Quinolinic Acid Toxicity Research Articles

Atorvastatin Prevents Glutamate Uptake Reduction Induced by Quinolinic Acid Via MAPKs Signaling.

Statins have been shown to promote neuroprotection in a wide range of neurological disorders. However, the mechanisms involved in such effects of statins are not fully understood. Quinolinic acid (QA) is a neurotoxin that induces seizures when infused in vivo and promotes glutamatergic excitotoxicity in the central nervous system. The aim of this study was to evaluate the putative glutamatergic mechanisms and the intracellular signaling pathways involved in the atorvastatin neuroprotective effects against QA toxicity. Atorvastatin (10mg/kg) treatment for 7days prevented the QA-induced decrease in glutamate uptake, but had no effect on increased glutamate release induced by QA. Moreover, atorvastatin treatment increased the phosphorylation of ERK1 and prevented the decrease in Akt phosphorylation induced by QA. Neither atorvastatin treatment nor QA infusion altered glutamine synthetase activity or the levels of phosphorylation of p38(MAPK) or JNK1/2 during the evaluation. Inhibition of MEK/ERK signaling pathway, but not PI3K/Akt signaling, abolished the neuroprotective effect of atorvastatin against QA-induced decrease in glutamate uptake. Our data suggest that atorvastatin protective effects against QA toxicity are related to modulation of glutamate transporters via MAPK/ERK signaling pathway.

Oxidative Stress, Disrupted Energy Metabolism, and Altered Signaling Pathways in Glutaryl-CoA Dehydrogenase Knockout Mice: Potential Implications of Quinolinic Acid Toxicity in the Neuropathology of Glutaric Acidemia Type I.

We investigated the effects of an acute intrastriatal QUIN administration on cellular redox and bioenergetics homeostasis, as well as on important signaling pathways in the striatum of wild-type (Gcdh +/+ , WT) and knockout mice for glutaryl-CoA dehydrogenase (Gcdh -/- ) fed a high lysine (Lys, 4.7%) chow. QUIN increased lactate release in both Gcdh +/+ and Gcdh -/- mice and reduced the activities of complex IV and creatine kinase only in the striatum of Gcdh -/- mice. QUIN also induced lipid and protein oxidative damage and increased the generation of reactive nitrogen species, as well as the activities of the antioxidant enzymes glutathione peroxidase, superoxide dismutase 2, and glutathione-S-transferase in WT and Gcdh -/- animals. Furthermore, QUIN induced DCFH oxidation (reactive oxygen species production) and reduced GSH concentrations (antioxidant defenses) in Gcdh -/- . An early increase of Akt and phospho-Erk 1/2 in the cytosol and Nrf2 in the nucleus was also observed, as well as a decrease of cytosolic Keap1caused by QUIN, indicating activation of the Nrf2 pathway mediated by Akt and phospho-Erk 1/2, possibly as a compensatory protective mechanism against the ongoing QUIN-induced toxicity. Finally, QUIN increased NF-κB and diminished IκBα expression, evidencing a pro-inflammatory response. Our data show a disruption of energy and redox homeostasis associated to inflammation induced by QUIN in the striatum of Gcdh -/- mice submitted to a high Lys diet. Therefore, it is presumed that QUIN may possibly contribute to the pathophysiology of striatal degeneration in children with glutaric aciduria type I during inflammatory processes triggered by infections or vaccinations.

Nitric oxide synthase inhibitors protect cholinergic neurons against quinolinic acid toxicity in the rat brain

The aim of this study was to examine the effects of intrastriatally injected nitric oxide synthase (NOS) inhibitors, Nω-nitro-l-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI), on quinolinic acid (QA)-induced toxicity in selective vulnerable brain regions of adult Wistar rats. QA was administered into the striatum unilaterally, in a single dose of 150 nM/L with a stereotaxic instrument. The other two experimental groups were pretreated with L-NAME and 7-NI, respectively. The control group of animals was treated with 0.154 mM/L saline solution. The animals were decapitated seven days after the treatment. Samples of both striatum and forebrain cortex were prepared for measurement of acetylcholinesterase (AChE) activity. QA injection revealed a significant increase in AChE activity in both the ipsi- and contralateral striatum and forebrain cortex compared to the control animals. Treatment with NOS inhibitors, followed by QA, very clearly demonstrated lower levels of AChE bilaterally in these brain structures, compared to the QA-treated group.

