Continuous measurement of changes in regional cerebral blood flow following cortical compression contusion trauma in the rat

What Happens in TBI? A Wide Talk on Animal Models and Future Perspective

Traumatic brain injury (TBI) is a global healthcare concern and a leading cause of death. The most common causes of TBI include road accidents, sports injuries, violence in warzones, and falls. TBI induces neuronal cell death independent of age, gender, and genetic background. TBI survivor patients often experience long-term behavioral changes like cognitive and emotional changes. TBI affects social activity, reducing the quality and duration of life. Over the last 40 years, several rodent models have been developed to mimic different clinical outcomes of human TBI for a better understanding of pathophysiology and to check the efficacy of drugs used for TBI. However, promising neuroprotective approaches that have been used preclinically have been found to be less beneficial in clinical trials. So, there is an urgent need to find a suitable animal model for establishing a new therapeutic intervention useful for TBI. In this review, we have demonstrated the etiology of TBI and post- TBI social life alteration, and also discussed various preclinical TBI models of rodents, zebrafish, and drosophila.

Impaired capillary-to-arteriolar electrical signaling after traumatic brain injury

Traumatic brain injury (TBI) acutely impairs dynamic regulation of local cerebral blood flow, but long-term (>72 h) effects on functional hyperemia are unknown. Functional hyperemia depends on capillary endothelial cell inward rectifier potassium channels (Kir2.1) responding to potassium (K+) released during neuronal activity to produce a regenerative, hyperpolarizing electrical signal that propagates from capillaries to dilate upstream penetrating arterioles. We hypothesized that TBI causes widespread disruption of electrical signaling from capillaries-to-arterioles through impairment of Kir2.1 channel function. We randomized mice to TBI or control groups and allowed them to recover for 4 to 7 days post-injury. We measured in vivo cerebral hemodynamics and arteriolar responses to local stimulation of capillaries with 10 mM K+ using multiphoton laser scanning microscopy through a cranial window under urethane and α-chloralose anesthesia. Capillary angio-architecture was not significantly affected following injury. However, K+-induced hyperemia was significantly impaired. Electrophysiology recordings in freshly isolated capillary endothelial cells revealed diminished Ba2+-sensitive Kir2.1 currents, consistent with a reduction in channel function. In pressurized cerebral arteries isolated from TBI mice, K+ failed to elicit the vasodilation seen in controls. We conclude that disruption of endothelial Kir2.1 channel function impairs capillary-to-arteriole electrical signaling, contributing to altered cerebral hemodynamics after TBI.

GABA beyond the synapse: defining the subtype-specific pharmacodynamics of non-synaptic GABAA receptors

KEY POINTS

Physiologically relevant combinations of recombinant GABAA receptor (GABAR) subunits were expressed in HEK293 cells. Using whole-cell voltage clamp and rapid drug application, we measured the GABAR-subtype-specific properties to convey either synaptic or extrasynaptic signalling in a range of physiological contexts. α4βδ GABARs are optimally tuned to submicromolar tonic GABA and transient surges of micromolar GABA concentrations. α5β2γ2l GABARs are better suited to higher tonic GABA levels, but also convey robust responses to brief synaptic and perisynaptic GABA fluctuations. α1β2/3δ GABARs function well at prolonged, micromolar (>2 μm) GABA levels, but not to low tonic (<1 μm GABA) or synaptic/transient GABAergic signalling. These results help illuminate the context- and isoform-specific modes of GABAergic signalling in the brain.

ABSTRACT

GABAA receptors (GABARs) mediate a remarkable diversity of signalling modalities in vivo. Yet most published work characterizing responses to GABA has focused on the properties needed to convey fast, phasic synaptic inhibition. We therefore aimed to characterize the most prevalent (α4βδ, α5β3γ2L) and least prevalent (α1β2δ) non-synaptic GABAR currents, using whole-cell voltage clamp recordings of recombinant GABAR expressed in HEK293 cells and drug application protocols to recapitulate the GABA concentration profiles occurring during both fast synaptic and slow extrasynaptic signalling. We found that α4βδ GABARs were very sensitive to submicromolar GABA, with a rank order potency of α4β2δ ≥ α4β1δ ≈ α4β3δ GABARs. In comparison, the GABA EC50 was up to 20 times higher for α1β2γ2L GABARs, with α1β2δ and α5β3γ2L GABARs having intermediate GABA potency. Both α4βδ and α5β3γ2L GABAR currents exhibited slow, but substantial, desensitization as well as prolonged rates of deactivation. These GABAR current properties defined distinct 'dynamic ranges' of responsiveness to changing GABA for α4β2δ (0.1-1 μm), α5β3γ2L (0.5-7 μm) and α1β2γ2L (0.6-9 μm) GABARs. Finally, α1β2δ GABARs were notable for their relative lack of desensitization and extremely quick deactivation. In summary, our results help delineate the roles that specific GABARs may play in mediating non-synaptic GABA signals. Since ambient GABA levels may be altered during development as well as by drugs and disease states, these findings may help future efforts to understand disrupted inhibition underlying a variety of neurological illnesses, such as epilepsy.

Intraoperative contrast-enhanced ultrasonography for microcirculatory evaluation in rhesus monkey with spinal cord injury

This study tried to quantify spinal cord perfusion by using contrast-enhanced ultrasound (CEUS) in rhesus monkey models with acute spinal cord injury. Acute spinal cord perfusion after injury was detected by CEUS, coupling with conventional ultrasound (US) and Color Doppler US (CDFI). Time-intensity curves and perfusion parameters were obtained by autotracking contrast quantification (ACQ) software in the epicenter and adjacent regions of injury, respectively. Neurological and histological examinations were performed to confirm the severity of injury. US revealed spinal cords were hypoechoic and homogeneous, whereas dura maters, pia maters, and cerebral aqueducts were hyperechoic. After spinal cord contusion, the injured spinal cord was hyperechoic on US, and intramedullary vessels of adjacent region of injury were increased and dilated on CDFI. On CEUS hypoperfusion were found in the epicenter of injury, while hyperperfusion in its adjacent region. Quantitative analysis showed that peak intensity (PI) decreased in epicenters of injury but significantly increased in adjacent regions at all time points (p < 0.05). Functional evaluation demonstrated significant deterioration compared to pre-contusion (p < 0.05). Quantitative analysis with CEUS is a promising method for monitoring perfusion changes of spinal cord injury in overall views and real-time.

