Nmol Quinolinic Acid Research Articles

Treadmill exercise improves short-term memory by enhancing hippocampal cell proliferation in quinolinic acid-induced Huntington's disease rats.

Huntington’s disease (HD) is an inherited genetic disorder, characterized by cognitive dysfunction and abnormal body movements called chorea. Quinolinic acid (QA) is an endogenous metabolite of tryptophan in the kynurenine pathway. QA-induced alterations are similar to the symptoms of HD patients. Physical exercise has beneficial effects on the brain functions. Exercise increases production of neurotrophic factors in the brain and improves learning ability and memory function. In the present study, we investigated the effects of treadmill exercise short-term memory on QA-induced HD rats in relation with cell proliferation. For the induction of Huntington’s animal model, 2 μL of 100 nmol QA was intrastriatal injected into the rats. The rats in the treadmill exercise groups were forced to run on a treadmill for 30 min once a day, five times a week for 2 weeks. Step-down avoidance test was conducted for the determination of short-term memory. Cell proliferation in the hippocampal dentate gyrus was determined by 5-bromo-2′-deoxyuridine (BrdU) and doublecortin (DCX) immunohistochemistry. Western blot for brain-derived neurotrophic factor (BDNF) and tyrosine kinase B (TrkB) were performed. In the present results, treadmill exercise alleviated QA-induced short-term memory impairment in HD rats. Treadmill exercise increased cell proliferation in the hippocampal dentate gyrus through enhancing BDNF expression in the HD rats. These results revealed that treadmill exercise is effective for the symptom improvement in the HD patients.

B14 Neurotrophic factors secreting mesenchymal stem cells attenuate quinolinic acid induced striatal lesion model suggesting autologous therapy for HD

BackgroundWe have been studying the potential of utilising the patients' own bone marrow derived mesenchymal stem cells (MSCs) which are transformed into cellular vectors secreting neurotrophic factors (NTF+ cells) in...

Fluorometric Determination of Quinolinic Acid Using the Catalytic Activity of Horseradish Peroxidase

The conversion of quinolinic acid (QA) into a fluorescent compound by the catalytic activity of horseradish peroxidase (HRP) was investigated in the presence of hydrogen peroxide without exposure to light. Nonfluorescent quinolinic acid was converted into a fluorescent compound with maximum excitation and emission wavelengths at 328 and 377 nm, respectively. This fluorescent derivatization reaction with HRP in the presence of hydrogen peroxide was adopted for the determination of trace amounts of QA. The calibration curve obtained was linear from 0.1 to 5.0 nmol of QA in a 1.0 ml sample solution. The detection limit was 0.04 nmol/ml. The relative standard deviation at 3.0 nmol of QA was 3.58% (n = 8). This method was applied to the determination of QA spiked in control serum I and II. The recovery rates of QA were greater than 98%, and satisfactory results were obtained for both control serum I and II.

Evidence that quinolinic acid severely impairs energy metabolism through activation of NMDA receptors in striatum from developing rats

In the present study we investigated the effect of intrastriatal administration of 150 nmol quinolinic acid to young rats on critical enzyme activities of energy production and transfer, as well as on 14CO2 production from [1-14C]acetate at distinct periods after quinolinic acid injection. We observed that quinolinic acid injection significantly inhibited complexes II (50%), III (46%) and II-III (35%), as well as creatine kinase (27%), but not the activities of complexes I and IV and citrate synthase in striatum prepared 12 h after treatment. In contrast, no alterations of these enzyme activities were observed 3 or 6 h after quinolinic acid administration. 14CO2 production from [1-14C]acetate was also significantly inhibited (27%) by quinolinic acid in rat striatum prepared 12 h after injection. However, no alterations of these activities were observed in striatum homogenates incubated in the presence of 100 microm quinolinic acid . Pretreatment with the NMDA receptor antagonist MK-801 and with creatine totally prevented all inhibitory effects elicited by quinolinic acid administration. In addition, alpha-tocopherol plus ascorbate and the nitric oxide synthase inhibitor l-NAME completely abolished the inhibitions provoked by quinolinic acid on creatine kinase and complex III. Furthermore, pyruvate pretreatment totally blocked the inhibitory effects of quinolinic acid injection on complex II activity and partially prevented quinolinic acid-induced creatine kinase inhibition. These observations strongly indicate that oxidative phosphorylation, the citric acid cycle and cellular energy transfer are compromised by high concentrations of quinolinic acid in the striatum of young rats and that these inhibitory effects were probably mediated by NMDA stimulation.

