An evaluation of the role of extracellular amino acids in the delayed neurodegeneration induced by quinolinic acid in the rat striatum

Zinc: indications in brain disorders

Zinc is the authoritative metal which is present in our body, and reactive zinc metal is crucial for neuronal signaling and is largely distributed within presynaptic vesicles. Zinc also plays an important role in synaptic function. At cellular level, zinc is a modulator of synaptic activity and neuronal plasticity in both development and adulthood. Different importers and transporters are involved in zinc homeostasis. ZnT-3 is a main transporter involved in zinc homeostasis in the brain. It has been found that alterations in brain zinc status have been implicated in a wide range of neurological disorders including impaired brain development and many neurodegenerative disorders such as Alzheimer's disease, and mood disorders including depression, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and prion disease. Furthermore, zinc has also been implicated in neuronal damage associated with traumatic brain injury, stroke, and seizure. Understanding the mechanisms that control brain zinc homeostasis is thus critical to the development of preventive and treatment strategies for these and other neurological disorders.

The Ayurvedic drug, Ksheerabala, ameliorates quinolinic acid-induced oxidative stress in rat brain

One of the mechanisms of neurotoxicity is the induction of oxidative stress. There is hardly any cure for neurotoxicity in modern medicine, whereas many drugs in Ayurveda possess neuroprotective effects; however, there is no scientific validation for these drugs. Ksheerabala is an ayurvedic drug which is used to treat central nervous system disorders, arthritis, and insomnia. The aim of our study was to evaluate the effect of Ksheerabala on quinolinic acid-induced toxicity in rat brain. The optimal dose of Ksheerabala was found from a dose escalation study, wherein it was found that Ksheerabala showed maximum protection against quinolinic acid-induced neurotoxicity at a dose of 15 µL/100 g body weight/day, which was selected for further experiments. Four groups of female albino rats were maintained for 21 days as follows: 1. Control group, 2. Quinolinic acid (55 µg/100 g body weight), 3. Ksheerabala (15 µL/100 g body weight), 4. Ksheerabala (15 µL/100 g body weight) + Quinolinic acid (55 µg/100 g body weight). At the end of the experimental period, levels of lipid peroxidation products, protein carbonyls, and activities of scavenging enzymes were analyzed. The results revealed that quinolinic acid intake caused enhanced lipid and protein peroxidation as evidenced by increased levels of peroxidation products such as malondialdehyde, hydroperoxide, conjugated dienes, and protein carbonyls. On the other hand, the activities of scavenging enzymes such as catalase, superoxide dismutase (SOD), glutathione peroxidase, and glutathione reductase as well as the concentration of glutathione were reduced. On coadminstration of Ksheerabala along with quinolinic acid, the levels of all the biochemical parameters were restored to near-normal levels, indicating the protective effect of the drug. These results were reinforced by histopathological studies.

The role of zinc in neurodegenerative inflammatory pathways in depression

According to new hypothesis, depression is characterized by decreased neurogenesis and enhanced neurodegeneration which, in part, may be caused by inflammatory processes. There is much evidence indicating that depression, age-related changes often associated with impaired brain function and cognitive performances or neurodegenerative processes could be related to dysfunctions affecting the zinc ion availability. Clinical studies revealed that depression is accompanied by serum hypozincemia, which can be normalized by successful antidepressant treatment. In patients with major depression, a low zinc serum level was correlated with an increase in the activation of markers of the immune system, suggesting that this effect may result in part from a depression-related alteration in the immune-inflammatory system. Moreover, a preliminary clinical study demonstrated the benefit of zinc supplementation in antidepressant therapy in both treatment non-resistant and resistant patients. In the preclinical study, the antidepressant activity of zinc was observed in the majority of rodent tests and models of depression and revealed a causative role for zinc deficiency in the induction of depressive-like symptoms, the reduction of neurogenesis and neuronal survival or impaired learning and memory ability. This paper provides an overview of the clinical and experimental evidence that implicates the role of zinc in the pathophysiology and therapy of depression within the context of the inflammatory and neurodegenerative hypothesis of this disease.