Cooperation of Non-Effective Concentration of Glutamatergic System Modulators and Antioxidant Against Oxidative Stress Induced by Quinolinic Acid

Excessive formation of reactive oxygen species (ROS) and disruption of glutamate uptake have been hypothesized as key mechanisms contributing to quinolinic acid (QA)-induced toxicity. Thus, here we investigate if the use of diphenyl diselenide (PhSe)(2), guanosine (GUO) and MK-801, alone or in combination, could protect rat brain slices from QA-induced toxicity. QA (1mM) increased ROS formation, thiobarbituric acid reactive substances (TBARS) and decreased cell viability after 2h of exposure. (PhSe)(2) (1μM) protected against this ROS formation in the cortex and the striatum and also prevented decreases in cell viability induced by QA. (PhSe)(2) (5μM) prevented ROS formation in the hippocampus. GUO (10 and 100μM) blocked the increase in ROS formation caused by QA and MK-801 (20 and 100μM) abolished the pro-oxidant effect of QA. When the noneffective concentrations were used in combination produced a decrease in ROS formation, mainly (PhSe)(2)+GUO and (PhSe)(2)+GUO+MK-801. These results demonstrate that this combination could be effective to avoid toxic effects caused by high concentrations of QA. Furthermore, the data obtained in the ROS formation and cellular viability assays suggest different pathways in amelioration of QA toxicity present in the neurodegenerative process.

Mesenchymal stem cells induced to secrete neurotrophic factors attenuate quinolinic acid toxicity: A potential therapy for Huntington's disease

Huntington's disease (HD) is a hereditary, progressive and ultimately fatal neurodegenerative disorder. Excitotoxicity and reduced availability of neurotrophic factors (NTFs) likely play roles in HD pathogenesis. Recently we developed a protocol that induces adult human bone marrow derived mesenchymal stem cells (MSCs) into becoming NTF secreting cells (NTF+ cells). Striatal transplantation of such cells represents a promising autologous therapeutic approach whereby NTFs are delivered to damaged areas. Here, the efficacy of NTF+ cells was evaluated using the quinolinic acid (QA) rat model for excitotoxicity. We show that NTF+ cells transplanted into rat brains after QA injection survive transplantation (19% after 6weeks), maintain their NTF secreting phenotype and significantly reduce striatal volume changes associated with QA lesions. Moreover, QA-injected rats treated with NTF+ cells exhibit improved behavior; namely, perform 80% fewer apomorphine induced rotations than PBS-treated QA-injected rats. Importantly, we found that MSCs derived from HD patients can be induced to become NTF+ cells and exert efficacious effects similarly to NTF+ cells derived from healthy donors. To our knowledge, this is the first study to take adult bone marrow derived mesenchymal stem cells from patients with an inherited disease, transplant them into an animal model and evidence therapeutic benefit. Using MRI we demonstrate in vivo that PBS-treated QA-injected striatae exhibit increasing T2 values over time in lesioned regions, whereas T2 values decrease in equivalent regions of QA-injected rats treated with NTF+ cells. We conclude that NTF cellular treatment could serve as a novel therapy for managing HD.

Quinolinate induces selective loss of melanin-concentrating hormone neurons, rather than orexin neurons, in the hypothalamus of mice and young rats

Orexins are neuropeptides produced in the lateral hypothalamus and implicated in regulation of sleep-wake cycle. Selective loss of orexin neurons is found in the brain of patients with narcolepsy, but the mechanisms of this pathological change are unclear. A previous study showed that excessive stimulation of N-methyl-d-aspartate (NMDA) receptors by quinolinic acid (QA) caused selective loss of orexin neurons in rat hypothalamic slice culture. Here we examined QA toxicity on orexin neurons and melanin-concentrating hormone (MCH) neurons in vivo. Contrary to the expectation, injection of QA (60 and 120 nmol) into the lateral hypothalamus of male C57BL/6 mice caused selective loss of MCH neurons rather than orexin neurons, and this toxicity of QA was attenuated by MK-801, an NMDA receptor antagonist. Selective loss of MCH neurons with preserved orexin neurons was observed even when GABAA receptor antagonists such as bicuculline and picrotoxin were injected with QA. A significant decrease in the number of orexin neurons was induced when QA injection was performed in the dark phase of diurnal cycle, but the degree of the decrease was still lower than that in the number of MCH neurons. Finally, QA (60 nmol) induced selective loss of MCH neurons also in young rats at 3–4 weeks of age. These results do not support the hypothesis that acute excitotoxicity mediated by NMDA receptors is responsible for the pathogenesis of narcolepsy.

