Increased cerebrospinal fluid glutamate and taurine concentrations are associated with traumatic brain edema formation in rats

Enhanced performance of enzymes confined in biocatalytic hydrogen-bonded organic frameworks for sensing of glutamate in the central nervous system

Glutamate (Glu) is a key excitatory neurotransmitter associated with various neurological disorders in the central nervous system, so its measurement is vital to both basic research and biomedical application. In this work, we propose the first example of using biocatalytic hydrogen-bonded organic frameworks (HOFs) as the hosting matrix to encapsulate glutamate oxidase (GLOD) via a de novo approach, fabricating a cascaded-enzyme nanoreactor for Glu biosensing. In this design, the ferriporphyrin ligands can assemble to form Fe-HOFs with high catalase-like activity, while offering a scaffold for the in-situ immobilization of GLOD. Moreover, the formed GLOD@Fe-HOFs are favorable for the efficient diffusion of Glu into the active sites of GLOD via the porous channels, accelerating the cascade reaction with neighboring Fe-HOFs. Consequently, the constructed nanoreactor can offer superior activity and operational stability in the catalytic cascade for Glu biosensing. More importantly, rapid and selective detection can be achieved in the cerebrospinal fluid (CSF) collected from mice in a low sample consumption. Therefore, the successful fabrication of enzyme@HOFs may offer promise to develop high-performance biosensor for further biomedical applications.

Quantifying acute changes in neurometabolism following blast-induced traumatic brain injury

Brain health is largely dependent on the metabolic regulation of amino acids. Brain injuries, diseases, and disorders can be detected through alterations in free amino acid (FAA) concentrations; and thus, mapping the changes has high diagnostic potential. Common methods focus on optimizing neurotransmitter quantification; however, recent focus has expanded to investigate the roles of molecular precursors in brain metabolism. An isocratic method using high performance liquid chromatography with electrochemical cell detection was developed to quantify a wide range of molecular precursors and neurotransmitters: alanine, arginine, aspartate, serine, taurine, threonine, tyrosine, glycine, glutamate, glutamine, and γ-Aminobutyric acid (GABA) following traumatic brain injury. First, baseline concentrations were determined in the serum, cerebrospinal fluid, hippocampus, cortex, and cerebellum of naïve male Sprague Dawley rats. A subsequent study was performed investigating acute changes in FAA concentrations following blast-induced traumatic brain injury (bTBI). Molecular precursor associated FAAs decreased in concentration at 4 h after injury in both the cortex and hippocampus while those serving as neurotransmitters remained unchanged. In particular, the influence of oxidative stress on the observed changes within alanine and arginine pathways following bTBI should be further investigated to elucidate the full therapeutic potential of these molecular precursors at acute time points.

LC-MS/MS analysis of twelve neurotransmitters and amino acids in mouse cerebrospinal fluid

BACKGROUND

So far, analytical investigation of neuroactive molecules in cerebrospinal fluid (CSF) of rodent models has been limited to rats, given the intrinsic anatomic difficulties related to mice sampling and the corresponding tiny amounts of CSF obtained. This poses a challenge for the research in neuroscience, where many, if not most, animal models for neuronal disorders rely on mice.

NEW METHOD

We introduce a new, sensitive and robust LC-MS/MS method to analyze a panel of twelve neuroactive molecules (NM) from mouse CSF (aspartic acid, serine, glycine, glutamate, γ-aminobutyric acid, norepinephrine, epinephrine, acetylcholine, dopamine, serotonin, histamine and its metabolite 1-metylhistamine). The paper describes the sampling procedure that allows the collection of 1-2 microliters of pure CSF from individual mouse specimens.

RESULTS

To test its applicability, we challenged our method on the field, by sampling 37 individual animals, thus demonstrating its strength and reliability.

COMPARISON WITH EXISTING METHOD(S)

Compared to other methods, our procedure does not involve any extraction nor derivatization steps: samples are simply diluted and analyzed as such by LC-MS/MS, using a dedicated ion pairing agent in the chromatographic setup. The panel of neuroactive molecules that is analyzed in a single run is also significantly higher compared to other methods.

CONCLUSIONS

Given the number of mouse models used in the neuroscience research, we believe that our work will pave new ways to more advanced research in this field.

Taurine and aneurysmal subarachnoid hemorrhage prognosis

Despite its beneficial effects for the cardiovascular system, taurine remains a controversial substance. Taurine increases cardiac muscle strength and prevents arrhythmias, but its benefits go beyond this. Determining taurine levels may become an issue of life or death. In aneurysmal subarachnoid hemorrhage, taurine may be a warning signal informing of the risk of death in a patient. High plasma taurine levels may identify those patients at a high risk for death or a vegetative state at discharge from the hospital; thus, taurine may be a vital marker for the prognosis of this disorder. This is even more relevant considering that the result occurred in patients with a good neurological grade at admission that would usually receive a good prognosis but, despite this, one out of four died or remained in a vegetative state. Maybe taurine is key to explain this apparent paradox.