Vascular pathology and blood-brain barrier disruption in cognitive and psychiatric complications of type 2 diabetes mellitus

Vascular pathology is recognized as a principle insult in type 2 diabetes mellitus (T2DM). Co-morbidities such as structural brain abnormalities, cognitive, learning and memory deficits are also prevailing in T2DM patients. We previously suggested that microvascular pathologies involving blood-brain barrier (BBB) breakdown results in leakage of serum-derived components into the brain parenchyma, leading to neuronal dysfunction manifested as psychiatric illnesses. The current postulate focuses on the molecular mechanisms controlling BBB permeability in T2DM, as key contributors to the pathogenesis of mental disorders in patients. Revealing the mechanisms underlying BBB dysfunction and inflammatory response in T2DM and their role in metabolic disturbances, abnormal neurovascular coupling and neuronal plasticity, would contribute to the understanding of the mechanisms underlying psychopathologies in diabetic patients. Establishing this link would offer new targets for future therapeutic interventions.

Inflammation, glutamate, and glia in depression: a literature review

Multiple lines of evidence suggest that inflammation and glutamate dysfunction contribute to the pathophysiology of depression. In this review we provide an overview of how these two systems may interact. Excess levels of inflammatory mediators occur in a subgroup of depressed patients. Studies of acute experimental activation of the immune system with endotoxin and of chronic activation during interferon-alpha treatment show that inflammation can cause depression. Peripheral inflammation leads to microglial activation which could interfere with excitatory amino acid metabolism leading to inappropriate glutamate receptor activation. Loss of astroglia, a feature of depression, upsets the balance of anti- and pro-inflammatory mediators and further impairs the removal of excitatory amino acids. Microglia activated by excess inflammation, astroglial loss, and inappropriate glutamate receptor activation ultimately disrupt the delicate balance of neuroprotective versus neurotoxic effects in the brain, potentially leading to depression.

A psychoneuroimmunological perspective to Emil Kraepelins dichotomy: schizophrenia and major depression as inflammatory CNS disorders

The Kraepelinian classification of psychiatric disorders, in particular the dichotomy of dementia praecox and manic-depressive psychosis is under discussion since a long time. In recent years, not only new research in the fields of psychopathology and clinical outcome, but also findings of biological markers in the areas of neurophysiology, neuroendocrinology, psychoneuroimmunology, genetics, or psychopharmacology show a big overlap between both groups of disorders. This overlap of symptoms and markers of both disorders intensified the discussion and the proposals for new criteria for the classification of psychiatric disorders. By means of findings from the field of psychoneuroimmunology and inflammation it will be shown that different pathological mechanisms in depression and schizophrenia may lead to the same final common pathway of inflammation. These mechanisms include the immunological balance between type-1 and type-2 immune activation which influences the tryptophan-degradating enzyme indoleamine 2,3-dioxygenase (IDO) in the CNS in opposite ways, leading to an altered availability of tryptophan and serotonin, and a disturbance of the kynurenine metabolism with an imbalance in favor of the production of the NMDA-receptor agonist quinolinic acid in depression and of the NMDA-receptor antagonist kynurenic acid in schizophrenia. In both disorders, however, an increased production of prostaglandin E2 and increased expression of cyclo-oxygenase-2 reflect a slight inflammatory process taking place probably in different regions of the CNS. Albeit this common inflammatory pathway--inflammation is a general pathway of the body as answer to a lot of different noxae and pathogens--the Kraepelinian dichotomy is important with respect to pathological mechanisms and therapeutic approaches, not only for further research in understanding the exact pathological mechanisms but also for the development of preventive strategies in high risk individuals and in patients. Opposite pathways regarding the immune activation, the neurotoxic versus neuroprotective kynurenine metabolites and the agonistic versus antagonistic effects on the NMDA receptor and the glutamatergic neurotransmission show despite a possible therapeutic advantage of anti-inflammatory therapy in both disorders that the Kraepelinian dichotomy still has a significant value from a biologic-psychiatric point of view.

The immune-mediated alteration of serotonin and glutamate: towards an integrated view of depression