Neuroprotective actions of the synthetic estrogen 17alpha-ethynylestradiol in the hippocampus.

17alpha-ethynylestradiol (EE2), a major constituent of many oral contraceptives, is similar in structure to 17beta-estradiol, which has neuroprotective properties in several animal models. This study explored the potential neuroprotective actions of EE2 against kainic and quinolinic acid toxicity in the hippocampus of adult ovariectomized Wistar rats. A decrease in the number of Nissl-stained neurons and the induction of vimentin immunoreactivity in astrocytes was observed in the hilus of the dentate gyrus of the hippocampus after the administration of either kainic acid or quinolinic acid. EE2 prevented the neuronal loss and the induction of vimentin immunoreactivity induced by kainic acid at low (1 microg/rat) and high (10-100 microg/rat) doses and exerted a protection against quinolinic acid toxicity at a low dose (1 microg/rat) only. These observations demonstrate that EE2 exerts neuroprotective actions against excitotoxic insults. This finding is relevant for the design of new neuroprotective estrogenic compounds.

Impact of co administration of selenium and quinolinic acid in the rat's brain

The effect of two different doses (1 μg and 50 μg Se/100 g body wt) of selenium on quinolinic acid toxicity was investigated in rat's brain. Male albino rats were maintained for 60 days as follows: (1) control group (normal diet), (2) Quinolinic acid group (55 μg/100 g body wt)/day, (3) high dose selenium (50 μg/100 g body wt)/day, (4) high dose selenium ((50 μg/100 g body wt) + Quinolinic acid (55 μg/100 g body wt)/day (5) low dose selenium (1 μg/100 g body wt)/day and (6) low dose selenium (1 μg/100 g body wt) + Quinolinic acid (55 μg/100 g body wt)/day. Results revealed that quinolinic acid intake lead to an increase in the oxidative stress as evidenced by decreased activity of antioxidant enzymes (SOD, catalase and GR), increased amount of lipid peroxidation products (MDA,HP and CD) and free fatty acids compared to control group. Co administration of selenium at a dose of 1 μg/100 g body wt along with quinolinic acid had reduced the oxidative stress induced by quinolinic acid and it also led to a change in the brain architecture as evidenced by the decreased activity of acetyl cholinesterase and decreased concentration of neurotransmitters. Histopathological studies revealed that selenium at a dose of 1 μg was more effective in reducing the oxidative stress and higher dose of selenium was toxic.

Evaluation of glutathione metabolism in NMDA preconditioning against quinolinic acid-induced seizures in mice cerebral cortex and hippocampus

Brain preconditioning refers to a wide range of treatments that induce a neuronal tolerance state where neuronal tissue become more resistant to a subsequent lethal insult. The mechanisms underlying the preconditioning-induced brain tolerance are not fully understood, but up-regulation of antioxidant enzymes activity has been suggested to play an important role. In order to test this hypothesis, evaluation of glutathione (GSH) scavenger system was carried out in mice showing the neuroprotective effect of NMDA preconditioning against quinolinic acid (QA)-induced seizures. NMDA is known to prevent seizures in 53% of the animals and completely prevent neural damage against QA. Mice were preconditioned by a non-convulsant NMDA dose (75 mg/kg, 10 ml/kg i.p.) 24 h before QA infusion (4 μl, 9.2 mM i.c.v.). GSH content and enzymatic activities of glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferase (GST) and glucose-6-phosphate dehydrogenase (G6PDH) were evaluated in the cerebral cortex and hippocampus 24 h after QA infusion. NMDA preconditioning and QA infusion did not alter GSH content, GR and G6PDH activities, however, an increase in GST activity was observed in the cerebral cortex from mice. Moreover, NMDA pretreatment was able to prevent the QA-induced decrease in hippocampal GPx activity, but it was not effective against the decreased cortical GPx activity. These results indicate that, although NMDA preconditioning and QA toxicity modulate the activity of some GSH related enzymes, GSH metabolism is not directly linked to the neuroprotective effect induced by NMDA preconditioning.