Epileptogenesis following experimentally induced traumatic brain injury - a systematic review

Traumatic brain injury (TBI) is a complex neurotrauma in civilian life and the battlefield with a broad spectrum of symptoms, long-term neuropsychological disability, as well as mortality worldwide. Posttraumatic epilepsy (PTE) is a common outcome of TBI with unknown mechanisms, followed by posttraumatic epileptogenesis. There are numerous rodent models of TBI available with varying pathomechanisms of head injury similar to human TBI, but there is no evidence for an adequate TBI model that can properly mimic all aspects of clinical TBI and the first successive spontaneous focal seizures follow a single episode of neurotrauma with respect to epileptogenesis. This review aims to provide current information regarding the various experimental animal models of TBI relevant to clinical TBI. Mossy fiber sprouting, loss of dentate hilar neurons along with recurrent seizures, and epileptic discharge similar to human PTE have been studied in fluid percussion injury, weight-drop injury, and cortical impact models, but further refinement of animal models and functional test is warranted to better understand the underlying pathophysiology of posttraumatic epileptogenesis. A multifaceted research approach in TBI model may lead to exploration of the potential treatment measures, which are a major challenge to the research community and drug developers. With respect to clinical setting, proper patient data collection, improved clinical trials with advancement in drug delivery strategies, blood-brain barrier permeability, and proper monitoring of level and effects of target drug are also important.

The acute phase of mild traumatic brain injury is characterized by a distance-dependent neuronal hypoactivity

The consequences of mild traumatic brain injury (TBI) on neuronal functionality are only now being elucidated. We have now examined the changes in sensory encoding in the whisker-recipient barrel cortex and the brain tissue damage in the acute phase (24 h) after induction of TBI (n=9), with sham controls receiving surgery only (n=5). Injury was induced using the lateral fluid percussion injury method, which causes a mixture of focal and diffuse brain injury. Both population and single cell neuronal responses evoked by both simple and complex whisker stimuli revealed a suppression of activity that decreased with distance from the locus of injury both within a hemisphere and across hemispheres, with a greater extent of hypoactivity in ipsilateral barrel cortex compared with contralateral cortex. This was coupled with an increase in spontaneous output in Layer 5a, but only ipsilateral to the injury site. There was also disruption of axonal integrity in various regions in the ipsilateral but not contralateral hemisphere. These results complement our previous findings after mild diffuse-only TBI induced by the weight-drop impact acceleration method where, in the same acute post-injury phase, we found a similar depth-dependent hypoactivity in sensory cortex. This suggests a common sequelae of events in both diffuse TBI and mixed focal/diffuse TBI in the immediate post-injury period that then evolve over time to produce different long-term functional outcomes.

Edaravone increases regional cerebral blood flow after traumatic brain injury in mice

Traumatic brain injury (TBI) is a major cause of preventable death and serious morbidity, with subsequent low cerebral blood flow (CBF) considered to be associated with poor prognosis. In the present study, we demonstrated the effect of the free radical scavenger edaravone on regional CBF (rCBF) after TBI. Male mice (C57/BL6) were subjected to TBI using a controlled cortical impactor device. Immediately after TBI, the animals were intravenously administered 3.0 mg/kg of edaravone or a vehicle saline solution. Two-dimensional rCBF images were acquired before and 24 h post-TBI, and were quantified in the ipsilateral and contralateral hemispheres (n = 5 animals per group). CBF in the vehicle-treated animals decreased broadly over the ipsilateral hemisphere, with the region of low rCBF spreading from the frontal cortex to the occipital lobe. The zone of lowest rCBF matched that of the contusion area. The mean rCBF at 24 h for a defined elliptical region between the bregma and lambda was 73.7 ± 5.8 %. In comparison, the reduction of rCBF in edaravone-treated animals was significantly attenuated (93.4 ± 5.7 %, p < 0.05). The edaravone-treated animals also exhibited higher rCBF in the contralateral hemisphere compared with that seen in -vehicle-treated animals. It is suggested that edaravone reduces neuronal damage by scavenging reactive oxygen species (ROS) and by maintaining intact the autoregulation of the cerebral vasculature.

Blood-brain barrier permeability is positively correlated with cerebral microvascular perfusion in the early fluid percussion-injured brain of the rat

The blood-brain barrier (BBB) opening following traumatic brain injury (TBI) provides a chance for therapeutic agents to cross the barrier, yet the reduction of the cerebral microvascular perfusion after TBI may limit the intervention. Meanwhile, optimizing the cerebral capillary perfusion by the strategies such as fluid administration may cause brain edema due to the BBB opening post trauma. To guide the TBI therapy, we characterized the relationship between the changes in the cerebral capillary perfusion and BBB permeability after TBI. First, we observed the changes of the cerebral capillary perfusion by the intracardiac perfusion of Evans Blue and the BBB disruption with magnetic resonance imaging (MRI) in the rat subjected to lateral fluid percussion (FP) brain injury. The correlation between two variables was next evaluated with the correlation analysis. Since related to BBB breakdown, matrix metalloproteinase-9 (MMP-9) activity was finally detected by gelatin zymography. We found that the ratios of the perfused microvessel numbers in the lesioned cortices were significantly reduced at 0 and 1 h post trauma compared with that in the normal cortex, which then dramatically recovered at 4 and 24 h after injury, and that the BBB permeability was greatly augmented in the ipsilateral parts at 4, 12, and 24 h, and in the contralateral area at 24 h after injury compared with that in the uninjured brain. The correlation analysis showed that the BBB permeability increase was related to the restoration of the cerebral capillary perfusion over a 24-h period post trauma. Moreover, the gelatin zymography analysis indicated that the MMP-9 activity in the injured brain increased at 4 h and significantly elevated at 12 and 24 h as compared to that at 0 or 1 h after TBI. Our findings demonstrate that the 4 h post trauma is a critical turning point during the development of TBI, and, importantly, the correlation analysis may guide us how to treat TBI.

Animal modelling of traumatic brain injury in preclinical drug development: where do we go from here?

Traumatic brain injury (TBI) is the leading cause of death and disability in young adults. Survivors of TBI frequently suffer from long-term personality changes and deficits in cognitive and motor performance, urgently calling for novel pharmacological treatment options. To date, all clinical trials evaluating neuroprotective compounds have failed in demonstrating clinical efficacy in cohorts of severely injured TBI patients. The purpose of the present review is to describe the utility of animal models of TBI for preclinical evaluation of pharmacological compounds. No single animal model can adequately mimic all aspects of human TBI owing to the heterogeneity of clinical TBI. To successfully develop compounds for clinical TBI, a thorough evaluation in several TBI models and injury severities is crucial. Additionally, brain pharmacokinetics and the time window must be carefully evaluated. Although the search for a single-compound, 'silver bullet' therapy is ongoing, a combination of drugs targeting various aspects of neuroprotection, neuroinflammation and regeneration may be needed. In summary, finding drugs and prove clinical efficacy in TBI is a major challenge ahead for the research community and the drug industry. For a successful translation of basic science knowledge to the clinic to occur we believe that a further refinement of animal models and functional outcome methods is important. In the clinical setting, improved patient classification, more homogenous patient cohorts in clinical trials, standardized treatment strategies, improved central nervous system drug delivery systems and monitoring of target drug levels and drug effects is warranted.

Cerebral glucose metabolism after traumatic brain injury in the rat studied by 13C-glucose and microdialysis

BACKGROUND

Following traumatic brain injury (TBI), a disturbed cerebral glucose metabolism contributes to secondary brain damage. To study local cerebral glucose metabolism after TBI, we delivered (13)C-labeled glucose into brain tissue by microdialysis (MD).

