Quinolinate mimics neurotoxic actions of N-methyl-D-aspartate in rat cerebellar slices

Are Anxiety Disorders Associated with Accelerated Aging? A Focus on Neuroprogression

Anxiety disorders (AnxDs) are highly prevalent throughout the lifespan, with detrimental effects on daily-life functioning, somatic health, and quality of life. An emerging perspective suggested that AnxDs may be associated with accelerated aging. In this paper, we explored the association between AnxDs and hallmarks of accelerated aging, with a specific focus on neuroprogression. We reviewed animal and human findings that suggest an overlap between processes of impaired neurogenesis, neurodegeneration, structural, functional, molecular, and cellular modifications in AnxDs, and aging. Although this research is at an early stage, our review suggests a link between anxiety and accelerated aging across multiple processes involved in neuroprogression. Brain structural and functional changes that accompany normal aging were more pronounced in subjects with AnxDs than in coevals without AnxDs, including reduced grey matter density, white matter alterations, impaired functional connectivity of large-scale brain networks, and poorer cognitive performance. Similarly, molecular correlates of brain aging, including telomere shortening, Aβ accumulation, and immune-inflammatory and oxidative/nitrosative stress, were overrepresented in anxious subjects. No conclusions about causality or directionality between anxiety and accelerated aging can be drawn. Potential mechanisms of this association, limitations of the current research, and implications for treatments and future studies are discussed.

The neuroprogressive nature of major depressive disorder: pathways to disease evolution and resistance, and therapeutic implications

In some patients with major depressive disorder (MDD), individual illness characteristics appear consistent with those of a neuroprogressive illness. Features of neuroprogression include poorer symptomatic, treatment and functional outcomes in patients with earlier disease onset and increased number and length of depressive episodes. In such patients, longer and more frequent depressive episodes appear to increase vulnerability for further episodes, precipitating an accelerating and progressive illness course leading to functional decline. Evidence from clinical, biochemical and neuroimaging studies appear to support this model and are informing novel therapeutic approaches. This paper reviews current knowledge of the neuroprogressive processes that may occur in MDD, including structural brain consequences and potential molecular mechanisms including the role of neurotransmitter systems, inflammatory, oxidative and nitrosative stress pathways, neurotrophins and regulation of neurogenesis, cortisol and the hypothalamic-pituitary-adrenal axis modulation, mitochondrial dysfunction and epigenetic and dietary influences. Evidence-based novel treatments informed by this knowledge are discussed.

Somatic drugs for psychiatric diseases: aspirin or simvastatin for depression?

The evolution in the understanding of the neurobiology of most prevalent mental disorders such as major depressive disorder (MDD), bipolar disorder or schizophrenia has not gone hand in hand with the synthesis and clinical use of new drugs that would represent a therapeutic revolution such as that brought about by selective serotonin reuptake inhibitors (SSRIs) or atypical antipsychotics. Although scientists are still a long way from understanding its true aetiology, the neurobiological concept of depression has evolved from receptor regulation disorder, to a neurodegenerative disorder with a hippocampal volume decrease with the controversial reduction in neurotrophins such as BDNF, to current hypotheses that consider depression to be an inflammatory and neuroprogressive process. As regards antidepressants, although researchers are still far from knowing their true mechanism of action, they have gone from monoaminergic hypotheses, in which serotonin was the main protagonist, to emphasising the anti-inflammatory action of some of these drugs, or the participation of p11 protein in their mechanism of action.In the same way, according to the inflammatory hypothesis of depression, it has been proposed that some NSAIDS such as aspirin or drugs like simvastatin that have an anti-inflammatory action could be useful in some depressive patients. Despite the fact that there may be some data to support their clinical use, common sense and the evidence advise us to use already tested protocols and wait for the future to undertake new therapeutic strategies.

Mechanistic explanations how cell-mediated immune activation, inflammation and oxidative and nitrosative stress pathways and their sequels and concomitants play a role in the pathophysiology of unipolar depression

