Andrew Beaumont

N-Acetylaspartate reduction as a measure of injury severity and mitochondrial dysfunction following diffuse traumatic brain injury

N-Acetylaspartate (NAA) is considered a neuron-specific metabolite and its reduction a marker of neuronal loss. The objective of this study was to evaluate the time course of NAA changes in varying grades of traumatic brain injury (TBI), in concert with the disturbance of energy metabolites (ATP). Since NAA is synthesized by the mitochondria, it was hypothesized that changes in NAA would follow ATP. The impact acceleration model was used to produce three grades of TBI. Sprague-Dawley rats were divided into the following four groups: sham control (n = 12); moderate TBI (n = 36); severe TBI (n = 36); and severe TBI coupled with hypoxia-hypotension (n = 16). Animals were sacrificed at different time points ranging from 1 min to 120 h postinjury, and the brain was processed for high-performance liquid chromatography (HPLC) analysis of NAA and ATP. After moderate TBI, NAA reduced gradually by 35% at 6 h and 46% at 15 h, accompanied by a 57% and 45% reduction in ATP. A spontaneous recovery of NAA to 86% of baseline at 120 h was paralleled by a restoration in ATP. In severe TBI, NAA fell suddenly and did not recover, showing critical reduction (60%) at 48 h. ATP was reduced by 70% and also did not recover. Maximum NAA and ATP decrease occurred with secondary insult (80% and 90%, respectively, at 48 h). These data show that, at 48 h post diffuse TBI, reduction of NAA is graded according to the severity of insult. NAA recovers if the degree of injury is moderate and not accompanied by secondary insult. The highly similar time course and correlation between NAA and ATP supports the notion that NAA reduction is related to energetic impairment.

The Permissive Nature of Blood Brain Barrier (BBB) Opening in Edema Formation Following Traumatic Brain Injury

The contribution of blood brain barrier opening to traumatic brain edema is not known. This study compares the course of traumatic BBB disruption and edema formation, with the hypothesis that they are not obligately related. Sprague-Dawley rats were divided into three groups: Group A (n = 47)--Impact Acceleration (IAM); Group B (n = 104)--lateral cortical impact (CCI); Group C (n = 26)--IAM + hypoxia & hypotension (THH). BBB integrity was assessed using i.v. markers (Evans Blue, or gadolinium-DTPA). Edema formation was evaluated with gravimetry, and T1-weighted MRI. In IAM, BBB opened immediately but closed rapidly, and remained closed for at least the next 36 hours whilst 24-hour hemispheric water content (HWC) rose by 0.9% (p < 0.01). In CCI, BBB opened in both hemispheres for up to 4 hours; four hour HWC in the uninjured hemisphere was indistinguishable from Sham, where HWC in the injured hemisphere rose by approximately 1.5% (p < 0.005). We distinguished two THH animals based on Apparent Diffusion Coefficient (ADC) recovery: in ADC-recovery animals 4 hour cortical water content (CWC) was 80.4 +/- 0.6%, cf 81.4 +/- 1.3% in ADC-non-recovery (p < 0.05). In all animals the BBB was open, however two populations of permeability were seen which likely related to flow-limited extravasation of gadolinium. In IAM edema forms despite only brief BBB opening. Although there is diffuse BBB opening with lateral contusion, edema only forms in the injured hemisphere. In THH, edema formation in the face of a widely permeable barrier is driven by ADC changes or cell swelling. Edema formation clearly does not correspond with BBB opening and an open BBB is clearly not required for edema formation. However we hypothesize that a permeable BBB permissively worsens the process, by acting as a low resistance pathway for ion and water movement. These findings are consistent with our general hypothesis that edema formation after TBI is mainly cytotoxic.

The impact-acceleration model of head injury: injury severity predicts motor and cognitive performance after trauma.

