Role of excitatory amino acid-mediated ionic fluxes in traumatic brain injury

Metabolic fate of glucose in rats with traumatic brain injury and pyruvate or glucose treatments: A NMR spectroscopy study

Administration of sodium pyruvate (SP; 9.08 μmol/kg, i.p.), ethyl pyruvate (EP; 0.34 μmol/kg, i.p.) or glucose (GLC; 11.1 μmol/kg, i.p.) to rats after unilateral controlled cortical impact (CCI) injury has been reported to reduce neuronal loss and improve cerebral metabolism. In the present study these doses of each fuel or 8% saline (SAL; 5.47 nmoles/kg) were administered immediately and at 1, 3, 6 and 23 h post-CCI. At 24 h all CCI groups and non-treated Sham injury controls were infused with [1,2 ¹³C] glucose for 68 min ¹³C nuclear magnetic resonance (NMR) spectra were obtained from cortex + hippocampus tissues from left (injured) and right (contralateral) hemispheres. All three fuels increased lactate labeling to a similar degree in the injured hemisphere. The amount of lactate labeled via the pentose phosphate and pyruvate recycling (PPP + PR) pathway increased in CCI-SAL and was not improved by SP, EP, and GLC treatments. Oxidative metabolism, as assessed by glutamate labeling, was reduced in CCI-SAL animals. The greatest improvement in oxidative metabolism was observed in animals treated with SP and fewer improvements after EP or GLC treatments. Compared to SAL, all three fuels restored glutamate and glutamine labeling via pyruvate carboxylase (PC), suggesting improved astrocyte metabolism following fuel treatment. Only SP treatments restored the amount of [4 ¹³C] glutamate labeled by the PPP + PR pathway to sham levels. Milder injury effects in the contralateral hemisphere appear normalized by either SP or EP treatments, as increases in the total pool of ¹³C lactate and labeling of lactate in glycolysis, or decreases in the ratio of PC/PDH labeling of glutamine, were found only for CCI-SAL and CCI-GLC groups compared to Sham. The doses of SP, EP and GLC examined in this study all enhanced lactate labeling and restored astrocyte-specific PC activity but differentially affected neuronal metabolism after CCI injury. The restoration of astrocyte metabolism by all three fuel treatments may partially underlie their abilities to improve cerebral glucose utilization and to reduce neuronal loss following CCI injury.

Recurrent coma and fever in familial hemiplegic migraine type 2. A prospective 15-year follow-up of a large family with a novel ATP1A2 mutation

Background Familial hemiplegic migraine (FHM) is a rare monogenic migraine subtype characterised by attacks associated with transient motor weakness. Clinical information is mainly based on reports of small families with only short follow-up. Here, we document a prospective 15-year follow-up of an extended family with FHM type 2. Patients and methods After diagnosing FHM in a patient with severe attacks associated with coma and fever, we identified eight more family members with FHM and one with possible FHM. All family members were prospectively followed for 15 years. In total 13 clinically affected and 21 clinically non-affected family members were genetically tested and repeatedly investigated. Results A novel p.Arg348Pro ATP1A2 mutation was found in 14 family members: 12 with clinical FHM, one with psychomotor retardation and possible FHM, and one without FHM features. In 9/12 (75%) family members with genetically confirmed FHM, attacks were severe, long-lasting, and often associated with impaired consciousness and fever. Such attacks were frequently misdiagnosed and treated as viral meningitis or stroke. Epilepsy was reported in three family members with FHM and in the one with psychomotor retardation and possible FHM. Ataxia was not observed. Conclusion FHM should be considered in patients with recurrent coma and fever.

Miro1 Regulates Activity-Driven Positioning of Mitochondria within Astrocytic Processes Apposed to Synapses to Regulate Intracellular Calcium Signaling

It is fast emerging that maintaining mitochondrial function is important for regulating astrocyte function, although the specific mechanisms that govern astrocyte mitochondrial trafficking and positioning remain poorly understood. The mitochondrial Rho-GTPase 1 protein (Miro1) regulates mitochondrial trafficking and detachment from the microtubule transport network to control activity-dependent mitochondrial positioning in neurons. However, whether Miro proteins are important for regulating signaling-dependent mitochondrial dynamics in astrocytic processes remains unclear. Using live-cell confocal microscopy of rat organotypic hippocampal slices, we find that enhancing neuronal activity induces transient mitochondrial remodeling in astrocytes, with a concomitant, transient reduction in mitochondrial trafficking, mediated by elevations in intracellular Ca(2+). Stimulating neuronal activity also induced mitochondrial confinement within astrocytic processes in close proximity to synapses. Furthermore, we show that the Ca(2+)-sensing EF-hand domains of Miro1 are important for regulating mitochondrial trafficking in astrocytes and required for activity-driven mitochondrial confinement near synapses. Additionally, activity-dependent mitochondrial positioning by Miro1 reciprocally regulates the levels of intracellular Ca(2+) in astrocytic processes. Thus, the regulation of intracellular Ca(2+) signaling, dependent on Miro1-mediated mitochondrial positioning, could have important consequences for astrocyte Ca(2+) wave propagation, gliotransmission, and ultimately neuronal function.

The HMGB1-RAGE Inflammatory Pathway: Implications for Brain Injury-Induced Pulmonary Dysfunction

SIGNIFICANCE

Deceased patients who have suffered severe traumatic brain injury (TBI) are the largest source of organs for lung transplantation. However, due to severely compromised pulmonary lung function, only one-third of these patients are eligible organ donors, with far fewer capable of donating lungs (∼ 20%). As a result of this organ scarcity, understanding and controlling the pulmonary pathophysiology of potential donors are key to improving the health and long-term success of transplanted lungs.

RECENT ADVANCES

Although the exact mechanism by which TBI produces pulmonary pathophysiology remains unclear, it may be related to the release of damage-associated molecular patterns (DAMPs) from the injured tissue. These heterogeneous, endogenous host molecules can be rapidly released from damaged or dying cells and mediate sterile inflammation following trauma. In this review, we highlight the interaction of the DAMP, high-mobility group box protein 1 (HMGB1) with the receptor for advanced glycation end-products (RAGE), and toll-like receptor 4 (TLR4).

CRITICAL ISSUES

Recently published studies are reviewed, implicating the release of HMGB1 as producing marked changes in pulmonary inflammation and physiology following trauma, followed by an overview of the experimental evidence demonstrating the benefits of blocking the HMGB1-RAGE axis.

FUTURE DIRECTIONS

Targeting the HMGB1 signaling axis may increase the number of lungs available for transplantation and improve long-term benefits for organ recipient patient outcomes.

Traumatic brain injury in vivo and in vitro contributes to cerebral vascular dysfunction through impaired gap junction communication between vascular smooth muscle cells

Gap junctions (GJs) contribute to cerebral vasodilation, vasoconstriction, and, perhaps, to vascular compensatory mechanisms, such as autoregulation. To explore the effects of traumatic brain injury (TBI) on vascular GJ communication, we assessed GJ coupling in A7r5 vascular smooth muscle (VSM) cells subjected to rapid stretch injury (RSI) in vitro and VSM in middle cerebral arteries (MCAs) harvested from rats subjected to fluid percussion TBI in vivo. Intercellular communication was evaluated by measuring fluorescence recovery after photobleaching (FRAP). In VSM cells in vitro, FRAP increased significantly (p<0.05 vs. sham RSI) after mild RSI, but decreased significantly (p<0.05 vs. sham RSI) after moderate or severe RSI. FRAP decreased significantly (p<0.05 vs. sham RSI) 30 min and 2 h, but increased significantly (p<0.05 vs. sham RSI) 24 h after RSI. In MCAs harvested from rats 30 min after moderate TBI in vivo, FRAP was reduced significantly (p<0.05), compared to MCAs from rats after sham TBI. In VSM cells in vitro, pretreatment with the peroxynitrite (ONOO(-)) scavenger, 5,10,15,20-tetrakis(4-sulfonatophenyl)prophyrinato iron[III], prevented RSI-induced reductions in FRAP. In isolated MCAs from rats treated with the ONOO(-) scavenger, penicillamine, GJ coupling was not impaired by fluid percussion TBI. In addition, penicillamine treatment improved vasodilatory responses to reduced intravascular pressure in MCAs harvested from rats subjected to moderate fluid percussion TBI. These results indicate that TBI reduced GJ coupling in VSM cells in vitro and in vivo through mechanisms related to generation of the potent oxidant, ONOO(-).