Beside the well-known deficiency in serotonergic neurotransmission as pathophysiological correlate of major depression (MD), recent evidence points to a pivotal role of increased glutamate receptor activation as well. However, cause and interaction of these neurotransmitter alterations are not understood. In this review, we present a hypothesis integrating current concepts of neurotransmission and hypothalamus-pituitary-adrenal (HPA) axis dysregulation with findings on immunological alterations and alterations in brain morphology in MD. An immune activation including increased production of proinflammatory cytokines has repeatedly been described in MD. Proinflammatory cytokines such as interleukin-2, interferon-gamma, or tumor necrosis factor-alpha activate the tryptophan- and serotonin-degrading enzyme indoleamine 2,3-dioxygenase (IDO). Depressive states during inflammatory somatic disorders are also associated with increased proinflammatory cytokines and increased consumption of tryptophan via activation of IDO. An enhanced consumption of serotonin and its precursor tryptophan through IDO activation could well explain the reduced availability of serotonergic neurotransmission in MD. An increased activation of IDO and its subsequent enzyme kynurenine monooxygenase by proinflammatory cytokines, moreover, leads to an enhanced production of quinolinic acid, a strong agonist of the glutamatergic N-methyl-D-aspartate receptor. In inflammatory states of the central nervous system, IDO is mainly activated in microglial cells, which preferentially metabolize tryptophan to the NMDA receptor agonist quinolinic acid, whereas astrocytes - counteracting this metabolism due to the lack of an enzyme of this metabolism - have been observed to be reduced in MD. Therefore the type 1/type 2 immune response imbalance, associated with an astrocyte/microglia imbalance, leads to serotonergic deficiency and glutamatergic overproduction. Astrocytes are further strongly involved in re-uptake and metabolic conversion of glutamate. The reduced number of astrocytes could contribute to both, a diminished counterregulation of IDO activity in microglia and an altered glutamatergic neurotransmission. Further search for antidepressant agents should take into account anti-inflammatory drugs, for example, cyclooxygenase-2 inhibitors, might exert antidepressant effects by acting on serotonergic deficiency, glutamatergic hyperfunction and antagonizing neurotoxic effects of quinolinic acid.

Neuroimmune-endocrine crosstalk in schizophrenia and mood disorders

This review focuses on possible causes and the impact of different immune states in schizophrenia and major depression. It discusses the fact that, in schizophrenia, an over-activation of the type 2 immune response may dominate, while the type 1 and the pro-inflammatory immune responses are over-activated in major depression. The consequence of these diverse immune states is the activation and, respectively, inhibition of different enzymes in tryptophan/kynurenine metabolism, which may lead to an overemphasis of N-methyl-D-aspartate (NMDA) receptor antagonism in schizophrenia and of NMDA-receptor agonism in depression, resulting in glutamatergic hypofunction in schizophrenia and glutamatergic hyperfunction in major depression. In addition, the activation of the type 1 and the pro-inflammatory immune responses in major depression result in increased serotonin degradation and a serotonergic deficit. While antipsychotics and antidepressants today mainly act on the dopaminergic-glutamatergic and the noradrenergic-serotonergic neurotransmission, anti-inflammatory and immune-modulating therapies might act more basically at the pathophysiological mechanism. The limitations of this concept, however, are critically discussed.

Participation of N-methyl-D-aspartate receptors on methylmercury-induced DNA damage in rat frontal cortex

Methylmercury (MeHg) inhibits glutamate uptake by astrocytes, which can contribute to neuronal loss through excitotoxicity. We explored the extent at which this phenomenon is involved in MeHg-induced DNA damage in the rat cortex. MeHg amounts that increase extracellular glutamate (1.5, 7.5 and 15 nmol, according to previous reports) were stereotaxically injected in the frontal cortex of adult rats before DNA-damage determination by means of a quantitative TUNEL assay. After either 24 or 48 h, the cortex of all exposed animals showed significant increments of damaged DNA, compared with rats that only received sterile saline. In parallel experiments, we found that the administration of a non competitive NMDA receptor antagonist (MK-801, 10 mg/kg, i.p.) 1 h before MeHg injection, significantly reduced DNA damage. These results demonstrate that activation of NMDA receptors contributes importantly to MeHg neurotoxicity.

NMDA preconditioning protects against seizures and hippocampal neurotoxicity induced by quinolinic acid in mice

PURPOSE

N-methyl D-aspartate (NMDA) preconditioning has been used to prevent cellular death induced by glutamate or NMDA in cultured neurons. Quinolinic acid (QA)-induced seizures are used to average NMDA receptors-evoked neurotoxicity in animal models. The purpose of this study was to investigate the potential neuroprotective effects of NMDA preconditioning against QA-induced seizures and hippocampal damage in vivo.

METHODS

Mice were pretreated with nonconvulsant doses of NMDA for different times before i.c.v. QA infusion and observed for the occurrence of seizures. Hippocampal slices from mice were assayed to measure cellular viability.

RESULTS

NMDA preconditioning presented 53% protection against QA-induced seizures, as well as QA-induced cellular death in the hippocampus. The NMDA receptor antagonist, MK-801, prevented the protection evoked by NMDA preconditioning. The adenosine A1 receptor antagonist, CPT, prevented the protection evoked by NMDA preconditioning against QA-induced seizures, but not against QA-induced hippocampal cellular damage. The adenosine A1 receptor agonist, CPA, did not mimic the NMDA preconditioning-evoked protective effects.

