Neuroprotective effect of hypothermia on neuronal injury in diffuse traumatic brain injury coupled with hypoxia and hypotension

Parthenolide ameliorates neurological deficits and neuroinflammation in mice with traumatic brain injury by suppressing STAT3/NF-κB and inflammasome activation

BACKGROUND

Traumatic brain injury (TBI) triggers a set of complex inflammation that results in secondary injury. Parthenolide (PTN) is a sesquiterpene lactone extracted from the herb Tanacetum parthenium (Feverfew) and has potent anti-inflammatory, anti-apoptosis and anti-oxidative stress effects in the central nervous system (CNS)-related diseases. This study focuses on investigating the potential neuroprotective effect of PTN on TBI and the related mechanism.

METHODS

Bv2 microglia, primary microglia were stimulated by LPS, and HT22 neuron cells were stimulated by OGD/R, and they were treated with different doses of PTN. The expression profiles of pro-inflammatory cytokines, proteins, oxidative stress mediators, STAT3/NF-κB pathway, inflammasomes were detected. Forty male/female C57BL/6 mice were randomly divided into the sham, PTN, TBI, and TBI + PTN groups (10 mice per group). A mouse TBI model was set up with a controlled cortical impact (CCI) device. The modified nerve severity score (mNSS) was implemented to check short-term neurological impairment in mice, and the mice's memory and learning were assessed by the Morris water maze test. The water content in the mice's brains was measured by the dry-wet method. Hematoxylin-eosin (H&E) staining, Nissl staining and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay were applied for neuronal apoptosis.

RESULTS

PTN dramatically alleviated LPS-induced inflammation in microglia, and OGD-mediated neuronal apoptosis and oxidative stress. In addition, PTN repressed LPS- or OGD-modulated STAT3/NF-κB and NLR family pyrin domain containing 1 (NLRP1), NLRP3, NLR family CARD domain containing 4 (NLRC4) inflammasomes activation. Administering the STAT3 inhibitor Stattic or NF-κB inhibitor Bay 11-7082 attenuated PTN-mediated effects. In vivo, PTN treatment relieved neural function deficits, brain edema and neuron apoptosis and improved the memory and learning function of TBI mice. Additionally, PTN impeded microglial activation and reduced the production of pro-inflammatory cytokines in brain lesions of TBI mice. Furthermore, PTN hindered STAT3/NF-κB and inflammasome activation.

CONCLUSION

PTN can curb microglial activation and neuron apoptosis by dampening the STAT3/NF-κB pathway, thus exerting neuroprotective effects in TBI mice.

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.

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

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

Selective Brain Cooling Reduces Motor Deficits Induced by Combined Traumatic Brain Injury, Hypoxemia and Hemorrhagic Shock

Selective brain cooling (SBC) can potentially maximize the neuroprotective benefits of hypothermia for traumatic brain injury (TBI) patients without the complications of whole body cooling. We have previously developed a method that involved extraluminal cooling of common carotid arteries, and demonstrated the feasibility, safety and efficacy for treating isolated TBI in rats. The present study evaluated the neuroprotective effects of 4-h SBC in a rat model of penetrating ballistic-like brain injury (PBBI) combined with hypoxemic and hypotensive insults (polytrauma). Rats were randomly assigned into two groups: PBBI+polytrauma without SBC (PHH) and PBBI+polytrauma with SBC treatment (PHH+SBC). All animals received unilateral PBBI, followed by 30-min hypoxemia (fraction of inspired oxygen = 0.1) and then 30-min hemorrhagic hypotension (mean arterial pressure = 40 mmHg). Fluid resuscitation was given immediately following hypotension. SBC was initiated 15 min after fluid resuscitation and brain temperature was maintained at 32-33°C (core temperature at ~36.5°C) for 4 h under isoflurane anesthesia. The PHH group received the same procedures minus the cooling. At 7, 10, and 21 days post-injury, motor function was assessed using the rotarod task. Cognitive function was assessed using the Morris water maze at 13-17 days post-injury. At 21 days post-injury, blood samples were collected and the animals were transcardially perfused for subsequent histological analyses. SBC transiently augmented cardiovascular function, as indicated by the increase in mean arterial pressure and heart rate during cooling. Significant improvement in motor functions were detected in SBC-treated polytrauma animals at 7, 10, and 21 days post-injury compared to the control group (p < 0.05). However, no significant beneficial effects were detected on cognitive measures following SBC treatment in the polytrauma animals. In addition, the blood serum and plasma levels of cytokines interleukin-1 and -10 were comparable between the two groups. Histological results also did not reveal any between-group differences in subacute neurodegeneration and astrocyte/ microglial activation. In summary, 4-h SBC delivered through extraluminal cooling of the common carotid arteries effectively ameliorated motor deficits induced by PBBI and polytrauma. Improving cognitive function or mitigating subacute neurodegeneration and neuroinflammation might require a different cooling regimen such as extended cooling, a slow rewarming period and a lower temperature.

Establishment of an ideal time window model in hypothermic-targeted temperature management after traumatic brain injury in rats

Although hypothermic-targeted temperature management (HTTM) holds great potential for the treatment of traumatic brain injury (TBI), translation of the efficacy of hypothermia from animal models to TBI patientshas no entire consistency. This study aimed to find an ideal time window model in experimental rats which was more in accordance with clinical practice through the delayed HTTM intervention. Sprague-Dawley rats were subjected to unilateral cortical contusion injury and received therapeutic hypothermia at 15mins, 2 h, 4 h respectively after TBI. The neurological function was evaluated with the modified neurological severity score and Morris water maze test. The brain edema and morphological changes were measured with the water content and H&E staining. Brain sections were immunostained with antibodies against DCX (a neuroblast marker) and GFAP (an astrocyte marker). The apoptosis levels in the ipsilateral hippocampi and cortex were examined with antibodies against the apoptotic proteins Bcl-2, Bax, and cleaved caspase-3 by the immunofluorescence and western blotting. The results indicated that each hypothermia therapy group could improve neurobehavioral and cognitive function, alleviate brain edema and reduce inflammation. Furthermore, we observed that therapeutic hypothermia increased DCX expression, decreased GFAP expression, upregulated Bcl-2 expression and downregulated Bax and cleaved Caspase-3 expression. The above results suggested that HTTM at 2h or even at 4h post-injury revealed beneficial brain protection similarly, despite the best effect at 15min post-injury. These findings may provide relatively ideal time window models, further making the following experimental results more credible and persuasive.

Protective effect of mild-induced hypothermia against moderate traumatic brain injury in rats involved in necroptotic and apoptotic pathways

AIM

To investigate the protective effect of hypothermia (HT) on brain injury in moderate traumatic brain injury (TBI) rat models and the potential mechanisms, especially the involvement of RIPK1 in apoptosis and necroptosis.