Biodegradable Spheres Protect Traumatically Injured Spinal Cord by Alleviating the Glutamate-Induced Excitotoxicity

New treatment strategies for spinal cord injury with good therapeutic efficacy are actively pursued. Here, acetalated dextran (AcDX), a biodegradable polymer obtained by modifying vicinal diols of dextran, is demonstrated to protect the traumatically injured spinal cord. To facilitate its administration, AcDX is formulated into microspheres (≈7.2 µm in diameter) by the droplet microfluidic technique. Intrathecally injected AcDX microspheres effectively reduce the traumatic lesion volume and inflammatory response in the injured spinal cord, protect the spinal cord neurons from apoptosis, and ultimately, recover the locomotor function of injured rats. The neuroprotective feature of AcDX microspheres is achieved by sequestering glutamate and calcium ions in cerebrospinal fluid. The scavenging of glutamate and calcium ion reduces the influx of calcium ions into neurons and inhibits the formation of reactive oxygen species. Consequently, AcDX microspheres attenuate the expression of proapoptotic proteins, Calpain, and Bax, and enhance the expression of antiapoptotic protein Bcl-2. Overall, AcDX microspheres protect traumatically injured spinal cord by alleviating the glutamate-induced excitotoxicity. This study opens an exciting perspective toward the application of neuroprotective AcDX for the treatment of severe neurological diseases.

Natural Compounds as a Therapeutic Intervention following Traumatic Brain Injury: The Role of Phytochemicals

There has been a tremendous focus on the discovery and development of neuroprotective agents that might have clinical relevance following traumatic brain injury (TBI). This type of brain injury is very complex and is divided into two major components. The first component, a primary injury, occurs at the time of impact and is the result of the mechanical insult itself. This primary injury is thought to be irreversible and resistant to most treatments. A second component or secondary brain injury, is defined as cellular damage that is not immediately obvious after trauma, but that develops after a delay of minutes, hours, or even days. This injury appears to be amenable to treatment. Because of the complexity of the secondary injury, any type of therapeutic intervention needs to be multi-faceted and have the ability to simultaneously modulate different cellular changes. Because of diverse pharmaceutical interactions, combinations of different drugs do not work well in concert and result in adverse physiological conditions. Research has begun to investigate the possibility of using natural compounds as a therapeutic intervention following TBI. These compounds normally have very low toxicity and have reduced interactions with other pharmaceuticals. In addition, many natural compounds have the potential to target numerous different components of the secondary injury. Here, we review 33 different plant-derived natural compounds, phytochemicals, which have been investigated in experimental animal models of TBI. Some of these phytochemicals appear to have potential as possible therapeutic interventions to offset key components of the secondary injury cascade. However, not all studies have used the same scientific rigor, and one should be cautious in the interpretation of studies using naturally occurring phytochemical in TBI research.

Severity of experimental traumatic brain injury modulates changes in concentrations of cerebral free amino acids

In this study, concentrations of free amino acids (FAA) and amino group containing compounds (AGCC) following graded diffuse traumatic brain injury (mild TBI, mTBI; severe TBI, sTBI) were evaluated. After 6, 12, 24, 48 and 120 hr aspartate (Asp), glutamate (Glu), asparagine (Asn), serine (Ser), glutamine (Gln), histidine (His), glycine (Gly), threonine (Thr), citrulline (Cit), arginine (Arg), alanine (Ala), taurine (Tau), γ‐aminobutyrate (GABA), tyrosine (Tyr), S‐adenosylhomocysteine (SAH), l‐cystathionine (l‐Cystat), valine (Val), methionine (Met), tryptophane (Trp), phenylalanine (Phe), isoleucine (Ile), leucine (Leu), ornithine (Orn), lysine (Lys), plus N‐acetylaspartate (NAA) were determined in whole brain extracts (n = 6 rats at each time for both TBI levels). Sham‐operated animals (n = 6) were used as controls. Results demonstrated that mTBI caused modest, transient changes in NAA, Asp, GABA, Gly, Arg. Following sTBI, animals showed profound, long‐lasting modifications of Glu, Gln, NAA, Asp, GABA, Ser, Gly, Ala, Arg, Citr, Tau, Met, SAH, l‐Cystat, Tyr and Phe. Increase in Glu and Gln, depletion of NAA and Asp increase, suggested a link between NAA hydrolysis and excitotoxicity after sTBI. Additionally, sTBI rats showed net imbalances of the Glu‐Gln/GABA cycle between neurons and astrocytes, and of the methyl‐cycle (demonstrated by decrease in Met, and increase in SAH and l‐Cystat), throughout the post‐injury period. Besides evidencing new potential targets for novel pharmacological treatments, these results suggest that the force acting on the brain tissue at the time of the impact is the main determinant of the reactions ignited and involving amino acid metabolism.

Mystixin-7 Peptide Protects Ionotropic Glutamatergic Mechanisms against Glutamate-Induced Excitotoxicity In Vitro

Hyperactivation of the N-methyl-D-aspartic acid type glutamate receptors (NMDARs) causes glutamate excitotoxicity, a process potentially important for many neurological diseases. This study aims to investigate protective effects of the synthetic corticotrophin-releasing factor-like peptide, mystixin-7 (MTX), on model glutamate-induced excitotoxicity in vitro. The technique online monitoring of electrophysiological parameters (excitatory glutamatergic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic (AMPAR) and NMDAR-dependent postsynaptic mechanisms) in the olfactory cortex slices was used. Application of L-glutamate in toxic concentration (20 mM) on slices evoked hyperactivation of NMDARs and weaker activation of the AMPARs. Upon further action agonist, the excessive activation of glutamate receptors was replaced by their irreversible blockade. Pretreatment of the slices using MTX in different concentrations (50 and 100 mg/mL) protected both NMDARs and AMPARs from glutamate-induced damage. An enzymatic treatment of MTX reduced hyperactivation of both NMDARs and AMPARs. The present study demonstrated that MTX minipeptide protected the functioning of both NMDARs and AMPARs against glutamate-induced damage. The MTX peptide is a prospective candidate for elaborated medication in treatment of neurological diseases.