METHOD

MD probes were inserted bilaterally into the parietal cortex of rat brain, one probe in the shear stress zone of the injury and the other at the corresponding contralateral coordinates. A moderately severe controlled cortical contusion was used to model TBI. Dialysate concentrations of glucose, pyruvate, lactate, and glycerol were measured, and following derivatization, (13)C enrichments of the compounds were determined by gas chromatography-mass spectrometry.

FINDINGS

We found that (13)C-labeled glucose was rapidly converted into (13)C-lactate and (13)C-glycerol. In the hours following TBI, concentrations and (13)C enrichments of lactate and glycerol increased.

CONCLUSIONS

The findings confirm the occurrence of anaerobic local glucose metabolism early after TBI. Only a small fraction of the glycerol was newly synthesized, suggesting that the hypothesis that most of the released glycerol after TBI comes from degradation of membrane phospholipids still holds. We conclude that the combination of microdialysis and stable isotope technique is a useful tool for investigating local glucose metabolism following brain injury.

Magnetic resonance imaging of regional hemodynamic and cerebrovascular recovery after lateral fluid-percussion brain injury in rats

Hemodynamic and cerebrovascular factors are crucially involved in secondary damage after traumatic brain injury (TBI). With magnetic resonance imaging, this study aimed to quantify regional cerebral blood flow (CBF) by arterial spin labeling and cerebral blood volume by using an intravascular contrast agent, during 14 days after lateral fluid-percussion injury (LFPI) in rats. Immunohistochemical analysis of vessel density was used to evaluate the contribution of vascular damage. Results show widespread ipsilateral and contralateral hypoperfusion, including both the cortex and the hippocampus bilaterally, as well as the ipsilateral thalamus. Hemodynamic unrest may partly be explained by an increase in blood vessel density over a period of 2 weeks in the ipsilateral hippocampus and perilesional cortex. Furthermore, three phases of perilesional alterations in CBF, progressing from hypoperfusion to normal and back to hypoperfusion within 2 weeks were shown for the first time in a rat TBI model. These three phases were similar to hemodynamic fluctuations reported in TBI patients. This makes it feasible to use LFPI in rats to study mechanisms behind hemodynamic changes and to explore novel therapeutic approaches for secondary brain damage after TBI.

Metabolic effects of a late hypotensive insult combined with reduced intracranial compliance following traumatic brain injury in the rat

INTRODUCTION

Traumatic brain injury makes the brain vulnerable to secondary insults. Post-traumatic alterations in intracranial dynamics, such as reduced intracranial compliance (IC), are thought to further potentiate the effects of secondary insults. Reduced IC combined with intracranial volume insults leads to metabolic disturbances in a rat model. The aim of the present study was to discern whether a post-traumatic hypotensive insult in combination with reduced IC caused more pronounced secondary metabolic disturbances in the injured rat brain.

MATERIALS AND METHODS

Rats were randomly assigned to four groups (n = 8/group): 1) trauma with hypotension; 2) trauma and reduced IC with hypotension; 3) sham injury with hypotension; and 4) sham injury and reduced IC with hypotension. A weight drop model of cortical contusion trauma was used. IC was reduced by gluing rubber film layers on the inside of bilateral bone flaps before replacement. Microdialysis probes were placed in the perimeter of the trauma zone. Hypotension was induced 2 h after trauma. Extracellular (EC) levels of lactate, pyruvate, hypoxanthine, and glycerol were analyzed.

RESULTS

The trauma resulted in a significant increase in EC dialysate levels of lactate, lactate/pyruvate ratio, hypoxanthine, and glycerol. A slight secondary increase in lactate was noted for all groups but group 2 during hypotension, otherwise no late effects were seen. There were no effects of reduced IC.

DISCUSSION

In conclusion, reduced IC did not increase the metabolic disturbances caused by the post-traumatic hypotensive insult. The results suggest that a mild to moderate hypotensive insult after initial post-traumatic resuscitation may be tolerated better than an early insult before resuscitation.

Experimental traumatic brain injury

Traumatic brain injury, a leading cause of death and disability, is a result of an outside force causing mechanical disruption of brain tissue and delayed pathogenic events which collectively exacerbate the injury. These pathogenic injury processes are poorly understood and accordingly no effective neuroprotective treatment is available so far. Experimental models are essential for further clarification of the highly complex pathology of traumatic brain injury towards the development of novel treatments. Among the rodent models of traumatic brain injury the most commonly used are the weight-drop, the fluid percussion, and the cortical contusion injury models. As the entire spectrum of events that might occur in traumatic brain injury cannot be covered by one single rodent model, the design and choice of a specific model represents a major challenge for neuroscientists. This review summarizes and evaluates the strengths and weaknesses of the currently available rodent models for traumatic brain injury.

Sustained focal cortical compression reduces electrically-induced seizure threshold

Brain injury can often result in the subsequent appearance of seizures, suggesting an alteration in neural excitability associated with the balance between neuronal excitation and inhibition. The process by which this occurs has yet to be fully elucidated. The specific nature of the changes in excitation and inhibition is still unclear, as is the process by which the seizures appear following injury. In this study, we investigated the effects of focal cortical compression on electrically-induced localized seizure threshold in rats. Male Long Evans rats were implanted with stimulating screw electrodes in their motor cortices above the regions controlling forelimb movement. Initial seizure threshold was determined in the animals using a ramped electrical stimulation procedure prior to any compression. Following initial threshold determination, animals underwent sustained cortical compression and then following a 24 h recovery period had their seizure thresholds tested again with electrical stimulation. Reliability of threshold measurements was confirmed through repeated measurements of seizure threshold. Localized seizure threshold was significantly lowered following sustained cortical compression as compared with control cases. Taken together, the results here suggest a change in global brain excitability following localized, focal compression.

Haemodynamic patterns in children with posttraumatic diffuse brain swelling. A preliminary study in 6 cases with neuroradiological features consistent with diffuse axonal injury

BACKGROUND

In the present report we describe the cerebral haemodynamics and the neuroradiological findings observed in six consecutive children, three males and three females aged 4-15.6 yrs (mean age 8.95) displaying a neuroradiological pattern consistent with diffuse axonal injury (DAI) along with slit ventricles.

METHODS

All the patients were admitted to the Paediatric Intensive Care Unit with GCS scores less than 8 after a severe brain injury. Serial head computed to mography (CT) and magnetic resonance (MR) scans demonstrated a radiological pattern of DAI. Transcranial Doppler Sonography (TCD) of the middle cerebral arteries was performed through the temporal bone window in all the patients. All patients but one underwent a continuous monitoring of intracranial pressure (ICP) and cerebral extraction of O(2) (CEO(2)). Treatment with barbiturates and hyperventilation was necessary in all the cases. In one patient, a bilateral decompressive cran iectomy was performed in order to decrease severe in tracranial hypertension.