Evidence for dopaminergic re-innervation by embryonic allografts in an optimized rat model of the Parkinsonian variant of multiple system atrophy

Embryonic transplantation has been considered as an alternative treatment strategy for drug resistant parkinsonian symptoms in multiple system atrophy. So far our group has created a number of animal models of striatonigral degeneration, the core pathology underlying progressive Parkinsonism associated with multiple system atrophy, as testbed for neurorestaurative and neuroprotective approaches. Using embryonic allografts of either nigral, striatal, or combined nigro-striatal tissue we were able to consistently show graft survival in a denervated and lesioned striatum as well as improvement of rotational behaviour. However, due to severe lesions of the striatum and the chosen time window of 3–6 weeks between lesion and grafting, severe gliosis led to demarcation of the graft and prevented re-innervation of the remaining adult striatum. The aim of the present study was to modify our “double toxin-double lesion” rat model by reducing the dose of quinolinic acid injected into the striatum from 150 to 75 nmol and shortening the interval between lesion and grafting to 1–2 weeks. Injection of 75 nmol quinolinic acid still led to a significant reduction of DARPP-32 positive neurons and volume in the striatum. Analysis of embryonic mesencephalic grafts revealed survival of dopaminergic neurons and outgrowth of fibres re-innervating the adult striatum. Rotation behaviour was improved in the graft group. Considering embryonic transplantation a possible future antiparkinson therapeutic intervention in multiple system atrophy patients our data stress the necessity of optimal patient selection, i.e. early stage disease with limited striatal dysfunction.

Quinolinic acid promotes seizures and decreases glutamate uptake in young rats: reversal by orally administered guanosine

Quinolinic acid (QA) has been used as a model for experimental overstimulation of the glutamatergic system. Glutamate uptake is the main mechanism involved in the maintenance of extracellular glutamate below toxic levels. Guanosine systemically administered prevents quinolinic acid-induced seizures in adult mice and increases basal glutamate uptake by cortical astrocyte culture and slices from young rats. The immature brain differs from the adult brain in its susceptibility to seizures, seizure characteristics, and responses to antiepileptic drugs (AED). Here we investigated the effect of guanosine p.o. on QA-induced seizures in young rats (P12–14) and upon ex vivo glutamate uptake by cortical slices from these animals. I.c.v. infusion of 250 nmol QA induced seizures in all animals and decreased glutamate uptake. I.p. injection of MK-801 and phenobarbital 30 min before QA administration prevented seizures in all animals. Guanosine (7.5 mg/kg) 75 min before QA prevented seizures in 50% of animals as well as prevented the decrease of glutamate uptake in the protected animals. To investigate if the anticonvulsive effect of guanosine was specific for QA-induced seizures, the picrotoxin-induced seizures model was also performed. Pretreatment with phenobarbital i.p. (60 mg/kg–30 min) prevented picrotoxin-induced seizures in all animals, whereas guanosine p.o. (7.5 mg/kg–75 min) and MK-801 i.p. (0.5 mg/kg–30 min) had no effect. Thus, guanosine protection on the QA-induced seizures in young rats and on the decrease of glutamate uptake showed some specificity degree towards the QA-induced toxicity. This points that guanosine could be considered for treatments of epilepsy, and possibly other neurological disorders in children.

Wandering Home

The excitotoxic hypothesis of Huntington's disease pathogenesis suggests that selective striatal neuronal loss results from excessive activation of striatal excitatory amino acid receptors. Using a microdialysis probe mated to an Alzet 2002 mini-osmotic pump three different concentrations of quinolinic acid or vehicle were administered to the striata of rats over a 3-week period. Animals that received a total of 3.3 μmol of quinolinic acid had significant striatal atrophy that could be attributed to two distinct areas of neuronal loss. First, an area of necrosis surrounding the probe was marked by inflammatory infiltrate and a lack of neurons. In the second region, surrounding the necrotic area, there was a significant reduction in nissl-stained cells, with relative sparing of NADPH-diaphorase-staining neurons. In addition, there was a reduction in cytochrome oxidase staining throughout both of the areas of cell loss. Beyond the area of cell loss, the striatum appeared normal in all respects. The striata of animals that received 880 nmol quinolinic acid appeared identical to those that received vehicle. The striata of animals that received 8.8 μmol quinolinic acid showed severe nonselective atrophy of the striatum and some surrounding structures. We conclude that dialytic delivery of 3.3 μmol quinolinic acid produces an area of neuronal destruction that resembles the selective neuronal loss seen in Huntington's disease. This selective neurodegeneration produced by chronic exposure to quinolinic acid simulates more closely the course of Huntington's disease than previously described methods.