This paper reviews that cell-mediated-immune (CMI) activation and inflammation contribute to depressive symptoms, including anhedonia; anxiety-like behaviors; fatigue and somatic symptoms, e.g. illness behavior or malaise; and mild cognitive impairment (MCI). These effects are in part mediated by increased levels of pro-inflammatory cytokines (PICs), e.g. interleukin-1 (IL-1), IL-6 and tumor necrosis factor (TNF)α, and Th-1-derived cytokines, such as IL-2 and interferon (IFN)γ. Moreover, new pathways, i.e. concomitants and sequels of CMI activation and inflammation, were detected in depression: (1) Induction of indoleamine 2,3-dioxygenase (IDO) by IFNγ and some PICs is associated with depleted plasma tryptophan, which may interfere with brain 5-HT synthesis, and increased production of anxiogenic and depressogenic tryptophan catabolites. (2) Increased bacterial translocation may cause depression-like behaviors by activating the cytokine network, oxidative and nitrosative stress (O&NS) pathways and IDO. (3) Induction of O&NS causes damage to membrane ω3 PUFAs, functional proteins, DNA and mitochondria, and autoimmune responses directed against intracellular molecules that may cause dysfunctions in intracellular signaling. (4) Decreased levels of ω3 PUFAs and antioxidants, such as coenzyme Q10, glutathione peroxidase or zinc, are associated with an increased inflammatory potential; more oxidative damage; the onset of specific symptoms; and changes in the expression or functions of brain 5-HT and N-methyl-d-aspartate receptors. (5) All abovementioned factors cause neuroprogression, that is a combination of neurodegeneration, neuronal apoptosis, and lowered neurogenesis and neuroplasticity. It is concluded that depression may be the consequence of a complex interplay between CMI activation and inflammation and their sequels/concomitants which all together cause neuroprogression that further shapes the depression phenotype. Future research should employ high throughput technologies to collect genetic and gene expression and protein data from patients with depression and analyze these data by means of systems biology methods to define the dynamic interactions between the different cell signaling networks and O&NS pathways that cause depression.

The new '5-HT' hypothesis of depression: cell-mediated immune activation induces indoleamine 2,3-dioxygenase, which leads to lower plasma tryptophan and an increased synthesis of detrimental tryptophan catabolites (TRYCATs), both of which contribute to the onset of depression

This paper reviews the body of evidence that not only tryptophan and consequent 5-HT depletion, but also induction of indoleamine 2,3-dioxygenase (IDO) and the detrimental effects of tryptophan catabolites (TRYCATs) play a role in the pathophysiology of depression. IDO is induced by interferon (IFN)γ, interleukin-6 and tumor necrosis factor-α, lipopolysaccharides and oxidative stress, factors that play a role in the pathophysiology of depression. TRYCATs, like kynurenine and quinolinic acid, are depressogenic and anxiogenic; activate oxidative pathways; cause mitochondrial dysfunctions; and have neuroexcitatory and neurotoxic effects that may lead to neurodegeneration. The TRYCAT pathway is also activated following induction of tryptophan 2,3-dioxygenase (TDO) by glucocorticoids, which are elevated in depression. There is evidence that activation of IDO reduces plasma tryptophan and increases TRYCAT synthesis in depressive states and that TDO activation may play a role as well. The development of depressive symptoms during IFNα-based immunotherapy is strongly associated with IDO activation, increased production of detrimental TRYCATs and lowered levels of tryptophan. Women show greater IDO activation and TRYCAT production following immune challenge than men. In the early puerperium, IDO activation and TRYCAT production are associated with the development of affective symptoms. Clinical depression is accompanied by lowered levels of neuroprotective TRYCATs or increased levels or neurotoxic TRYCATs, and lowered plasma tryptophan, which is associated with indices of immune activation and glucocorticoid hypersecretion. Lowered tryptophan and increased TRYCATs induce T cell unresponsiveness and therefore may exert a negative feedback on the primary inflammatory response in depression. It is concluded that activation of the TRYCAT pathway by IDO and TDO may be associated with the development of depressive symptoms through tryptophan depletion and the detrimental effects of TRYCATs. Therefore, the TRYCAT pathway should be a new drug target in depression. Direct inhibitors of IDO are less likely to be useful drugs than agents, such as kynurenine hydroxylase inhibitors; drugs which block the primary immune response; compounds that increase the protective effects of kynurenic acid; and specific antioxidants that target IDO activation, the immune and oxidative pathways, and 5-HT as well.

The inflammatory & neurodegenerative (I&ND) hypothesis of depression: leads for future research and new drug developments in depression