METHODS

Adult Sprague-Dawley rats were randomized to four groups: sham+normothermia (sham+NT), sham+hypothermia (sham+HT), moderate TBI+normothermia (TBI+NT) and moderate TBI+hypothermia (TBI+HT). The sham+HT and TBI+HT groups were submitted to 32°C for 6 hours. The regional cerebral blood flow (rCBF) was assessed 24 hours after TBI; 24 and 48 hours after TBI, the modified neurological severity score (mNSS) was assessed. Immediately after behavioural tests, rats were sacrificed to harvest the brain tissues.

RESULTS

mNSS scores were lower in the TBI+HT group compared with the TBI+NT group (p < 0.01) and cerebral blood flow was better (p < 0.01). H&E staining of the cortex and ipsilateral hippocampus showed pyknotic and irregularly shaped neurons in TBI+NT rats, which were less frequent in TBI+HT rats. The TBI+NT and TBI+HT groups showed higher TNF-α, TRAIL, FasL, FADD, caspase-3, caspase-8, PARP-1, RIPK-1 and RIPK-3 levels than the sham+NT group (all p < 0.05), but the levels of these proteins were all lower in the TBI+HT group compared with the TBI+NT group (all p < 0.01).

CONCLUSION

HT treatment significantly reduced RIPK-1 upregulation, which may inhibit necroptosis and apoptosis pathways after moderate TBI.

Selective Brain Hypothermia Mitigates Brain Damage and Improves Neurological Outcome after Post-Traumatic Decompressive Craniectomy in Mice

Hypothermia and decompressive craniectomy (DC) have been considered as treatment for traumatic brain injury. The present study investigates whether selective brain hypothermia added to craniectomy could improve neurological outcome after brain trauma. Male CD-1 mice were assigned into the following groups: sham; DC; closed head injury (CHI); CHI followed by craniectomy (CHI+DC); and CHI+DC followed by focal hypothermia (CHI+DC+H). At 24 h post-trauma, animals were subjected to Neurological Severity Score (NSS) test and Beam Balance Score test. At the same time point, magnetic resonance imaging using a 9.4 Tesla scanner and subsequent volumetric evaluation of edema and contusion were performed. Thereafter, the animals were sacrificed and subjected to histopathological analysis. According to NSS, there was a significant impairment among all the groups subjected to trauma. Animals with both trauma and craniectomy performed significantly worse than animals with craniectomy alone. This deleterious effect disappeared when additional hypothermia was applied. BBS was significantly worse in the CHI and CHI+DC groups, but not in the CHI+DC+H group, compared to the sham animals. Edema and contusion volumes were significantly increased in CHI+DC animals, but not in the CHI+DC+H group, compared to the DC group. Histopathological analysis showed that neuronal loss and contusional blossoming could be attenuated by application of selective brain hypothermia. Selective brain cooling applied post-trauma and craniectomy improved neurological function and reduced structural damage and may be therefore an alternative to complication-burdened systemic hypothermia. Clinical studies are recommended in order to explore the potential of this treatment.

Stem cells and combination therapy for the treatment of traumatic brain injury

TBI is a nondegenerative, noncongenital insult to the brain from an external mechanical force; for instance a violent blow in a car accident. It is a complex injury with a broad spectrum of symptoms and has become a major cause of death and disability in addition to being a burden on public health and societies worldwide. As such, finding a therapy for TBI has become a major health concern for many countries, which has led to the emergence of many monotherapies that have shown promising effects in animal models of TBI, but have not yet proven any significant efficacy in clinical trials. In this paper, we will review existing and novel TBI treatment options. We will first shed light on the complex pathophysiology and molecular mechanisms of this disorder, understanding of which is a necessity for launching any treatment option. We will then review most of the currently available treatments for TBI including the recent approaches in the field of stem cell therapy as an optimal solution to treat TBI. Therapy using endogenous stem cells will be reviewed, followed by therapies utilizing exogenous stem cells from embryonic, induced pluripotent, mesenchymal, and neural origin. Combination therapy is also discussed as an emergent novel approach to treat TBI. Two approaches are highlighted, an approach concerning growth factors and another using ROCK inhibitors. These approaches are highlighted with regard to their benefits in minimizing the outcomes of TBI. Finally, we focus on the consequent improvements in motor and cognitive functions after stem cell therapy. Overall, this review will cover existing treatment options and recent advancements in TBI therapy, with a focus on the potential application of these strategies as a solution to improve the functional outcomes of TBI.

Therapeutic hypothermia and ischemic stroke: A literature review

BACKGROUND

Ischemic stroke is the fifth leading cause of death in the US. Clinical techniques aimed at helping to reduce the morbidity associated with stroke have been studied extensively, including therapeutic hypothermia. In this study, the authors review the literature regarding the role of therapeutic hypothermia in ischemic stroke to appreciate the evolution of hypothermia technology over several decades and to critically analyze several early clinical studies to validate its use in ischemic stroke.

METHODS

A comprehensive literature search was performed using PubMed and Google Scholar databases. Search terms included "hypothermia and ischemic stroke" and "therapeutic hypothermia." A comprehensive search of the current clinical trials using clinicaltrials.gov was conducted using the keywords "stroke and hypothermia" to evaluate early and ongoing clinical trials utilizing hypothermia in ischemic stroke.

RESULTS

A comprehensive review of the evolution of hypothermia in stroke and the current status of this treatment was performed. Clinical studies were critically analyzed to appreciate their strengths and pitfalls. Ongoing and future registered clinical studies were highlighted and analyzed compared to the reported results of previous trials.

CONCLUSION

Although hypothermia has been used for various purposes over several decades, its efficacy in the treatment of ischemic stroke is debatable. Several trials have proven its safety and feasibility; however, more robust, randomized clinical trials with large volumes of patients are needed to fully establish its utility in the clinical setting.

Lesion Size Is Exacerbated in Hypoxic Rats Whereas Hypoxia-Inducible Factor-1 Alpha and Vascular Endothelial Growth Factor Increase in Injured Normoxic Rats: A Prospective Cohort Study of Secondary Hypoxia in Focal Traumatic Brain Injury

BACKGROUND

Hypoxia following traumatic brain injury (TBI) is a severe insult shown to exacerbate the pathophysiology, resulting in worse outcome. The aim of this study was to investigate the effects of a hypoxic insult in a focal TBI model by monitoring brain edema, lesion volume, serum biomarker levels, immune cell infiltration, as well as the expression of hypoxia-inducible factor-1 alpha (HIF-1α) and vascular endothelial growth factor (VEGF).