CONCLUSIONS

These results suggest that in vivo preconditioning with subtoxic doses of NMDA protected mice against seizures and cellular hippocampal death elicited by QA, probably through mechanisms involving NMDA receptors operating with adenosine A1 receptors.

Arsenite-induced formation of hydroxyl radical in the striatum of awake rats

Recent studies on the mechanisms of arsenite toxicity report that some of its effects have been traced to the generation of reactive oxygen species during oxidative stress. In this study we analyze the formation of hydroxyl radicals in the brain of awake, freely moving rats, in order to obtain direct evidence of arsenic-induced oxidative stress in this tissue. We examined the time-course of hydroxyl radical formation in the striatum of both female and male rats who underwent a direct infusion during 60 min of different concentrations of arsenite in that structure through a microdialysis probe. We report here that basal levels of hydroxyl radical production in female rats are significantly higher than those in male rats (91.9+/-16.1 vs. 59.2+/-18.1 pmol/ml, P<0.001) and that the treatment with arsenite induced significant increases of hydroxyl radical formation over basal levels at 50, 100, 200 and 400 microM (95, 98, 98 and 99% increases, respectively, P<0.05 in all cases). The maximal response to 100 microM arsenite is significantly higher in female than in male rats (194.6+/-50.1 female rats and 88.1+/-11.6 pmol/ml male rats, P=0.036). These results support the participation of hydroxyl radicals in arsenic-induced disturbances in the central nervous system.

In vivo hydroxyl radical formation after quinolinic acid infusion into rat corpus striatum

We studied the effect of an acute infusion of quinolinic acid (QUIN) on in vivo hydroxyl radical (.OH) formation in the striatum of awake rats. Using the microdialysis technique, the generation of.OH was assessed through electrochemical detection of the salicylate hydroxylation product 2,3-dihydroxybenzoic acid (2,3-DHBA). The .OH extracellular levels increased up to 30 times over basal levels after QUIN infusion (240 nmol/microl), returning to the baseline 2 h later. This response was attenuated, but not abolished, by pretreatment with the NMDA receptor antagonist MK-801 (10 mg/kg, i.p.) 60 min before QUIN infusion. The mitochondrial toxin 3-nitropropionic acid (3-NPA, 500 nmol/microl) had stronger effects than QUIN on .OH generation, as well as on other markers of oxidative stress explored as potential consequences of .OH increased levels. These results support the hypothesis that early .OH generation contributes to the pattern of toxicity elicited by QUIN. The partial protection by MK-801 suggests that QUIN neurotoxicity is not completely explained through NMDA receptor overactivation, but it may also involve intrinsic QUIN oxidative properties.

NMDA and non-NMDA receptor-mediated excitotoxicity are potentiated in cultured striatal neurons by prior chronic depolarization

The excitatory input from cortex and/or thalamus to striatum appears to promote the maturation of glutamate receptors on striatal neurons, but the mechanisms by which it does so have been uncertain. To explore the possibility that the excitatory input to striatum might influence glutamate receptor maturation on striatal neurons, at least in part, by its depolarizing effect on striatal neurons, we examined the influence of chronic KCl depolarization on the development of glutamate receptor-mediated excitotoxic vulnerability and glutamate receptors in cultured striatal neurons. Dissociated striatal neurons from E17 rat embryos were cultured for 2 weeks in Barrett's medium containing either low (3 mM) or high (25 mM) KCl. The vulnerability of these neurons to NMDA receptor agonists (NMDA and quinolinic acid), non-NMDA receptor agonists (AMPA and KA), and a metabotropic glutamate receptor agonist (trans-ACPD) was examined by monitoring cell loss 24 h after a 1-h agonist exposure. We found that high-KCl rearing potentiated the cell loss observed with 500 microM NMDA or 250 microM KA and yielded cell loss with 250 microM AMPA that was not evident under low KCl rearing. In contrast, neither QA up to 5 mM nor trans-ACPD had a significant toxic effect in either KCl group. ELISA revealed that chronic high KCl doubled the abundance of NMDA NR2A/B, AMPA GluR2/3, and KA GluR5-7 receptor subunits on cultured striatal neurons and more than doubled AMPA GluR1 and GluR4 subunits, but had no effect on NMDA NR1 subunit levels. These receptor changes may contribute to the potentiation of NMDA and non-NMDA receptor-mediated excitotoxicity shown by these neurons following chronic high-KCl rearing. Our studies suggest that membrane depolarization produced by corticostriatal and/or thalamostriatal innervation may be required for maturation of glutamate receptors on striatal neurons, and such maturation may be important for expression of NMDA and non-NMDA receptor-mediated excitotoxicity by striatal neurons. Striatal cultures raised under chronically depolarized conditions may, thus, provide a more appropriate culture model to study the role of NMDA or non-NMDA receptor subtypes in excitotoxicity in striatum.

