION BRAIN INJURY IN RATS

Previous investigations have demonstrated the beneficial effects of mild hypothermia following different types of traumatic brain injury (TBI). In some models, early cooling following TBI has been shown to reduce the frequency of axonal damage, a major consequence of head injury. The purpose of this study was to evaluate the effects of posttraumatic hypothermia in a model that has been shown to be sensitive to temperature manipulations in the early injury setting. Animals underwent moderate parasagittal fluid percussion (FP) brain injury and were then either randomized into normothermic or hypothermic groups. In the hypothermic groups, brain temperature was reduced to either 30 or 33°C 5 minutes after trauma and maintained for a three hour period. Normothermic or sham-operated animals were held under normal temperature conditions. At three days after TBI, animals were perfusion-fixed for quantitative assessment of β-APP immunohistochemistry and silver staining. Traumatic injury led to a significant increase in the frequency of β-APP immunoreactive profiles both within the corpus callosum, external capsule, as well as internal capsule. While early cooling revealed a trend for protection, no significant differences were shown between normothermic and hypothermic animals in terms of the frequency of injured axons at 3 days posttrauma. These results emphasize that axonal pathology is a major consequence of brain injury using this particular model. It is concluded that longer periods of posttraumatic hypothermia may be required to chronically protect axon populations undergoing progressive injury.

Quantitative relationship between axonal injury and mechanical response in a rodent head impact acceleration model

A modified Marmarou impact acceleration model was developed to study the mechanical responses induced by this model and their correlation to traumatic axonal injury (TAI). Traumatic brain injury (TBI) was induced in 31 anesthetized male Sprague-Dawley rats (392±13 g) by a custom-made 450-g impactor from heights of 1.25 m or 2.25 m. An accelerometer and angular rate sensor measured the linear and angular responses of the head, while the impact event was captured by a high-speed video camera. TAI distribution along the rostro-caudal direction, as well as across the left and right hemispheres, was determined using β-amyloid precursor protein (β-APP) immunocytochemistry, and detailed TAI injury maps were constructed for the entire corpus callosum. Peak linear acceleration 1.25 m and 2.25 m impacts were 666±165 g and 907±501 g, respectively. Peak angular velocities were 95±24 rad/sec and 124±48 rad/sec, respectively. Compared to the 2.25-m group, the observed TAI counts in the 1.25-m impact group were significantly lower. Average linear acceleration, peak angular velocity, average angular acceleration, and surface righting time were also significantly different between the two groups. A positive correlation was observed between normalized total TAI counts and average linear acceleration (R(2)=0.612, p<0.05), and time to surface right (R(2)=0.545, p<0.05). Our study suggested that a 2.25-m drop in the Marmarou model may not always result in a severe injury, and TAI level is related to the linear and angular acceleration response of the rat head during impact, not necessarily the drop height.

GPI-1046 increases presenilin-1 expression and restores NMDA channel activity

BACKGROUND

Previously we showed that 6-hydroxydopamine lesions of the substantia nigra eliminate corticostriatal LTP and that the neuroimmunolophilin ligand (NIL), GPI-1046, restores LTP.

METHODS

We used cDNA microarrays to determine what mRNAs may be over- or under-expressed in response to lesioning and/or GPI-1046 treatment. Patch clamp recordings were performed to investigate changes in NMDA channel function before and after treatments.

RESULTS

We found that 51 gene products were differentially expressed. Among these we found that GPI-1046 treatment up-regulated presenilin-1 (PS-1) mRNA abundance. This finding was confirmed using QPCR. PS-1 protein was also shown to be over-expressed in the striatum of lesioned/GPI-1046-treated rats. As PS-1 has been implicated in controlling NMDA-receptor function and LTP is reduced by lesioning we assayed NMDA mediated synaptic activity in striatal brain slices. The lesion-induced reduction of dopaminergic innervation was accompanied by the near complete loss of NDMA receptor-mediated synaptic transmission between the cortex and striatum. GPI-1046 treatment of the lesioned rats restored NMDA-mediated synaptic transmission but not the dopaminergic innervation. Restoration of NDMA channel function was apparently specific as the sodium channel current density was also reduced due to lesioning but GPI-1046 did not reverse this effect. We also found that restoration of NMDA receptor function was also not associated with either an increase in NMDA receptor mRNA or protein expression.