This study examines neuropsychological dysfunction after varying severities of the Impact Acceleration Model of diffuse traumatic brain injury. Adult rats (340 g-400 g) were divided into five groups, and exposed to varying degrees of Impact Acceleration Injury (1 m, 2 m, 2.1 m/500 g and second insult). After injury, animals were allowed to recover; acute neurological reflexes, beam walk score, beam balance score, inclined plane score, and Morris Water Maze score were then assessed at multiple time points. Injury of all severities caused significant motor and cognitive deficits. With milder injuries these effects were transient; however, with more severe injuries no recovery in function was seen. The addition of hypoxia and hypotension made a moderate injury worse than a severe injury. The acute neurological reflexes, the beam balance test and the inclined plane test distinguished between the more severely injured groups, but were affected less by mild injury. The beam walk test was sensitive to mild injury, but appeared unable to distinguish between the severe groups. The Morris Water Maze was sensitive for all injury groups, but appeared to adopt a different response profile with secondary insult. This study has for the first time characterized the degree of motor and cognitive deficits in rodents exposed to differing severities of Impact Acceleration Injury. These data confirm that the tests considered, and the Injury Model used, provide a useful system for the consideration of potential therapies which might ameliorate neuropsychological deficits in diffuse brain injury.

Secondary Insults Worsen Blood Brain Barrier Dysfunction Assessed by MRI in Cerebral Contusion

OBJECT Understanding the cause of post-traumatic intracranial hypertension requires information about the pathophysiology of edema formation. Secondary insults are known to exacerbate edema formation following experimental contusion, however the influence of these insults on blood brain barrier (BBB) integrity is not known. This study non-invasively assesses the influence of hypoxia and hypotension on BBB permeability following experimental cortical contusion. METHODS Sprague-Dawley rats (350-380 g) were divided into three groups. Group A: (n = 3) Sham, Group B (n = 8) focal injury (controlled cortical impact 6.0 m/sec, 3 mm depth), Group C (n = 8), focal injury with secondary insult. Cortical BBB integrity was assessed four hours post-trauma using an i.v. bolus of 0.2 mmol/kg Gd-DTPA with serial T1 MR images, over 30 minutes. Absolute tissue concentrations of Gd were measured empirically using known references. The time course of accumulation was analyzed with respect to BBB permeability. RESULTS BBB permeability was greatest in the site of contusion, and Gd accumulation was greatly enhanced by secondary insult (p < 0.01). Regions of lowest ADC and maximal swelling correlated with regions of maximal BBB permeability (p < 0.05). CONCLUSIONS Secondary insults enhance BBB dysfunction in contusion. Positive relationships between low ADC, tissue swelling and BBB dysfunction suggest synergy between underlying cytotoxic swelling and BBB permeability in contusion. These data also suggest that restoration of BBB integrity after injury may be an energy dependent process. These findings have important implications for the pathophysiology of ICP elevations following cerebral contusion.

Acute subdural hematoma associated with diffuse brain injury and hypoxemia in the rat: effect of surgical evacuation of the hematoma.

The aim of this study was to assess the effect of rapid or delayed surgical evacuation on the physiological consequence and brain edema formation in a rat model of acute subdural hematoma (SDH) coupled with either diffuse brain injury (DBI) or hypoxemia. The SDH was made by an autologous blood injection, while DBI was induced using the impact acceleration model (mild, 450 g/1 m; severe, 450 g/2 m). Physiological parameters measured included intracranial pressure (ICP), mean arterial blood pressure (MABP), cerebral blood flow (CBF), and brain tissue water content. At 1 h (rapid evacuation) or 4 h (delayed evacuation) after the SDH induction, surgical evacuation following a craniotomy was performed using saline irrigation and forceps. The study consisted of three different series, including 400 microL of SDH alone (Series 1), SDH400 + mild DBI (Series 2), and SDH300 + severe DBI + 20 min hypoxemia (Series 3). The hypoxemia was added in Group 3 to produce a steadily increasing ICP. In Series 1 and 2, all rats were randomized into the three following groups: non-, rapid, and delayed evacuation; Series 3 had two groups: non- and rapid evacuation. In Series 1, the surgical evacuation showed no beneficial effects on the brain edema formation assessed at 5 h post-injury. In Series 2, the rapid, but not delayed, evacuation significantly reduced both the increased ICP level and brain water content. The additional insult of hypoxemia (Series 3) resulted in a progressive ICP elevation, persistently depressed CBF, and severe brain swelling. Under this situation, the rapid evacuation exacerbated brain edema. These results have clinical implications for the management of severe traumatic SDH, especially its operative indication and timing.