MATERIALS AND METHODS

Female Sprague-Dawley rats (n = 73, including sham and naive) were used. The rats were intubated and mechanically ventilated. A controlled cortical impact device created a 3-mm deep lesion in the right parietal hemisphere. Post-injury, rats inhaled either normoxic (22% O2) or hypoxic (11% O2) mixtures for 30 min. The rats were sacrificed at 1, 3, 7, 14, and 28 days post-injury. Serum was collected for S100B measurements using ELISA. Ex vivo magnetic resonance imaging (MRI) was performed to determine lesion size and edema volume. Immunofluorescence was employed to analyze neuronal death, changes in cerebral macrophage- and neutrophil infiltration, microglia proliferation, apoptosis, complement activation (C5b9), IgG extravasation, HIF-1α, and VEGF.

RESULTS

The hypoxic group had significantly increased blood levels of lactate and decreased pO2 (p < 0.0001). On MRI post-traumatic hypoxia resulted in larger lesion areas (p = 0.0173), and NeuN staining revealed greater neuronal loss (p = 0.0253). HIF-1α and VEGF expression was significantly increased in normoxic but not in hypoxic animals (p < 0.05). A trend was seen for serum levels of S100B to be higher in the hypoxic group at 1 day after trauma (p = 0.0868). No differences were observed between the groups in cytotoxic and vascular edema, IgG extravasation, neutrophils and macrophage aggregation, microglia proliferation, or C5b-9 expression.

CONCLUSION

Hypoxia following focal TBI exacerbated the lesion size and neuronal loss. Moreover, there was a tendency to higher levels of S100B in the hypoxic group early after injury, indicating a potential validity as a biomarker of injury severity. In the normoxic group, the expression of HIF-1α and VEGF was found elevated, possibly indicative of neuro-protective responses occurring in this less severely injured group. Further studies are warranted to better define the pathophysiology of post-TBI hypoxia.

Combined hypoxemic and hypotensive insults altered physiological responses and neurofunction in a severity-dependent manner following penetrating ballistic-like brain injury in rats

BACKGROUND

Traumatic brain injury often occurs with concomitant hypoxemia (HX) and hemorrhagic shock (HS), leading to poor outcomes. This study characterized the acute physiology and subacute behavioral consequences of these additional insults in a model of penetrating ballistic-like brain injury (PBBI).

METHODS

Rats were randomly assigned into sham control, HX + HS (HH), 5% PBBI alone, 5% PBBI + HH, 10% PBBI alone, and 10% PBBI + HH groups. Mean arterial pressure, heart rate, and breathing rate were monitored continuously. In the combined injury groups, animals were subjected to 30-minute HX (Pao2, 30-40 mm Hg) and then 30-min HS (mean arterial pressure, 40 mm Hg) followed by fluid resuscitation with lactated Ringer's solution after PBBI or sham PBBI. Motor function was assessed using the rotarod task at 7 days and 14 days after injury. Cognitive function was assessed in the Morris water maze task from 13 days to 17 days after injury.

RESULTS

Combined HH caused acute bradycardia that was reversed by fluid resuscitation. During HX phase, tachypnea was observed in all HH groups. Persistent bradypnea was detected in 10% PBBI + HH group during the resuscitation phase. PBBI produced significant decrements in motor performance (vs. sham and HH groups). Additional insults significantly worsened motor deficits following 5% PBBI but not 10% PBBI. Both 5% PBBI and 10% PBBI produced significant cognitive deficits in the Morris water maze task with worsened deficits evident following the more severe injury (i.e., 10% PBBI). Alternatively, rats subjected to 5% PBBI + HH exhibited cognitive impairment that was significantly worse compared with 5% PBBI alone, whereas this worsening effect was not detected in the 10% PBBI groups.

CONCLUSION

This study characterized the physiological responses and neurobehavioral profiles following combined PBBI and HH. Ten percent PBBI produces motor and cognitive deficits, which may exceed a sensitivity threshold capacity. In contrast, 5% PBBI produces a lower, albeit significant, magnitude of deficits and thus provides a more sensitive screen for evaluating the cumulative effects of additional insults, which were indeed demonstrated to significantly worsen outcome.

Experimental Models Combining Traumatic Brain Injury and Hypoxia

Traumatic brain injury (TBI) is one of the most common causes of death and disability, and cerebral hypoxia is a frequently occurring harmful secondary event in TBI patients. The hypoxic conditions that occur on the scene of accident, where the airways are often obstructed or breathing is in other ways impaired, could be reproduced using animal TBI models where oxygen delivery is strictly controlled throughout the entire experimental procedure. Monitoring physiological parameters of the animal is of utmost importance in order to maintain an adequate quality of the experiment. Peripheral oxygen saturation, O2 pressure (pO2) in the blood, or fraction of inhaled O2 (FiO2) could be used as goals to validate the hypoxic conditions. Different models of traumatic brain injury could be used to inflict desired injury type, whereas effects then could be studied using radiological, physiological and functional tests. In order to confirm that the brain has been affected by a hypoxic injury, appropriate substances in the affected cerebral tissue, cerebrospinal fluid, or serum should be analyzed.

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.

The effect of hypothermia on sensory-motor function and tissue sparing after spinal cord injury

BACKGROUND CONTEXT

In recent years, hypothermia has been described as a therapeutic approach that leads to potential protective effects via minimization of secondary damage consequences, reduction of neurologic deficit, and increase of motor performance after spinal cord injury (SCI) in animal models and humans.

PURPOSE

The objective of this study was to determine the therapeutic efficacy of hypothermia treatment on sensory-motor function and bladder activity outcome correlated with the white and gray matter sparing and neuronal survival after SCI in adult rats.

STUDY DESIGN

A standardized animal model of compression SCI was used to test the hypothesis that hypothermia could have a neuroprotective effect on neural cell death and loss of white and/or gray matter.

METHODS

Animals underwent spinal cord compression injury at the Th8-Th9 level followed by systemic hypothermia of 32.0°C with gradual re-warming to 37.0°C. Motor function of hind limbs (BBB score) and mechanical allodynia (von Frey hair filaments) together with function of urinary bladder was monitored in all experimental animals throughout the whole survival period.

RESULTS

Present results showed that hypothermia had beneficial effects on urinary bladder activity and on locomotor function recovery at Days 7 and 14 post-injury. Furthermore, significant increase of NeuN-positive neuron survival within dorsal and ventral horns at Days 7, 14, and 21 were documented.

CONCLUSIONS

Our conclusions suggest that hypothermia treatment may not only promote survival of neurons, which can have a significant impact on the improvement of motor and vegetative functions, but also induce mechanical allodynia.

Pharmacologic resuscitation for hemorrhagic shock combined with traumatic brain injury

BACKGROUND

We have previously demonstrated that valproic acid (VPA), a histone deacetylase inhibitor, can improve survival after hemorrhagic shock (HS), protect neurons from hypoxia-induced apoptosis, and attenuate the inflammatory response. We have also shown that administration of 6% hetastarch (Hextend [Hex]) after traumatic brain injury (TBI) decreases brain swelling, without affecting size of the lesion. This study was performed to determine whether addition of VPA to Hex would decrease the lesion size in a clinically relevant large animal model of TBI + HS.