CONCLUSION

As it has been previously shown that PS-1 is critical for normal NMDA receptor function, our data suggest that the improvement of excitatory neurotransmission occurs through the GPI-1046-induced up-regulation of PS-1.

Combinatorial techniques for enhancing neuroprotection: hypothermia and alkalinization

Brain and spinal cord (CNS) trauma typically kill a number of neurons, but even more neurons are killed by secondary causes triggered by the initial trauma. Thus, a minor insult may rapidly cause the death of a vastly larger number of neurons and complete paralysis. The best mechanism for reducing the extent of neurological deficits is to minimize the number of neurons killed by post-trauma sequelae. Neuroprotection techniques take many diverse forms with a breadth too great for a short review. Therefore, this review focuses on the neuroprotection provided by hypothermia and a number of other neuroprotective techniques, when administered singly or in combination, because it is generally found that combinations of applications lead to significantly better neuroprotection than is achieved by any one alone. The combinatorial approach to neuroprotection holds great promise for enhancing the degree of neuroprotection following trauma, leading to maximum maintenance of neurological function.

Posthypothermic rewarming considerations following traumatic brain injury

To date, considerable attention has been focused upon the use of hypothermia as a therapeutic strategy for attenuating many of the damaging consequences of traumatic brain injury (TBI). Despite the promise of hypothermic intervention following TBI, many questions remain regarding the optimal use of hypothermic intervention, including, but not limited to, the rewarming rates needed to assure optimal brain protection. In this review, we revisit the relatively limited literature examining the issue of hypothermia and differing rewarming rates following TBI. Considering both experimental and clinical literature, evidence is presented that the rate of posthypothermic rewarming is an important variable for influencing the protective effects of hypothermic intervention following TBI. In the experimental setting, posttraumatic hypothermia followed by slow rewarming appears to provide maximal protection in terms of traumatically induced axonal damage, microvascular damage and dysfunction, and contusional expansion. In contrast, hypothermia followed by rapid rewarming not only reverses the protective effects associated with hypothermic intervention, but in many cases, exacerbates the traumatically induced pathology and its functional consequences. While similar evaluations have not been conducted in the clinical setting, multiple lines of clinical evidence suggest the benefits of posttraumatic hypothermia are optimized through the use of slow rewarming, with the suggestion that such a strategy reduces the potential for rebound vasodilation, elevated intracranial pressure (ICP), and impaired neurocognitive recovery. Collectively, this review highlights not only the benefits of hypothermic intervention, but also the rate of posthypothermic rewarming as an important variable in assuring maximal efficacy following the use of hypothermic intervention.

Multifunctional drugs for head injury

Traumatic brain injury (TBI) remains one of the leading causes of mortality and morbidity worldwide in individuals under the age of 45 years, and, despite extensive efforts to develop neuroprotective therapies, there has been no successful outcome in any trial of neuroprotection to date. In addition to recognizing that many TBI clinical trials have not been optimally designed to detect potential efficacy, the failures can be attributed largely to the fact that most of the therapies investigated have been targeted toward an individual injury factor. The contemporary view of TBI is that of a very heterogenous type of injury, one that varies widely in etiology, clinical presentation, severity, and pathophysiology. The mechanisms involved in neuronal cell death after TBI involve an interaction of acute and delayed anatomic, molecular, biochemical, and physiological events that are both complex and multifaceted. Accordingly, neuropharmacotherapies need to be targeted at the multiple injury factors that contribute to the secondary injury cascade, and, in so doing, maximize the likelihood of a successful outcome. This review focuses on a number of such multifunctional compounds that have shown considerable success in experimental studies and that show maximum promise for success in clinical trials.