A new rat model of diffuse brain injury associated with acute subdural hematoma: Assessment of varying hematoma volume, insult severity, and the presence of hypoxemia

The aim of this study was to develop a new rat model of diffuse brain injury (DBI) associated with acute subdural hemorrhage (SDH). In order to make this model more clinically relevant, we determined whether the varying hematoma volume, severity of DBI, or the presence of hypoxemia could influence the physiological consequence. SDH was made by an autologous blood injection, while DBI was induced using the impact acceleration model (mild, 450 g/1 m, severe, 450 g/2 m). Physiological parameters measured included intracranial pressure (ICP), mean arterial blood pressure (MABP), cerebral blood flow (CBF), and brain tissue water content. In the first series, 23 rats were randomized into the five following groups: Group 1, sham; Group 2, 400 (microL SDH; Group 3, SDH400 + mild DBI; Group 4, SDH400 + severe DBI; and Group 5, SDH300 + severe DBI. Results suggested that SDH300 + severe DBI (Group 5) may be the most suitable model, in which the MABP and CBF temporarily decreased during the SDH induction, but thereafter recovered to the baseline. Conversely, ICP was persistently elevated throughout the experiment. The water content was also significantly higher in both hemispheres compared to that of sham. In the second series, the animal was exposed to a hypoxemic insult (10 or 30 min) in addition to SDH300 + severe DBI (Group 6). The prolonged hypoxemia caused both a severe CBF reduction without recovery and a bilateral brain swelling, whereas the brief hypoxemia showed a gradual CBF recovery from the transient reduction and an increased water content only in the SDH side. These results suggest that these models may be potentially useful to study the combination of DBI and SDH with or without hypoxemia.

The effects of human corticotrophin releasing factor on motor and cognitive deficits after impact acceleration injury.

Abstract Corticotrophin releasing factor has been shown in several models of tissue injury to be an effective treatment for edema. In a previous study we demonstrated this ability in two models of traumatic brain injury (TBI). The aim of this study was to assess whether human corticotrophin releasing factor (hCRF) could additionally improve motor and cognitive deficits. Adult male Sprague-Dawtey rats were randomised into five groups and injured with the Impact Acceleration Model of TBI. Groups I and II received sham injury followed by treatment with either drug vehicle or 100 γg kg-1 hCRF respectively. Group III was injured with no treatment; Group IV animals were injured and treated with 50 γg kg-1 hCRF and Group V were injured and treated with 100 γg kg-1. Animals were assessed both before and after injury with a battery of standardised neuropsychological tests including the Morris Water Maze, the Beam Walk Test, the Beam Balance Test and the Inclined Plane Test. Both 50 γg kg-1 and 100 γg kg-1 hCRF caused significant improvements in motor and cognitive functioning, confirming that in addition to edema-reducing properties, human corticotrophin releasing factor is also capable of improving motor and cognitive functioning. Given the beneficial experimental effects of this compound, hCRF may be a useful clinical treatment, which requires formal evaluation. [Neurol Res 2000; 22: 665-673]

Characterizing Edema Associated with Cortical Contusion and Secondary Insult Using Magnetic Resonance Spectroscopy