Real-time optical diagnosis of the rat brain exposed to a laser-induced shock wave: observation of spreading depolarization, vasoconstriction and hypoxemia-oligemia

Despite many efforts, the pathophysiology and mechanism of blast-induced traumatic brain injury (bTBI) have not yet been elucidated, partially due to the difficulty of real-time diagnosis and extremely complex factors determining the outcome. In this study, we topically applied a laser-induced shock wave (LISW) to the rat brain through the skull, for which real-time measurements of optical diffuse reflectance and electroencephalogram (EEG) were performed. Even under conditions showing no clear changes in systemic physiological parameters, the brain showed a drastic light scattering change accompanied by EEG suppression, which indicated the occurrence of spreading depression, long-lasting hypoxemia and signal change indicating mitochondrial energy impairment. Under the standard LISW conditions examined, hemorrhage and contusion were not apparent in the cortex. To investigate events associated with spreading depression, measurement of direct current (DC) potential, light scattering imaging and stereomicroscopic observation of blood vessels were also conducted for the brain. After LISW application, we observed a distinct negative shift in the DC potential, which temporally coincided with the transit of a light scattering wave, showing the occurrence of spreading depolarization and concomitant change in light scattering. Blood vessels in the brain surface initially showed vasodilatation for 3-4 min, which was followed by long-lasting vasoconstriction, corresponding to hypoxemia. Computer simulation based on the inverse Monte Carlo method showed that hemoglobin oxygen saturation declined to as low as ∼35% in the long-term hypoxemic phase. Overall, we found that topical application of a shock wave to the brain caused spreading depolarization/depression and prolonged severe hypoxemia-oligemia, which might lead to pathological conditions in the brain. Although further study is needed, our findings suggest that spreading depolarization/depression is one of the key events determining the outcome in bTBI. Furthermore, a rat exposed to an LISW(s) can be a reliable laboratory animal model for blast injury research.

Postconcussion syndrome: a review of pathophysiology and potential nonpharmacological approaches to treatment

The incidence of all-cause concussions in the United States is estimated to range from 1.6 to 3.8 million annually, with the reported number of sport- or recreation-related concussions increasing dramatically, especially in youth sports.(1,2) Additionally, the use of roadside bombs in Iraq and Afghanistan has propelled the incidence of concussion and other traumatic brain injuries to the highest levels ever encountered by the US military. As a result, there has also been a marked increase in postconcussion syndrome (PCS) and the associated cognitive, emotional, and memory disabilities associated with the condition. Unfortunately, however, there have been no significant advancements in the understanding or treatment of PCS for decades. The current management of PCS mainly consists of rest, reduction of sensory inputs, and treating symptoms as needed. Recently, researchers investigating the underlying mechanisms of PCS have proposed that activation of the immune inflammatory response may be an underlying pathophysiology that occurs in those who experience prolonged symptoms after a concussion. This article reviews the literature and summarizes the immune inflammatory response known as immunoexcitotoxicity. This article also discusses the use of nonpharmacological agents for the management of PCS that directly address this underlying mechanism.

Spontaneous cortical spreading depression and intracranial pressure following acute subdural hematoma in a rat

Acute subdural hemorrhage (ASDH) is a frequent and devastating consequence of traumatic brain injury. Tissue damage develops rapidly and makes treatment even more difficult. Management of increased intracranial pressure (ICP) due to extravasated blood volume and brain swelling is often insufficient to control all adverse effects of ASDH. In addition to sheer volume, spontaneously triggered cortical spreading depression (CSD) that leads to cell death following ischemia or trauma may contribute to injury development after ASDH. Therefore, we explored the occurrence of CSD by tissue impedance (IMP) measurement in a rat model subjected to ASDH. IMP and intraventricular and mean arterial pressure were monitored before (baseline), during (blood infusion), and after ASDH for 3 h.Tissue impedance increased by around 203% of baseline during subdural infusion of 300 μl of autologous, venous blood and dropped back to baseline within 22 min. Fifty-six minutes after the start of ASDH a cluster of four short-lasting (3-3.5 min; 140-160% of baseline) IMP increases started that reflected spontaneous CSDs. This pattern presumes that CSD occurs early after ASDH and therefore may contribute to the rapid lesion development in this disease.

Ketogenic diet prevents alterations in brain metabolism in young but not adult rats after traumatic brain injury

Previous studies have shown that the change of cerebral metabolic rate of glucose (CMRglc) in response to traumatic brain injury (TBI) is different in young (PND35) and adult rats (PND70), and that prolonged ketogenic diet treatment results in histological and behavioral neuroprotection only in younger rat brains. However, the mechanism(s) through which ketones act in the injured brain and the biochemical markers of their action remain unknown. Therefore, the current study was initiated to: 1) determine the effect of injury on the neurochemical profile in PND35 compared to PND70 rats; and 2) test the effect of early post-injury administration of ketogenic diet on brain metabolism in PND35 versus PND70 rats. The data show that alterations in energy metabolites, amino acid, and membrane metabolites were not evident in PND35 rats on standard diet until 24  h after injury, when the concentration of most metabolites was reduced from sham-injured values. In contrast, acute, but transient deficits in energy metabolism were measured at 6  h in PND70 rats, together with deficits in N-acetylaspartate that endured until 24  h. Administration of a ketogenic diet resulted in significant increases in plasma β-hydroxybutyrate (βOHB) levels. Similarly, brain βOHB levels were significantly elevated in all injured rats, but were elevated by 43% more in PND35 rats compared to PND70 rats. As a result, ATP, creatine, and phosphocreatine levels at 24  h after injury were significantly improved in the ketogenic PND35 rats, but not in the PND70 group. The improvement in energy metabolism in the PND35 brains was accompanied by the recovery of NAA and reduction of lactate levels, as well as amelioration of the deficits of other amino acids and membrane metabolites. These results indicate that the PND35 brains are more resistant to the injury, indicated by a delayed deficit in energy metabolism. Moreover, the younger brains revert to ketones metabolism more quickly than do the adult brains, resulting in better neurochemical and cerebral metabolic recovery after injury.

Aging-related alterations in the expression and distribution of GluR2 and PICK1 in the rat hippocampus

Deficit in synaptic plasticity in the hippocampus frequently occurs during normal aging. Although the protein level and calcium permeability of AMPARs alter with aging, the alteration of AMPARs and their regulatory proteins during aging are far from understanding. Dynamics of GluR2 subunit are dependent on the function of protein interacting with Cα kinase 1 (PICK1), PKCα and calcineurin (CaN). Here, we firstly show that the expression of PICK1 and CaN B decreased significantly in the hippocampus of old rats compared to that of young and adult rats. The decrease was accompanied by a reduction of GluR2 and PKCα and an increase in CaN A. Next, we found that in young and adult rats, the distribution of PICK1 and GluR2 diffused in the cytoplasm of hippocampal neurons, but closely around perinuclear in the hippocampal neurons of old rats. These results suggest that the expression of GluR2, PICK1, PKCα and CaN B significant decreased in the hippocampus and these alterations may lead to altered distribution of GluR2 and PICK1 during aging.