RESULTS

Hyperflow along with intracranial hyper tension, variably responsive to barbiturate medication, was observed in all the patients by means of TCD and CEO(2).

CONCLUSIONS

Intracranial hypertension can be elevated in pediatric posttraumatic hyperflow syndromes associated with DAI. The observation of the time course of the parameters studied allowed us to modify the pharmacological treatment and/or perform surgical decompression (external cerebrospinal fluid (CSF) drainage in five cases; decompressive craniectomy in one case). Compartmental hyperflow TCD pattern was evident in only one patient. Although the limited number of pa tients in our series does not allow definite conclusions, we strongly believe that TCD, with ICP and CEO(2) monitoring, are useful tools in planning surgical strategy in children with neuroradiological signs of DAI.

Energy metabolic changes in the early post-injury period following traumatic brain injury in rats

Impaired cerebral energy metabolism may be a major contributor to the secondary injury cascade that occurs following traumatic brain injury (TBI). To estimate the cortical energy metabolic state following mild and severe controlled cortical contusion (CCC) TBI in rats, ipsi-and contralateral cortical tissues were frozen in situ at 15 and 40 min post-injury and adenylate (ATP, ADP, AMP) levels were analyzed using high-performance liquid chromatography (HPLC) and the energy charge (EC) was calculated. At 15 min post-injury, mildly brain-injured animals showed a 43% decrease in cortical ATP levels and a 2.4-fold increase in AMP levels (P < 0.05), and there was a significant reduction of the ipsilateral cortical EC when compared to sham-injured animals (P < 0.05). At 40 min post-injury, the ipsilateral adenylate levels and EC had recovered to the values observed in the sham-injury group. In the severe CCC group, there was a 51% decrease in ipsilateral cortical ATP levels and a 5.3-fold increase in AMP levels with a significant reduction of cortical EC at 15 min post-injury (P < 0.05). At 40 min post-injury, a 2.6-fold ipsilateral increase in AMP levels and an 11% and 44% decrease in EC and ATP levels, respectively, remained (P < 0.05). A 37-38% reduction of the total adenylate pool was observed ipsilaterally in both CCC severity groups at the early time-point, and a 19% and 28% decrease remained in the mild and severe CCC groups, respectively, at 40 min post-injury. Significant contralateral ATP and EC changes were only observed in the severe CCC group at 40 min post-injury (P < 0.05). The energy-requiring secondary injury cascades that occur early post-injury do not challenge the brain tissue to the extent of ATP depletion and may provide a window of opportunity for therapeutic intervention.

Instability of Doppler cerebral blood flow in monochorionic twins

OBJECTIVE

The purpose of this study was to evaluate Doppler flow velocity changes in cerebral vessels of monochorionic twins with twin-twin transfusion syndrome (TTTS).

METHODS

Repeated Doppler umbilical and cerebral blood flow studies were performed in 7 twin pairs with TTTS. Eight monochorionic twin pairs and 11 dichorionic twin pairs served as control groups. The following Doppler parameters were assessed: umbilical artery pulsatility index (PI), middle cerebral artery (MCA) PI, cerebroplacental ratio, delta PI between the umbilical artery and MCA, and peak systolic velocity (PSV) in the MCA.

RESULTS

Significant variations in PSV in the MCA and cerebral indices were found in the study group of monochorionic twins with TTTS. Periods of high PSV with low PI in the MCA were followed by lower PSV in the same fetus. Repeated measurements in the comparison groups were stable without significant variations. The delta cerebroplacental ratio was significantly higher in the study group (0.38 versus 0.09 and 0.19 in the comparison groups; P < .02).

CONCLUSIONS

Significant changes in Doppler flow velocity and indices suggest instability of cerebral blood flow with episodes of "hyperperfusion" in monochorionic twins with TTTS. Further studies are needed to elucidate the relationship of these transient changes to neurologic sequelae in the neonate.

Relationship between Intracranial Pressure and Cortical Spreading Depression following Fluid Percussion Brain Injury in Rats

Traumatic brain injury (TBI) is known to be accompanied by an increase in intracranial pressure (ICP) and in some cases, by spontaneous generation of cortical spreading depression (CSD) cycles. However, the role of CSD in the pathophysiology of cerebral contusion is still unknown. A multiparametric monitoring assembly was placed on the right hemisphere of the rat brain to evaluate ICP, DC potential, extracellular K(+), cerebral blood flow (CBF), and electrocorticogram in 27 rats during 5 h. Fluid percussion brain injury (FPBI) with the magnitude of the impact 2.9, 3.3, 4.1, and 5.0 atmospheres was induced to the left parietal cortex in animal groups A, B, C, and D, respectively. A slow increase in ICP was evident, and was pronounced in group C and especially in group D, where four of nine animals died during the monitoring. At the end of the 5 h experiment, the mean ICP levels were 6.75 +/- 2.87, 8.40 +/- 2.70, 12.75 +/- 4.03, 29.56 +/- 9.25, and the mean total number of CSD cycles was 2.00 +/- 1.41, 4.29 +/- 4.23, 11.71 +/- 13.29, and 20.11 +/- 19.26 in groups A, B, C, and D, respectively. The maximal level of intensity of CSD cycle generation after FPBI was obtained in group D, where almost constant activity was maintained until the end of the experiment. A significant coefficient of correlation between ICP level and total number of CSD cycles was found for all ICP measurements (r = 0.47-0.63, p < 0.05, n = 27), however more significant (p < 0.001) was the coefficient during the period of monitoring between 2 and 4 h after FPBI. Our results suggest that numerous repeating CSD cycles are typical phenomena in moderate and especially severe forms of FPBI. The rising number of CSD cycles under condition of an ICP level >/=20 mm Hg may demonstrate, with high probability, the unfavorable development of TBI, caused by growing secondary hypoxic insult.

Relative cerebral blood flow during the secondary expansion of a cortical lesion in rats

The size of a cerebral contusion is not finite at the moment of trauma, but liable to secondary increase during the following hours and days. In the present study we investigated whether this phenomenon may be related to changes in cortical blood flow (cCBF). In rats a cortical lesion grew to 140% of its initial volume during the first 24 h after injury. During the time of most rapid lesion expansion (<6 h after the insult) marked hypoperfusion (approximately 30% of baseline) was found in the ipsilateral hemisphere by laser Doppler scanning fluxmetry. In the peri-contusional area cCBF slowly recovered to approximately 80% of baseline, while in the distant brain not affected by delayed cell death, significant hyperperfusion (approximately 160% of baseline) was observed. Thus, early hypoperfusion might be an important mechanism for secondary lesion expansion.