Combination therapies for neurobehavioral and cognitive recovery after experimental traumatic brain injury: Is more better?

Traumatic brain injury (TBI) is a significant health care crisis that affects two million individuals in the United Sates alone and over ten million worldwide each year. While numerous monotherapies have been evaluated and shown to be beneficial at the bench, similar results have not translated to the clinic. One reason for the lack of successful translation may be due to the fact that TBI is a heterogeneous disease that affects multiple mechanisms, thus requiring a therapeutic approach that can act on complementary, rather than single, targets. Hence, the use of combination therapies (i.e., polytherapy) has emerged as a viable approach. Stringent criteria, such as verification of each individual treatment plus the combination, a focus on behavioral outcome, and post-injury vs. pre-injury treatments, were employed to determine which studies were appropriate for review. The selection process resulted in 37 papers that fit the specifications. The review, which is the first to comprehensively assess the effects of combination therapies on behavioral outcomes after TBI, encompasses five broad categories (inflammation, oxidative stress, neurotransmitter dysregulation, neurotrophins, and stem cells, with and without rehabilitative therapies). Overall, the findings suggest that combination therapies can be more beneficial than monotherapies as indicated by 46% of the studies exhibiting an additive or synergistic positive effect versus on 19% reporting a negative interaction. These encouraging findings serve as an impetus for continued combination studies after TBI and ultimately for the development of successful clinically relevant therapies.

Common biochemical defects linkage between post-traumatic stress disorders, mild traumatic brain injury (TBI) and penetrating TBI

Post-traumatic stress disorder (PTSD) is a complex mental disorder with psychological and emotional components, caused by exposure to single or repeated extreme traumatic events found in war, terrorist attacks, natural or man-caused disasters, and by violent personal assaults and accidents. Mild traumatic brain injury (TBI) occurs when the brain is violently rocked back and forth within the skull following a blow to the head or neck as in contact sports, or when in close proximity to a blast pressure wave following detonation of explosives in the battlefield. Penetrating TBI occurs when an object penetrates the skull and damages the brain, and is caused by vehicle crashes, gunshot wound to the head, and exposure to solid fragments in the proximity of explosions, and other combat-related head injuries. Despite clinical studies and improved understanding of the mechanisms of cellular damage, prevention and treatment strategies for patients with PTSD and TBI remain unsatisfactory. To develop an improved plan for treating and impeding progression of PTSD and TBI, it is important to identify underlying biochemical changes that may play key role in the initiation and progression of these disorders. This review identifies three common biochemical events, namely oxidative stress, chronic inflammation and excitotoxicity that participate in the initiation and progression of these conditions. While these features are separately discussed, in many instances, they overlap. This review also addresses the goal of developing novel treatments and drug regimens, aimed at combating this triad of events common to, and underlying, injury to the brain.

Novel therapeutic strategies for traumatic brain injury: acute antioxidant reinforcement

Traumatic brain injury (TBI) is the most important cause of disability in individuals under the age of 45 years and thus represents a significant social and economic burden. Evidence strongly suggests that oxidative stress is a cornerstone event leading to and propagating secondary injury mechanisms such as excitotoxicity, mitochondrial dysfunction, apoptosis, autophagy, brain edema, and inflammation. TBI has defied conventional approaches to diagnosis and therapy development because of its heterogeneity and complexity. Therefore, it is necessary to explore alternative approaches to therapy development for TBI. The aim of this review is to present a therapeutic approach for TBI, taking into account the evidence supporting the role for oxidative stress in the pathophysiological processes of secondary brain injury. The role of agents such as mitochondria-targeted antioxidants (melatonin and new mitochondria-targeted antioxidants), nicotinamide adenine dinucleotide phosphate (NADPH) inhibitors (antioxidant vitamins and apocynin), and other compounds having mainly antioxidant properties (hydrogen-rich saline, sulforaphane, U-83836E, omega-3, and polyphenols) is covered. The rationale for innovative antioxidant therapies based on current knowledge and particularly the most recent studies regarding this field is discussed. Particular considerations and translational potential of new TBI treatments are examined and a novel therapeutic proposal for TBI is presented.