CR 2249: a new putative memory enhancer. Behavioural studies on learning and memory in rats and mice

The effects of S-4-amino-5-[4,4-dimethylcyclohexyl)amino]-5-oxopentanoic acid (CR 2249), a new entity selected from a new series of glutamic acid derivatives, has been investigated in different paradigms for screening nootropics. CR 2249 ameliorated the memory retention deficit produced by scopolamine in step-through-type passive avoidance in rats and by electroconvulsive shock in step-down-type passive avoidance in mice. CR 2249 was also capable of improving performance in behavioural tests of learning and memory in the absence of cholinergic hypofunction or cognitive deficit. The activity was determined using different passive and active avoidance behavioural test procedures on rats. CR 2249 was active only when given 45 min before training and did not show any effect when administered immediately after the learning training or before the retention trial. No changes in the general behaviour or motor activity of the animals were observed, indicating that CR 2249 effects cannot be attributed to sensory-motor deficit. Microdialysis experiments have shown that CR 2249 significantly increased noradrenaline release in the hippocampus of freely moving rats and reduced 3,4-dihydroxyphenylglycol efflux. These effects have led us to hypothesize that CR 2249 memory effect might be mediated by a direct or indirect action on noradrenergic transmission. These behavioural results suggest that this new agent has clinical application in memory disorders.

Reduction of excitotoxicity-induced brain damage by the competitive NMDA antagonist CGP 40116: a longitudinal study using diffusion-weighted imaging

The cerebroprotective properties of the competitive N-methyl-D-aspartate (NMDA) antagonist CGP 40116 were evaluated in a rat model of excitotoxicity-induced brain damage using direct intrastriatal injection of quinolinic acid and subsequent (5 or 45 min later) i.p. administration of the drug. Diffusion-weighted magnetic resonance imaging (DWI) was used to follow the temporal lesion growth during the acute phase (4 h) and T2-weighted MRI (T2WI) to quantify vasogenic edema extent 2 days later. For control animals, we found a rapid increase in lesion volume during the first hour followed by a moderate growth over the following hours. The DWI-visible hyperintensity was partially reversible after treatment with CGP 40116. The onset of action of CGP 40116 was immediate. The final outcome (63% reduction of lesion volume within 2-4 h post-surgery) was independent of the time of drug administration. DWI data after 4 h correlated well with those obtained by T2WI 2 days later. DWI is a valuable method for early prediction of the outcome of therapeutic interventions of excitotoxic insults.

Effect of riluzole on quinolinate-induced neuronal damage in rats: comparison with blockers of glutamatergic neurotransmission

Intrastriatal injection of quinolinate, an N-methyl-D-aspartate (NMDA) agonist, induces a local neuronal lesion, and provides an excitotoxic model of Huntington's disease. In this study, we investigated the effect of different agents acting at various levels of the glutamatergic neurotransmission: (i) dizocilpine (MK801) (0.5 mg/kg ip) significantly reduced the lesion by 74%; (ii) 6-(1-imidazolyl)-7-nitroquinoxaline-2,3(1H,4H)-dione (YM-90K) (3 x 10 and 3 x 20 mg/kg ip) and (iii) lamotrigine (50 mg/kg ip) had no effect; (iv) riluzole (4 and 8 mg/kg per os) significantly reduced the lesion by 35%. The inefficiency of YM-90K suggested that alpha-amino-3-hydroxy-5-methylisoxasole-4-propionate (AMPA) receptors do not participate to the quinolinate-induced excitotoxicity. The mechanism of action of riluzole may be related also to a combination of its different properties. This study indicates that riluzole may be useful for treatment of Huntington's disease.