Total synthesis studies on macrocyclic pipecolic acid natural products: FK506, the antascomicins and rapamycin

This chapter derives its inspiration from the challenges presented to total synthesis chemists, by a particular group of macrocyclic pipecolic acid natural products. Although there is considerable emphasis on the completed syntheses of the main characters (FK506 (1), the antascomycins (4 and 5) and rapamycin (7)), the overall complexity of the molecular problem has stimulated a wealth of new knowledge, including the development of novel strategies and the invention of new synthetic methods. The ingenious and innovative approaches to these targets have enabled new generations of analogues, and provided material to further probe the biology of these fascinating molecules. With pharmaceutical application as an immunosuppressant, as well as potential use for the treatment of cancer and neurodegenerative diseases, this family of natural products continues to inspire new and interesting science while providing solutions to healthcare problems of the world.

Rescuing neurons and glia: is inhibition of apoptosis useful?

Traumatic brain injury (TBI) represents a leading cause of death in western countries. Despite all research efforts we still lack any pharmacological agent that could effectively be utilized in the clinical treatment of TBI. Detailed unraveling of the pathobiological processes initiated by/operant in TBI is a prerequisite to the development of rational therapeutic interventions. In this review we provide a summary of those therapeutic interventions purported to inhibit the cell death (CD) cascades ignited in TBI. On noxious stimuli three major forms of CD, apoptosis, autophagia and necrosis may occur. Apoptosis can be induced either via the mitochondrial (intrinsic) or the receptor mediated (extrinsic) pathway; endoplasmic reticular stress is the third trigger of caspase-mediated apoptotic processes. Although, theoretically pan-caspase inhibition could be an efficient tool to limit apoptosis and thereby the extent of TBI, potential cross-talk between various avenues of CD suggests that more upstream events, particularly the preservation of the cellular energy homeostasis (cyclosporine-A, poly ADP ribose polymerase (PARP) inhibition, hypothermia treatment) may represent more efficient therapeutic targets hopefully also translated to the clinical care of the severely head injured.

Preferential neuroprotective effect of tacrolimus (FK506) on unmyelinated axons following traumatic brain injury

Prior investigations of traumatic axonal injury (TAI), and pharmacological treatments of TAI pathology, have focused exclusively on the role of myelinated axons, with no systematic observations directed towards unmyelinated axon pathophysiology. Recent electrophysiological evidence, however, indicates that unmyelinated axons are more vulnerable than myelinated axons in a rodent model of experimental TAI. Given their susceptibility to TAI, the present study examines whether unmyelinated axons also respond differentially to FK506, an immunophilin ligand with well-established neuroprotective efficacy in the myelinated fiber population. Adult rats received 3.0 mg/kg FK506 intravenously at 30 min prior to midline fluid percussion injury. In brain slice electrophysiological recordings, conducted at 24 h postinjury, compound action potentials (CAPs) were evoked in the corpus callosum, and injury effects quantified separately for CAP waveform components generated by myelinated axons (N1 wave) and unmyelinated axons (N2 wave). The amplitudes of both CAP components were suppressed postinjury, although this deficit was 16% greater for the N2 CAP. While FK506 treatment provided significant neuroprotection for both N1 and N2 CAPs, the drug benefit for the N2 CAP amplitude was 122% greater than that for the N1 CAPs, and improved postinjury strength-duration and refractoriness properties only in N2 CAPs. Immunocytochemical observations, of TAI reflected in intra-axonal pooling of amyloid precursor protein, indicated that FK506 reduced the extent of postinjury impairments to axonal transport and subsequent axonal damage. Collectively, these studies further substantiate a distinctive role of unmyelinated axons in TAI, and suggest a highly efficacious neuroprotective strategy to target this axonal population.