METHODS

Yorkshire swine (42-50 kg) were instrumented to measure hemodynamic parameters, intracranial pressure, and brain tissue oxygenation. A custom-designed, computer-controlled cortical impact device was used to create a TBI through a 20-mm craniotomy: 15-mm cylindrical tip impactor at 4-m/s velocity, 100-millisecond dwell time, and 12-mm penetration depth. Volume-controlled hemorrhage was started (40% blood volume) concurrent with the TBI. After 2 hours of shock, animals were randomized to one of three resuscitation groups (n = 7 per group) as follows: (1) isotonic sodium chloride solution; (2) 6% hetastarch, Hex; and (3) Hex and VPA 300 mg/kg (Hex + VPA). Volumes of Hex matched the shed blood, whereas that of the isotonic sodium chloride solution was three times the volume. VPA treatment was started after an hour of shock. After 6 hours of postresuscitation monitoring, brains were sectioned into 5-mm slices and stained with 2, 3, 5-Triphenyltetrazolium chloride to quantify the lesion size (mm) and brain swelling (percent change compared with uninjured side). Levels of acetylated histone H3 were determined to quantify acetylation, and myeloperoxidase and interleukine-1β (IL-1β) levels were measured as markers of brain inflammation.

RESULTS

Combination of 40% blood loss with cortical impact and a period of shock (2 hours) and resuscitation resulted in a highly reproducible brain injury. Lesion size and brain swelling in the Hex + VPA group (1,989 [156.8] mm, and 19% [1.6%], respectively) were significantly smaller than the isotonic sodium chloride solution group (3,335 [287.9] mm and 36% [2.2%], respectively). Hex alone treatment significantly decreased the swelling (27% [1.6%]) without reducing the lesion size. The number of CD11b-positive cells as well as myeloperoxidase and IL-1 levels in the brains were significantly reduced by the VPA treatment.

CONCLUSION

In a combined HS and TBI model, treatment with artificial colloid (Hex) improves hemodynamic parameters and reduces swelling, without affecting the actual size of the brain lesion. Addition of VPA effectively reduces both the size of brain lesion and associated swelling by attenuating the inflammatory response.

The effect of hypothermia on the expression of TIMP-3 after traumatic brain injury in rats

Here we investigate the effect of hypothermia on the expression of apoptosis-regulating protein TIMP-3 after fluid percussion traumatic brain injury (TBI) in rats. We began with 210 adult male Sprague-Dawley rats and randomly assigned them to three groups: TBI with hypothermia treatment (32°C), TBI with normothermia (37°C), and sham-injured controls. TBI was induced by a fluid percussion TBI device. Mild hypothermia (32°C) was achieved by partial immersion in a water bath (0°C) under general anesthesia for 4 h. The rats were killed at 4, 6, 12, 24, 48, and 72 h and 1 week after TBI. The mRNA and protein level of TIMP-3 in both the injured and uninjured hemispheres of the brains from each group were measured using RT-PCR and Western blotting. In the normothermic group, TIMP-3 levels in both the injured and uninjured hemispheres were significantly increased after TBI compared with those of sham-injured animals (p < 0.01). In contrast, post-traumatic hypothermia significantly attenuated this increase. According to the RT-PCR and Western blot analyses, the maximum mRNA levels of TIMP-3 were reduced to 60.60 ± 2.30%, 55.83 ± 1.80%, 66.03 ± 2.10%, and 64.51 ± 1.50%, respectively, of the corresponding values in the normothermic group in the injured and uninjured hemispheres (cortex and hippocampus) of the hypothermia group (p < 0.01), while the respective maximum protein levels of TIMP-3 were reduced to 57.50 ± 1.50, 52.67 ± 2.20, 60.31 ± 2.50 and 54.76 ± 1.40 (p < 0.01). Our data suggest that moderate fluid percussion brain injury significantly upregulates TIMP-3 expression, and that this increase may be suppressed by hypothermia treatment.

Traumatic brain injury and hemorrhagic shock: evaluation of different resuscitation strategies in a large animal model of combined insults

Traumatic brain injury (TBI) and hemorrhagic shock (HS) are the leading causes of trauma-related mortality and morbidity. Combination of TBI and HS (TBI + HS) is highly lethal, and the optimal resuscitation strategy for this combined insult remains unclear. A critical limitation is the lack of suitable large animal models to test different treatment strategies. We have developed a clinically relevant large animal model of TBI + HS, which was used to evaluate the impact of different treatments on brain lesion size and associated edema. Yorkshire swine (42-50 kg) were instrumented to measure hemodynamic parameters and intracranial pressure. A computer-controlled cortical impact device was used to create a TBI through a 20-mm craniotomy: 15-mm cylindrical tip impactor at 4 m/s velocity, 100-ms dwell time, and 12-mm penetration depth. Volume-controlled hemorrhage was started (40% blood volume) concurrent with the TBI. After 2 h of shock, animals were randomized to one of three resuscitation groups (n = 5/group): (a) normal saline (NS); (b) 6% hetastarch, Hextend (Hex); and (c) fresh frozen plasma (FFP). Volumes of Hex and FFP matched the shed blood, whereas NS was three times the volume. After 6 h of postresuscitation monitoring, brains were sectioned into 5-mm slices and stained with TTC (2,3,5-triphenyltetrazolium chloride) to quantify the lesion size and brain swelling. Combination of 40% blood loss with cortical impact and a period of shock (2 h) resulted in a highly reproducible brain injury. Total fluid requirements were lower in the Hex and FFP groups. Lesion size and brain swelling in the FFP group (2,160 ± 202.63 mm and 22% ± 1.0%, respectively) were significantly smaller than those in the NS group (3,285 ± 130.8 mm3 and 37% ± 1.6%, respectively) (P < 0.05). Hex treatment decreased the swelling (29% ± 1.6%) without reducing the lesion size. Early administration of FFP reduces the size of brain lesion and associated swelling in a large animal model of TBI + HS. In contrast, artificial colloid (Hex) decreases swelling without reducing the actual size of the brain lesion.

Hypothermia in Traumatic Brain Injury – A Literature Review

Traumatic brain injury is the leading cause of death in young people. Induced hypothermia has been used as a therapeutic intervention to improve outcome, based on results of animal studies. This article reviews the mechanisms of brain injury, the results of animal and human studies and the reasons that human studies do not always reflect the success seen in animal studies and why results may be ‘lost in translation’ to treatment of patients. It concludes by suggesting further areas of work to investigate the clinical use of therapeutic hypothermia.