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

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

Effects of LY379268, a selective group II metabotropic glutamate receptor agonist on EEG activity, cortical perfusion, tissue damage, and cortical glutamate, glucose, and lactate levels in brain-injured rats

Activating presynaptic group II metabotropic glutamate (mGlu II) receptors reduces synaptic glutamate release. Attenuating glutamatergic transmission without blocking ionotropic glutamate receptors, thus avoiding unfavorable psychomimetic side effects, makes mGlu II receptor agonists a promising target in treating brain-injured patients. Neuroprotective effects of LY379268 were investigated in rats following controlled cortical impact injury (CCI). At 30 min after CCI, rats received a single intraperitoneal injection of LY379268 (10 mg/kg/body weight) or NaCl. Changes in EEG activity and pericontusional cortical perfusion were determined before trauma, at 4, 24, and 48 h, and 7 days after CCI. Brain edema and contusion volume were determined at 24 h and 7 days after CCI, respectively. Before brain removal pericontusional cortical glutamate, glucose, and lactate were measured via microdialysis. During the early period following CCI, EEG activity and cortical perfusion were significantly reduced in rats receiving LY379268. At 7 days, cortical perfusion was significantly increased in rats treated with LY379268, while EEG activity was depressed as in control rats. While brain edema remained unchanged at 24 h, cortical contusion was significantly decreased by 56% at 7 days after CCI. Cortical glutamate, glucose, and lactate were not influenced. Significant reductions in EEG activity and contusion volume by LY379268 do not appear mediated by attenuated excitotoxicity and energetic impairment. Overall, an additional decrease in cortical perfusion seems to interfere with the anti-edematous potential of LY379268 during the early period following CCI, while an increase in perfusion in LY379268-treated rats at 7 days might contribute to tissue protection.

Intravascular coagulation: a major secondary insult in nonfatal traumatic brain injury

OBJECT

The goal of this study was to determine the frequency with which cerebral intravascular coagulation (IC) complicates traumatic brain injury (TBI). The authors also investigated the incidence of IC in relation to varying mechanisms, time courses, and severities of TBI and in different species.

METHODS

Tissue was sampled from surgical specimens of human cerebral contusions, from rats with lateral fluid-percussion injuries, and from pigs with head rotational acceleration injuries. Immunohistochemical fluorescent staining for antithrombin III was performed to detect cerebral intravascular microthrombi. Abundant IC was found in all specimens, and microthrombi had formed in arterioles and venules of all sizes, ranging from 10 to 600 microm. Although it was more pronounced in focal lesions and more severe injuries, considerable IC was also observed in mild and diffuse injuries. The authors found a strong association between the severity of coagulopathy and the density of IC.

CONCLUSIONS

These results strongly support the contention that IC is a universal response to TBI and an important secondary cerebral insult.

Effect of traumatic brain injury and nitrone radical scavengers on relative changes in regional cerebral blood flow and glucose uptake in rats

Changes in regional cerebral blood flow (rCBF) and glucose metabolism are commonly associated with traumatic brain injury (TBI). Reactive oxygen species (ROS) have been implicated as key contributors to the secondary injury process after TBI. Here, pretreatment with the nitrone radical scavengers (alpha-phenyl-N-tert-butyl nitrone (PBN) or its sulfonated analogue sodium 2-sulfophenyl-N-tert-butyl nitrone (S-PBN) were used as tools to study the effects of ROS on rCBF and glucose metabolism after moderate (2.4-2.6 atm) lateral fluid percussion injury (FPI) in rats. S-PBN has a half-life in plasma of 9 min and does not penetrate the blood-brain barrier (BBB). In contrast, PBN has a half-life of 3 h and readily penetrates the BBB. Regional cerebral blood flow (rCBF) and glucose metabolism was estimated by using (99m)Tc-HMPAO and [(18)F]Fluoro-2-deoxyglucose (FDG) autoradiography, respectively, at 42 min (n = 37) and 12 h (n = 34) after the injury. Regions of interest were the parietal cortex and hippocampus bilaterally. As expected, FPI produced an early (42-min) hypoperfusion in ipsilateral cortex and an increase in glucose metabolism in both cortex and hippocampus, giving way to a state of hypoperfusion and decreased glucose metabolism at 12 h postinjury. On the contralateral side, a hypoperfusion in the cortex and hippocampus was seen at 12 h only, but no significant changes in glucose metabolism. Both S-PBN and PBN attenuated the trauma-induced changes in rCBF and glucose metabolism. Thus, the early improvement in rCBF and glucose metabolism correlates with and may partly mediate the improved functional and morphological outcome after TBI in nitrone-treated rats.

Reversal of attenuation of cerebrovascular reactivity to hypercapnia by a nitric oxide donor after controlled cortical impact in a rat model of traumatic brain injury

OBJECT

Traumatic brain injury (TBI) attenuates the cerebral vasodilation to hypercapnia. Cortical spreading depression (CSD) also transiently reduces hypercapnic vasodilation. The authors sought to determine whether the CSD elicited by a controlled cortical impact (CCI) injury masks the true effect of TBI on hypercapnic vasodilation, and whether a nitric oxide (NO) donor can reverse the attenuation of hypercapnic vasodilation following CCI.

METHODS

Anesthetized rats underwent moderate CCI. Cerebral blood flow was monitored with laser Doppler flowmetry and the response to hypercapnia was determined for injured and sham-injured animals. The effect of the NO donor, S-nitroso-N-acetylpenicillamine (SNAP), on this response was also assessed. At an uninjured cortical site ipsilateral to the CCI, a single wave of CSD was recorded and the CO2 response at this location was significantly attenuated for up to 30 minutes (seven rats, p < 0.05). At the injured cortex, hypercapnic vasodilation continued to be attenuated for 7 hours. The cerebral vasodilation to CO2 was 37 +/- 5% in injured rats (six) compared with 84 +/- 10% in the sham-injured group (five rats, p < 0.05). After 30 minutes of topical superfusion with SNAP, hypercapnic vasodilation was restored to 74 +/- 7% (nine rats, p > 0.1 compared with that in the sham-injured group). In contrast, papaverine, an NO-independent vasodilator, failed to reverse the attenuation of the CO2 response to CCI.

CONCLUSIONS

The authors conclude that CSD elicited by CCI can mask the true effect of TBI on hypercapnic vasodilation for at least 30 minutes. Exogenous NO, but not papaverine, can reverse the attenuation of cerebrovascular reactivity to CO2 caused by TBI. This result supports the hypothesis that NO production is reduced after TBI and that the NO donor has a potential beneficial role in the clinical management of head injury.