Metabolic and histologic effects of sodium pyruvate treatment in the rat after cortical contusion injury

This study determined the effects of intraperitoneal sodium pyruvate (SP) treatment on the levels of circulating fuels and on cerebral microdialysis levels of glucose (MD(glc)), lactate (MD(lac)), and pyruvate (MD(pyr)), and the effects of SP treatment on neuropathology after left cortical contusion injury (CCI) in rats. SP injection (1000 mg/kg) 5 min after sham injury (Sham-SP) or CCI (CCI-SP) significantly increased arterial pyruvate (p < 0.005) and lactate (p < 0.001) compared to that of saline-treated rats with CCI (CCI-Sal). Serum glucose also increased significantly in CCI-SP compared to that in CCI-Sal rats (p < 0.05), but not in Sham-SP rats. MD(pyr) was not altered after CCI-Sal, whereas MD(lac) levels within the cerebral cortex significantly increased bilaterally (p < 0.05) and those for MD(glc) decreased bilaterally (p < 0.05). MD(pyr) levels increased significantly in both Sham-SP and CCI-SP rats (p < 0.05 vs. CCI-Sal) and were higher in left/injured cortex of the CCI-SP group (p < 0.05 vs. sham-SP). In CCI-SP rats the contralateral MD(lac) decreased below CCI-Sal levels (p < 0.05) and the ipsilateral MD(glc) levels exceeded those of CCI-Sal rats (p < 0.05). Rats with a single low (500 mg/kg) or high dose (1000 mg/kg) SP treatment had fewer damaged cortical cells 6 h post-CCI than did saline-treated rats (p < 0.05), but three hourly injections of SP (1000 mg/kg) were needed to significantly reduce contusion volume 2 weeks after CCI. Thus, a single intraperitoneal SP treatment increases circulating levels of three potential brain fuels, attenuates a CCI-induced reduction in extracellular glucose while increasing extracellular levels of pyruvate, but not lactate, and can attenuate cortical cell damage occurring within 6 h of injury. Enduring (2 week) neuronal protection was achieved only with multiple SP treatments within the first 2 h post-CCI, perhaps reflecting the need for additional fuel throughout the acute period of increased metabolic demands induced by CCI.

Genetic regulation of microglia activation, complement expression, and neurodegeneration in a rat model of traumatic brain injury

Secondary brain damage following traumatic brain injury in part depends on neuroinflammation, a process where genetic factors may play an important role. We examined the response to a standardized cortical contusion in two different inbred rat strains, Dark Agouti (DA) and Piebald Virol Glaxo (PVG). Both are well characterized in models of autoimmune neuroinflammation, where DA is susceptible and PVG resistant. We found that infiltration of polymorphonuclear granulocytes (PMN) at 3-day postinjury was more pronounced in PVG. DA was more infiltrated by T cells at 3-day postinjury, showed an enhanced glial activation at 7-day postinjury and higher expression of C3 complement at 7-day postinjury. Neurodegeneration, assessed by Fluoro-Jade, was also more pronounced in the DA strain at 30-day postinjury. These results demonstrate differences in the response to cortical contusion injury attributable to genetic influences and suggest a link between injury-induced inflammation and neurodegeneration. Genetic factors that regulate inflammation elicited by brain trauma may be important for the development of secondary brain damage.

Time Course of Early Metabolic Changes following Diffuse Traumatic Brain Injury in Rats as Detected by1H NMR Spectroscopy

Experimental models of traumatic brain injury (TBI) provide a useful tool for understanding the cerebral metabolic changes induced by this pathological condition. Here, we report on the time course of changes in cerebral metabolites after TBI and its correlation with early brain morphological changes using a combination of high-resolution proton magnetic resonance spectroscopy ((1)H MRS) and magnetic resonance imaging (MRI). Adult male Sprague-Dawley rats were subjected to closed head impact and examined by MRI at 1, 9, 24, 48, and and 72 h after the injury. Extracts from funnel frozen rat brains were then obtained and analyzed quantitatively by high-resolution (1)H MRS. Finally, statistical multivariate analysis was carried out to identify the combination of cerebral metabolites that best described the time evolution of diffuse TBI. The temporal changes observed in the concentration of cerebral metabolites followed three different patterns. The first pattern included taurine, threonine, and glycine, with concentrations peaking 24 h after the injury. The second pattern included glutamate, GABA, and alanine, with concentrations remaining elevated between 24 and 48 h post-injury. The third one involved creatine-phosphocreatine, N-acetylaspartate, and myo-inositol, with concentrations peaking 48 h after the injury. A multivariate stepwise discriminant analysis revealed that the combination of the organic osmolytes taurine and myo-inositol allowed optimal discrimination among the different time groups. Our findings suggest that the profile of some specific brain molecules that play a role as organic osmolytes can be used to follow-up the progression of the early diffuse brain edema response induced by TBI.

LACTATE, NOT GLUCOSE, UP-REGULATES MITOCHONDRIAL OXYGEN CONSUMPTION BOTHIN SHAM AND LATERAL FLUID PERCUSSED RAT BRAINS

OBJECTIVE

Failure of energy metabolism after traumatic brain injury may be a major factor limiting outcome. Although glucose is the primary metabolic substrate in the healthy brain, the well documented surge in tissue lactate after traumatic brain injury suggests that lactate may provide an energy need that cannot be met by glucose. We hypothesized, therefore, that administration of lactate or the combination of lactate and supraphysiological oxygen may improve mitochondrial oxidative respiration in the brain after rat fluid percussion injury. We measured oxygen consumption (VO2) to determine what effects glucose, lactate, oxygen, and the combination of lactate and oxygen have on mitochondrial respiration in both injured and uninjured rat brain tissue.

METHODS

Anesthetized Sprague-Dawley rats were intubated and ventilated with either 0.21 or 1.0 fraction of inspired oxygen (FIO2). Brain tissue from acute sham animals was subjected in vitro to 1.1 mM, 12 mM and 100 mM concentrations of glucose and L-lactate. In another group, injury (fluid percussion injury of 2.5 +/- 0.02 atmospheres) was induced over the left hemisphere. The VO2 of mug amounts of brain tissues were measured in a microrespirometry system (Cartesian diver).

RESULTS

The VO2 was found to be independent of glucose concentrations, but dose-dependent for lactate. Moreover, the lactate dependent VO2s were all significantly higher than those generated by glucose. Injured rats on FIO2 0.21 had brain tissue VO2 rates that were significantly lower than those of shams or preinjury levels. In injured rats treated with FIO2 1.0, the reduction in VO2 levels was prevented. Injured rats that received an intravenous infusion of 100 mM lactate had VO2 rates that were significantly higher than those obtained with FIO2 1.0. Combined treatment further boosted the lactate generated VO2 rates by approximately 15%.

CONCLUSION

Glucose sustains mitochondrial respiration at a low level "fixed" rate because, despite increasing its concentration nearly 100-fold, it cannot up-regulate VO2 after fluid percussion injury. Lactate produces a dose-dependent VO2 response, possibly enabling mitochondria to meet the increased energy needs of the injured brain.

Matrix metalloproteinase-9 is associated with blood-brain barrier opening and brain edema formation after cortical contusion in rats

Matrix metalloproteinases (MMPs) are associated with blood-brain opening and may be involved in the pathophysiology of acute brain injury. Previous research demonstrated that knockout mice deficient in MMP-9 subjected to transient focal cerebral ischemia had reduced blood-brain barrier (BBB) disruption and attenuated cerebral infarction. In this study, we examined MMP-9 up-regulation, BBB disruption, and brain edema formation after cortical impact injury in rats. Cortical contusion was induced by controlled cortical impact. Animals were sacrificed at intervals after injury. MMP up-regulation was assessed by gelatin zymography, and BBB integrity was evaluated using Evans blue dye with a spectrophotometric assay. Brain water content was measured by comparing wet and dry weights of each hemisphere as an indicator of brain edema. Zymograms showed elevated MMP-9 as early as at 3 hours after injury, reaching a maximum at 18 hours. Peak levels of BBB disruption occurred 6 hours after injury. Brain edema became progressively more severe, peaking 24 hours after injury. Compared to control group, treatment with MMP-inhibitor GM6001 significantly reduced BBB disruption 6 hours and brain water content (85.9 +/- 0.5% vs. 82.6 +/- 0.3%; p < 0.05) 24 hours after injury. These findings suggest that MMP-9 may contribute to BBB disturbance and subsequent brain edema after traumatic brain injury.