Pharyngeal selective brain cooling is associated with reduced CNS cortical lesion after experimental traumatic brain injury in rats

Therapeutic hypothermia (TH) is still being explored as a therapeutic option after traumatic brain injury (TBI) but clinical data has not supported its efficacy. Experimental approaches were promising, but clinical data did not support its efficacy in the treatment of TBI. A novel approach of pharyngeal selective brain cooling (pSBC), recently introduced by our group, has been accompanied by superior neurofunctional, sensorimotor, and cognitive outcomes. This work is now extended by data on histomorphological and physical outcomes after pSBC in a model of experimental TBI. Male Sprague-Dawley rats were subjected to lateral fluid-percussion (LFP) brain injury, and randomized to the following experimental groups: (1) TBI with pSBC, (2) TBI without pSBC, and (3) sham animals. On day post-injury (DPI) 14, the animals were sacrificed and their brains were harvested for immunohistochemistry using the following antibodies: (1) glial fibrillary acidic protein (GFAP), (2) neurofilament (NF), and (3) synaptophysin (SY). In pSBC animals brain temperature was selectively lowered to 33 ± 0.5°C within 15 min post-injury, and maintained for 180 min after induction, while keeping rectal temperatures at physiological levels. Animals that had undergone pSBC showed a significantly faster recovery of body weight starting on DPI 3, and had gained substantially more weight than TBI-only animals on DPI 14 (p < 0.001), indicating superior physical recovery. Areas of cortical damage were significantly smaller in pSBC animals compared to TBI-only animals (p < 0.01). pSBC was associated with preservation of cortical tissue ipsilateral to the lesion, and superior physical recovery after experimental TBI. These results complement earlier reports in which pSBC was associated with superior neurofunctional and cognitive outcomes using the same experimental model.

Effect of secondary insults upon aquaporin-4 water channels following experimental cortical contusion in rats

Although secondary insults of hypoxia and hypotension (HH) are generally considered to cause fulminant brain edema in traumatic brain injury (TBI), the combined effect of TBI with HH on brain edema and specifically the expression of aquaporin-4 (AQP4) have not been fully elucidated. The goal of this study was to document the effect of secondary insults on brain water, AQP4 expression, electrolytes, and blood-brain barrier (BBB) permeability during the acute stage of edema development. We measured brain water content and electrolytes (series 1); BBB permeability based on Evans blue (EB) dye extravasation (series 2); and AQP4 expression using immunoblotting (series 3) at 1 h and 5 h following cortical contusion injury (CCI). Secondary insults significantly worsened BBB function at 5 h post injury. Moreover, a significant reduction of upregulation on AQP4 expression was observed in trauma, coupled with a mild secondary insult of hypoxia hypotension. These findings indicate that a secondary insult following CCI at 5 h post injury worsens brain edema, disrupts ionic homeostasis, and blunts the normal upregulation of AQP4 that occurs after trauma, suggesting that the blunting of AQP4 may contribute to the detrimental effects of secondary insults.

The adverse pial arteriolar and axonal consequences of traumatic brain injury complicated by hypoxia and their therapeutic modulation with hypothermia in rat

This study examined the effect of posttraumatic hypoxia on cerebral vascular responsivity and axonal damage, while also exploring hypothermia's potential to attenuate these responses. Rats were subjected to impact acceleration injury (IAI) and equipped with cranial windows to assess vascular reactivity to topical acetylcholine, with postmortem analyses using antibodies to amyloid precursor protein to assess axonal damage. Animals were subjected to hypoxia alone, IAI and hypoxia, IAI and hypoxia before induction of moderate hypothermia (33 degrees C), IAI and hypoxia induced during hypothermic intervention, and IAI and hypoxia initiated after hypothermia. Hypoxia alone had no impact on vascular reactivity or axonal damage. Acceleration injury and posttraumatic hypoxia resulted in dramatic axonal damage and altered vascular reactivity. When IAI and hypoxia were followed by hypothermic intervention, no axonal or vascular protection ensued. However, when IAI was followed by hypoxia induced during hypothermia, axonal and vascular protection followed. When this same hypoxic insult followed the use of hypothermia, no benefit ensued. These studies show that early hypoxia and delayed hypoxia exert damaging axonal and vascular consequences. Although this damage is attenuated by hypothermia, this follows only when hypoxia occurs during hypothermia, with no benefit found if the hypoxic insult proceeds or follows hypothermia.

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.

Pharyngeal selective brain cooling improves neurofunctional and neurocognitive outcome after fluid percussion brain injury in rats

Therapeutic hypothermia (TH) after cardiac arrest reduces mortality and improves neurological outcome. Experimental TH after traumatic brain injury (TBI) indicated similar effects, but benefits were not reproducible in large clinical trials. Therefore, a novel approach of pharyngeal selective brain cooling (pSBC) was tested in respect to neurological outcome in a model of experimental TBI. Male Sprague-Dawley rats were subjected to lateral fluid percussion (LFP) brain injury and received pSBC for 3h post-injury. All animals were examined for neuromotor and sensorimotor dysfunction and coordination: before and after injury, and during recovery on day post-injury (DPI) 7 and 14 using (i) the standardized Composite Neuroscore (NS) test and (ii) the Rotarod test. Recovery of cognitive function was assessed on days 10-14 using (iii) the Barnes Circular Maze (BCM). In pSBC-animals, brain temperature was selectively lowered to 33 +/- 0.5 degrees C at 15 min post-injury, keeping rectal temperature at a physiologic level. All animals subjected to TBI via LFP showed an identical pattern of severe neurofunctional impairment at 24 h after injury. In the time course of the experiment, pSBC-animals showed superior neurofunctional recovery on DPI 7 (p = 0.03) and 14 (p = 0.002). Similarly, distance, time, and maximum speed on the Rota-Rod were significantly increased in pSBC-animals on DPI 7 (p < 0.01) and 14 (p < 0.01), as well as latency, distance, and mean number of errors in the BCM on DPI 14 (p < 0.01). The novel approach of pSBC was associated with improved neuromotor, sensormotor, and neurocognitive outcome after experimental TBI.

Effect of post-traumatic mild hypothermia on hippocampal cell death after traumatic brain injury in rats