Multifunctional drugs for head injury

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

Purinergic activation of anion conductance and osmolyte efflux in cultured rat hippocampal neurons

The majority of mammalian cells demonstrate regulatory volume decrease (RVD) following swelling caused by hyposmotic exposure. A critical signal initiating RVD is activation of nucleotide receptors by ATP. Elevated extracellular ATP in response to cytotoxic cell swelling during pathological conditions also may initiate loss of taurine and other intracellular osmolytes via anion channels. This study characterizes neuronal ATP-activated anion current and explores its role in net loss of amino acid osmolytes. To isolate anion currents, we used CsCl as the major electrolyte in patch electrode and bath solutions and blocked residual cation currents with NiCl(2) and tetraethylammonium. Anion currents were activated by extracellular ATP with a K(m) of 70 microM and increased over fourfold during several minutes of ATP exposure, reaching a maximum after 9.0 min (SD 4.2). The currents were blocked by inhibitors of nucleotide receptors and volume-regulated anion channels (VRAC). Currents showed outward rectification and inactivation at highly depolarizing membrane potentials, characteristics of swelling-activated anion currents. P2X agonists failed to activate the anion current, and an inhibitor of P2X receptors did not block the effect of ATP. Furthermore, current activation was observed with extracellular ADP and 2-(methylthio)adenosine 5'-diphosphate, a P2Y(1) receptor-specific agonist. Much less current activation was observed with extracellular UTP, suggesting the response is mediated predominantly by P2Y(1) receptors. ATP caused a dose-dependent loss of taurine and alanine that could be blocked by inhibitors of VRAC. ATP did not inhibit the taurine uptake transporter. Thus extracellular ATP triggers a loss of intracellular organic osmolytes via activation of anion channels. This mechanism may facilitate neuronal volume homeostasis during cytotoxic edema.

Diazepam attenuates the post-traumatic hyperactivity of excitatory synapses in rat hippocampal CA1 neurons

The effect of diazepam, a benzodiazepine derivative, on the post-traumatic hyperactivity of excitatory synaptic transmission was examined in rat hippocampal CA1 area. Optical recordings showed that the activity of hippocampal neurons was enhanced in rats treated with fluid percussion injury (FPI) as compared with that of sham-operated rats. The optical response was characterized by fast and slow components. FPI did not affect the fast component that reflects presynaptic action potentials, but enhanced the slow component that reflects excitatory synaptic responses. Intracellular recordings showed that the amplitude and duration of the excitatory postsynaptic potential (EPSP) were increased after FPI. However, FPI did not affect the resting membrane potential and action potentials of hippocampal neurons. Intraperitoneal (i.p.) administration of diazepam (30 and 90 min after FPI) attenuated the post-traumatic hyperactivity of the slow optical response. The slope of input-to-output relation of excitatory synapses was decreased by acute administration of diazepam to FPI rats, but not by delayed administration of diazepam (4 and 5 h after FPI). The fast optical responses were not affected by either FPI or i.p. administration of diazepam. These results suggest that administration of diazepam at early post-traumatic period prevents the FPI-induced delayed enhancement of excitatory synaptic transmission in rat hippocampal CA1 neurons.

Heterogeneous regional and temporal energetic impairment following controlled cortical impact injury in rats

OBJECTIVES

Following traumatic brain injury metabolic stability is impaired. Duration and reversibility of these changes might be important to guide specific interventions.

METHODS

To characterize temporal and regional changes in cerebral metabolism, 68 male Sprague-Dawley rats were subjected to a focal cortical contusion. Lesion progression and mitochondrial impairment were determined by magnetic resonance imaging (MRI) and triphenyl tetrazolium chloride (TTC) staining, respectively. Metabolic alterations were determined at hours 6 and 24 and day 7 by measuring extracellular glucose, lactate and hypoxanthine levels with microdialysis catheters placed adjacent and distant to the contusion and by quantifying changes in tissue ATP, lactate and glucose using bioluminescence imaging.

RESULTS

The cortical lesion reached its maximal extent at hour 24 and remained confined to the ipsilateral hemisphere. In microdialysate, at hour 6, extracellular hypoxanthine and lactate reached maximal values, thereafter hypoxanthine normalized while lactate remained increased. Extracellular glucose reached the highest values at hour 24 and remained elevated. Bioluminescence imaging revealed heterogeneous changes in areas distant to the contusion. No significant changes were found in ATP content. Slightly elevated tissue glucose until 24 hours in the ipsilateral hemisphere was observed. Following a continuous increase, lactate levels were the highest by 6 hours in the ipsilateral cortex and hippocampus.

DISCUSSION

CCI is associated with disturbances in energetic metabolism. Metabolic perturbation is not restricted to the early phase and the contusional region following focal cortical contusion, but also involves hippocampus and primarily uninjured parts of the hemisphere.

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.

Cortical edema in moderate fluid percussion brain injury is attenuated by vagus nerve stimulation

Development of cerebral edema (intracellular and/or extracellular water accumulation) following traumatic brain injury contributes to mortality and morbidity that accompanies brain injury. Chronic intermittent vagus nerve stimulation (VNS) initiated at either 2 h or 24 h (VNS: 30 s train of 0.5 mA, 20 Hz, biphasic pulses every 30 min) following traumatic brain injury enhances recovery of motor and cognitive function in rats in the weeks following brain injury; however, the mechanisms of facilitated recovery are unknown. The present study examines the effects of VNS on development of acute cerebral edema following unilateral fluid percussion brain injury (FPI) in rats, concomitant with assessment of their behavioral recovery. Two hours following FPI, VNS was initiated. Behavioral testing, using both beam walk and locomotor placing tasks, was conducted at 1 and 2 days following FPI. Edema was measured 48 h post-FPI by the customary method of region-specific brain weights before and after complete dehydration. Results of this study replicated that VNS initiated at 2 h after FPI: 1) effectively facilitated the recovery of vestibulomotor function at 2 days after FPI assessed by beam walk performance (P<0.01); and 2) tended to improve locomotor placing performance at the same time point (P=0.18). Most interestingly, results of this study showed that development of edema within the cerebral cortex ipsilateral to FPI was significantly attenuated at 48 h in FPI rats receiving VNS compared with non-VNS FPI rats (P<0.04). Finally, a correlation analysis between beam walk performance and cerebral edema following FPI revealed a significant inverse correlation between behavior performance and cerebral edema. Together, these results suggest that VNS facilitation of motor recovery following experimental brain injury in rats is associated with VNS-mediated attenuation of cerebral edema.