Monitoring of reactive oxygen species production after traumatic brain injury in rats with microdialysis and the 4-hydroxybenzoic acid trapping method

The detection of reactive oxygen species (ROS) after traumatic brain injury (TBI) is based on indirect methods due to the high reactivity and short half-life of ROS in biological tissue. The commonly used salicylate trapping method has several disadvantages making it unsuitable for human use. We have evaluated 4-hydroxybenzoic acid (4-HBA) together with microdialysis (MD) in the rat as an alternative method. 4-HBA forms one stable adduct, 3,4-dihydroxybenzoic acid (3,4-DHBA), when reacting with ROS and has not previously been used together with MD after TBI. Twenty-seven rats were used for the assessment of 3,4-DHBA production as an indicator of ROS formation in a controlled contusion injury model using intracerebral MD with 3 mM 4-HBA in the perfusate. For comparison, salicylate trapping was used in eight rats. TBI caused a 250% increase of 3,4-DHBA that peaked at 30 min after injury in severely injured rats and remained significantly elevated as compared to baseline for 90 min after trauma. The mild injury level caused a 100% increase in 3,4-DHBA formation at 30 min after the injury. When the MD probe was placed in the perimeter of the injury site, no significant increase in ROS formation occurred. Salicylate trapping showed a similar increase in adduct formation after severe injury. In addition, high cortical concentrations of 4-HBA and salicylate were found. It is concluded that microdialysis with 4-HBA as a trapping agent appears to be a useful method for ROS detection in the rat with a potential clinical utility.

Effects of the nitrone radical scavengers PBN and S-PBN on in vivo trapping of reactive oxygen species after traumatic brain injury in rats

In previous studies, the authors showed that the nitrone radical scavenger alpha-phenyl-N- tert -butyl nitrone (PBN) and its sulfo-derivative, 2-sulfo-phenyl-N- tert -butyl nitrone (S-PBN), attenuated cognitive disturbance and reduced tissue damage after traumatic brain injury (TBI) in rats. In the current study, the production of reactive oxygen species (ROS) after TBI was monitored with microdialysis and the 4-hydroxybenzoic acid (4-HBA) trapping method. A single dose of PBN (30 mg/kg) or an equimolar dose of S-PBN (47 mg/kg) was administered intravenously 30 minutes before a controlled cortical contusion injury in rats. Plasma and brain tissue drug concentrations were analyzed at the end of the microdialysis experiment (3 hours after injury) and, in a separate experiment with S-PBN, at 30 and 60 minutes after injury. Traumatic brain injury caused a significant increase in ROS formation that lasted for 60 minutes after the injury as evidenced by increased 3,4-dihydroxybenzoic acid (3,4-DHBA) concentrations in the dialysate. PBN and S-PBN equally and significantly attenuated the posttraumatic increase in 3,4-DHBA formation. High PBN concentrations were found bilaterally in brain tissue up to 3 hours after injury. In contrast, S-PBN was rapidly cleared from the circulation and was not detectable in brain at 30 minutes after injury or at any later time point. The results suggest that scavenging of ROS after TBI may contribute to the neuroprotective properties observed with nitrone spin-trapping agents. S-PBN, which remained undetectable even in traumatized brain tissue, reduced ROS production to the same extent as PBN that readily crossed the blood-brain barrier. This finding supports an important role for ROS production at the blood-endothelial interface in TBI.

Delayed hemorrhagic hypotension exacerbates the hemodynamic and histopathologic consequences of traumatic brain injury in rats

Alterations in cerebral autoregulation and cerebrovascular reactivity after traumatic brain injury (TBI) may increase the susceptibility of the brain to secondary insults, including arterial hypotension. The purpose of this study was to evaluate the consequences of mild hemorrhagic hypotension on hemodynamic and histopathologic outcome after TBI. Intubated, anesthetized male rats were subjected to moderate (1.94 to 2.18 atm) parasagittal fluid-percussion (FP) brain injury. After TBI, animals were exposed to either normotension (group 1: TBI alone, n = 6) or hypotension (group 2: TBI + hypotension, n = 6). Moderate hypotension (60 mm Hg/30 min) was induced 5 minutes after TBI or sham procedures by hemorrhage. Sham-operated controls (group 3, n = 7) underwent an induced hypotensive period, whereas normotensive controls (group 4, n = 4) did not. For measuring regional cerebral blood flow (rCBF), radiolabeled microspheres were injected before, 20 minutes after, and 60 minutes after TBI (n = 23). For quantitative histopathologic evaluation, separate groups of animals were perfusion-fixed 3 days after TBI (n = 22). At 20 minutes after TBI, rCBF was bilaterally reduced by 57% +/- 6% and 48% +/- 11% in cortical and subcortical brain regions, respectively, under normotensive conditions. Compared with normotensive TBI rats, hemodynamic depression was significantly greater with induced hypotension in the histopathologically vulnerable (P1) posterior parietal cortex (P < 0.01). Secondary hypotension also increased contusion area at specific bregma levels compared with normotensive TBI rats (P < 0.05), as well as overall contusion volume (0.96 +/- 0.46 mm(3) vs. 2.02 +/- 0.51 mm(3), mean +/- SD, P < 0.05). These findings demonstrate that mild hemorrhagic hypotension after FP injury worsens local histopathologic outcome, possibly through vascular mechanisms.

Cortical spreading depression and migraine: new insights from imaging?

The possibility that spreading depression (SD) of cortical activity, a phenomenon observed in all vertebrates, causes the aura of migraine remains an open question in spite of nearly half a century of investigation. SD is also thought to be associated with the progressive neuronal injury observed during cerebral ischaemia. Thus, the ability to detect and investigate SD in humans might prove clinically significant. Animal studies of cortical spreading depression (CSD) have benefited greatly from the advent of relatively non-invasive imaging techniques. The use of these new imaging techniques for clinical studies will accelerate progress in this area of neurobiology.

Spinal cord blood flow changes following systemic hypothermia and spinal cord compression injury: an experimental study in the rat using Laser-Doppler flowmetry

STUDY DESIGN

It is well known that changes of the body temperature as well as trauma influence the blood flow in the brain and spinal cord. However, there is still a lack of knowledge concerning the levels of blood flow changes, especially during hypothermia.

OBJECTIVES

This investigation was carried out to examine the effects of systemic hypothermia and trauma on spinal cord blood flow (SCBF).

METHODS

Twenty-four rats were randomized either to thoracic laminectomy only (Th VII-IX) or to 35 g spinal cord compression trauma. The animals were further randomized to either constant normothermia (38 degrees C) or to a systemic cooling procedure, ie reduction of the esophageal temperature from 38 to 30 degrees C. SCBF was recorded 5 mm caudal to the injury zone using Laser-Doppler flowmetry which allows a non-invasive continuous recording of local changes in the blood flow. The autoregulation ability was tested at the end of the experiments by inducing a 30-50 mmHg blood-pressure fall, using blood-withdrawal from the carotid artery.

RESULTS

The mean SCBF decreased 2.8% and 3.5% per centigrade reduction of esophageal temperature in the animals sustained to hypothermia with and without trauma, respectively. This could be compared to a decrease of 0.2%/min when only trauma was applied. No significant differences were seen between the groups concerning auto regulatory ability.

CONCLUSIONS

Our results indicate that the core temperature has a high impact on the SCBF independent of previous trauma recorded by Laser-Doppler flowmetry. This influence exceeds the response mediated by moderate compression trauma alone.