Tacrolimus depresses local immune cell infiltration but fails to reduce cortical contusion volume in brain-injured rats

The immunosuppressant drug tacrolimus (FK-506) failed to show an anti-edematous effect despite suppressing pro-inflammatory cytokines in cerebrospinal fluid following focal traumatic brain injury. By questioning the role of the inflammatory response as a pharmacological target, we investigated the effects of FK-506 on immune cell infiltration in brain-injured rats. Following induction of a cortical contusion, male Sprague-Dawley rats received FK-506 or physiological saline intraperitoneally. Brains were removed at 24 h, 72 h or 7 days, respectively. Frozen brain sections (7 microm) were stained immunohistologically for markers of endothelial activation (intercellular adhesion molecule-1--ICAM-1), neutrophil infiltration (His-48), and microglial and macrophage activation (Ox-6; ED-1), respectively. Immunopositive cells were counted microscopically. Contusion volume (CV) was quantified morphometrically 7 days after trauma. Inflammatory response was confined to the ipsilateral cortex and hippocampal formation, predominating in the contusion and pericontusional cortex. Strongest ICAM-1 expression coincided with sustained granulocyte accumulation at 72h which was suppressed by FK-506. Ox-6+ cells prevailing at 72 h were also significantly reduced by FK-506. ED-1+ cells reaching highest intensity at 7 days were significantly attenuated at 72 h. Cortical CV was not influenced. FK-506 significantly decreased post-traumatic local inflammation which, however, was not associated with a reduction in cortical CV. These results question the importance of post-traumatic local immune cell infiltration in the secondary growth of a cortical contusion.

Polyethylene glycol treatment after traumatic brain injury reduces beta-amyloid precursor protein accumulation in degenerating axons

Polyethylene glycol (PEG; 2,000 MW; 30% v/v) is a nontoxic molecule that can be injected intravenously and possesses well-documented neuroprotective properties in the spinal cord of the guinea pig. Recent studies have shown that intravenous PEG can also enter the rat brain parenchyma after injury and repair cellular membrane damage in the region of the corpus callosum. Disrupted anterograde axonal transport and resulting beta-amyloid precursor protein (APP) accumulation are byproducts of traumatic axonal injury (TAI) in the brain. APP accumulation indicates axonal degeneration as a result of axotomy, a detriment that can lead to cell death. In this study, we show that PEG treatment can eliminate APP accumulation in specific brain areas of rats receiving TAI. Six areas of the brain were analyzed: the medial cortex, hippocampus, lateral cortex, thalamus, medial lemniscus, and medial longitudinal fasciculus. Increased APP expression after injury was abolished in the thalamus and reduced in the medial longitudinal fasciculus by PEG treatment. In all remaining areas except for the lateral cortex, APP expression was not increased between injured and uninjured brains, indicating that damage was undetected in those brain areas in this study.

Postinjury administration of pituitary adenylate cyclase activating polypeptide (PACAP) attenuates traumatically induced axonal injury in rats

Pituitary adenylate cyclase activating polypeptide (PACAP) has several different actions in the nervous system. Numerous studies have shown its neuroprotective effects both in vitro and in vivo. Previously, it has been demonstrated that PACAP reduces brain damage in rat models of global and focal cerebral ischemia. Based on the protective effects of PACAP in cerebral ischemia and the presence of common pathogenic mechanisms in cerebral ischemia and traumatic brain injury (TBI), the aim of the present study was to investigate the possible protective effect of PACAP administered 30 min or 1 h postinjury in a rat model of diffuse axonal injury. Adult Wistar male rats were subjected to impact acceleration, and PACAP was administered intracerebroventricularly 30 min (n = 4), and 1 h after the injury (n = 5). Control animals received the same volume of vehicle at both time-points (n = 5). Two hours after the injury, brains were processed for immunohistochemical localization of damaged axonal profiles displaying either beta-amyloid precursor protein (beta-APP) or RMO-14 immunoreactivity, both considered markers of specific features of traumatic axonal injury. Our results show that treatment with PACAP (100 microg) 30 min or 1 h after the induction of TBI resulted in a significant reduction of the density of beta-APP-immunopositive axon profiles in the corticospinal tract (CSpT). There was no significant difference between the density of beta-APP-immunopositive axons in the medial longitudinal fascicle (MLF). PACAP treatment did not result in significantly different number of RMO-14-immunopositive axonal profiles in either brain areas 2 hours post-injury compared to normal animals. While the results of this study highlighted the complexity of the pathogenesis and manifestation of diffuse axonal injury, they also indicate that PACAP should be considered a potential therapeutic agent in TBI.