Effects of anesthesia on the responses to cortical spreading depression in the rat brain in vivo

OBJECTIVES

The aim of this study was to evaluate the effect of cortical spreading depression (CSD) on the metabolic, hemodynamic, electrical and ionic properties during anesthesia as compared with the awake state.

METHODS

The mitochondrial NADH redox state, reflected light, direct current (DC) potential, electrocorticography (ECoG), cerebral blood flow (CBF) and volume (CBV), and extracellular K(+) concentrations ([K(+)](e)), were measured continuously and simultaneously in real time using two unique monitoring systems that evaluate brain function. Three consecutive CSD waves were initiated using a KCl solution in both awake and anesthetized rats.

RESULTS AND DISCUSSION

CSD caused typical amplitude changes: biphasic waves in reflectance, oxidation cycles in NADH, an increase in CBF, CBV and in [K(+)](e), a negative shift in DC potential and depression in ECoG. Anesthesia by equithesin decreased significantly the baseline levels of CBF and [K(+)](e), showing a reduction in oxygen supply and demand. After anesthesia, CSD significantly decreased [K(+)](e) and NADH oxidation cycles, indicating a reduction in oxygen demand and in oxygen balance, respectively. Furthermore, anesthesia reduced CSD wave frequencies by slowing the recovery period, showing a decline in energy production during brain activation, or by changing electrophysiological properties of the tissue. No changes were found in the propagation rate and in the initiation period of CSD, which may indicate that equithesin does not block CSD initiation. In addition, we found that the whole cerebral cortex reacts homogenously to CSD and that equithesin may reduce oxygen demand and energy production, which may have a protective effect on the brain exposed to pathophysiological conditions.

In vivo co-ordinated interactions between inhibitory systems to control glutamate-mediated hippocampal excitability

We present an overview of the long-term adaptation of hippocampal neurotransmission to cholinergic and GABAergic deafferentation caused by excitotoxic lesion of the medial septum. Two months after septal microinjection of 2.7 nmol alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA), a 220% increase of GABA(A) receptor labelling in the hippocampal CA3 and the hilus was shown, and also changes in hippocampal neurotransmission characterised by in vivo microdialysis and HPLC. Basal amino acid and purine extracellular levels were studied in control and lesioned rats. In vivo effects of 100 mm KCl perfusion and adenosine A(1) receptor blockade with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) on their release were also investigated. In lesioned animals GABA, glutamate and glutamine basal levels were decreased and taurine, adenosine and uric acid levels increased. A similar response to KCl infusion occurred in both groups except for GABA and glutamate, which release decreased in lesioned rats. Only in lesioned rats, DPCPX increased GABA basal level and KCl-induced glutamate release, and decreased glutamate turnover. Our results evidence that an excitotoxic septal lesion leads to increased hippocampal GABA(A) receptors and decreased glutamate neurotransmission. In this situation, a co-ordinated response of hippocampal retaliatory systems takes place to control neuron excitability.

Mechanical strain injury increases intracellular sodium and reverses Na+/Ca2+ exchange in cortical astrocytes

Traditionally, astrocytes have been considered less susceptible to injury than neurons. Yet, we have recently shown that astrocyte death precedes neuronal death in a rat model of traumatic brain injury (TBI) (Zhao et al.: Glia 44:140-152, 2003). A main mechanism hypothesized to contribute to cellular injury and death after TBI is elevated intracellular calcium ([Ca2+]i). Since calcium regulation is also influenced by regulation of intracellular sodium ([Na+]i), we used an in vitro model of strain-induced traumatic injury and live-cell fluorescent digital imaging to investigate alterations in [Na+]i in cortical astrocytes after injury. Changes in [Na+]i, or [Ca2+]i were monitored after mechanical injury or L-glutamate exposure by ratiometric imaging of sodium-binding benzofuran isophthalate (SBFI-AM), or Fura-2-AM, respectively. Mechanical strain injury or exogenous glutamate application produced increases in [Na+]i that were dependent on the severity of injury or concentration. Injury-induced increases in [Na+]i were significantly reduced, but not completely eliminated, by inhibition of glutamate uptake by DL-threo-beta-benzyloxyaspartate (TBOA). Blockade of sodium-dependent calcium influx through the sodium-calcium exchanger with 2-[2-[4-(4-Nitrobenzyloxy)phenyl]ethyl]isothiourea mesylate (KB-R7943) reduced [Ca2+]i after injury. KB-R7943 also reduced astrocyte death after injury. These findings suggest that in astrocytes subjected to mechanical injury or glutamate excitotoxicity, increases in intracellular Na+ may be a critical component in the injury cascade and a therapeutic target for reduction of lasting deficits after traumatic brain injury.

Pre-Injury Magnesium Treatment Prevents Traumatic Brain Injury–Induced Hippocampal ERK Activation, Neuronal Loss, and Cognitive Dysfunction in the Radial-Arm Maze Test

We studied the effect of pre-injury magnesium (Mg(2+)) treatment on hippocampal extracellular signal- regulated kinase (ERK) activation induced by lateral fluid-percussion (FP) brain injury, and on working and reference memory in the radial-arm maze test in rats subjected to such traumatic brain injury (TBI) (n = 56) or to sham injury (n = 12). In the ipsilateral hippocampus, an increase in the phospho-ERK level was detected at 10 min after injury in rats subjected to FP brain injury of moderate severity (1.9-2.0 atm) as compared to sham-injured controls (p < 0.01), and was maintained for at least 120 min after injury (p < 0.05). In the contralateral hippocampus, the phospho-ERK level was transiently increased at 10 min after injury but fell to nearly its basal level by 30 min. When MgCl(2) solution (150 micromol) was infused intravenously from 20 min to 5 min before injury (n = 4-5), brain injury-induced ERK activation was significantly inhibited in the ipsilateral hippocampus at 60 min but not at 10 min after injury. Mg(2+) treatment also significantly prevented injury- induced neuronal loss in the ipsilateral hippocampus (p < 0.05 vs. vehicle-treated, brain-injured controls). At 2 weeks after injury, Mg2+ treatment was found to have significantly prevented injury-induced impairments in working (p < 0.0001 vs. vehicle-treated, brain-injured controls) and reference memory (p < 0.05) in the radial-arm maze test. The present study demonstrates that pretreatment with Mg(2+) prevents post-traumatic hippocampal ERK activation and neuronal loss, and cognitive dysfunction in the radial-arm maze test.

Analysis of long-term gene expression in neurons of the hippocampal subfields following traumatic brain injury in rats

After experimental traumatic brain injury (TBI), widespread neuronal loss is progressive and continues in selectively vulnerable brain regions, such as the hippocampus, for months to years after the initial insult. To clarify the molecular mechanisms underlying secondary or delayed cell death in hippocampal neurons after TBI, we compared long-term changes in gene expression in the CA1, CA3 and dentate gyrus (DG) subfields of the rat hippocampus at 24 h and 3, 6, and 12 months after TBI with changes in gene expression in sham-operated rats. We used laser capture microdissection to collect several hundred hippocampal neurons from the CA1, CA3, and DG subfields and linearly amplified the nanogram samples of neuronal RNA with T7 RNA polymerase. Subsequent quantitative analysis of gene expression using ribonuclease protection assay revealed that mRNA expression of the anti-apoptotic gene, Bcl-2, and the chaperone heat shock protein 70 was significantly downregulated at 3, 6 (Bcl-2 only), and 12 months after TBI. Interestingly, the expression of the pro-apoptotic genes caspase-3 and caspase-9 was also significantly decreased at 3, 6 (caspase-9 only), and 12 months after TBI, suggesting that long-term neuronal loss after TBI is not mediated by increased expression of pro-apoptotic genes. The expression of two aging-related genes, p21 and integrin beta3 (ITbeta3), transiently increased 24 h after TBI, returned to baseline levels at 3 months and significantly decreased below sham levels at 12 months (ITbeta3 only). Expression of the gene for the antioxidant glutathione peroxidase-1 also significantly increased 6 months after TBI. These results suggest that decreased levels of neuroprotective genes may contribute to long-term neurodegeneration in animals and human patients after TBI. Conversely, long-term increases in antioxidant gene expression after TBI may be an endogenous neuroprotective response that compensates for the decrease in expression of other neuroprotective genes.