The consequences of traumatic brain injury on cerebral blood flow and autoregulation: a review

In this decade, the brain argueably stands as one of the most exciting and challenging organs to study. Exciting in as far as that it remains an area of research vastly unknown and challenging due to the very nature of its anatomical design: the skull provides a formidable barrier and direct observations of intraparenchymal function in vivo are impractical. Moreover, traumatic brain injury (TBI) brings with it added complexities and nuances. The development of irreversible damage following TBI involves a plethora of biochemical events, including impairment of the cerebral vasculature, which render the brain at risk to secondary insults such as ischemia and intracranial hypertension. The present review will focus on alterations in the cerebrovasculature following TBI, and more specifically on changes in cerebral blood flow (CBF), mediators of CBF including local chemical mediators such as K+, pH and adenosine, endothelial mediators such as nitric oxide and neurogenic mediators such as catecholamines, as well as pressure autoregulation. It is emphasized that further research into these mechanisms may help attenuate the prevalence of secondary insults and therefore improve outcome following TBI.

Effect of cerebral perfusion pressure on contusion volume following impact injury

OBJECT

Although it is generally acknowledged that a sufficient cerebral perfusion pressure (CPP) is necessary for treatment of severe head injury, the optimum CPP is still a subject of debate. The purpose of this study was to investigate the effect of various levels of blood pressure and, thereby, CPP on posttraumatic contusion volume.

METHODS

The left hemispheres of 60 rats were subjected to controlled cortical impact injury (CCII). In one group of animals the mean arterial blood pressure (MABP) was lowered for 30 minutes to 80, 70, 60, 50, or 40 mm Hg 4 hours after contusion by using hypobaric hypotension. In another group of animals the MABP was elevated for 3 hours to 120 or 140 mm Hg 4 hours after contusion by administering dopamine. The MABP was not changed in respective control groups. Intracranial pressure (ICP) was monitored with an ICP microsensor. The rats were killed 28 hours after trauma occurred and contusion volume was assessed using hematoxylin and eosin-stained coronal slices. No significant change in contusion volume was caused by a decrease in MABP from 94 to 80 mm Hg (ICP 12+/-1 mm Hg), but a reduction of MABP to 70 mm Hg (ICP 9+/-1 mm Hg) significantly increased the contusion volume (p < 0.05). A further reduction of MABP led to an even more enlarged contusion volume. Although an elevation of MABP to 120 mm Hg (ICP 16+/-2 mm Hg) did not significantly affect contusion volume, there was a significant increase in the contusion volume at 140 mm Hg MABP (p < 0.05; ICP 18+/-1 mm Hg).

CONCLUSION

Under these experimental conditions, CPP should be kept within 70 to 105 mm Hg to minimize posttraumatic contusion volume. A CPP of 60 mm Hg and lower as well as a CPP of 120 mm Hg and higher should be considered detrimental.

Regional changes in cerebral extracellular glucose and lactate concentrations following severe cortical impact injury and secondary ischemia in rats

Traumatic brain injury (TBI) causes the brain to be more susceptible to secondary insults, and the occurrence of a secondary insult after trauma increases the damage that develops in the brain. To study the synergistic effect of trauma and ischemia on brain energy metabolites, regional changes in the extracellular concentrations of glucose and lactate following a severe cortical impact injury were measured employing a microdialysis technique. Three microdialysis probes were placed in center of the impact site, in an area adjacent to the impact site, and in the contralateral parietal cortex, and perfused with artificial cerebrospinal fluid (CSF) at 2 microl/min. Rats were assigned to one of the following experimental groups (n = 7 per group): (1) combined impact injury and secondary insult, (2) impact injury with sham secondary insult, (3) sham impact with secondary insult, or (4) sham impact and sham secondary insult. The impact injury was produced with a pneumatic impactor (5 m/sec, 3-mm deformation). One hour following the impact injury, a secondary insult was produced by bilateral carotid occlusion for 1 h. The impact injury resulted in a three- to fivefold global increase in dialysate lactate concentrations, with a corresponding fall in dialysate glucose concentration by 50% compared to no change in lactate or glucose concentrations in sham-injured animals (p < .0001 for both lactate and glucose). The secondary insult resulted in a second increase in dialysate lactate and decrease in dialysate glucose concentration that was significantly greater in the animals that had suffered the impact injury than in the sham-injured animals. Ischemia and traumatic injury have synergistic effects on lactate accumulation and on glucose depletion in the brain that probably reflects persisting ischemia, but may also indicate mitochondrial abnormalities and inhibition of oxidative metabolism.

CSF dynamics in a rodent model of closed head injury

Using ICP measurements and the bolus injection technique dynamic parameters of the cerebrospinal fluid system as there are pressure-volume-index (PVI) and resistance to CSF outflow (Rout) were investigated in a new model of diffuse closed head injury (CHI) in the rat. It was found that in the absence of brain oedema and ICP alterations an increase in PVI and Rout was present in the early (4h) period following head injury. This may be indicative for a reduction in cerebral blood flow and cerebral blood volume, both shown previously to occur after CHI. Furthermore an early impairment of CSF absorption mechanisms is evident. To answer the question, whether bolus injection techniques are advisable for clinical routine and whether results might have a predictive value, further investigations covering longer observation intervals and in the presence of secondary insults to the brain are necessary.

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

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

Posttraumatic cerebral ischemia after fluid percussion brain injury: an autoradiographic and histopathological study in rats

OBJECTIVES

Mild-to-moderate reductions in local cerebral blood flow (ICBF) have been reported to occur in rats after moderate (1.7-2.2 atm) fluid percussion brain injury. The purpose of this study was to determine whether evidence for severe ischemia (i.e., mean ICBF < 0.25 ml/g/min) could be demonstrated after severe brain injury. In addition, patterns of indium-labeled platelet accumulation and histopathological outcome were correlated with the hemodynamic alterations.

METHODS

Sprague-Dawley rats (n = 23), anesthetized with halothane and maintained on a 70:30 mixture of nitrous oxide:oxygen and 0.5% halothane, underwent normothermic (37 degrees C) parasagittal fluid percussion brain injury (2.4-2.6 atm). Indium-111-tropolone-labeled platelets were injected 30 minutes before traumatic brain injury (TBI), while 14C-iodoantipyrine was infused 30 minutes after trauma for ICBF determination. Sham-operated animals (n = 8) underwent similar surgical procedures but were not injured. For histopathological analysis, traumatized rats (n = 5) were perfusion-fixed 3 days after TBI.

RESULTS

In autoradiographic images of indium-labeled platelets, abnormal platelet accumulation that was most pronounced overlying the pial surface was commonly associated with severe reductions in ICBF within underlying cortical regions 30 minutes after TBI. For example, within the lateral parietal cortex, ICBF was significantly reduced from 1.67 +/- 0.11 ml/g per minute (mean +/- standard error of the mean) in sham-operated animals to 0.23 +/- 0.03 ml/g per minute within the traumatized group. In addition to focal severe ischemia, moderate reductions in ICBF were detected throughout the traumatized hemisphere, including the frontal and occipital cortices, hippocampus, thalamus, and striatum. Mild decreases in ICBF were also observed throughout the contralateral cerebral cortex. At 3 days after severe TBI, histopathology demonstrated intracerebral and subarachnoid hemorrhage associated with cerebral contusion and selective neuronal necrosis.