All roads lead to disconnection?--Traumatic axonal injury revisited

Traumatic brain injury (TBI) evokes widespread/diffuse axonal injury (TAI) significantly contributing to its morbidity and mortality. While classic theories suggest that traumatically injured axons are mechanically torn at the moment of injury, studies in the last two decades have not supported this premise in the majority of injured axons. Rather, current thought considers TAI a progressive process evoked by the tensile forces of injury, gradually evolving from focal axonal alteration to ultimate disconnection. Recent observations have demonstrated that traumatically induced focal axolemmal permeability leads to local influx of Ca2+ with the subsequent activation of the cysteine proteases, calpain and caspase, that then play a pivotal role in the ensuing pathogenesis of TAI via proteolytic digestion of brain spectrin, a major constituent of the subaxolemmal cytoskeletal network, the "membrane skeleton". In this pathological progression this local Ca2+ overloading with the activation of calpains also initiates mitochondrial injury that results in the release of cytochrome-c, with the activation of caspase. Both the activated calpain and caspases then participate in the degradation of the local axonal cytoskeleton causing local axonal failure and disconnection. In this review, we summarize contemporary thought on the pathogenesis of TAI, while discussing the potential diversity of pathological processes observed within various injured fiber types. The anterograde and retrograde consequences of TAI are also considered together with a discussion of various experimental therapeutic approaches capable of attenuating TAI.

Quantitative analysis of the relationship between intra- axonal neurofilament compaction and impaired axonal transport following diffuse traumatic brain injury

Traumatic axonal injury (TAI) following traumatic brain injury (TBI) contributes to morbidity and mortality. TAI involves intra-axonal changes assumed to progress to impaired axonal transport (IAT), disconnection, and axonal bulb formation. Immunocytochemical studies employing antibodies to amyloid precursor protein (APP), a marker of IAT and RMO14, a marker of neurofilament compaction (NFC), have shown that TAI involves both NFC and IAT, with the suggestion that NFC leads to IAT. Recently, new data has suggested that NFC may occur independently of IAT. The objective of this study was to determine quantitatively the precise relationship between NFC and IAT. Following TBI, rats were studied at 30 min, 3 h, and 24 h. Using single-label immunocytochemistry employing the antibodies RM014, APP, or a combined labeling strategy targeting APP/RMO14 in aggregate, the immunoreactive (IR) profiles were counted in the corticospinal tract (CSpT) and medial lemniscus (ML). In the CSpT, the number of axons demonstrating RMO14-IR approximated the number of axons showing APP-IR, with the APP-IR population showing a significant increase over 24 h (p < 0.05). The sum of both single-label counts equaled the aggregate APP/RMO14 numbers, demonstrating little relationship between NFC and IAT. In the ML, 75% of fibers demonstrated a separation of APP-IR and NFC-IR; however, 25% of the ML fibers showed co-localization of APP-IR and RMO14. The results of these studies indicate that, in the majority of damaged axons, NFC is not associated with IAT. Our findings argue for the use of multiple markers when evaluating the extent of TAI or the efficacy of therapies targeting the treatment of TAI.

Administration of the immunophilin ligand FK506 differentially attenuates neurofilament compaction and impaired axonal transport in injured axons following diffuse traumatic brain injury

Traumatic axonal injury (TAI) following traumatic brain injury (TBI) remains a clinical problem for which no effective treatment exists. TAI was thought to involve intraaxonal changes that universally led to impaired axonal transport (IAT), disconnection and axonal bulb formation. However, recent, immunocytochemical studies employing antibodies to amyloid precursor protein (APP), a marker of IAT and antibodies to neurofilament compaction (NFC), RM014, demonstrated that NFC typically occurs independent of IAT, indicating the existence of different populations of damaged axons. FK506 administration has been shown to attenuate IAT. However, in light of the above, the ability of FK506 to attenuate axonal damage demonstrating NFC requires evaluation. The current study explored the potential of FK506 to attenuate both populations of damaged axons. Rats were administered FK506 (3 mg/kg) or vehicle 30 min preinjury. Three hours post-TBI, tissue was prepared for the visualization of TAI using antibodies targeting IAT (APP) or NFC (RMO14) or a combined labeling strategy. Confirming previous reports, FK506 treatment reduced the number of axons demonstrating IAT in the CSpT, from 411 +/- 54.70 to 91.00 +/- 33.87 (P <or= 0.05) and in the ML from 78.62 +/- 16.87 to 41.00 +/- 5.80 (P <or= 0.05). FK506 treatment failed to reduce the number of axons demonstrating NFC in either the CSpT or ML. FK506's failure to attenuate NFC suggests that additional therapeutic agents may be necessary to blunt the full burden of TAI. Because FK506 targets IAT, calcineurin appears to be a major target for neuroprotection in damaged axons demonstrating IAT.