L‐NAME reverses quinolinic acid‐induced toxicity in rat corticostriatal slices: Involvement of src family kinases

Quinolinic acid (QA) is an endogenous excitotoxin acting on N-methyl-d-aspartate receptors (NMDARs) that leads to the pathologic and neurochemical features similar to those observed in Huntington's disease (HD). The mechanism of QA toxicity also involves free radicals formation and oxidative stress. NMDARs are particularly vulnerable to the action of reactive oxygen species (ROS) and reactive nitrogen species (RNS) that can act as modulators of the activity of protein tyrosine kinases (PTKs) and phosphotyrosine phosphatases (PTPs). Because QA is able to activate neuronal nitric oxide synthase (nNOS) as well as to stimulate the NMDARs, we evaluated the effect of Nomega-Nitro-l-arginine-methyl ester (l-NAME), a selective nNOS inhibitor, on QA-induced neurotoxicity in rat corticostriatal slices. In electrophysiologic experiments we observed that slice perfusion with QA induced a strong reduction of field potential (FP) amplitude, followed by a partial recovery at the end of the QA washout. In the presence of l-NAME the recovery of FP amplitude was significantly increased with respect to QA alone. In synaptosomes, prepared from corticostriatal slices after the electrophysiologic recordings, we observed that l-NAME pre-incubation reversed the QA-mediated inhibitory effects on protein tyrosine phosphorylation pattern, c-src, lyn, and fyn kinase activities and tyrosine phosphorylation of NMDAR subunit NR2B, whereas the PTP activity was not recovered in the presence of l-NAME. These findings suggest that NO plays a key role in the molecular mechanisms of QA-mediated excitotoxicity in experimental model of HD.

Quinolinic acid toxicity on orexin neurons blocked by gamma aminobutyric acid type A receptor stimulation

Selective degeneration of hypothalamic orexin neurons, a hallmark of pathology in narcolepsy patients, is in part reproduced in hypothalamic slice cultures by application of an endogenous excitotoxin quinolinic acid. Depolarized membrane potential may be responsible for the vulnerability of orexin neurons to excitotoxicity. We show that stimulation of gamma-aminobutyric acid type A receptors, which is known to hyperpolarize orexin neurons, by muscimol or isoguvacine potently inhibits quinolinic acid cytotoxicity on orexin neurons. In addition, the protective effect of gamma-aminobutyric acid and a gamma-aminobutyric acid uptake blocker nipecotic acid is abolished by a gamma-aminobutyric acid type A antagonist picrotoxin. Norepinephrine and serotonin do not provide a neuroprotective effect. Thus, GABAergic inhibitory control may be a decisive factor regulating survival of orexin neurons under excitotoxic insults.

Adenosine A2A Receptor Antagonism and Neuroprotection: Mechanisms, Lights, and Shadows

Adenosine A2A receptor antagonists are regarded as potential neuroprotective drugs, although the mechanisms underlying their effects remain to be elucidated. In this review, quinolinic acid (QA)-induced striatal toxicity was used as a tool to investigate the mechanisms of the neuroprotective effects of A2A receptor antagonists. After having examined the effects of selective A2A receptor antagonists toward different mechanisms of QA toxicity, we conclude that (1) the effect elicited by A2A receptor blockade on QA-induced glutamate outflow may be one of the mechanisms of the neuroprotective activity of A2A receptor antagonists; (2) A2A receptor antagonists have a potentially worsening influence on QA-dependent NMDA receptor activation; and (3) the ability of A2A receptor antagonists to prevent QA-induced lipid peroxidation does not correlate with the neuroprotective effects. These results suggest that A2A receptor antagonists may have either potentially beneficial or detrimental influence in models of neurodegeneration that are mainly due to increased glutamate levels or enhanced sensitivity of NMDA receptors, respectively.