Spreading depression expands traumatic injury in neocortical brain slices

Traumatic brain injury (TBI) is particularly common in young people, generating healthcare costs that can span decades. The cellular processes activated in the first minutes following injury are poorly understood, and the 3-4 h following trauma are crucial for reducing subsequent injury. Spreading depression (SD) is a profound inactivation of neurons and glia lasting 1-2 min that arises focally and migrates outward across gray matter. In the hours following focal stroke, the metabolic stress of energy reduction and recurring SD-like events (peri-infarct depolarizations, PIDs) interact to promote neuronal injury. Similar recurring depolarizations might evolve immediately following TBI and exacerbate neuronal damage peripheral to the impact site. To test this possibility and examine if certain drugs might limit damage by inhibiting what we term traumatic spreading depression (tSD), we developed a technique whereby a small weight was dropped onto a live slice of rat neocortex while imaging changes in light transmittance (LT). Imaging revealed a propagating front of increased LT arising at the border of the impact site. Traumatic SD significantly expanded the region of ensuing damage. Both tSD and subsequent damage were blocked by the NMDA receptor antagonist MK-801 (100 microM) or the sigma-1 receptor (sigma1R) ligands dextromethorphan (30 microM) or BD-1063 (100 microM). Co-application of the sigma1R antagonist (+)3-PPP with DM reversed the block as did lowering temperature from 35 degrees C to 32 degrees C. This study provides evidence that an event similar to peri-infarct depolarization can arise from an injury site in neocortex within seconds following impact and act to expand the region of acute neuronal damage.

Heterogeneity between hippocampal and septal astroglia as a contributing factor to differential in vivo AMPA excitotoxicity

Astroglial participation in the regional differences of vulnerability to alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-induced neurodegeneration was investigated in the rat hippocampus and medial septum using L-alpha-aminoadipate (alpha-AA) as a specific astroglial toxin. alpha-AA was microinjected in the hippocampus and the medial septum and a time-course study was carried out between 2 hr and 3 days. When compared to controls, microinjection of alpha-AA in the hippocampus induced within 3 days a reversible loss of glial fibrillary acidic protein (GFAP) immunostaining and a microglial reaction without any neuronal loss, whereas in the medial septum it caused no effects on astroglial, microglial, or neuronal populations. Differences in hippocampus and medial septum vulnerability were also evidenced when alpha-AA was co-injected with AMPA and neurodegeneration was assessed in terms of neuronal loss, glial reactions, calcification, and atrophy of the area. In the hippocampus, alpha-AA increased AMPA excitotoxicity with marked disorganization of all hippocampal subfields, increased neuronal loss, a more important astroglial reaction, a larger area of microgliosis, and a greater abundance of calcium deposits. By contrast, in the medial septum alpha-AA did not modify any parameter of the AMPA-induced lesion. In conclusion, the presence of different astroglial populations in hippocampus and medial septum results in a different participation to AMPA excitotoxicity that may determine, at least in part, the specific regional vulnerability to neurodegeneration.

Overexpression of genes in the CA1 hippocampus region of adult rat following episodes of global ischemia

Ischemic stress is associated with marked changes in gene expression in the hippocampus--albeit little information exists on the activation of nonabundant genes. We have examined the expression of several known genes and identified novel ones in the adult rat hippocampus after a mild, transient, hypovolemic and hypotensive, global ischemic stress. An initial differential screening using a prototype array to assess gene expression after stress followed by a suppression subtractive hybridization protocol and cDNA microarray revealed 124 nonoverlapped transcripts predominantly expressed in the CA1 rat hippocampus region in response to ischemic stress. About 78% of these genes were not detected with nonsubtracted probes. Reverse transcription polymerase chain reaction (RT-PCR) and in situ hybridization on these 124 transcripts confirmed the differential expression of at least 83. Most robustly expressed were gene sequences NFI-B, ATP1B1, RHOGAP, PLA2G4A, BAX, CASP3, P53, MAO-A, FRA1, HSP70.2, and NR4A1 (NUR77), as well as sequence tags of unknown function. New stress-related genes of similar functional motifs were identified, reemphasizing the importance of functional grouping in the analysis of multiple gene expression profiles. These data indicate that ischemia elicits expression of an array of functional gene clusters that may be used as an index for stress severity and a template for target therapy design.

Nitric oxide in traumatic brain injury

Nitric oxide (NO) is a gaseous chemical messenger which has functions in the brain in a variety of broad physiological processes, including control of cerebral blood flow, interneuronal communications, synaptic plasticity, memory formation, receptor functions, intracellular signal transmission, and release of neurotransmitters. As might be expected from the numerous and complex roles that NO normally has, it can have both beneficial and detrimental effects in disease states, including traumatic brain injury. There are two periods of time after injury when NO accumulates in the brain, immediately after injury and then again several hours-days later. The initial immediate peak in NO after injury is probably due to the activity of endothelial NOS and neuronal NOS. Pre-injury treatment with 7-nitroindazole, which probably inhibits this immediate increase in NO by neuronal NOS, is effective in improving neurological outcome in some models of traumatic brain injury (TBI). After the initial peak in NO, there can be a period of relative deficiency in NO. This period of low NO levels is associated with a low cerebral blood flow (CBF). Administration of L-arginine at this early time improves CBF, and outcome in many models. The late peak in NO after traumatic injury is probably due primarily to the activity of inducible NOS. Inhibition of inducible NOS has neuroprotective effects in most models.

Activation of Microglial Cells and Complement following Traumatic Injury in Rat Entorhinal-Hippocampal Slice Cultures

The complement cascade has been suggested to be involved in development of secondary brain damage following traumatic brain injury (TBI). Previous studies have shown that reactive microglia are involved in activation of the complement cascade following various injuries to the nervous system. Macrophages seem to have a significant role in this process, but it is still unclear whether these cells, as well as the complement components, are derived from reactive microglia or if these biological events only can occur as a result from the influx of plasma and monocytes via a disrupted blood-brain barrier (BBB). The aim of this study was to investigate the response of microglial cells and the complement system in the absence of plasma/blood components following a standardized crush injury in an entorhinal-hippocampal slice culture. There was a clear increase in complement component C1q and C5b-9-IR (Membrane Attack Complex, MAC) in the area near the crush injury. MAC-IR appeared as numerous dots in clusters which co-localized with anti-NeuN labelled neurons in the injury border zone. Complement C1q-IR co-localized with reactive microglia, co-labelled with OX42 antisera. These findings show activation of the complement cascade near the injury zone and in particular, formation of MAC at the surface of neurons in this area. There was a distinct activation of microglial cells (OX42-IR) near the site of injury, as well as an increase in ED-1 expressing macrophages. In the absence of blood and plasma components it is likely that ED-1-labelled cells represent reactive microglia transformed into macrophages. In addition, Neurons (Neun-IR) near the injury were found to co-localize with clusterin-IR indicating upregulation of a defense system to the endogenous complement attack. The present study provides evidence that microglia and complement is activated in the injury border zone of the tissue slice in a similar fashion as in vivo following TBI, despite the absence of plasma/blood products and cells. These findings support the hypothesis that reactive microglia have a key role in complement activation following TBI by local synthesis of complement with a potential impact on development of secondary neuronal insults.