In this investigation, we evaluated the effect of post-traumatic mild hypothermia on cell death in the hippocampus after fluid percussion traumatic brain injury (TBI) in rats. Adult male Sprague-Dawley rats were randomly divided into three groups (n = 40/group): TBI with hypothermia treatment (32 degrees C), TBI with normothermia (37 degrees C), and sham injury. The TBI model was induced by a fluid percussion TBI device. Mild hypothermia (32 degrees C) was achieved by partial immersion in a water bath (0 degrees C) under general anesthesia for 4h. All rats were killed at 24 or 72h after TBI. The ipsilateral hippocampal CA1 in all rats were analyzed by hematoxylin and eosin staining, terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick end labeling (TUNEL), and 4',6-diamidino-2-phenylindole (DAPI) staining for determining cell death. Caspase-3 expression was examined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting. At 24h, based on TUNEL and DAPI results, the cell death index was 28.80 +/- 2.60% and 32.10 +/- 1.40% in the normothermia TBI group, while reaching only 14.30 +/- 2.70% and 18.40 +/- 2.10% in the hypothermic TBI group (p < 0.01). Based on RT-PCR and Western blotting results, the expression of caspase-3 was 210.20 +/- 5.30% and 170.30 +/- 4.80% in the normothermic TBI group, while reaching only 165.10 +/- 3.70% and 130.60 +/- 4.10% in the hypothermic TBI group (p < 0.05). At 72h, based on TUNEL and DAPI results, the cell death index was 20.80 +/- 2.50% and 25.50 +/- 1.80% in the normothermic TBI group, while reaching only 10.20 +/- 2.60% and 15.50 +/- 2.10% in the hypothermic TBI group (p < 0.01). Based on RT-PCR and Western blotting results, the expression of caspase-3 was 186.20 +/- 6.20% and 142.30 +/- 5.10% in the normothermic TBI group, versus only 152.10 +/- 3.60% and 120.60 +/- 3.90% in the hypothermic TBI group (p < 0.05). Based on our findings, we conclude that post-traumatic hypothermia significantly attenuates cell death within the hippocampus following fluid percussion injury. Taken together with other studies, these observations support the premise that post-traumatic mild hypothermia can provide cerebral protection for patients with TBI.

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.

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

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

Effects of resuscitation fluid on neurologic physiology after cerebral trauma and hemorrhage

BACKGROUND

The current standard of care for fluid resuscitation of hemorrhagic hypotensive patients involves the use of crystalloid solutions. Traumatic brain injury (TBI) is often associated with hemorrhage and hypotension, which can contribute significantly to morbidity and mortality. Guidelines for the choice of fluid resuscitation and the use of red blood cell transfusions are not yet clear in the context of brain injury.

METHODS

Various fluid resuscitation strategies were evaluated in Sprague-Dawley rats using fresh blood, normal saline, hypertonic saline, and albumin fluid resuscitation protocols. Mean arterial blood pressure (MAP) and cerebral oximetry were assessed in hemorrhaged groups and the mean population spike amplitudes (PSA) from the hippocampus were examined in fluid percussion injured (FPI) animals subject to hemorrhage and fluid resuscitation.

RESULTS

MAP in control animals, hemorrhage and hemorrhage + albumin treated groups was 82.4 +/- 1.5 mm Hg, 55.7 +/- 1.5 mm Hg, and 97.0 +/- 3.4 mm Hg, respectively. Arterial PaO2 was higher in albumin-treated animals relative to other fluid alternatives. Regional tissue oxygen tension (PbrO2) levels in hemorrhaged animals reached significantly higher levels in albumin treated group compared with in normal saline and hypertonic saline (p < 0.001, p = 0.034, respectively). After FPI+hemorrhage, PSA values in albumin- resuscitated animals were significantly higher than in normal saline-resuscitated animals (p = 0.012).

CONCLUSIONS

The results of normal saline resuscitation, relative to other fluid alternatives, suggest that a re-evaluation of current treatment strategies in hemorrhagic hypotensive TBI patients is warranted. Albumin demonstrated the greatest beneficial effects on neurophysiology endpoints over crystalloid alternatives. These data suggests that albumin resuscitation may play an important role in the treatment of hemorrhagic hypotension and TBI.

Posttraumatic secondary brain insults exacerbates neuronal injury by altering metabotropic glutamate receptors

Background

Our previous studies indicated that metabotropic glutamate receptors (mGluRs) are deeply involved in the secondary processes after diffuse brain injury (DBI). In the present study, we used a rodent DBI model to determine whether hypotension exacerbates neuronal injury as a secondary brain insult (SBI) after traumatic brain injury (TBI) by changing the expression of metabotropic glutamate receptors (mGluRs) in the cerebral cortex.

Results

Three hundred and eleven male Sprague-Dawley rats were randomly assigned into five groups: normal control, sham-operated control, SBI alone, DBI alone, or DBI with SBI. DBI was produced in rats by Marmarou's methods and the SBI model was produced by hypotension. The alteration of neuronal expression of mGluRs after DBI and DBI coupled with SBI was observed by hybridization in situ at different time points in the experiment. We found a higher mortality and neurological severity score (NSS) for rats in the DBI with SBI group compared with those in the DBI alone group. Although there was a significant rise in the expression of group I and group III mGluRs (except mGluR6) and a decrease in the expression of group II mGluRs after DBI (P < 0.05), the changes were more severe when DBI was coupled with SBI (P < 0.05). The expression of group I mGluRs peaked at 24 hours, while the expression of the group III mGluRs peaked at 6 hours after injuries, which may reflect a self-protection first mechanism of the damaged neurons. Moreover, the overall neuro-harmful effects of mGluRs on neurons were seemly associated with higher mortality and NSS in the DBI with SBI group.

Conclusion

The results suggest posttraumatic SBI may exacerbate neuronal injury or brain injury by altering expression of mGluRs, and more emphasis should therefore be put on the prevention and treatment of SBI.

Posttraumatic brain vulnerability to hypoxia-hypotension: the importance of the delay between brain trauma and secondary insult

OBJECTIVE

To examine whether the effect of hypoxia-hypotension (HH) after traumatic brain injury (TBI) is affected by the delay between insults.

DESIGN

Thirty Sprague-Dawley rats were randomized into five groups: sham, TBI alone (trauma alone, impact-acceleration, 450 g weight drop from 1.8 m), HH alone (blood depletion, mean arterial pressure 40 mmHg, FIO2=10%, 15 min), TBI+early HH (TBI followed by HH, 45-min delay), and TBI+late HH (225-min delay). Cerebral perfusion pressure was continuously recorded. Brain microdialysis and PtiO2 probes were inserted stereotaxically into the right thalamus.

MEASUREMENTS AND RESULTS

After the HH period and for 60 min a significant increase in cerebral lactate-pyruvate ratio was observed in groups subjected to HH vs. TBI alone and sham groups (33.0+/-5.1 for HH alone and 51.9+/-6.7 for TBI+early HH vs. 16.7+/-2.4 for TBI alone at the same time, 27.6+/-4.4 for TBI+late HH vs. 13.1+/-1 for TBI alone at the same time). There was no significant difference in lactate-pyruvate ratio peaks between HH alone and TBI+late HH while it was higher in TBI+early HH. Similar results were obtained for cerebral glycerol. PtiO2 during HH phase did not differ between HH alone, TBI+early HH and TBI+late HH (respectively, 4.2+/-3.1, 4.9+/-5.7, and 2.9+/-1.8 mmHg).

CONCLUSIONS

A 45-min delay between HH and TBI has important metabolic consequences while a 225-min delay has a similar effect as HH in a noninjured brain. The posttraumatic brain vulnerability to HH depends on the delay between cerebral aggressions.