Neuroprotective effects of pyruvate in the quinolinic acid rat model of Huntington’s disease

The neuroprotective effects of pyruvate, the end metabolite of glycolysis, were studied in an animal model of Huntington’s disease (HD). Intrastriatal injection of quinolinic acid (QA) caused widespread damage to rat striatum as determined from cresyl violet staining and immunohistochemical analysis. Intraperitoneal administration of pyruvate at doses of 500–1000 mg/kg significantly reduced striatal lesions induced by QA. A lower pyruvate concentration of 250 mg/kg was not protective; however, quadruple applications at this dosage was effective in reducing lesion volumes. The protective effects of pyruvate were found over a range of times, from application at the time of QA injection to 1 h post-administration; however, no protection was conferred if pyruvate was applied 30 min prior to QA injection or 3 h post-administration. We also found pyruvate protects different types of striatal neurons against QA toxicity including GABAergic projection neurons, cholinergic interneurons and NADPH-diaphorase interneurons. These results suggest that pyruvate may be effective in reducing neuronal damage in HD.

Dose-Dependent Neuroprotective Effect of Ciliary Neurotrophic Factor Delivered via Tetracycline-Regulated Lentiviral Vectors in the Quinolinic Acid Rat Model of Huntington's Disease

The ability to regulate gene expression constitutes a prerequisite for the development of gene therapy strategies aimed at the treatment of neurologic disorders. In the present work, we used tetracycline (Tet)-regulated lentiviral vectors to investigate the dose-dependent neuroprotective effect of human ciliary neurotrophic factor (CNTF) in the quinolinic acid (QA) model of Huntington's disease (HD). The Tet system was split in two lentiviruses, the first one containing the CNTF or green fluorescent protein (GFP) cDNAs under the control of the Tet-response element (TRE) and a second vector encoding the transactivator (tTA). Preliminary coinfection study demonstrated that 63.8% +/- 2.0% of infected cells contain at least two viral copies. Adult rats were then injected with CNTF- and GFP-expressing viral vectors followed 3 weeks later by an intrastriatal administration of QA. A significant reduction of apomorphine-induced rotations was observed in the CNTF-on group. In contrast, GFP-treated animals or CNTF-off rats displayed an ipsilateral turning behavior in response to apomorphine. A selective sparing of DARPP-32-, choline acetyltransferase (ChAT)-, and NADPH-d-positive neurons was observed in the striatum of CNTF-on rats compared to GFP animals and CNTF-off group. Enzyme-linked immunosorbent assay (ELISA) performed on striatal samples of rats sacrificed at the same time point indicated that this neuroprotective effect was associated with the production of 15.5 +/- 4.7 ng CNTF per milligram of protein whereas the residual CNTF expression in the off state (0.54 +/- 0.02 ng/mg of protein) was not sufficient to protect against QA toxicity. These results establish the proof of principle of neurotrophic factor dosing for neurodegenerative diseases and demonstrate the feasibility of lentiviral-mediated tetracycline-regulated gene transfer in the brain.

Neuroprotection by estrogen via extracellular signal-regulated kinase against quinolinic acid-induced cell death in the rat hippocampus.

Extracellular signal-regulated kinase (ERK) belongs to the family of mitogen-activated protein kinases (MAPKs), which are serine-threonine kinases activated by phosphorylation in response to a variety of mitogenic signals. We previously reported that 17 beta-estradiol rapidly activates ERK in the rat hippocampus. However, the physiological role of this rapid activation of ERK by estrogen in vivo has not yet been elucidated. This study investigated whether ERK may participate in mediating the neuroprotective effects of estrogen against quinolinic acid (QA) toxicity in the rat hippocampus in vivo. Injection of QA into the hippocampi of male rats produced a loss of Nissl-stained neurons in the CA1 after 24 h. Prior administration of 17 beta-estradiol (50 pmol/animal) to the ventricles prevented the QA-induced decrease in Nissl-stained neurons. Pretreatment with U0126, an inhibitor of MAPK/ERK kinase, inhibited the rapid activation of ERK by 17 beta-estradiol in the rat hippocampus. Moreover, the neuroprotective effects of 17beta-estradiol against QA toxicity were blocked by the pretreatment with U0126. U0126 alone did not produce a loss of neurons. These results indicate that ERK mediates estrogen neuroprotection after QA toxicity in the rat hippocampus.