Despite extensive research, the current theories on serotonergic dysfunctions and cortisol hypersecretion do not provide sufficient explanations for the nature of depression. Rational treatments aimed at causal factors of depression are not available yet. With the currently available antidepressant drugs, which mainly target serotonin, less than two thirds of depressed patients achieve remission. There is now evidence that inflammatory and neurodegenerative (I&ND) processes play an important role in depression and that enhanced neurodegeneration in depression may-at least partly-be caused by inflammatory processes. Multiple inflammatory-cytokines, oxygen radical damage, tryptophan catabolites-and neurodegenerative biomarkers have been established in patients with depression and these findings are corroborated by animal models of depression. A number of vulnerability factors may predispose towards depression by enhancing inflammatory reactions, e.g. lower peptidase activities (dipeptidyl-peptidase IV, DPP IV), lower omega-3 polyunsaturated levels and an increased gut permeability (leaky gut). The cytokine hypothesis considers that external, e.g. psychosocial stressors, and internal stressors, e.g. organic inflammatory disorders or conditions, such as the postpartum period, may trigger depression via inflammatory processes. Most if not all antidepressants have specific anti-inflammatory effects, while restoration of decreased neurogenesis, which may be induced by inflammatory processes, may be related to the therapeutic efficacy of antidepressant treatments. Future research to disentangle the complex etiology of depression calls for a powerful paradigm shift, i.e. by means of a high throughput-high quality screening, including functional genetics and genotyping microarrays; established and novel animal and ex vivo-in vitro models for depression, such as new transgenic mouse models and endophenotype-based animal models, specific cell lines, in vivo and ex vivo electroporation, and organotypic brain slice culture models. This screening will allow to: 1) discover new I&ND biomarkers, both at the level of gene expression and the phenotype; and elucidate the underlying molecular I&ND pathways causing depression; and 2) identify new therapeutic targets in the I&ND pathways; develop new anti-I&ND drugs for these targets; select existing anti-I&ND drugs or substances that could augment the efficacy of antidepressants; and predict therapeutic response by genetic I&ND profiles.

Aciclovir protects against quinolinic-acid-induced oxidative neurotoxicity

AIDS-related encephalopathy, including AIDS dementia complex (ADC) and the opportunistic disease, herpes simplex encephalitis (HSE), are postulated to arise due to the release of neurotoxic products, such as quinolinic acid (QUIN), by activated microglial cells in the brain. QUIN causes a cascade of events to occur, which leads to the production of reactive oxygen species (ROS), these being ultimately responsible for oxidative neurotoxicity. The antiherpes antiviral aciclovir has been reported to protect against neuron loss in HSE, but the mechanism for this neuroprotection is unknown. Therefore, this study was conducted to investigate whether aciclovir has the ability to inhibit QUIN-induced lipid peroxidation in rat brain homogenates, after in-vitro and in-vivo exposure to QUIN and aciclovir. The thiobarbituric acid (TBA) assay was the method used to analyse lipid peroxidation. Rat brains were also examined histologically after in-vivo exposure to visually assess whether neuron loss was suppressed. The results show that aciclovir inhibits the QUIN-induced lipid peroxidation, in a dose-dependent manner. Furthermore, aciclovir reduced necrosis of hippocampal neurons and retained the characteristic morphology, integrity and arrangement of these cells. Thus, it appears that aciclovir has neuroprotective properties, which could possibly be useful in the treatment of AIDS-related encephalopathy.

Polyamines reduces lipid peroxidation induced by different pro-oxidant agents

Polyamines, among other functions, are considered to act as a free radical scavenger and antioxidant. The quinolinic acid (QA), sodium nitroprusside (SNP) and iron (Fe+2) stimulate production of free radicals and lipid peroxidation. In the present study, we investigated the free radical and/or aldehyde scavenger effects of polyamines spermine and spermidine on thiobarbituric acid reactive species (TBARS) production induced by QA, SNP, Fe+2/EDTA system and free Fe2+ in rat brain. Spermine and spermidine inhibited QA-induced TBARS production; however spermine was a better antioxidant than spermidine. Spermine also inhibited SNP-, Fe+2/EDTA- and free Fe2+-induced TBARS production, but had a modest effect. Spermidine, in turn, also discretely inhibited SNP-, Fe+2/EDTA- and free Fe2+-induced TBARS production. In the presence of MK-801, QA-induced TBARS production was considerably more inhibited by polyamines. In addition, arcaine does not affect the reducer effect of polyamines. The present findings suggest that the observed effects of polyamines are not related to the activation of NMDA receptor but with their antioxidant and free radical scavenger properties.

Neuroprotection by scatter factor/hepatocyte growth factor and FGF-1 in cerebellar granule neurons is phosphatidylinositol 3-kinase/akt-dependent and MAPK/CREB-independent