Failure of Neuroprotection by Embryonic Striatal Grafts in a Double Lesion Rat Model of Striatonigral Degeneration (Multiple System Atrophy)

In the present experiment we studied the ability of embryonic striatal grafts to protect against striatal quinolinic acid (QA)-induced excitotoxicity in a previously established double lesion rat model of striatonigral degeneration (SND), the neuropathological substrate of parkinsonism associated with multiple system atrophy (MSA). Male Wistar rats received under halothane inhalation anesthesia a 6-hydroxydopamine 6-OHDA injection into the left medial forebrain bundle. Four to 5 weeks later apomorphine-induced rotation behavior was tested. Rats were divided into two treatment groups receiving either embryonic striatal cell suspensions or sham injections. Apomorphine-induced rotation behavior was retested 2 and 4 weeks after the grafting procedure. Following the rotation test animals of the striatal and sham graft group received a stereotaxic injection of 150 nmol QA. Again rotation behavior was assessed 2 and 4 weeks after lesioning. Brains were then processed to dopamine reuptake ([3H]mazindol), dopamine D1 ([3H]SCH23390), and D2 ([3H]spiperone) receptor autoradiography. Gliosis was detected using [3H]PK11195, a marker for peripheral benzodiazepine binding sites. Behavioral and autoradiographic analysis failed to show striatal protection in 6-OHDA prelesioned animals receiving embryonic striatal grafts. These findings indicate that beneficial protective effects of striatal grafts implanted into host striatum prior to excitotoxic insults are abolished in the presence of severe dopaminergic denervation. Our present results are relevant to future applications of neural grafting in MSA-SND.

Comparison of intrastriatal injections of quinolinic acid and 3-nitropropionic acid for use in animal models of Huntington's disease

1. 1. The present study compared the effects of acute intrastriatal administration of quinolinic acid (QA) and 3-nitropropionic acid (3-NP), two neurotoxins used in animal models of Huntington's disease (HD), on the following behavioral and histological measures: (1) open field activity levels; (2) performance on balance beam and grip strength tasks; (3) acquisition of a radial-arm-water-maze (RAWM) task; (4) size of striatum and lateral ventricles; (5) amount of cytochrome oxidase (CYO) labeling; and (6) counts of Nissl-stained neurons and NADPH-diaphorase-labeled neurons in the striatum. 2. 2. Rats were given bilateral intrastriatal injections of either 200 nmol QA, 750 nmol 3-NP, or phosphate buffered saline (PBS) two weeks prior to behavioral testing and four weeks prior to histological processing. 3. 3. The behavioral results indicated that both QA and 3-NP injections caused an increase in activity levels at two weeks postlesion, but only the QA rats showed hyperactivity at four weeks postlesion. Both QA and 3-NP rats showed significant impairment in the balance beam task, but only 3-NP rats differed significantly on the grip-strength task. Both toxins caused learning impairments in the RAWM task, with 3-NP rats being more severely impaired. 4. 4. The neuroanatomical results indicated that both QA and 3-NP produced significant striatal atrophy and ventricular dilation, as well as a reduction in CYO staining and loss of Nissl-stained neurons, but only the 3-NP lesions created necrotic cavities in the striatum. However, the QA treatments resulted in significant loss of NADPH-diaphorase neurons in regions peripheral to the site of injection. 5. 5. In general, these results suggest that QA treatments produce milder behavioral and neuroanatomical effects that mimic some of the earlier symptoms of HD, while 3-NP produced more severe effects which mimic both the later symptoms and the juvenile onset of HD.