Intrastriatal injections of the succinate dehydrogenase inhibitor, malonate, cause a rise in extracellular amino acids that is blocked by MK-801

The effects of intrastriatal injections of a reversible inhibitor of succinate dehydrogenase, malonate, on the extracellular concentrations of amino acid neurotransmitters were examined using a microdialysis probe that was positioned a fixed distance from an injection cannula. Malonate (2 mumol) caused a 23 +/- 5-fold increase in extracellular glutamate (Glu), a 18 +/- 6-fold increase extracellular gamma-aminobutyric acid (GABA) and a modest increase in extracellular aspartate (Asp, 2.9 +/- 0.8-fold increase). Administration of the NMDA receptor antagonist MK-801 (5 mg/kg) prior to injection of malonate almost completely blocked these increases. This study provides direct evidence that inhibition of succinate dehydrogenase causes an increase in extracellular amino acid neurotransmitters and further evidence that bioenergetic defects may contribute to the pathogenesis of chronic neurodegenerative diseases through an excitotoxic mechanism.

Characterisation of extracellular amino acids in striatum of freely moving rats by in vivo microdialysis

To investigate the characteristics of extracellular amino acids released from the striatum, we performed in vivo microdialysis in non-anaesthetised, freely moving rats. Amino acids were determined after precolumn derivatisation with o-phthalaldehyde by high-performance liquid chromatography and fluorescence detection. The omission of Ca2+ in the perfusion medium partially decreased the basal concentration of aspartate and glutamate. This shows that a small fraction of basal concentration of aspartate and glutamate is of neuronal origin. The effect of high K+ and veratrine stimulation was evaluated in the presence or absence of Ca2+ or tetrodotoxin (1 microM). High K+ and veratrine caused a remarkable increase in the aspartate and glutamate efflux. The omission of Ca2+ only partially decreased K(+)-stimulated aspartate and glutamate efflux. Tetrodotoxin completely antagonised veratrine-stimulated aspartate and glutamate efflux. Although glycine and taurine releases were stimulated by high K+ and veratrine, their release was not always antagonised with Ca2+ omission or tetrodotoxin inclusion. Thus, the neuronal origin of stimulated release of glycine and taurine is unclear. Although tetrodotoxin sensitivity and Ca2(+)-dependency are regarded as a basic criterion for classical neurotransmitters in microdialysis experiments, they should not be adapted to the physiological characteristics of the release of amino acids.

2,3-Dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline protects against both AMPA and kainate-induced lesions in rat striatum in vivo

In the present work we have tested the neuroprotective effect of 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX) on the excitotoxic damage induced by the injection of several glutamate receptor agonists into the rat striatum. NBQX was co-injected with each of the agonists studied (1 microliter) in the striatum and damage was assessed by the determination of both glutamate decarboxylase and choline acetyltransferase activities in striatal homogenates, five days after the lesion. Additionally, animals were transcardially perfused with 0.9% saline/4% paraformaldehyde and brain coronal sections were stained with Cresyl Violet for histological analysis. Our results show that NBQX (25 nmol) did not protect against the damage induced by the intrastriatal injection of 200 nmol quinolinic acid monitored by either choline acetyltransferase or glutamate decarboxylase activity. In contrast, the same concentration of NBQX partially protected against 200 nmol N-methyl-D-aspartate induced damage; this protection was more notable as detected by changes in choline acetyltransferase activity. When non-N-methyl-D-aspartate receptor agonists were used as excitotoxins, coinjection of NBQX (25 nmol) resulted in a notable protection against both alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA, 40 nmol) and kainate (10 nmol) induced neurodegeneration. At this concentration, protection was slightly better in AMPA-injected animals (71% protection averaged from choline acetyltransferase and glutamate decarboxylase enzyme activities) as compared to kainate-injected animals (47.5% protection). When a higher concentration of NBQX was tested (40 nmol) the protection against kainate improved to 65% while that against AMPA remained constant (64% protection).(ABSTRACT TRUNCATED AT 250 WORDS)

Elevation of the neurotoxin quinolinic acid occurs following spinal cord trauma

Excitatory amino acid neurotoxicity and the inflammatory response are suspected as mediators of some of the pathological sequelae occurring as a result of spinal cord injury. Here we report temporal and regional increases of the NMDA receptor agonist, quinolinic acid (QUIN), in an experimental model of spinal contusion injury. These changes occurred at a time when the blood-brain barrier is known to be dysfunctional and the activation state and density of microglia and macrophages are increased. Thus, alterations in tissue QUIN levels may occur as a result of secondary activation of CNS inflammatory cells or from peripherally derived sources across a damaged blood-brain barrier.