Neuroprotective actions of scatter factor/hepatocyte growth factor (SF/HGF) have not been described. We examined the effects of SF/HGF in comparison to acidic fibroblast growth factor-1 (FGF-1) on N-methyl-D-aspartate (NMDA) and quinolinic acid (QUIN)-induced excitotoxicity in primary cerebellar granule neurons. Exposure to NMDA or QUIN for 24 h resulted in concentration-dependent cell death (p < 0.001) that was completely attenuated (p < 0.001) by pre-treatment of cells with SF/HGF (50 ng/mL) or FGF-1 (40 ng/mL). SF/ HGF and FGF-1 activated both Akt and MAP-kinase > threefold (p < 0.001). Neither SF/HGF nor FGF-1 activated cyclic AMP-response element binding protein (CREB), a downstream target of MAP-kinase, whereas brain-derived neurotrophic factor (BDNF) activated both MAP-kinase and CREB in granule neurons. Neuroprotection against NMDA or QUIN by SF/HGF and FGF-1 was negated by the addition of LY294002 (10 microM) or wortmannin (100 microM), two distinct inhibitors of phosphatidylinositol 3-kinase (P13-K), but not by the MAP-kinase kinase (MEK) inhibitor PD98059 (33 microm). Likewise, expression of a dominant-negative mutant of Akt (Akt-kd) completely prevented the neuroprotective actions of SF/HGF and FGF-1. Overexpression of a constitutively activated Akt (Akt-myr) or wild-type Akt (wtAkt) attenuated excitotoxic cell death. These data show that both SF/HGF and FGF-1 protect cerebellar granule neurons against excitotoxicity with similar potency in a P13-K/Akt-dependent and MAP-kinase/CREB-independent manner.

Altered tryptophan metabolism in mice with herpes simplex virus encephalitis: increases in spinal cord quinolinic acid

Mice infected with the herpes simplex virus, type-1, developed a paralysis which was associated with increased levels of the neurotoxin quinolinic acid (QUIN). The largest increases in QUIN were observed in the spinal cord with much smaller changes in the rostral forebrain or serum. The time course for the paralysis coincided with the increase in spinal cord QUIN, a maximal 40-fold elevation, at 7-10 days post infection. The time course suggested that the increases in QUIN were due to its local synthesis. Consistent with this possibility, herpes virus-infected mice had increased activities of indoleamine 2,3-dioxygenase and kynurenine hydroxylase (two key enzymes in QUIN formation), when compared to non-infected controls. Since QUIN is formed by activated macrophages, these new data are consistent with QUIN formation as part of the host response to a pathogen whose importance is discussed.

The endogenous agonist quinolinic acid and the non endogenous homoquinolinic acid discriminate between NMDAR2 receptor subunits

Quinolinic acid is an endogenous neurotoxin with NMDA receptor agonist properties. As such it may be the etiologic agent in many diseases. In this paper the NMDA receptor agonist properties of quinolinic acid, as well as those of homoquinolinic acid, a non endogenous analogue, were investigated in Xenopus oocytes injected with 12-day-old rat cortical mRNA or with recombinant NMDA receptors. In oocytes injected with cortical mRNA, quinolinic acid was a weak NMDA receptor agonist: millimolar concentrations were necessary to induce responses that were smaller than maximal responses induced by NMDA; homoquinolinic acid and NMDA had similar affinities but different efficacies: maximal responses induced by homoquinolinic acid were larger than maximal responses induced by NMDA. Cortical mRNA, as verified by RT-PCR and restriction analysis, contains various NMDA subunits. In order to investigate if the low affinity or efficacy of quinolinic acid could be explained by receptor composition, the pharmacological properties of the putative agonists were investigated in oocytes expressing binary combinations of recombinant NMDA receptors. Quinolinic acid did not activate receptors containing NR1 + NR2C but did activate receptors containing NR1 + NR2A and NR1 + NR2B even if only at millimolar concentrations; homoquinolinic acid activated all subunit combinations but was less efficient than NMDA only in the NR1 + NR2C subunit combination. The relative efficacies of quinolinic acid and homoquinolinic acid were evaluated by comparing the maximal responses induced by these agonists with those induced by NMDA and glutamate in the same oocytes. The rank order of potency was quinolinic acid < NMDA < homoquinolinic acid < or = glutamate for the NR1 + NR2A and NR1 + NR2B combinations whereas for NR1 + NR2C it was quinolinic acid << << homoquinolinic acid < NMDA < or = glutamate. The use of quinolinic acid and homoquinolinic acid may thus help to identify endogenous receptors containing the NR2C subunit.