Low sensitivity of retina to AMPA-induced calcification

Glutamate is involved in most CNS neurodegenerative diseases. In particular, retinal diseases such as retinal ischemia, retinitis pigmentosa, and diabetic retinopathy are associated with an excessive synaptic concentration of this neurotransmitter. To gain more insight into retinal excitotoxicity, we carried out a dose-response study in adult rats using alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), a glutamate analogue. AMPA intraocular injections (between 0.27 and 10.8 nmol) caused no morphologic modification, but a 10.8 + 21 nmol double injection in a 10-day interval produced a lesion characterized by discrete neuronal loss, astroglial and microglial reactions, and calcium precipitation. Abundant calcium deposits similar to those present in rat and human brain excitotoxicity or hypoxia-ischemia neurodegeneration were detected by alizarin red staining within the retinal surface and the optic nerve. Glial reactivity, associated normally with astrocytes in the nerve fiber, was assessed in Müller cells. GABA immunoreactivity was detected not only in neuronal elements but also in Müller cells. In contrast to the high vulnerability of the brain to excitotoxin microinjection, AMPA-induced retinal neurodegeneration may provide a useful model of low central nervous system sensitivity to excitotoxicity.

[Treatment of cerebral oedema]

Progress in brain imaging, monitoring and physiopathology allows the identification of brain oedema from brain swelling, determination of its interstitial or intracellular nature, as well as blood-brain barrier permeability and the evaluation of the impact on cerebral haemodynamic. Common treatment of all types of cerebral oedema is based on prevention of self-sustained disorders due to increased intracranial pressure resulting in ischemic cerebral oedema. The specific treatment of each type of cerebral oedema is reviewed. Optimization of conventional anti-oedematous strategies is based on the precise determination of the nature of the cerebral oedema and of the blood-brain barrier status.

Effects of antioxidant, OPC-14117, on secondary cellular damage and behavioral deficits following cortical contusion in the rat

In the present study, we examined the effects of OPC-14117, a superoxide radical scavenger, on the secondary cellular damage and cognitive dysfunction occurring in a rat model of cerebral contusion induced by a controlled cortical impact (CCI). Histological examinations revealed that the contusion necrosis volume reached 13.6+/-5.3 mm(3) in non-treated animals and declined to 1.9+/-0.6 mm(3) in OPC-14117-treated animals (P<0.01). The cell number of the CA3 region was 120.0+/-12.4 cells/mm in the normal controls, 73.6+/-9.9 cells/mm in the non-treated animals, and 111.2+/-10.2 cells/mm in the OPC-14117-treated animals, indicating that CCI-induced selective neuronal cell death in the CA3 region was attenuated by the OPC-14117 administration (P<0.01). The tissue osmolality, as determined with a vapor pressure osmometer, was 314.5+/-15.4 mmol/kg in the normal brain and increased to 426.0+/-20.1 mmol/kg at 12 h following CCI. The increase in tissue osmolality was significantly attenuated by OPC-14117 administration (P<0.01). The OPC-14117 administration also attenuated the CCI-induced cognitive deficits. The OPC-14117-treated animals showed a tendency to improve on the Morris water maze performance test. The impairment of the habituation of exploratory activity elicited by CCI was significantly attenuated by OPC-14117 administration (P<0.05). In conclusion, OPC-14117 may have a potential for decreasing secondary cellular damage due to traumatic brain injury since it is as efficacious as any other compound tested in this model.

High-density microarray analysis of hippocampal gene expression following experimental brain injury

Behavioral, biophysical, and pharmacological studies have implicated the hippocampus in the formation and storage of spatial memory. Traumatic brain injury (TBI) often causes spatial memory deficits, which are thought to arise from the death as well as the dysfunction of hippocampal neurons. Cell death and dysfunction are commonly associated with and often caused by altered expression of specific genes. The identification of the genes involved in these processes, as well as those participating in postinjury cellular repair and plasticity, is important for the development of mechanism-based therapies. To monitor the expression levels of a large number of genes and to identify genes not previously implicated in TBI pathophysiology, a high-density oligonucleotide array containing 8,800 genes was interrogated. RNA samples were prepared from ipsilateral hippocampi 3 hr and 24 hr following lateral cortical impact injury and compared to samples from sham-operated controls. Cluster analysis was employed using statistical algorithms to arrange the genes according to similarity in patterns of expression. The study indicates that the genomic response to TBI is complex, affecting approximately 6% (at the time points examined) of the total number of genes examined. The identity of the genes revealed that TBI affects many aspects of cell physiology, including oxidative stress, metabolism, inflammation, structural changes, and cellular signaling. The analysis revealed genes whose expression levels have been reported to be altered in response to injury as well as several genes not previously implicated in TBI pathophysiology.

Neuropathological protection after traumatic brain injury in intact female rats versus males or ovariectomized females

An important consideration in traumatic brain injury (TBI) in females is the influence of hormones on recovery. Recent studies in both cerebral ischemia and TBI have demonstrated an attenuation in both damage and neurologic recovery following hormonal treatment. However, the ability of endogenous hormone levels to provide neuropathological protection after fluid percussion (FP) brain injury has not been studied. The purpose of this experiment was to determine whether endogenous circulating hormones in the female rat could provide neuroprotection compared to males and ovariectomized female animals. Sixty-four Sprague-Dawley rats underwent a moderate (1.7-2.2 atm) right parasagittal FP injury. Intact females (i.e., nonovariectomized) were subjected to injury either during the proestrous (TBI-FP, n = 18) phase of their cycle or nonproestrous (TBI-FNP, n = 19) phase. A separate group of females were ovariectomized (TBI-OVX, n = 10) 10 days prior to FP injury in order to reduce hormone levels. Male animals were also traumatized (TBI-M, n = 17). Appropriate sham controls (Sham-FP, n = 2; Sham-FNP, n = 2; Sham-OVX, n = 2; Sham-M, n = 2) also underwent all aspects of surgery except for the actual FP injury. All groups were sacrificed 3 days following TBI for analysis. Both intact female groups had significantly (p < 0.05) smaller cortical contusions compared to male animals. In addition to this finding, the TBI-FNP group was significantly (p < 0.04) different from the ovariectomized female animals. Ovariectomized rats had larger areas of damage compared to intact females. The TBI-OVX group's cortical contusion volume was similar to male animals. These results provide evidence for endogenous hormonal histopathological protection following parasagittal FP brain injury. The use of hormone therapy after TBI warrants continued exploration.

Substrate delivery and ionic balance disturbance after severe human head injury

The most important early pathomechanism in traumatic brain injury (TBI) is alteration of the resting membrane potential. This may be mediated via voltage, or agonist-dependent ion channels (e.g. glutamate-dependent channels). This may result in a consequent increase in metabolism with increased oxygen consumption, in order to try to restore ionic balance via the ATP-dependent pumps. We hypothesize that glutamate is an important agonist in this process and may induce an increase in lactate, potassium and brain tissue CO2, and hence a decrease in brain pH. Further we propose that an increase in lactate is thus not an indicator of anaerobic metabolic conditions as has been thought for many years. We therefore analyzed a total of 85 patients with TBI, Glasgow Coma Scale (GCS) < 8 using microdialysis, brain tissue oxygen, CO2 and pH monitoring. Cerebral blood flow studies (CBF) were performed to test the relationship between regional cerebral blood flow (rCBF) and the metabolic determinants. Glutamate was significantly correlated with lactate (p < 0.0001), potassium (p < 0.0001), brain tissue pH (p = 0.0005), and brain tissue CO2 (p = 0.006). rCBF was inversely correlated with glutamate, lactate and potassium. 44% of high lactate values were observed in brain with tissue oxygen values, above the threshold level for cell damage. These results support the hypothesis of a glutamate driven increase in metabolism, with secondary traumatic depolarization and possibly hyperglycolysis. Further, we demonstrate evidence for lactate production in aerobic conditions in humans after TBI. Finally, when reduced regional cerebral blood flow (rCBF) is observed, high dialysate glutamate, lactate and potassium values are usually seen, suggesting ischemia worsens these TBI-induced changes.