It is traditionally believed that edema associated with brain contusion is vasogenic. The objective of this study was to quantify and characterize the edema in cortical contusion coupled with early hypoxia and hypotension. Sprague-Dawley rats were randomised into six groups: Sham, Trauma moderate (Tm), Trauma severe (Ts), Hypoxia and Hypotension (HH), Tm and Ts with HH (THHm; THHs). Trauma was induced with controlled cortical impact; associated secondary insults lasted 30 minutes. Water content was measured using tissue longitudinal relaxation time (T1). Apparent diffusion coefficient of water (ADC) was calculated from diffusion-weighted imaging and single voxel spectroscopy. In the trauma groups ICP increased at 30 minutes post trauma (p < 0.05) and then gradually decreased. Only in the THH groups, ICP showed a trend to continually rise. No ICP variations were seen in the others groups. The increase in water content at 4 hours post trauma was inversely related to ADC variation (p < 0.0001). A significant increase in water content with low ADC, developed in the injured region in Ts, THHm (p < 0.05) and THHs (p < 0.01) compared to Sham. Intracellular water rose in the whole brain in THH groups although more severely in the THHs (p < 0.01). Immediately after trauma ADC fell in the THH groups, but gradually increased in the THHm, whereas there was no recovery in THHs. The results indicate that the type of edema in the injured area, with and without superimposed secondary insult, is predominantly cytotoxic (cellular). Moreover, secondary insults act synergistically with focal injury to increase cellular water in both injured tissue and remote regions.

Diffuse brain injury complicated by acute subdural hematoma in the rodents: the effect of early or delayed surgical evacuation.

Of all the possible clinical factors affecting the outcome of patients suffering acute subdural hematomas (SDH), timing of surgical evacuation is certainly the most debated. The purpose of this study was to develop an experimental model able to reproduce the clinical behavior of post-traumatic SDH as observed in head injured patients. We present a novel model of SDH combined with diffuse brain injury (DBI), and investigate the effects of early and delayed surgical evacuation. Following Impact Acceleration DBI, adult Sprague-Dawley rats were given a 400 microliters SDH. Hematoma was then evacuated at one (rapid evacuation) or four hours (delayed evacuation) post-injury. Physiological parameters were measured for 5 hours, followed by the assessment of brain water content. In this experimental model, there is strong evidence that trauma acts synergistically with SDH enhancing brain edema formation and increasing ICP. In absence of secondary insult, rapid evacuation of traumatic SDH limits exposure to high ICP, reduces brain edema and is beneficial.

The Synergistic Effect of Acute Subdural Hematoma Combined with Diffuse Traumatic Brain Injury on Brain Edema

It is well-documented that acute subdural hematoma (ASDH) following diffuse traumatic brain injury (dTBI) contributes to severe disability and high mortality. The objective of this study was to characterize edema formation in a model of ASDH and ASDH following dTBI. Eighteen Sprague-Dawley rats were separated into three groups: Sham operated (n = 6), ASDH (n = 6), ASDH following dTBI (n = 6). Diffuse TBI was produced via the Impact-Acceleration Model [10]. ASDH was induced in the left hemisphere using the well-described method [11]. Total tissue water content was determined 4 hours after TBI utilizing wet-weight/dry-weight assessment. Our results show that ASDH causes a significant increase in tissue water content in the left hemisphere (79.2 +/- 0.7%) compared with the contralateral hemisphere (78.5 +/- 0.5%, p = 0.009). Animals exposed to ASDH following dTBI had significantly greater edema formation than those with ASDH (right: 80.9 +/- 0.4%, left: 80.5 +/- 0.7, p = 0.008). There was no significant difference between the left and right hemisphere. We conclude that edema formation in ASDH is worsened by the combination of dTBI and ASDH. Furthermore a diffuse and focal injury in combination retain the features of the diffuse injury, but with increased severity. Further studies are required to elucidate the synergistic mechanisms involved in these pathological processes.