Quinolinate-induced injury is enhanced in developing rat brain

Quinolinate, a metabolite of tryptophan in the kynurenine pathway, has been hypothesized to play a role in neuronal injury through activation of the N-methyl-D-aspartate (NMDA) receptor. We evaluated the ontogeny and neuroprotective pharmacology of quinolinate-induced injury in the immature rat brain. Unilateral striatal microinjections of quinolinate (150 nmol/0.5 microliter) were performed at seven ages between postnatal day (PND) 1 and 90. Injury was assessed by comparing the cross-sectional areas of the cerebral hemispheres ipsilateral and contralateral to the injection site in Nissl-stained coronal sections. The susceptibility to quinolinate-induced injury was enhanced in the immature brain with peak toxicity at PND 7 when the ipsilateral cerebral hemisphere was reduced by 16.1 +/- 3.2%. In a dose-response comparison with NMDA-induced injury at PND 7, quinolinate injury was directly related to the dose injected (r2 = 0.73, P < 0.0001), but the neurotoxicity of quinolinate was 20-times less potent than NMDA. In the PND 7 rat brain, quinolinate-induced injury was completely blocked by MK-801 (1 mg/kg, i.p.) and CGS-19755 (10 mg/kg). Dextromethorphan (20 mg/kg) and dextrorphan (20 mg/kg) were partially protective. Ifenprodil, carbamazepine, and nifedipine did not significantly protect against quinolinate-induced injury. Finally, pretreatment with MK-801 (1 mg/kg) 24 h before intracerebral injection of quinolinate resulted in greater injury compared to controls. The findings indicate that quinolinate-induced injury is enhanced in the immature brain in a pattern that is similar to NMDA-induced injury.

Chronic infusion of quinolinic acid in rat striatum: effects on discrete neuronal populations

The intrastriatal infusion of relatively low doses of quinolinic acid (Quin, 4-10 nmol/h) for 1 or 2 weeks induced time-dependent degeneration of neuronal cells. We examined the effects of these infusions on discrete cellular populations. The distribution of somatostatin (SOM)-positive neurons labelled by immunocytochemistry or by NADPH-diaphorase histochemistry and of cholinergic cells stained by acetylcholinesterase was quantified in the peripheral portion of the lesioned area. SOM-positive cells did not appear selectively spared by Quin infusion. The proportion of SOM- and NADPH-diaphorase-positive neurons killed by exposure to Quin was similar to or higher than the percentage of total neurons degenerated (from 30 to 85%). A selective sparing of cholinergic cells was observed in all conditions examined; perfusion of 6 nmol/h for a week induced 65% of cell death while not more than 30% of cholinergic neurons were killed. Thus, the neurochemical similarity between the degenerative effects of intrastriatal Quin and Huntington's disease (HD) did not appear confirmed by the chronic perfusion of low doses of Quin for SOM-positive neurons, whereas an analogy between Quin's effects and HD was suggested by the pattern of AChE staining.

Quinolinic acid is a potent lipid peroxidant in rat brain homogenates

In this study, we describe the lipoperoxidative effect of quinolinic acid (QUIN) in vitro. The formation of thiobarbituric acid reactive products (TBA-RP), an index of lipid peroxidation, was measured in rat brain homogenates after incubation at 37 degrees C for 30 min in the presence of QUIN and some structurally and metabolically related compounds such as Kynurenine, Kynurenic acid, Glutamate, Aspartate and Kainate. Concentrations of QUIN in the range of 20 to 80 microM increased lipid peroxidation in a concentration-dependent manner from about 15% to about 50%. Kynurenic acid, a compound metabollically related to QUIN that can block its neurotoxic actions in vivo, also inhibited completely the QUIN-induced TBA-RP formation in our system. Lipid fluorescent material, another index of lipid peroxidation was also found increased by 49% after incubation with 40 microM QUIN. It is concluded that lipid peroxidation may be a damaging process involved in the neurotoxicity of QUIN.

Neurodegenerative Effects Induced by Chronic Infusion of Quinolinic Acid in Rat Striatum and Hippocampus

In this study we examined whether the potency of quinolinic acid (Quin) in inducing neurodegeneration in vivo was dependent on the exposure time of the tissue to the excitotoxin. The effect of chronic infusion of Quin into rat striatum and hippocampus was examined at the light microscopic level and by cell count on 40 microm Cresyl violet stained brain sections. Continuous infusion was at a constant speed (0.5 microl/h) for various times (15 h - 2 weeks) by osmotic minipumps (Alzet 2002). No build up of [3H]Quin occurred in the tissue during infusion; this was assessed by measuring the radioactivity 3 - 14 days after minipump placement. Intrastriatal infusion of 6 and 10 nmol/h Quin, but not of nicotinic acid, for 1 week induced a dose-dependent neurodegeneration (70 and 90% loss of neurons, respectively, compared to the contralateral striatum) extending 1.2 - 2 mm from the centre of the injection. The onset of the neurotoxicity caused by 10 nmol/h Quin was >24 h. One week's infusion of 4 nmol/h Quin did not induce neurotoxicity, but a 40% drop of neurons, compared to the contralateral side, occurred after 2 weeks. One week's intrahippocampal infusion of 2.4 and 6 nmol/h Quin, but not of nicotinic acid, caused a dose-dependent neurodegeneration with a radius of approximately 1 - 1.5 mm around the injection track. The onset of the neurotoxicity induced by 2.4 nmol/h Quin was < 15 h. The pattern of nerve cell loss induced by 1.2 nmol/h Quin after 1 week (CA4 cells lost in 50% of the rats) did not differ from that observed after 2 weeks of infusion. Nerve cell loss caused by Quin in the striatum and in the hippocampus was restricted to the injected area and antagonized by coinfusion with d(-)-2-amino-7-phosphonoheptanoic and kynurenic acids in molar ratios of 1:0.1 and 1:3, respectively. These data show that Quin's potency in inducing neurodegeneration in the striatum, but not in the hippocampus, depends on the exposure time of the tissue to the excitotoxin. In addition, neurodegeneration is induced faster by Quin in the hippocampus than in the striatum. The usefulness of this model to study the sequelae of the neurotoxic process in vivo will be discussed.