Acute alterations of glutamate, glutamine, GABA, and other amino acids after spinal cord contusion in rats

Spinal cord injury (SCI) leads to an alteration of energetic metabolism. As a consequence, glutamate, glutamine, aspartate and other important amino acids are altered after damage, leading to important disregulation of the neurochemical pathways. In the present study, we characterized the acute-phase changes in tissue concentration of amino acids involved in neurotransmitter and non-neurotransmitter actions after SCI by contusion in rats. Animals were submitted to either laminectomy or SCI by contusion and sacrificed at 2, 4, 8, and 12 h after lesion, for the analysis of tissue amino acids by HPLC. Results showed that both aspartate and glutamate contents diminished after SCI, while glutamine concentrations raised, however, the sum of molar concentrations of glutamate plus glutamine remained unchanged at all time points. GABA concentrations increased versus control group, while glycine remained unchanged. Finally, citrulline levels increased by effect of SCI, while taurine-increased only 4 h after lesion. Results indicate complex acute-phase changes in amino acids concentrations after SCI, reflecting the different damaging processes unchained after lesion.

Changes in concentration of cerebrospinal fluid components in patients with traumatic brain injury

Brain injury, like other central nervous system pathologies, causes changes in the composition of the cerebrospinal fluid (CSF). In this study, changes in the concentration of small molecules of the CSF, which are in the minimal micromolar concentration, were observed and monitored using high-resolution proton (NMR) spectroscopy. Twenty-two patients with isolated traumatic brain injuries (TBI) and 15 patients making up the control group were recruited for the study. CSF samples were collected by lumbar puncture from the lumbar subarachnoid space in the patients just before commencement of therapy and on the first, third, seventh and fourteenth days of therapy at the ICU. Forty-four signals of the NMR spectra and NO concentration of the CSF samples were analyzed. The analysis shows that the amino acid and organic acid concentrations change during the therapy and mostly are higher than in the control group. Significant differences in concentration of the analyzed CSF components between the TBI patients and the control group have been noted. The rate of the lactate to pyruvate conversion increased because the L/P ratio showed no significant differences between the TBI group and the control group, while the concentrations of both components were significantly higher in the TBI patients than in the control group. Citrulline, arginine and nitric oxide concentrations were the focus of the analysis. Citrulline concentration changes overlapped NO changes from 0 until 3rd day of therapy, while for the remaining days of observation the NO concentration stabilized at the control level, whereas citrulline concentration significantly decreased.

Granulocyte colony-stimulating factor does not affect contusion size, brain edema or cerebrospinal fluid glutamate concentrations in rats following controlled cortical impact

INTRODUCTION

Granulocyte colony-stimulating factor (G-CSF) is an established treatment in the neutropenic host. Usage in head-injured patients at risk for infection may aggravate brain damage. In contrast, evidence of G-CSF neuroprotective effects has been reported in rodent models of focal cerebral ischemia. We investigated effects of G-CSF in acute focal traumatic brain injury (TBI) in rats.

METHODS

Thirty-six male Sprague-Dawley rats were anesthetized with 1.2%) to 2.0% isoflurane and subjected to controlled cortical impact injury (CCII). Thirty minutes following CCII, either vehicle or G-CSF was administered intravenously. Animals were sacrificed 24 hours following CCII. Glutamate concentrations were determined in cisternal cerebrospinal fluid (CSF). Brain edema was assessed gravimetrically. Contusion size was estimated by 2,3,5-triphenyltetrazolium chloride staining and volumetric analysis.

RESULTS

Dose-dependent leukocytosis was induced by infusion of G-CSF. Physiological variables were unaffected. Water content of the traumatized hemisphere and CSF glutamate concentrations were unchanged by treatment. Contusion volume was similar in all groups.

CONCLUSIONS

A single injection of G-CSF did not influence cortical contusion volume, brain edema, or glutamate concentrations in CSF determined 24 hours following CCII in rats. G-CSF, administered 30 minutes following experimental TBI, failed to exert neuroprotective effects.

Regulation of taurine transport in rat hippocampal neurons by hypo-osmotic swelling