The Role of Group I and Group II Metabotropic Glutamate Receptors in Modulation of Striatal NMDA and Quinolinic Acid Toxicity

Excitotoxic lesions of the striatum are mediated by the combined activity of N-methyl-d-aspartate (NMDA) receptors and metabotropic glutamate receptors (mGluRs). Intrastriatal injection of the NMDA receptor agonists NMDA or quinolinic acid creates large lesions, but in rats that have been decorticated to remove endogenous glutamatergic input, NMDA and quinolinic acid are no longer toxic. We report that NMDA toxicity can be restored in decorticated animals by coinjection of the group I mGluR agonists t-ACPD, t-ADA, or CHPG. In addition, injections of two group I mGluR antagonists, AIDA and (S)-4C3HPG, can protect against striatal lesions produced by quinolinic acid or NMDA injections in normal rats by blocking activation of group I mGluRs. The group II mGluR agonist APDC fails to protect against quinolinic acid or NMDA toxicity in intact animals or to restore NMDA toxicity in decorticated animals, suggesting that the role of group II receptors in this excitotoxic model is minimal. These observations confirm the important role of group I mGluRs in excitotoxicity and identify these receptors as promising targets for therapeutic intervention in neurodegenerative disease processes.

Simultaneous Intrastriatal 6-Hydroxydopamine and Quinolinic Acid Injection: A Model of Early-Stage Striatonigral Degeneration

Animal models reproducing early stages of striatonigral degeneration (SND), the core pathology underlying parkinsonism in multiple system atrophy, are lacking. We have developed a new model of early-stage SND by using a simultaneous unilateral administration of quinolinic acid (QA) and 6-hydroxydopamine (6-OHDA) into the putaminal equivalent of the rat striatum. Spontaneous and drug-induced behavior, thigmotactic scanning, paw reaching deficits, and histopathology were studied in rat groups: group 1 (control), group 2 (QA), group 3 (6-OHDA), and group 4 (QA + 6-OHDA). The double toxin administration resulted in reduction of the spontaneous and the amphetamine-induced ipsiversive bias in the 6-OHDA group and in a reduction of the apomorphine-induced ipsiversive rotations in the QA group. Simultaneous QA and 6-OHDA also reduced the thigmotactic bias observed in the 6-OHDA rats. Combined toxin elicited a nonsignificant contralateral deficit in paw reaching but a significant deficit on the ipsilateral side. Histopathology revealed a significant reduction of the lesioned striatal surface (−27%) with neuronal loss and increased astrogliosis in group 4 compared to group 2, consistent with an exacerbation of QA toxicity by additional 6-OHDA. By contrast, the mean loss of the TH-positive neurons in the ipsilateral substantia nigra pars compacta (SNc) of group 4 was less marked (−15%) than in the 6-OHDA group (−36%), indicating a possible protective action of intrastriatal QA upon 6-OHDA retrograde SNc degeneration. This study shows that a combined unilateral intrastriatal administration of QA and 6-OHDA may serve as a model of early stage SND which is more suitable for early therapeutic interventions.

Protective effects of neurotrophin-4/5 and transforming growth factor- α on striatal neuronal phenotypic degeneration after excitotoxic lesioning with quinolinic acid

Lesioning of the mammalian striatum with the excitotoxin quinolinic acid results in a pattern of neuropathology that resembles that of post mortem Huntington's disease brain. Certain neurotrophic factors can rescue degenerating cells in a variety of lesion types, including those produced by neurotoxins. Several neurotrophic factors promote the survival of striatal neurons and/or are localized within the striatum. Of these factors, neurotrophin-4/5 and transforming growth factor- α were chosen for administration to rats lesioned with quinolinic acid. Adult rats received a single unilateral intrastriatal injection of quinolinic acid (120 nmol) and either trophic factors or the control protein cytochrome c for seven days thereafter. The pattern of phenotypic degeneration was assessed by immunocytochemical labeling of various striatal neuronal populations at five rostrocaudal levels. Quinolinic acid produced a preferential loss in the number of cells immunoreactive for glutamate decarboxylase, with a relative sparing of the number of choline acetyltransferase-immunoreactive cells and, to a lesser degree, calretinin-immunoreactive cells. None of these phenotypic populations was protected by either neurotrophin-4/5 or transforming growth factor- α. In contrast, when glutamate decarboxylase cells were alternatively identified by calbindin immunolabeling, both factors were found to have partially reversed the loss in the number of calbindin-positive cells induced by excitolesioning. In addition, the loss in the number of parvalbumin-immunopositive cells due to quinolinic acid was partially reversed by neurotrophin-4/5, while the loss in the number of NADPH-diaphorase-stained cells was partially reversed by transforming growth factor- α. These findings reveal a new population of striatal cells, calretinin neurons, that are relatively resistant to quinolinic acid toxicity and that neurotrophin-4/5 and transforming growth factor- α partially protect against the phenotypic degeneration of striatal cell populations in an in vivo animal model of Huntington's disease.