Slow, medium, or fast re-warming following post-traumatic hypothermia therapy? An ultrastructural perspective

It was hypothesized that rapid rather than slow re-warming following traumatic brain injury (TBI) and short-term hypothermia results in secondary, ultrastructural pathology. After stretch injury to the right optic nerve, adult guinea pigs were randomly allocated to one of six experimental groups. Either (1) sham (all procedures but not stretch-injured; n = 4); injured and (2) maintained at normal temporalis core temperature (38.5 degrees C) for 8 hours (n = 6); (3) cooled rapidly to 32.5 degrees C (temporalis temperature), maintained for 4 h and re-warmed to 38.5 degrees C at 1 degrees C rise every 10 min (fast; n = 6); (4) cooled and re-warmed at 1 degrees C rise every 20 min (medium; n = 6); (5) cooled and rewarmed at 1 degrees C rise every 40 min (slow; n = 6) before being killed 8 h after injury; and (6) uninjured animals (n = 6) cooled to 32.5 degrees C for 4 h and then re-warmed at 1 degrees C every 10 min before killing 4 h later. Tissue was processed for light immunocytochemistry (beta-APP and RMO-14) and ultrastructural stereology. In both uninjured and injured fast re-warmed animals, there was almost total loss of axonal microtubules (MT) and an increased number of neurofilaments (NF) within the axoplasm. In the former, there was also compaction of NF. The number of MT was reduced to 40% of control values, NFs were increased but were not compacted after medium rate re-warming. Following slow re-warming the axonal cytoskeleton did not differ from that in control animals. It is concluded that re-warming faster than 1 degrees C every 40 min following mild post-traumatic hypothermia induces secondary axonal pathology.

Immunosuppressants: neuroprotection and promoting neurological recovery following peripheral nerve and spinal cord lesions

No clinical techniques induce restoration of neurological losses following spinal cord trauma. Peripheral nerve damage also leads to permanent neurological deficits, but neurological recovery can be relatively good, especially if the ends of a transected nerve are anastomosed soon after the injury. The time until recovery generally depends on the distance the axons must regenerate to their targets. Neurological recovery following the destruction of a length of a peripheral nerve requires a graft to bridge the gap that is permissive to, and promotes, axon regeneration. But neurological recovery is slow and limited, especially for gaps longer than 1.5 cm, even using autologous peripheral nerve grafts. Without a reliable means of bridging long nerve gaps, such injuries commonly result in amputations. Promoting extensive neurological recovery requires techniques that simultaneously provide protection to injured neurons and increase the numbers of neurons that extend axons, while inducing more rapid and extensive axon regeneration across long nerve gaps. Although conduits filled with various materials enhance axon regeneration across short nerve gaps, pure sensory nerve graft remains the gold standard for use across long nerve gaps, even though they lead to only limited neurological recovery. Consistent results demonstrate that several immunosuppressive agents enhance the number of axons and the rate at which they regenerate. This review examines the roles played by immunosuppressants, especially FK506, with primary focus on its role as a neuroprotectant and neurotrophic agent, and its potential clinical use to promote improved neurological recovery following peripheral nerve and spinal cord injuries.