Taurine, an important mediator of cellular volume regulation in the central nervous system, is accumulated into neurons and glia by means of a highly specific sodium-dependent membrane transporter. During hyperosmotic cell shrinkage, net cellular taurine content increases as taurine transporter activity is enhanced via elevated gene expression of the transporter protein. In hypo-osmotic conditions, taurine is rapidly lost from cells by means of taurine-conducting membrane channels. We reasoned that changes in taurine transporter activity also might accompany cell swelling to minimize re-accumulation of taurine from the extracellular space. Thus, we determined the kinetic and pharmacological characteristics of neuronal taurine transport and the response to osmotic swelling. Accumulation of radioactive taurine is strongly temperature dependent and occurs via saturable and non-saturable pathways. At concentrations of taurine expected in extracellular fluid in vivo, 98% of taurine accumulation would occur via the saturable pathway. This pathway obeys Michaelis-Menten kinetics with a Km of 30.0 +/- 8.8 microm (mean +/- SE) and Jmax of 2.1 +/- 0.2 nmol/mg protein min. The saturable pathway is dependent on extracellular sodium with an effective binding constant of 80.0 +/- 3.1 mm and a Hill coefficient of 2.1 +/- 0.1. This pathway is inhibited by structural analogues of taurine and by the anion channel inhibitors, 4,4'-diisothiocyanostilbene-2, 2'-disulfonic acid (DIDS) and 5-nitro-2-(3 phenylpropylamino) benzoic acid (NPPB). NPPB, but not DIDS, also reduces the ATP content of the cell cultures. Osmotic swelling at constant extracellular sodium concentration reduces the Jmax of the saturable transport pathway by approximately 48%, increases Kdiff for the non-saturable pathway by 77%, but has no effect on cellular ATP content. These changes in taurine transport occurring in swollen neurons in vivo would contribute to net reduction of taurine content and resulting volume regulation.

Heat Shock Protein HSP70 Increases the Resistance of Cortical Cells to Glutamate Excitotoxicity

Preincubation of cultured slices of the olfactory cortex of rat brain with heat shock protein in a concentration of 1 microg/ml protected the pre- and postsynaptic mechanisms of glutamatergic synaptic transmission from glutamate excitotoxicity (50 mM) inducing blockade of excitatory postsynaptic function and reducing presynaptic processes. It was hypothesized that heat shock protein protects AMPA and NMDA receptor-mediated processes.

Proton MR spectroscopy detected glutamate/glutamine is increased in children with traumatic brain injury

Adults with traumatic brain injury (TBI) have been shown by invasive methods to have increased levels of the excitatory neurotransmitter glutamate. It is unclear whether glutamate release contributes to primary or secondary injury and whether its protracted elevation is predictive of a poor outcome. Preliminary studies at our institution in adults found that early increases in magnetic resonance spectroscopy (MRS)-detected glutamate/glutamine (Glx) were associated with poor outcomes. We therefore studied 38 children (mean age, 11 years; range, 1.6-17 years) who had TBI with quantitative short-echo time (STEAM, TE = 20 msec) proton MRS, a mean of 7 +/- 4 (range, 1-17) days after injury in order to determine if their occipital or parietal Glx levels correlated with the severity of injury or outcome. Occipital Glx was significantly increased in children with TBI compared to controls (13.5 +/- 2.4 vs. 10.7 +/- 1.8; p = 0.002), but there was no difference between children with good compared to poor outcomes as determined by the Pediatric Cerebral Performance Category Scale score at 6-12 months after injury. We also did not find a correlation between the amount of Glx and the initial Glasgow Coma Scale score, duration of coma, nor with changes in spectral metabolites, including N-acetyl aspartate, choline, and myoinositol. In part, this may have occurred because, in this study, most patients with poor outcomes were studied later than patients with good outcomes, potentially beyond the time frame for peak elevation of Glx after injury. Additional early and late studies of patients with varying degrees of injury are required to assess the importance to the pathophysiology of TBI of this excitatory neurotransmitter.

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

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

Short-term lithium treatment promotes neuronal survival and proliferation in rat striatum infused with quinolinic acid, an excitotoxic model of Huntington's disease

We assessed the ability of lithium to reduce neurodegeneration and to stimulate cell proliferation in a rat model of Huntington's disease in which quinolinic acid (QA) was unilaterally infused into the striatum. LiCl (0.5-3.0 mEq/kg) was injected subcutaneously 24 h before and 1 h after QA infusion. At 7 days after QA injection, lithium significantly diminished the loss of neurons immunostained for Neuronal Nuclei (NeuN) in the injured striatum, but failed to prevent the reduction of NADPH-diaphorase-positive striatal interneurons. Lithium also reduced the number of neurons showing DNA damage or activated caspase-3. This neuroprotection was associated with an upregulation of Bcl-2 protein levels in the striatal tissue and an increase in the number and density of Bcl-2 immunostaining in striatal neurons. Bromodeoxyuridinie (BrdU) labeling in the lithium-treated injured striatum revealed the presence of large numbers of proliferating cells near the QA-injection site, with a reduction of BrdU-labeled cells in the subventricular zone (SVZ). All BrdU-labeled cells in the SVZ and the majority of BrdU-labeled cells near the QA-injection site were negative for either NeuN or glial fibrillary acidic protein (GFAP), suggesting that they are undifferentiated progenitor cells. However, a small number of BrdU-positive cells found in the QA-injected and lithium-treated striatum site were positive for either NeuN or GFAP. Our results suggest that lithium is neuroprotective in the QA-injection model of Huntington's disease not only due to its ability to inhibit apoptosis but also because it can stimulate neuronal and astroglial progenitor proliferation in the QA-injected striatum or their migration from the SVZ.