Glutamate uptake

Brain tissue has a remarkable ability to accumulate glutamate. This ability is due to glutamate transporter proteins present in the plasma membranes of both glial cells and neurons. The transporter proteins represent the only (significant) mechanism for removal of glutamate from the extracellular fluid and their importance for the long-term maintenance of low and non-toxic concentrations of glutamate is now well documented. In addition to this simple, but essential glutamate removal role, the glutamate transporters appear to have more sophisticated functions in the modulation of neurotransmission. They may modify the time course of synaptic events, the extent and pattern of activation and desensitization of receptors outside the synaptic cleft and at neighboring synapses (intersynaptic cross-talk). Further, the glutamate transporters provide glutamate for synthesis of e.g. GABA, glutathione and protein, and for energy production. They also play roles in peripheral organs and tissues (e.g. bone, heart, intestine, kidneys, pancreas and placenta). Glutamate uptake appears to be modulated on virtually all possible levels, i.e. DNA transcription, mRNA splicing and degradation, protein synthesis and targeting, and actual amino acid transport activity and associated ion channel activities. A variety of soluble compounds (e.g. glutamate, cytokines and growth factors) influence glutamate transporter expression and activities. Neither the normal functioning of glutamatergic synapses nor the pathogenesis of major neurological diseases (e.g. cerebral ischemia, hypoglycemia, amyotrophic lateral sclerosis, Alzheimer's disease, traumatic brain injury, epilepsy and schizophrenia) as well as non-neurological diseases (e.g. osteoporosis) can be properly understood unless more is learned about these transporter proteins. Like glutamate itself, glutamate transporters are somehow involved in almost all aspects of normal and abnormal brain activity.

Mechanisms of spreading depression and hypoxic spreading depression-like depolarization

Spreading depression (SD) and the related hypoxic SD-like depolarization (HSD) are characterized by rapid and nearly complete depolarization of a sizable population of brain cells with massive redistribution of ions between intracellular and extracellular compartments, that evolves as a regenerative, "all-or-none" type process, and propagates slowly as a wave in brain tissue. This article reviews the characteristics of SD and HSD and the main hypotheses that have been proposed to explain them. Both SD and HSD are composites of concurrent processes. Antagonists of N-methyl-D-aspartate (NMDA) channels or voltage-gated Na(+) or certain types of Ca(2+) channels can postpone or mitigate SD or HSD, but it takes a combination of drugs blocking all known major inward currents to effectively prevent HSD. Recent computer simulation confirmed that SD can be produced by positive feedback achieved by increase of extracellular K(+) concentration that activates persistent inward currents which then activate K(+) channels and release more K(+). Any slowly inactivating voltage and/or K(+)-dependent inward current could generate SD-like depolarization, but ordinarily, it is brought about by the cooperative action of the persistent Na(+) current I(Na,P) plus NMDA receptor-controlled current. SD is ignited when the sum of persistent inward currents exceeds persistent outward currents so that total membrane current turns inward. The degree of depolarization is not determined by the number of channels available, but by the feedback that governs the SD process. Short bouts of SD and HSD are well tolerated, but prolonged depolarization results in lasting loss of neuron function. Irreversible damage can, however, be avoided if Ca(2+) influx into neurons is prevented.

New treatments for concussion: the next millennium beckons

As increased understanding of the pathophysiology of mild traumatic brain injury and concussion develops, so the scientific rationale for interventional pharmacological therapy becomes paramount. A number of agents have been postulated or have been the subject of anecdotal noncontrolled trials. This paper reviews the published evidence in this regard. To date no effective pharmacological therapy exists that satisfies Class I evidence-based medicine criteria.

Delayed cerebral edema and fatal coma after minor head trauma: role of the CACNA1A calcium channel subunit gene and relationship with familial hemiplegic migraine

Trivial head trauma may be complicated by severe, sometimes even fatal, cerebral edema and coma occurring after a lucid interval ("delayed cerebral edema"). Attacks of familial hemiplegic migraine (FHM) can be triggered by minor head trauma and are sometimes accompanied by coma. Mutations in the CACNA1A calcium channel subunit gene on chromosome 19 are associated with a wide spectrum of mutation-specific episodic and chronic neurological disorders, including FHM with or without coma. We investigated the role of the CACNA1A gene in three subjects with delayed cerebral edema. Two subjects originated from a family with extreme FHM, and one subject was the previously asymptomatic daughter of a sporadic patient with hemiplegic migraine attacks. In all three subjects with delayed severe edema, we found a C-to-T substitution resulting in the substitution of serine for lysine at codon 218 (S218L) in the CACNA1A gene. The mutation was absent in nonaffected family members and 152 control individuals. Haplotype analysis excluded a common founder for both families. Neuropathological examination in one subject showed Purkinje cell loss with relative preservation of granule cells and sparing of the dentate and inferior olivary nuclei. We conclude that the novel S218L mutation in the CACNA1A calcium channel subunit gene is involved in FHM and delayed fatal cerebral edema and coma after minor head trauma. This finding may have important implications for the understanding and treatment of this dramatic syndrome.

Neuroprotective agents in traumatic brain injury

The role of neuroprotection in traumatic brain injury (TBI) is reviewed. Basic research and experimental investigations have identified many different compounds with potential neuroprotective effect. However, none of the Phase III trials performed in TBI have been successful in convincingly demonstrating efficacy in the overall population. A common misconception is that consequently these agents are ineffective. The negative results as reported in the overall population may in part be caused by specific aspects of the head injury population as well as by aspects of clinical trial design and analysis. The heterogeneity of the TBI population causes specific problems, such as a risk of imbalances between placebo and treated groups but also causes problems when a possible treatment effect is evaluated in relation to the prognostic effect present. Trials of neuroprotective agents should be targeted first of all to a population in which the mechanism at which the agent is directed is likely to be present and secondly to a population in which the chances of demonstrating efficacy are realistic, e.g., to patients with an intermediate prognosis. The possibilities for concomitant or sequential administration of different neuroprotective agents at different times deserve consideration. The potential for neuroprotection in TBI remains high and we should not be discouraged by recent failures obtained up until now. Rather, prior to initiating new trials, careful consideration of experimental evidence is required in order to optimise chances for mechanistic targeting and lessons learned from previous experience need to be taken to heart in the design of future studies.

Perinatal human hypoxia-ischemia vulnerability correlates with brain calcification

Deregulation of intracellular calcium homeostasis is widely considered as one of the underlying pathophysiological mechanisms of hypoxic-ischemic brain injury. Whether this alteration can result in cerebral calcification was investigated in basal ganglia, cerebral cortex, and hippocampus of human premature and term neonates together with glial reaction. In all samples nonarteriosclerotic calcifications were observed, their number and size were area-specific and increased in term neonates. Basal ganglia always presented the highest degree of calcification and hippocampus the lowest, located mainly in the CA1 subfield. In all cases, neuronal damage was associated with astroglial reaction and calcium precipitates, with microglial reaction only in basal ganglia and cerebral cortex, and argues for the participation of excitatory amino acid receptors in hypoxia-ischemia damage. These data correlate with hypoxia-ischemia vulnerability in the perinatal period. The clinical relevance of these precipitates and the neuroprotective interest of non-NMDA receptor manipulation are discussed in the light of our results.

High level of extracellular potassium and its correlates after severe head injury: relationship to high intracranial pressure

OBJECT

Disturbed ionic and neurotransmitter homeostasis are now recognized as probably the most important mechanisms contributing to the development of secondary brain swelling after traumatic brain injury (TBI). Evidence obtained in animal models indicates that posttraumatic neuronal excitation by excitatory amino acids leads to an increase in extracellular potassium, probably due to ion channel activation. The purpose of this study was therefore to measure dialysate potassium in severely head injured patients and to correlate these results with measurements of intracranial pressure (ICP), patient outcome, and levels of dialysate glutamate and lactate, and cerebral blood flow (CBF) to determine the role of ischemia in this posttraumatic ion dysfunction.