CONCLUSION

These data indicate that multiple cerebrovascular abnormalities, including subarachnoid hemorrhage, focal platelet accumulation, and severe ischemia, are important early events in the pathogenesis of cortical contusion formation after TBI. Injury severity is expected to be a critical factor in determining what therapeutic strategies are attempted in the clinical setting.

The Dorothy Russell Memorial Lecture. The molecular and cellular sequelae of experimental traumatic brain injury: pathogenetic mechanisms

The mechanisms underlying secondary or delayed cell death following traumatic brain injury (TBI) are poorly understood. Recent evidence from experimental models of TBI suggest that diffuse and widespread neuronal damage and loss is progressive and prolonged for months to years after the initial insult in selectively vulnerable regions of the cortex, hippocampus, thalamus, striatum, and subcortical nuclei. The development of new neuropathological and molecular techniques has generated new insights into the cellular and molecular sequelae of brain trauma. This paper will review the literature suggesting that alterations in intracellular calcium with resulting changes in gene expression, activation of reactive oxygen species (ROS), activation of intracellular proteases (calpains), expression of neurotrophic factors, and activation of cell death genes (apoptosis) may play a role in mediating delayed cell death after trauma. Recent data suggesting that TBI should be considered as both an inflammatory and/or a neurodegenerative disease is also presented. Further research concerning the complex molecular and neuropathological cascades following brain trauma should be conducted, as novel therapeutic strategies continue to be developed.

Recent advances in mechanisms of spreading depression

Although spreading depression has been known for over 50 years, recent research into this interesting experimental phenomenon provides evidence for an integrative role of spreading depression in brain pathophysiology. Spreading depression activates neurophysiological pathways that may have widespread consequences on brain function, but depends on the basal energy state of the brain.

Protective effects of aptiganel HCl (Cerestat) following controlled cortical impact injury in the rat

Recent studies have demonstrated a neuroprotective effect of the noncompetitive N-methyl-D-aspartate receptor antagonist aptiganel HCl (Cerestat) in focal cerebral ischemia. In the present study, we investigated the protective ability of aptiganel HCl after controlled cortical impact injury (impact depth = 2 mm; impactor velocity = 7 mm/sec) of the left temporoparietal cortex in rats. Intravenous aptiganel HCl (2 mg/kg) or a respective volume of vehicle was injected 15 min after trauma. Animals were sacrificed 24 h after trauma. Contusion volume was measured planimetrically from hematoxylin-eosin-stained coronal slices. Hemispheric swelling and water content were determined gravimetrically. Thirty minutes before sacrifice, a Codman intracranial pressure (ICP) probe was placed in the right hemisphere, and ICP as well as mean arterial blood pressure (MABP) and cerebral perfusion pressure (CPP) were monitored. Aptiganel HCl reduced contusion volume by 13.6% in treated rats (p < 0.05). Hemispheric swelling was also significantly diminished by 31.5% in accordance to a decrease in hemispheric water content (controls, 82.78 +/- 0.12%, vs. aptiganel HCl, 82.30 +/- 0.18%, p < 0.05). Posttraumatic ICP was not significantly lower in the aptiganel HCl treated animals (25.5 +/- 2.4 mm Hg vs. 32.0 +/- 2.7 mm Hg, p = 0.096). MABP was found to be higher in the treatment group 24 h after injury (107.8 +/- 3.6 mm Hg vs. 89.9 +/- 2.4 mm Hg, p < 0.001), resulting in a higher CPP (82.6 +/- 4.2 mm Hg vs. 57.2 +/- 4.6 mm Hg, p < 0.05). Taken together, aptiganel HCl exerts various beneficial effects following experimental traumatic brain injury. It decreases contusion volume and hemispheric swelling as well as water content. Thus, this drug appears promising for further clinical trials in brain trauma.

Cholinergic modulation of cerebral cortical blood flow changes induced by trauma

These experiments tested the role of cholinergic mechanisms in the changes of cerebral cortical blood flow (CBF) induced by brain trauma. CBF was measured with Iodo-14C-antipyrine autoradiography, in 128 cerebral cortex regions of both hemispheres, distributed in eight coronal slices. The effects of a 6.3-mm diameter craniotomy over the left motor-sensory cortex with no weight drop, and of trauma (drop weight of 20 g from 30 cm height on left motor-sensory cortex through a 6.3 mm circular craniotomy) on CBF were studied at 2 and 24 h after the interventions. A group of control animals that received no intervention was also set up. Animals were treated with the cholinesterase inhibitor physostigmine salicylate (3.3 microg/kg/min i.v. infusion started 60 min before CBF measurements), the cholinergic blocker scopolamine hydrobromide (1 mg/kg i.v. pulse, 18 min before CBF measurements), or with the drugs vehicle (saline). A focus of decreased CBF at the site of impact was observed 2 h after trauma, extending caudally as far as the occipital cortex. CBF on the contralateral cerebral cortex was also decreased. Both phenomena reversed partially at 24 h. This spontaneous recovery of CBF was blocked by scopolamine. Physostigmine reversed the decrease in CBF of the traumatized cortex, partially around the contused area and completely in more distant regions. The cerebral cortex contralateral to the trauma showed significantly higher CBF 24 h after trauma when compared to intact controls or craniotomy that peaked at the area symmetrical to the center of trauma. This phenomenon was also enhanced by physostigmine and completely blocked by scopolamine. These results suggest a prominent role of cholinergic mechanisms in the vascular adjustments that accompany cerebral trauma.

Mitochondrial dysfunction and calcium perturbation induced by traumatic brain injury

Traumatic brain injury (TBI) is associated with primary and secondary injury. A thorough understanding of secondary injury will help to develop effective treatments and improve patient outcome. In this study, the GM model of controlled cortical impact injury (CCII) of Lighthall (1988) was used with modification to induce lateral TBI in rats. Forebrain mitochondria isolated from ipsilateral (IH) and contralateral (CH) hemispheres to impact showed a distinct difference. With glutamate + malate as substrates, mitochondria from the IH showed a significant decrease in State 3 respiratory rates, respiratory control indices (RCI), and P/O ratios. This decrease occurred as early as 1 h and persisted for at least 14 days following TBI. The State 3 respiratory rates, RCI, and P/O ratios could be restored to sham values by the addition of EGTA to the assay mixture. A significant amount of Ca2+ was found to be adsorbed to the mitochondria of both the IH and the CH with higher values seen in the IH. The rate of energy-linked Ca2+ transport in the IH was significantly decreased at 6 and 12 h. These data indicate that CCII-induced TBI perturbs cellular Ca2+ homeostasis and results in excessive Ca2+ adsorption to the mitochondrial membrane, which subsequently inhibits the respiratory chain-linked electron transfer and energy transduction.