Differential Concentration-Dependent Effects of Prolonged Norepinephrine Infusion on Intraparenchymal Hemorrhage and Cortical Contusion in Brain-Injured Rats

Under clinical conditions catecholamines are infused to elevate cerebral perfusion pressure and improve impaired posttraumatic cerebral microcirculation. This, however, is associated with the risk of additional hemorrhage in the acute phase following traumatic brain injury. In the present study we investigated the dose-dependent effects of prolonged norepinephrine infusion on arterial blood pressure, blood glucose, and structural damage in brain-injured rats. At 4 h following induction of a focal cortical contusion (CCI), 40 rats were randomized to receive low (0.15), medium (0.3), or high dose (1 microg/kg/min) norepinephrine. Control rats were given equal volume of NaCl. Norepinephrine and NaCl were infused intravenously via Alzet osmotic pumps for 44 h. Mean arterial blood pressure (MABP), blood gases and blood glucose were determined before, at 4, 24, 48 h after CCI in repeatedly anesthetized rats (n = 28). Systolic arterial blood pressure (SABP) was measured using the tail cuff method in awake, restrained rats (n = 12). Cortical contusion and intraparenchymal hemorrhage volume were quantified at 48 h in all rats. MABP determined in anesthetized rats was only marginally increased. SABP was significantly elevated during infusion of medium and high dose norepinephrine in awake rats, exceeding 140 mm Hg. Medium and high dose norepinephrine significantly increased cortical hemorrhage by 157% and 142%, without increasing the cortical contusion volume. Low dose norepinephrine significantly reduced the cortical contusion by 44%. Norepinephrine aggravates the underlying brain damage during the acute posttraumatic phase. Future studies are needed to determine the least deleterious norepinephrine concentration.

Acute etomidate treatment reduces cognitive deficits and histopathology in rats with traumatic brain injury

OBJECTIVE

To test the hypothesis that etomidate treatment improves functional, cognitive, and histologic outcome after experimental traumatic brain injury.

DESIGN

Controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Traumatic brain injury was produced by controlled cortical impact injury (4 m/sec, 2.6 mm of tissue deformation). Etomidate (2 mg/kg) was administered intravenously immediately before injury (n = 13) or 5 mins after injury (n = 12). Additional rats received saline treatment 5 mins after injury (n = 12) or served as sham controls (n = 10).

MEASUREMENTS AND MAIN RESULTS

Rats were evaluated on beam balance and beam walk tasks on postoperative days 1-5 and then trained in the Morris water maze on postoperative days 14-18. On day 28, the rats were killed, and hippocampal CA1 and CA3 neuron counts and cortical lesion volume were measured in histologic brain sections. Preinjury etomidate attenuated beam balance deficits, water maze deficits, hippocampal CA3 neuronal loss, and cortical tissue loss but did not attenuate beam walk deficits or hippocampal CA1 neuronal loss. Postinjury etomidate attenuated water maze deficits, but it did not affect any other outcome measure.

CONCLUSIONS

Administration of etomidate both before and after injury attenuates secondary injury resulting from traumatic brain injury, but the effect is more pronounced with pretreatment. The ineffectiveness of postinjury etomidate on motor and histologic tasks suggests a brief therapeutic treatment window in rats. However, the treatment window in humans is unknown. Lastly, postinjury etomidate did not exacerbate neurologic or histologic outcome.

Effects of early and late intravenous norepinephrine infusion on cerebral perfusion, microcirculation, brain-tissue oxygenation, and edema formation in brain-injured rats

OBJECTIVES

Reduction of cerebral perfusion during the early phase after traumatic brain injury is followed by a later phase of normal to increased perfusion. Thus, pharmacologically elevating mean arterial blood pressure with the aim of improving cerebral perfusion may exert different time-dependent effects on cortical perfusion, microcirculation, tissue oxygenation and brain edema formation after traumatic brain injury.

DESIGN

Randomized, placebo-controlled trial.

SETTING

Experimental laboratory at a university hospital.

SUBJECTS

A total of 37 male Sprague-Dawley rats subjected to a focal cortical contusion.

INTERVENTIONS

At 4 or 24 hrs after focal traumatic brain injury, mean arterial blood pressure was increased to 120 mm Hg for 90 mins by infusing norepinephrine. In rats receiving physiologic saline, mean arterial blood pressure remained unchanged. In the first series, pericontusional cortical perfusion was measured using the laser Doppler flowmetry scanning technique before injury and before, during, and after the infusion period. In a second series, intracranial and cerebral perfusion pressure and intraparenchymal perfusion and tissue oxygen measured within the contused and pericontusional cortex were recorded continuously before, during, and after norepinephrine infusion. Changes in cortical microcirculation were investigated by orthogonal polarization spectral imaging. At the end of each experiment, hemispheric swelling and water content were determined gravimetrically.

MEASUREMENTS AND MAIN RESULTS

At 4 and 24 hrs after traumatic brain injury, intravenous norepinephrine significantly increased pericontusional cortical perfusion, which was also reflected by an increase in diameters and flow velocities of pericontusional arterioles and venules. Cerebral perfusion pressure and intraparenchymal perfusion and tissue oxygen were significantly increased during norepinephrine infusion at 4 and 24 hrs. Hemispheric swelling and water content showed no difference between the groups.

CONCLUSIONS

After cortical impact injury, early and late intravenous norepinephrine infusion pressure-dependently increased cerebral perfusion and tissue oxygenation without aggravating or reducing brain edema formation. Future studies are warranted to determine long-term changes of short and prolonged norepinephrine-induced increases in mean arterial blood pressure and cerebral perfusion pressure.

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.