METHODS

Eighty-five patients with severe TBI (Glasgow Coma Scale Score < 8) were treated according to an intensive ICP management-focused protocol. All patients underwent intracerebral microdialyis. Dialysate potassium levels were analyzed using flame photometry, and dialysate glutamate and dialysate lactate levels were measured using high-performance liquid chromatography and an enzyme-linked amperometric method in 72 and 84 patients, respectively. Cerebral blood flow studies (stable xenon computerized tomography scanning) were performed in 59 patients. In approximately 20% of the patients, dialysate potassium values were increased (dialysate potassium > 1.8 mM) for 3 hours or more. A mean amount of dialysate potassium greater than 2 mM throughout the entire monitoring period was associated with ICP above 30 mm Hg and fatal outcome, as were progressively rising levels of dialysate potassium. The presence of dialysate potassium correlated positively with dialysate glutamate (p < 0.0001) and lactate (p < 0.0001) levels. Dialysate potassium was significantly inversely correlated with reduced CBF (p = 0.019).

CONCLUSIONS

Dialysate potassium was increased after TBI in 20% of measurements. High levels of dialysate potassium were associated with increased ICP and poor outcome. The simultaneous increase in dialysate potassium, together with dialysate glutamate and lactate, supports the concept that glutamate induces ionic flux and consequently increases ICP, which the authors speculate may be due to astrocytic swelling. Reduced CBF was also significantly correlated with increased levels of dialysate potassium. This may be due to either cell swelling or altered vasoreactivity in cerebral blood vessels caused by higher levels of potassium after trauma. Additional studies in which potassium-sensitive microelectrodes are used are needed to validate these ionic events more clearly.

Brain nitric oxide changes after controlled cortical impact injury in rats

Nitric oxide (NO) and the NO end products, nitrate and nitrite, were measured at the impact site after a 5-m/s, 3-mm deformation controlled cortical impact injury in rats. Immediately after the impact injury and the NO and microdialysis probes could be replaced, there was an increase from baseline in NO concentration of 83 +/- 16 (SE) nM, compared with 0.5 +/- 4 nM in the sham injured animals (P < 0.001). This marked increase in NO occurred at the time of the initial rise in blood pressure (BP) and intracranial pressure (ICP) in response to the injury. After the initial increase in BP and ICP, the BP decreased and stabilized at a value which was approximately 20 mmHg below the preinjury values, and ICP plateaued at an average value of 20 mmHg, compared with 8 mmHg in the sham-injured animals. This provided an average cerebral perfusion pressure of 40-50 mmHg, compared with 65-75 mmHg for the sham-injured animals. These values were relatively constant for the remainder of the 3-h monitoring period. The NO values also stabilized during this time period. By 1 h after the impact injury the NO concentration measured directly using the NO electrode had decreased from baseline values by an average value of 25 +/- 6 nM. NO concentration remained significantly lower than baseline values throughout the remainder of the 3-h monitoring period. The concentration of nitrate/nitrite in the dialysate fluid also decreased by an average value of 341 +/- 283 nM 20-40 min after the injury. Dialysate nitrite/nitrate concentrations remained less than the preinjury baseline values throughout the remainder of the 3-h monitoring period. Preinjury treatment with L-nitro-arginine methyl ester (L-NAME) blunted the injury-induced increase in NO and resulted in more severe immediate intracranial hypertension and more severe systemic hypotension at one hour after injury. Mortality was also 67% with L-NAME pretreatment, compared with 1% in untreated animals.

Excitatory amino acids and neurodegeneration: a hypothetical role of calcium precipitation

Activation of excitatory amino acid (EAA) receptors can induce neurodegeneration by two major mechanisms of excitotoxicity, one related to the influx of Na(+), Cl(-) and water, and the other to the increase in intracellular calcium concentration ([Ca(2+)](i)). Thus, acute microinjection of EAAs in several areas of the central nervous system (CNS) has been used to produce neurodegenerative models. We studied the excitotoxic pattern associated with acute microinjection of AMPA in rat hippocampus, medial septum-diagonal band of Broca (MS-DBB), prefrontal cortex and retina. In all cases progressive neuronal loss, glial reaction and development of intra- and extracellular calcium concretions were observed. However, a CNS-area differential vulnerability was revealed, as shown by the specific atrophy of MS-DBB and its limited calcification. Whether calcium deposits are a defensive mechanism against the massive increment of free cytoplasmatic calcium is discussed on the basis of ultrastructural data and previous results.

Differential effects of NMDA-receptor antagonists on long-term potentiation and hypoxic/hypoglycaemic excitotoxicity in hippocampal slices

Whole-cell patch clamp recording from cultured hippocampal neurones was used to investigate the NMDA antagonistic effects of the glycineB antagonist 5,7-DCKA and the competitive antagonist CGP 37849. Extracellular field potential recording from area CA1 of hippocampal slices was used to investigate their effects on the induction of LTP and hypoxia/hypoglycaemia-induced suppression of fEPSPs. Additionally, memantine and (+)MK-801 were tested in the later model. 5,7-DCKA inhibited NMDA-induced plateau currents (IC50=0.24+/-0.02 microM) with around nine times higher potency than against peak (IC50=2.14+/-0.17 microM). In contrast, CGP 37849 slowed the onset of NMDA-induced currents considerably and antagonized currents at the time point when the peak component occurred in control responses (IC50=0.18+/-0.01 microM) with around seven times higher potency than against plateau (IC50=1.26+/-0.19 microM). Both 5,7-DCKA and CGP 37849 inhibited the induction of LTP (IC50s=2.53+/-0.13 and 0.37+/-0.04 microM respectively) with potencies close to those inhibiting peak currents in patch clamp studies. 5,7-DCKA and CGP 37849 also blocked the hypoxia/hypoglycaemia-induced suppression of fEPSPs but CGP 37849 (EC50=4.3+/-0.33 microM) was far less potent than against the induction of LTP whilst 5,7-DCKA (EC50=1.47+/-0.04 microM) had similar potency in these two models. Memantine and (+)MK-801 also blocked hypoxia/hypoglycaemia-induced suppression of fEPSPs with EC50s of 14.1+/-0.52 and 0.53+/-0.02 microM respectively. Whereas memantine blocked this effect with similar potency as we previously reported for LTP, (+)MK-801 was four time less potent in this model. The calculated relative therapeutic indices (IC50 LTP over EC50 hypoxia/hypoglycaemia) for 5,7-DCKA, CGP 37849, memantine and (+)MK-801 were 1.72, 0.09, 0.82 and 0.24 respectively. These results show that even in a severe model of hypoxia/hypoglycaemia, glycineB site antagonists and moderate affinity channel blockers exhibit a better therapeutic index than competitive antagonists and high affinity channel blockers. It is likely that in milder forms of pathology the observed differences in therapeutic indices remain the same but the absolute values are expected to be higher.

Emergency management of the head trauma patient. Principles and practice

Management of the severely brain-injured dog or cat can be frustrating, especially considering the lack of proven effective therapies for head trauma patients. A working knowledge of the basic pathophysiology of head trauma and intracranial pressure (ICP) dynamics is essential to the logical treatment of head traumatized patients. Prevention and correction of hypotension and hypoxemia are necessary for preventing progressive increases in ICP. Mannitol is recommended in most cases of severe head trauma, but there is little evidence to support the use of glucocorticoids in acutely brain-injured dogs and cats. The role of surgical intervention for head-traumatized dogs and cats is still uncertain, but may be beneficial in some cases. Aggressive, expedient treatment and attentive patient monitoring are key aspects of successfully managing canine and feline head trauma patients.