The effect of nitric oxide synthase inhibition on quinolinic acid toxicity in the rat striatum.

Neurons containing reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase and acetylcholinesterase in the striatum are spared in Huntington's disease. It has been claimed that these neurons are also spared after intrastriatal injection of the N-methyl-D-aspartate receptor agonist, quinolinic acid. In the present study the effects of intrastriatal injection of quinolinic acid (15, 30 and 60 nmol) on neurons containing NADPH diaphorase and acetylcholinesterase were examined in rats. Neurons identified histochemically were counted in whole striatal sections at the level of the injection site and at 400 microns intervals anterior and posterior to the injection site. There was a dose-related reduction in the total number of NADPH diaphorase-containing neurons counted in these levels, but only a mild loss of acetylcholinesterase-containing neurons. Acetylcholinesterase-positive neurons were observed near the injection site following administration of all doses. The effects of the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (50 mg/kg, i.p. twice daily for seven days), on quinolinic acid (30 nmol. day 5)-induced toxicity were also investigated. Striatal sections were stained for NADPH diaphorase-, nitric oxide synthase- and acetylcholinesterase-containing neurons and cells were counted in whole striatal sections at the level of the injection site and at four levels posterior to the injection site. Nitric oxide synthase activity was measured in striatal homogenates. NG-Nitro-L-arginine methyl ester did not protect against or potentiate the loss of NADPH diaphorase-, nitric oxide synthase- or acetylcholinesterase-containing neurons or the loss in nitric oxide synthase activity. Acute intrastriatal injection of quinolinic acid may not be a suitable model for Huntington's disease and a role for nitric oxide in quinolinic acid-induced toxicity is not supported in this model.

Quantitative assessment of quinolinic acid-induced striatal toxicity in rats using radioligand binding assays

To validate specific, sensitive and quantitative markers of the rat model of Huntington's disease produced by the intrastriatal injection of quinolinic acid, we used striatal homogenate binding assays for [3H]MK-801-labelled N-methyl-D-aspartate receptors, [3H]SCH 23390-labelled D1 and [3H]sulpiride-labelled D2 dopamine receptors, [3H]CGS 21680-labelled adenosine A2 receptors, [3H]GBR 12935-labelled dopamine uptake sites, [3H]hemicholinium-3-labelled high affinity choline uptake sites and [3H]PK 11195-labelled glial cells, in 3 groups of rats: 1) lesioned only, 2) pretreated with MK-801, an antagonist of the N-methyl-D-aspartate receptor, to assess the non-N-methyl-D-aspartate-mediated toxicity of quinolinic acid, and 3) pretreated with MK-801 plus scopolamine, an anticholinergic drug that prevents MK-801 neuronal toxicity. [3H]MK-801 and [3H]PK 11195 are sensitive markers of quinolinic acid toxicity. In addition, [3H]SCH 23390, [3H]CGS 21680 and [3H]hemicholinium-3, are found to be specific markers of quinolinic acid-induced toxicity on striatonigral and striatopallidal projecting neurons, and on large interneurons, respectively. MK-801 pretreatment prevented the quinolinic acid-induced reduction in binding of [3H]MK-801, [3H]SCH 23390 and [3H]CGS 21680 but failed to do so for [3H]sulpride and [3H]hemicholinium-3, suggesting that quinolinic acid may act by mechanisms other than direct activation of N-methyl-D-aspartate receptors. Combined pretreatment with MK-801 and scopolamine increased the protection against quinolinic acid, suggesting an involvement of the cholinergic system.