Regional variations in [3H]MK801 binding to rat brain N-methyl-D-aspartate receptors

This study examined (+)-[3H]5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine maleate [( 3H]MK801) binding to the N-methyl-D-aspartate (NMDA) receptor in membranes prepared from six regions of rat brain. Highest levels of binding were found in hippocampus and cortex, whereas much lower densities were found in brainstem and cerebellum. NMDA receptors in cerebellum exhibited a significantly lower affinity for [3H]MK801 than cortical NMDA receptors. To determine whether forebrain and hindbrain NMDA receptors were distinct, the actions of glutamate, NMDA, ibotenate, quinolinate, glycine, and spermine were investigated. These agents increased [3H]MK801 binding in all brain regions examined. However, agonists were uniformly less efficacious in hindbrain compared to forebrain regions. NMDA mimetics and spermine were less potent in cerebellum compared to cortex whereas glycine was equipotent. Antagonists that act at the various modulatory sites on the NMDA receptor were also examined. DL-Amino-phosphonopentanoic acid and 7-chlorokynurenate were approximately equipotent in cortex and cerebellum. However, antagonists that are believed to act inside the NMDA-operated ion channel, including Mg2+ and phencyclidine, were approximately threefold less potent in cerebellum. The diminished regulation of [3H]MK801 binding by glutamate and glycine in the cerebellum was associated with a smaller effect of these agonists on the dissociation of [3H]MK801 from its binding site. The levels of glutamate, aspartate, glycine, serine, and glutamine in the membrane preparations were determined. However, variations in the levels of endogenous amino acids were not sufficient to account for the regional differences in [3H]MK801 binding. These results do not support the hypothesis that a distinct NMDA receptor exists in hindbrian regions of the rat CNS.(ABSTRACT TRUNCATED AT 250 WORDS)

Quinolinic acid catabolism is increased in cerebellum of patients with dominantly inherited olivopontocerebellar atrophy

We measured the activities of the enzymes responsible for the metabolism of the excitotoxin quinolinic acid, 3-hydroxyanthranilate oxygenase and quinolinic acid phosphoribosyltransferase, in autopsied brain of 11 patients with olivopontocerebellar atrophy. In cerebellar cortex, severe Purkinje cell loss was evident but with relative preservation of granule cells. As compared with the control subjects (n = 14), mean activity of 3-hydroxyanthranilate oxygenase was normal in cerebellar cortex from the patients with olivopontocerebellar atrophy, whereas quinolinic acid phosphoribosyltransferase activity was markedly increased (+92%, p less than 0.02). No significant changes in enzyme activities were found in samples from occipital cortex. Increased quinolinic acid phosphoribosyltransferase activity may represent a mechanism, in the degenerating cerebellum, to protect quinolinic acid-sensitive granule cells in patients with olivopontocerebellar atrophy.

An investigation of the mechanisms of delayed neurodegeneration caused by direct injection of quinolinate into the rat striatum in vivo