Therapeutic effect of hypothermia and dizocilpine maleate on traumatic brain injury in neonatal rats

This study was undertaken to evaluate the therapeutic effect of hypothermia and dizocilpine maleate in traumatic brain injury (TBI) on newborn rats. After induction of TBI, physiologic and histopathological assessments were performed on both the control and therapeutic groups to evaluate the effects of both agents. Rats were assigned into four groups as follows: normothermic (n = 23), hypothermic (n = 18), normothermia plus dizocilpine maleate (n = 18) and hypothermia plus dizocilpine maleate (n = 18). All the rats were injured using a weight-drop head injury model, artificially ventilated with a 33% O(2) and 66% NO(2) mixture, and physiological parameters, intracranial pressure, and brain and rectal temperatures were recorded. Mortality, physiological, neurological parameters, and histopathological changes were assessed after 24 h. As a result, intracranial pressure, cerebral perfusion pressure, morbidity, weight loss, and microscopic changes were significantly worse in the normothermic group (p <0.05). There was no statistical difference between other groups (p > 0.05). Hypothermia and dizocilpine maleate displayed similar neuroprotective effects in TBI on newborn rats, but no additive effect was observed.

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

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

Intracerebral microdialysis and intracranial compliance monitoring of patients with traumatic brain injury

OBJECTIVE

The aims of this study were to get an impression of the relationships between intracranial compliance (IC) and Lactate/Pyruvate (L/P) ratio and temperature and L/P ratio, and to determine if patients with low IC had an increased vulnerability for the secondary insult hyperthermia (as reflected in the L/P ratio). The effects of coma treatment on the results were also studied.

METHODS

Ten TBI patients were monitored for IC, in vivo microdialysis (MD) and bladder temperature. Mean Glasgow Coma Scale (GCS) score was 7 (range 4-10). Three patients underwent induced coma treatment. Three statistical models were used to look at the relationships between IC, temperature and L/P ratio in patients with and without coma.

RESULTS

We found that with high temperature L/P ratios increased as IC decreased (P < 0.0001). The patients with coma treatment had significantly higher average L/P ratios (P < 0.02). The effect of IC on the L/P ratio differed by coma treatment (P < 0.02). The temperature effect was not dependent on coma treatment (P < 0.49).

CONCLUSIONS

These findings suggest the importance of avoiding hyperthermia in TBI patients, especially in patients with low or decreased IC (monitored or anticipated). The present technical solution seems promising for analysis of complex clinical data.

CURRENT CONTROVERSIES IN THE MANAGEMENT OF PATIENTS WITH SEVERE TRAUMATIC BRAIN INJURY

BACKGROUND

Traumatic brain injury is a major cause of mortality and morbidity, particularly among young men. The efficacy and safety of most of the interventions used in the management of patients with traumatic brain injury remain unproven. Examples include the 'cerebral perfusion pressure-targeted' and 'volume-targeted' management strategies for optimizing cerebrovascular haemodynamics and specific interventions, such as hyperventilation, osmotherapy, cerebrospinal fluid drainage, barbiturates, decompressive craniectomy, therapeutic hypothermia, normobaric hyperoxia and hyperbaric oxygen therapy.

METHODS

A review of the literature was performed to examine the evidence base behind each intervention.

RESULTS

There is no class I evidence to support the routine use of any of the therapies examined.

CONCLUSION

Well-designed, large, randomized controlled trials are needed to determine therapies that are safe and effective from those that are ineffective or harmful.

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.

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

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

Secondary ischemia impairing the restoration of ion homeostasis following traumatic brain injury

Object. It is well established that posttraumatic secondary ischemia contributes to poor outcome. Ion dysfunction leading to cytotoxic edema is a primary force in the formation of ischemic brain edema and is a principal component of traumatic brain swelling. Because cell swelling is the result of net ion and water movement, it is crucial to have a thorough understanding of these transient phenomena. The purpose of this study was to characterize the effects of secondary ischemia following traumatic brain injury (TBI) on the ability to restore ion homeostasis.

Methods. Twenty-four Sprague—Dawley rats were divided into four groups of six animals each. The rats underwent transient forebrain ischemia via bilateral carotid artery occlusion combined with hypotension: 15 minutes of forebrain ischemia (Group 1); 60 minutes of forebrain ischemia (Group 2); impact acceleration/TBI (Group 3); and impact acceleration/TBI followed by 15 minutes of ischemia (Group 4).

Ischemia resulted in a rapid accumulation of [K+]e: 41.94 ± 13.65 and 66.33 ± 6.63 mM, respectively, in Groups 1 and 2, with a concomitant decrease of [Na+]e: 64 ± 18 mM and 72 ± 11 mM in Groups 1 and 2. Traumatic brain injury resulted in a less severe although identical trend in ion dysfunction ([K+]e 30.42 ± 11.67 mM and [Na+]e 63 ± 33 mM). Secondary ischemia resulted in prolonged and sustained ion dysfunction with a concomitant elevation of intracranial pressure (ICP).

Conclusions. Analysis of these results indicates that ischemia and TBI are sublethal in isolation; however, when TBI is associated with secondary ischemia, ion dysfunction is sustained and is associated with elevated ICP.

Animal models of head trauma

Animal models of traumatic brain injury (TBI) are used to elucidate primary and secondary sequelae underlying human head injury in an effort to identify potential neuroprotective therapies for developing and adult brains. The choice of experimental model depends upon both the research goal and underlying objectives. The intrinsic ability to study injury-induced changes in behavior, physiology, metabolism, the blood/tissue interface, the blood brain barrier, and/or inflammatory- and immune-mediated responses, makes in vivo TBI models essential for neurotrauma research. Whereas human TBI is a highly complex multifactorial disorder, animal trauma models tend to replicate only single factors involved in the pathobiology of head injury using genetically well-defined inbred animals of a single sex. Although such an experimental approach is helpful to delineate key injury mechanisms, the simplicity and hence inability of animal models to reflect the complexity of clinical head injury may underlie the discrepancy between preclinical and clinical trials of neuroprotective therapeutics. Thus, a search continues for new animal models, which would more closely mimic the highly heterogeneous nature of human TBI, and address key factors in treatment optimization.

Cerebral oxidative stress and depression of energy metabolism correlate with severity of diffuse brain injury in rats

OBJECTIVE

The combined effect of traumatic brain injury (TBI) and secondary insult on biochemical changes of cerebral tissue is not well known. For this purpose, we studied the time-course changes of parameters reflecting ROS-mediated oxidative stress and modifications of cell energy metabolism determined in rats subjected to cerebral insult of increasing severity.

METHODS

Rats were divided into four groups: 1) sham-operated, 2) subjected to 10 minutes of hypoxia and hypotension (HH), 3) subjected to severe diffuse TBI, and 4) subjected to severe diffuse TBI + HH. Rats were killed at different times after injury, and analyses of malondialdehyde, ascorbate, high-energy phosphates, nicotinic coenzymes, oxypurines, nucleosides, and N-acetylaspartate (NAA) were made by high-performance liquid chromatography on whole-brain tissue extracts.