A persistent change in subcellular distribution of calcineurin following fluid percussion injury in the rat

Calcineurin, a neuronally enriched, calcium-stimulated phosphatase, is an important modulator of many neuronal processes, including several that are physiologically related to the pathology of traumatic brain injury. The effect of moderate, central fluid percussion injury on the subcellular distribution of this important neuronal enzyme was examined. Animals were sacrificed at several time points post-injury and calcineurin distribution in subcellular fractions was assayed by Western blot analysis and immunohistochemistry. A persistent increase in calcineurin concentration was observed in crude synaptoplasmic membrane-containing fractions. In cortical fractions, calcineurin immunoreactivity remained persistently increased for 2 weeks post-injury. In hippocampal homogenates, calcineurin immunoreactivity remained increased for up to 4 weeks. Finally, immunohistochemical analysis of hippocampal slices revealed increased staining in the apical dendrites of CA1 neurons. The increased staining was greatest in magnitude 24 h post-injury; however, staining was still more intense than control 4 weeks post-injury. The data support the conclusion that fluid percussion injury results in redistribution of the enzyme in the rat forebrain. These changes have broad physiological implications, possibly resulting in altered cellular excitability or a greater likelihood of neuronal cell death.

Update of neuropathology and neurological recovery after traumatic brain injury

This review focuses on the potential for traumatic brain injury to evoke both focal and diffuse changes within the brain parenchyma, while considering the cellular constituents involved and the subcellular perturbations that contribute to their dysfunction. New insight is provided on the pathobiology of traumatically induced cell body injury and diffuse axonal damage. The consequences of axonal damage in terms of subsequent deafferentation and any potential retrograde cell death and atrophy are addressed. The regional and global metabolic sequelae are also considered. This detailed presentation of the neuropathological consequences of traumatic brain injury is used to set the stage for better appreciating the neurological recovery occurring after traumatic injury. Although the pathological and clinical effects of focal and diffuse damage are usually intermingled, the different clinical manifestations of recovery patterns associated with focal versus diffuse injuries are presented. The recognizable patterns of recovery, involving unconsciousness, posttraumatic confusion/amnesia, and postconfusional restoration, that typically occur across the full spectrum of diffuse injury are described, recognizing that the patient's long-term recovery may involve more idiosyncratic combinations of dysfunction. The review highlights the relationship of focal lesions to localizing syndromes that may be embedded in the evolving natural history of diffuse pathology. It is noted that injuries with primarily focal pathology do not necessarily follow a comparable pattern of recovery with distinct phases. Potential linkages of these recovery patterns to the known neuropathological sequelae of injury and various reparative mechanisms are considered and it is proposed that potential biological markers and newer imaging technologies will better define these linkages.

Recent advances in the development of multifactorial therapies for the treatment of traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of death and disability in the industrialised world and remains a major health problem with serious socioeconomic consequences. So far, despite encouraging preclinical results, almost all neuroprotection trials have failed to show any significant efficacy in the treatment of clinical TBI. This may be due, in part, to the fact that most of the therapies investigated have targeted an individual injury factor. It is now recognised that TBI is a very heterogeneous type of injury that varies widely in its aetiology, clinical presentation, severity and pathophysiology. The pathophysiological sequelae of TBI are mediated by an interaction of acute and delayed molecular, biochemical and physiological events that are both complex and multifaceted. Accordingly, a successful TBI treatment may have to simultaneously attenuate many injury factors. Recent efforts in experimental TBI have, therefore, focused on the development of neuropharmacotherapies that target multiple injury factors and thus improve the likelihood of a successful outcome. This review will focus on three such novel compounds that are currently being assessed in clinical trials; progesterone, dexanabinol and dexamethasone, and provide an update on the progress of both magnesium and cyclosporin A.

Neuroimmunophilins: A novel drug therapy for the reversal of neurodegenerative disease?