Injection of the N-methyl-D-aspartate receptor agonist quinolinate, or N-methyl-D-aspartate itself, into the rat brain produces neurodegeneration which can be prevented by N-methyl-D-aspartate receptor antagonists administered up to 5 h after excitotoxin injection. The present study was designed to investigate aspects of the mechanisms involved in this delayed form of neurodegeneration. Following its injection into the rat striatum, extracellular levels of [3H]quinolinate were monitored using a microdialysis probe located 1 mm from the site of injection. Peak concentrations were observed 10-20 min after injection and [3H]quinolinate levels decayed in a biexponential fashion, the initial component having an apparent t1/2 of 13.7 +/- 5.2 min (n = 3). Estimations of the extracellular concentrations of quinolinate after an injection of 200 nmol indicated a peak level of 13.7 +/- 6.0 mM (n = 3) at 10-20 min which declined to 1.2 +/- 0.13 mM (n = 3) by 2 h and substantial levels were present up to 5 h, the period over which N-methyl-D-aspartate receptor antagonists are effective in this model. Administration of dizocilpine at 1, 2, 3 or 5 h after injection of 100, 200 or 400 nmol quinolinate resulted in a similar temporal profile of neuroprotection, as assessed by measuring the activities of choline acetyltransferase and glutamate decarboxylase in striatal homogenates, which was independent of the degree of neurodegeneration produced by the different excitotoxin doses. Overall, these results suggest that the neuronal degeneration caused by quinolinate in vivo is critically dependent upon events occurring after the initial peak of excitoxin levels in the extracellular space.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypodense eosinophils and interleukin 5 activity in the blood of patients with the eosinophilia-myalgia syndrome

The recent recognition of the eosinophilia-myalgia syndrome (EMS) associated with the ingestion of L-tryptophan prompted an analysis of the peripheral blood eosinophil phenotypes and of the serum eosinophil hematopoietins in this disorder. Five patients with an illness characterized by the abrupt onset of aching skeletal muscles, edema, thickening and induration of the skin, and marked blood eosinophilia associated with L-tryptophan ingestion provided eosinophils, serum, or both, for evaluation. Gradient sedimentation density analysis of the peripheral blood eosinophils from four of these patients revealed that 43 +/- 13% (mean +/- SEM) of the cells had converted to the abnormal (hypodense) sedimenting phenotype. When normodense eosinophils from the reference donors were cultured for 3 days in medium supplemented with increasing concentrations of serum from the patients with EMS, their viability increased in a dose-dependent manner to 45%, which was significantly augmented over the effect of normal serum. This eosinophil viability-sustaining activity was inhibited by 76 +/- 7% (mean +/- SEM; n = 3) by the addition of anti-interleukin 5 (IL-5) but not by neutralizing antibodies monospecific for either granulocyte/macrophage colony-stimulating factor (GM-CSF) or IL-3. IL-5, an eosinophilopoietic factor, converts normodense peripheral blood eosinophils in vitro to a hypodense sedimenting form with extended viability and augmented biologic responses to activating stimuli. Thus, the presence of IL-5 in the sera of patients with EMS may contribute to the development and maintenance of the eosinophilia and may regulate the conversion of the peripheral blood eosinophils to the hypodense phenotype with augmented pathobiologic potential.

Interactive effects involving different classes of excitatory amino acid receptors and the survival of cerebellar granule cells in culture

Differentiating granule cells develop survival requirements in culture which can be met by treatment with high K+ or N-methyl-D-aspartate (NMDA) and, according to our recent findings, also with low concentrations of kainic acid (KA, 50 microM). We have now attempted to elucidate the mechanism(s) underlying the trophic effect of KA. KA rescue of cells was completely suppressed by blockers of voltage-sensitive calcium channels, such as nifedipine in low concentrations (5 x 10(-7) M), indicating that the promotion of cell survival is mediated through the activation of these channels by membrane depolarization. Thus the trophic influences of KA and NMDA share a common mechanism, increased Ca2+ influx (albeit through different routes), a conclusion that is supported by the observation that the effects of these agonists at concentrations causing maximal promotion of cell survival were not additive. Interactive effects involving different classes of excitatory amino acid receptors were revealed by the potentiation of the KA rescue of cells by the NMDA receptor antagonists, 2-amino 5-phosphonovalerate (APV) or (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohept-5,10-imine hydrogen maleate (MK-801), which on their own failed to promote, but rather reduced cell survival. The potentiation of the KA effect by the competitive NMDA antagonist APV was counteracted by the weak NMDA agonist, quinolinic acid. These observations suggest that KA alone has both trophic and toxic effects, the latter being mediated secondarily through an NMDA-like glutamate receptor, which is distinct from the conventional NMDA, KA and quisqualate preferring subtypes.

Prevention of quinolinic acid neurotoxicity in rat hippocampus in vitro by zinc. Ultrastructural observations

The effect of zinc on the development and evolution of quinolinic acid-induced alterations in the rat hippocampus in culture was studied ultrastructurally. Zinc, although it possesses intrinsic cytotoxic properties, after application in concentrations comparable with those encountered in vivo, was able to prevent typically observed responses after quinolinic acid exposure, either early or late damage to hippocampal neurons. The results further support the concept of a potential protective effect of zinc against the neurotoxicity of particular excitotoxins.