RESULTS

Data indicated a close relationship between degree of oxidative stress and severity of brain insult, as evidenced by the highest malondialdehyde values and lowest ascorbate levels in rats subjected to TBI + HH. Similarly, modifications of parameters related to cell energy metabolism were modulated by increasing severity of brain injury, as demonstrated by the lowest values of energy charge potential, nicotinic coenzymes, and NAA and the highest levels of oxypurines and nucleosides recorded in TBI + HH rats. Both the intensity of oxidative stress-mediated cerebral damage and perturbation of energy metabolism were minimally affected in rats subjected to HH only.

CONCLUSION

These results showed that the severity of brain insult can be graded by measuring biochemical modifications, specifically, reactive oxygen species-mediated damage, energy metabolism depression, and NAA, thereby validating the rodent model of closed-head diffuse TBI coupled with HH and proposing NAA as a marker with diagnostic relevance to monitor the metabolic state of postinjured brain.

Neuroprotection of adult rat dorsal root ganglion neurons by combined hypothermia and alkalinization against prolonged ischemia

Ischemia and ischemia-induced secondary events, such as acidosis and excessive activation of receptors by amino acids, trigger neuron death. The isolation and dissociation of dorsal root ganglion (DRG) involves time during which the neurons are ischemic due to being densely packed within the intact DRG and surrounded by a connective tissue coat. Thus, the longer the time between killing the host animal and when the DRG are dissociated, the longer the neurons are ischemic and exposed to ischemia-induced secondary causes of neuron death. It is well established that hypothermia and alkalinization each separately protect neurons from ischemia and ischemia-induced secondary causes of neuron death, but there are no data on the neuroprotection provided by simultaneous hypothermia and alkalinization. The present experiments were designed to determine the combination of hypothermic and alkaline conditions that yield the largest number of viable neurons dissociated from intact DRG maintained ischemic for up to 4 h. Hypothermia (20 degrees C>15 degrees C>37 degrees C) and alkalinization (pH 9.3>pH 8.3>pH 7.4) increased the yield of viable neurons compared with the yield from DRG maintained under physiological conditions. Hypothermia and alkalinization combined (20 degrees C/pH 9.3) provided the greatest neuroprotection with a yield of viable neurons after 1 h of ischemia 2.5-fold larger than that from DRG maintained under physiological conditions (37 degrees C/pH 7.6). Over 4 h of ischemia, the yield of viable neurons from DRG maintained under both hypothermic/alkaline and physiological conditions decreased in a linear manner, but those at 20 degrees C/pH 9.3 had a 4.5-fold greater yield of viable neurons than those at 37 degrees C/pH 7.6. Thus, combined hypothermia and alkalinization provide significantly greater protection against ischemia and ischemia-induced secondary causes of neuron death than either alone.

Traumatic injury in the developing brain–effects of hypothermia

Little is known about the underlying mechanisms of head trauma in the developing brains, despite considerable social and economic impact following such injuries. Age has been shown to substantially influence morbidity and mortality. Children younger than 4 years of age had worse cognitive, motor, and brain atrophy outcomes than children 6 years of age and older. Younger children tend to more frequently suffer from diffuse cerebral swelling compared to adults. Typical autoptic findings also include axonal injury and ischemic neurodegeneration. These differences impact not only the primary response of the brain to injury but the secondary response as well. The complexity of damaging mechanisms in traumatic brain injury contributes to the problem of determining effective therapy. As an alternative/ adjunct to pharmacological approaches, hypothermia has been shown to be cerebroprotective in traumatized adult brains. Although a large number of animal studies have shown protective effects of hypothermia in a variety of damaging mechanisms after TBI, little data exist for young, developing brains. The injury mechanisms of TBI in the immature, effects of hypothermia following resuscitation on adult and immature traumatized brains, and some possible mechanisms of action of hypothermia in the immature traumatized brain are discussed in this review.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Secondary injuries in brain trauma: effects of hypothermia

Hypothermia has been shown to be cerebroprotective in traumatized brains. Although a large number of traumatic brain injury (TBI) studies in animals have shown that hypothermia is effective in suppressing a variety of damaging mechanisms, clinical investigations have shown less consistent results. The complexity of damaging mechanisms in human TBI may contribute to these discrepancies. In particular, secondary injuries such as hypotension and hypoxemia may promote poor outcome. However, few experimental TBI studies have employed complex models that included such secondary injuries to clarify the efficacy of hypothermia. This review discusses the effects of hypothermia in various TBI models addressing primary and acute secondary injuries. Included are recently published clinical data using hypothermia as a therapeutic tool for preventing or reducing the detrimental posttraumatic secondary injuries and neurobehavioral deficits. Also discussed are recent successful applications of hypothermia from outside the TBI realm. Based on all available data, some general considerations for the application of hypothermia in TBI patients are given.

The importance of gender on the beneficial effects of posttraumatic hypothermia

The authors studied the importance of gender on the consequences of mild posttraumatic hypothermia following parasagittal fluid-percussion (F-P) brain injury in rats. After traumatic brain injury (TBI), brain temperature was maintained at normothermia (37 degrees C) or reduced to 33 degrees C for 4 h starting 30 min after the insult followed by a 1.5-h slow rewarming period. Animals (n = 48) were allowed to survive for 3 days before quantitative histopathological and immunocytochemical examination. As previously reported, contusion volume in normothermic animals (37 degrees C) was smaller (P < 0.05) in intact females compared to males. In addition, numbers of NeuN-positive cortical neurons were greater in females versus males after TBI. Posttraumatic hypothermia significantly reduced overall contusion volume in males (P < 0.05), while not significantly reducing contusion volume in females. Likewise, hypothermia protected against the loss of cortical neurons in males but had no effect in females. Ovariectomized females showed contusion volumes and neuronal cell counts comparable to those seen in males as well as a significant reduction in contusion volumes and greater neuronal counts following posttraumatic hypothermia. These data are the first to demonstrate that posttraumatic hypothermia (4 h) does not affect short-term histopathological outcomes in female rats. Potential mechanisms underlying this gender difference are discussed. Finally, these experimental findings may have important implications in terms of clinical trials using therapeutic hypothermia targeting patients with central nervous system (CNS) injury.

Basic science of closed head injuries and spinal cord injuries

Traumatic CNS injury is one of the most important health issues in our society and is a risk to all athletes, both in competitive and recreational sports. Our understanding of the pathophysiology has improved tremendously in the last 20 years. This progress has led to the identification of several possible treatments for improving outcome following spinal cord injury and traumatic brain injury. As no panacea exists, improvements in experimental models have empowered researchers in their search for novel therapeutic strategies.