Neuroimmunophilin ligands (NILs) are drugs derived from the immunosuppressant FK506 (tacrolimus) that have been shown to have variable efficacy in reversing neuronal degeneration and preventing cell death. In a wide range of animal models mimicking Parkinson's disease, dementia and even surgical nerve damage they induce re-sprouting, are neurotrophic or prevent nerve damage. The neurotrophic mechanism of action of these compounds is not known and may be dependent on the type of damage and genetic variability at the species or cellular level. Some evidence suggests that NILs may act through a family of proteins called FK506 binding proteins, some of which may regulate steroid hormone receptors. Other evidence suggests that NILs may protect neurons by upregulating the antioxidant glutathione and stimulating nerve regrowth by inducing the production of neurotrophic factors. Initial clinical trials have had mixed success. In one, patients with moderately severe Parkinson's disease showed no overall improvement in fine motor skills following 6 months of treatment by the neuroimmunophilin GPI 1485. But these patients did exhibit decreased loss of dopaminergic nerve terminals with a low dose of GPI 1485 and in fact some increase in dopaminergic terminals within 6 months of the higher dose of GPI 1485 drug treatment. As a result, a second phase II clinical trial using a patient population with less severe degeneration has been initiated concurrent with an investigation of GPI 1485 and other neuroprotective therapies funded by the National Institute of Neurological Disorders and Stroke. Another clinical trial ongoing at this time is exploring the use of a neuroimmunophilin ligand to prevent nerve degeneration and erectile dysfunction resulting from prostatectomy. In summary, neuroimmunophilins show promise to reverse some forms of neurodegeneration but exact factors that predict outcome have not been identified.

Mitochondrial permeability transition in CNS trauma: Cause or effect of neuronal cell death?

Experimental traumatic brain injury (TBI) and spinal cord injury (SCI) result in a rapid and significant necrosis of neuronal tissue at the site of injury. In the ensuing hours and days, secondary injury exacerbates the primary damage, resulting in significant neurologic dysfunction. It is believed that alterations in excitatory amino acids (EAA), increased reactive oxygen species (ROS), and the disruption of Ca(2+) homeostasis are major factors contributing to the ensuing neuropathology. Mitochondria serve as the powerhouse of the cell by maintaining ratios of ATP:ADP that thermodynamically favor the hydrolysis of ATP to ADP + P(i), yet a byproduct of this process is the generation of ROS. Proton-pumping by components of the electron transport system (ETS) generates a membrane potential (DeltaPsi) that can then be used to phosphorylate ADP or sequester Ca(2+) out of the cytosol into the mitochondrial matrix. This allows mitochondria to act as cellular Ca(2+) sinks and to be in phase with changes in cytosolic Ca(2+) levels. Under extreme loads of Ca(2+), however, opening of the mitochondrial permeability transition pore (mPTP) results in the extrusion of mitochondrial Ca(2+) and other high- and low-molecular weight components. This catastrophic event discharges DeltaPsi and uncouples the ETS from ATP production. Cyclosporin A (CsA), a potent immunosuppressive drug, inhibits mitochondrial permeability transition (mPT) by binding to matrix cyclophilin D and blocking its binding to the adenine nucleotide translocator. Peripherally administered CsA attenuates mitochondrial dysfunction and neuronal damage in an experimental rodent model of TBI, in a dose-dependent manner. The underlying mechanism of neuroprotection afforded by CsA is most likely via interaction with the mPTP because the immunosuppressant FK506, which has no effect on the mPT, was not neuroprotective. When CsA was administrated after experimental SCI at the same dosage and regimen used TBI paradigms, however, it had no beneficial neuroprotective effects. This review takes a comprehensive and critical look at the evidence supporting the role for mPT in central nervous system (CNS) trauma and highlights the differential responses of CNS mitochondria to mPT induction and the implications this has for therapeutically targeting the mPT in TBI and SCI.

Hyperthermia following traumatic brain injury: a critical evaluation

Hyperthermia, frequently seen in patients following traumatic brain injury (TBI), may be due to posttraumatic cerebral inflammation, direct hypothalamic damage, or secondary infection resulting in fever. Regardless of the underlying cause, hyperthermia increases metabolic expenditure, glutamate release, and neutrophil activity to levels higher than those occurring in the normothermic brain-injured patient. This synergism may further compromise the injured brain, enhancing the vulnerability to secondary pathogenic events, thereby exacerbating neuronal damage. Although rigorous control of normal body temperature is the current standard of care for the brain-injured patient, patient management strategies currently available are often suboptimal and may be contraindicated. This article represents a compendium of published work regarding the state of knowledge of the relationship between hyperthermia and TBI, as well as a critical examination of current management strategies.