No changes in central quinolinic acid levels in Alzheimer's disease

Levels of the endogenous excitotoxin quinolinic acid were measured in brain and lumbar spinal fluid from Alzheimer patients and age-matched controls. Values in post mortem brain tissue, unlike those in spinal fluid, showed considerable variability among subjects. In the control group, frontal cortex and caudate nucleus had higher concentrations of quinolinic acid compared to other regions studied. No significant differences were found between Alzheimer brains and controls in any of the regions analyzed. Studies in lumbar spinal fluid showed no gradient for quinolinic acid along the neuraxis, a trend for increasing levels with normal aging, and no difference between Alzheimer patients and age-matched control subjects. The lack of increased central quinolinic acid levels in Alzheimer's disease does not necessarily negate the possibility of excitotoxins contributing to cell death in this disorder.

N-methyl-D-aspartate promotes the survival of cerebellar granule cells: pharmacological characterization

The survival of cerebellar granule cells in culture is promoted by chronic exposure to N-methyl-D-aspartate (NMDA). The effect is due to the stimulation of 'conventional' NMDA receptor-ionophore complex: it is concentration dependent, voltage dependent and blocked by the selective antagonists D-2-amino-5-phosphonovalerate, D-2-amino-7-phosphonoheptanoate, dextromethorphan and (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imin emaleate (MK 801). The most potent antagonist tested was MK-801. In contrast, non-selective antagonists, including kynurenate, were much less effective. Further, the trophic effect of NMDA is not reproduced by ibotenate or quinolinate at the concentration range tested. It could also be shown that glutamate released into the culture medium is responsible for limited cell survival in the absence of NMDA.

Prolonged exposure to submicromolar concentrations of quinolinic acid causes excitotoxic damage in organotypic cultures of rat corticostriatal system

Mature organotypic cultures of rat corticostriatal system (CXCA cultures) or caudate nucleus (CA cultures) were chronically exposed to 100 nM quinolinic acid (QUIN) for up to 7 weeks. Light and electron microscopic analysis showed no pathological changes in QUIN-exposed CA cultures or in control cultures incubated in regular feeding medium for this time period. In contrast, in CXCA cultures exposed to QUIN, there was focal degeneration characterized by the presence of vacuoles in neuropil, swollen dendrites, occasional swollen post-synaptic elements and degenerated neurons. Prolonged exposure to only slightly hyper-physiological concentrations of QUIN may cause neuronal death in slowly progressive neurodegenerative disorders such as Huntington's disease (HD).

Differential sparing of somatostatin-neuropeptide Y and cholinergic neurons following striatal excitotoxin lesions

We previously found that quinolinic acid striatal excitotoxin lesions result in a relative sparing of somatostatin and neuropeptide Y neurons. In the present study we examined dose-response effects of excitotoxins acting at the three subtypes of glutamate receptors: N-methyl-D-aspartate (AA1), quisqualate (AA2), and kainic acid (AA3). Concentrations of both somatostatin-like immunoreactivity (SLI) and neuropeptide a Y-like immunoreactivity (NPYLI) were compared with those of substance P-like immunoreactivity (SPLI) and GABA. Kainic acid (AA3), quisqualic acid (AA2), and AMPA (AA2) resulted in dose-dependent reductions in all four neurochemical markers examined, while N-methyl-D,L-aspartate (AA1) and quinolinic acid (AA1) resulted in relative sparing of SLI and NPYLI. At doses of each excitotoxin which resulted in comparable 50% reductions in both GABA and SPLI only N-methyl-D,L-aspartate and quinolinic acid had no significant effect on concentrations of SLI and NPYLI. The relative sparing of somatostatin-neuropeptide Y neurons was confirmed histologically by using histochemical staining for NADPH-diaphorase neurons combined with either Nissl stains, or immunohistochemical staining for enkephalin. Lesions with N-methyl-D-aspartate agonists resulted in preferential sparing of NADPH-diaphorase neurons while these neurons were more vulnerable than other neurons to kainic acid or AMPA. Choline acetyltransferase neurons were relatively spared, as compared with other neurons, by agents acting at all three glutamate receptor subtypes. N-methyl-D,L-aspartate lesions were blocked with MK-801, while there was no effect on quisqualic acid or kainic acid lesions. The relative sparing of somatostatin-neuropeptide Y neurons following striatal excitotoxin lesions with N-methyl-D-aspartate (AA1) agonists probably reflects a paucity of AA1 receptors on these neurons. Since these neurons are also spared in Huntington's disease, excitotoxins acting at the N-methyl-D-aspartate (AA1) site provide an improved neurochemical model of this illness.