Guanine and adenine nucleotidase activities in rat cerebrospinal fluid

Adenine and guanine nucleotides have been shown to exert multiple roles in central and peripheral nervous systems, and the sequential breakdown of these nucleotides by enzymatic systems is an important step in the modulation of their extracellular effects. The aim of this study was to investigate whether nucleotide hydrolysis also occurs in the cerebrospinal fluid (CSF) of rats. CSF was able to hydrolyze all guanine and adenine nucleotides investigated (2.0 mM): GDPz.Gt;ADP=ATP=GTPz.Gt;AMP=GMP. More detailed studies with the diphosphate nucleotides showed that the hydrolysis of ADP and GDP was linear with incubation time and protein concentration. The apparent K(M) (Henry-Michaelis-Menten constant) and V (maximal velocity) values for ADP and GDP were 164.3+/-54.7 microM and 12.2+/-3.8 nmol P(i)/min per mg protein, and 841.0+/-90.2 microM and 22.8+/-8.0 nmol P(i)/min per mg protein. The sum of ADP, GDP and UDP hydrolysis (2.0 mM) upon individual incubations with CSF was similar to the hydrolysis observed when all three nucleotides were incubated together. This pattern of hydrolysis strongly suggests the involvement of more than one enzyme activity. The higher maximum activity for GDP and UDP compared to ADP is compatible with presence of a soluble NTDPase5.

Guanosine enhances glutamate uptake in brain cortical slices at normal and excitotoxic conditions

1. The effect of guanosine on L-[2,3-3H]glutamate uptake was investigated in brain cortical slices under normal or oxygen-glucose deprivation (OGD) conditions. 2. In slices exposed to physiological conditions, guanosine (1-100 microM) stimulated glutamate uptake (up to 100%) in a concentration-dependent manner when a high (100 microM) but not a low (1 microM) concentration of glutamate was used. 3. In slices submitted to OGD, guanosine 1 and 100 microM also increased 100 microM glutamate uptake (38 and 70%, respectively). 4. The increasing of glutamate and taurine released to the incubation medium in cortical slices submitted to OGD were significantly attenuated by the presence of guanosine in the incubation medium. 5. Guanosine prevented the increase in propidium iodide incorporation into cortical slices induced by OGD, indicating a protective role against ischemic injury. 6. These results support the hypothesis of a protective role for guanosine during brain ischemia, possibly by activating glutamate uptake into neural cells.

Release of excitatory amino acids in the penumbra of a focal cortical necrosis

A cortical tissue necrosis from focal trauma expands between 30% and 300% from its initial size within 24 h, depending on the species studied. To shed light on the pathophysiological processes in the penumbra 1 zone after a focal cortical lesion, the release of excitatory amino acids into the traumatic penumbra zone 1 was measured throughout the entire period of necrosis expansion. A microdialysis probe was inserted at an oblique angle into the cortex of Sprague-Dawley rats 2 mm below the brain surface. One day later, a highly standardized cortical freezing lesion was induced at the brain cortex above the microdialysis probe. Dialysate was continuously collected prior to, during, and up to 24 h after trauma and analyzed for primary amino acids. In each animal, it was confirmed histologically that the tip of the microdialysis probe was localized in the gray matter in close proximity to the primary lesion. Following induction of the trauma, a statistically significant sharp increase of the dialysate level of aspartate, glutamate, glycine, and serine was observed. Thereafter, the dialysate levels of these amino acids returned to baseline levels without any further increase throughout the remaining observation period. This process ranged in time from a few minutes to a few hours. The level of alanine in the dialysate was essentially not altered throughout the experiment. Although the early post-traumatic increase of the excitatory neurotransmitters aspartate and glutamate may well contribute to the secondary lesion growth of a cortical necrosis after trauma, glutamate receptor targeted therapeutic intervention may be in view of these findings of limited use when initiated post trauma.

Early expression of glutamate transporter proteins in ramified microglia after controlled cortical impact injury in the rat

Traumatic brain injury is followed by increased extracellular glutamate concentration. Uptake of glutamate is mainly mediated by the glial glutamate transporters GLAST and GLT-1. Extent and distribution of GLAST and GLT-1 were studied in a rat model of controlled cortical impact injury (CCII). Western Blot analysis revealed lowest levels of GLAST and GLT-1 with a decrease by 40%-54% and 42%-49% between 24 and 72 h posttrauma. By 8 h after CCII, CSF glutamate levels were increased (10.5 microM vs. 2.56 microM in controls; P < 0.001), reaching maximum values by 48 h. A significant increase in de novo GLAST and GLT-1 expressing ramified microglia was observed within 4 h, reached a stable level by 48 h, and remained high up to 72 h after CCII. Furthermore, ramified microglia de novo expressed the neuronal glutamate transporter EAAC1 after CCII. Following CCII, GLAST/GLT-1 and GFAP coexpressing astrocytes were immediately reduced, reaching minimum levels within 8 h. This reduction of expression could be either due to protein downregulation or loss of astrocytes. At 72 h, a marked population of GLAST- and GLT-1-positive reactive astrocytes appeared. These results support the hypothesis that reduced astrocytic GLAST and GLT-1 protein levels following CCII contribute to evolving secondary injury. Microglia are capable of de novo expressing glutamate transporter proteins, indicating that the expression of glial and neuronal glutamate transporters is not restricted to a specific glial or neuronal lineage. Ramified microglia may play an important compensatory role in the early regulation of extracellular glutamate after CCII.