The effects of globus pallidus lesions on dopamine-dependent motor behaviour in rats

Motor effects of bilateral lesions of the globus pallidus induced by quinolinic acid (30 and 60 nmol in 0.5 μl) were investigated in rats. Globus pallidus lesions with 60 nmol quinolinic acid produced a significant reduction of spontaneous motor activity measured by a reduced locomotor activity in an open field and by a reduced sniffing activity in an experimental chamber. In addition, d-amphetamine (1 mg/kg, i.p.)-induced hyperlocomotion and d-amphetamine (3 mg/kg, i.p.)-induced stereotyped sniffing were significantly reduced in animals with quinolinic acid lesions (60 nmol). Globus pallidus lesions with 60 nmol quinolinic acid potently reversed catalepsy induced by systemic administration of the dopamine D 1 receptor antagonist SCH23390 (0.75 and 1 mg/kg, i.p.) or the dopamine D 2 receptor antagonist raclopride (1.25 and 5 mg/kg, i.p.), while lesions with 30 nmol quinolinic acid exerted anti-cataleptic effects which were only partly significant. In line with current models of basal ganglia functions, these findings indicate that inactivation of the globus pallidus reduced spontaneous motor activity and motor hyperactivity after dopamine receptor stimulation. However, the present data also demonstrate that inactivation of the globus pallidus reversed motor hypoactivity induced by a blockade of dopamine D 1 and D 2 receptors. Therefore, a more complex functional model of the globus pallidus is required to account for the opposite effects on motor behaviour observed after lesions of this basal ganglia nucleus.

Nerve growth factor and basic fibroblast growth factor protect cholinergic neurons against quinolinic acid excitotoxicity in rat neostriatum.

In the present work we have characterized a possible mechanism leading to the early survival of neostriatal cholinergic neurons after quinolinic acid injection. Different doses of quinolinic acid were injected in rat neostriatum and two different parameters were analysed 7 days after the lesion: choline acetyltransferase (ChAT) activity and nerve growth factor (NGF) levels. We have observed that ChAT activity decreased (until 68 nmol quinolinic acid) and NGF levels increased (until 34 nmol quinolinic acid) in a dose-dependent manner. In order to characterize the time-course of the lesion on NGF levels and ChAT activity, and the possible protective effect of NGF and basic fibroblast growth factor (bFGF) on cholinergic neurons, we have used the quinolinic acid dose (68 nmol) at which the first decrease of ChAT activity was observed. ChAT activity and NGF levels showed different patterns of response to quinolinic acid injection, since the maximal effect was reached at 1 day for ChAT activity and at 2 days for NGF levels. NGF or bFGF simultaneously injected with quinolinic acid (68 nmol) completely prevented the decrease in ChAT activity in a dose-dependent manner but NGF was more effective than bFGF. Furthermore, differences observed in ChAT activity after NGF but not bFGF treatment were correlated with changes in the number of ChAT immunoreactive cells. Finally, we have also observed that, although bFGF alone was not able to modify NGF levels, bFGF simultaneously injected with quinolinic acid produced an increase of NGF levels higher than that observed after quinolinic acid injection alone.(ABSTRACT TRUNCATED AT 250 WORDS)

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 μl) in the striatum and damage was assessed by the determination of both glutamate decar☐ylase 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 decar☐ylase 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 α-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 decar☐ylase 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). Quantitative analysis of damaged cells in Cresyl Violet-stained sections corroborated the protective effect of NBQX against neuronal damage mediated bynon- N-methyl- d-aspartate receptors. p ]It is concluded that NBQX equally protects against AMPA- and kainate-induced lesions in the striatum in vivo and that non- N-methyl- d-aspartate receptor antagonists might be useful as protectors against neuronal damage produced by excess activation of glutamate receptors.

A comparative analysis of the neuroprotective properties of competitive and uncompetitive n-methyl- d-aspartate receptor antagonists in vivo: Implications for the process of excitotoxic degeneration and its therapy

Injection of the N-methyl- d-aspartate receptor agonist, quinolinic acid, into the rat striatum in vivo results in the degeneration of cholinergic and GABAergic neurons, as determined seven days later using the marker enzymes, choline acetyltransferase and glutamate decarboxylase, respectively. Such damage was dose-dependently prevented by CGP 37849 or MK-801 (competitive and uncompetitive N-methyl- d-aspartate receptor antagonists, respectively) administered systemically or intrastriatally at the same time as quinolinic acid. The neuroprotective activity of CGP 37849 was associated with the d-enantiomer, CGP 40116 (ED 507.5 mg/kg i.p.), which was approximately 1.5-fold and 3.5-fold more potent than the related compounds, d-CPPene and CGS 19755, respectively. CGP 37849 was a weaker neuroprotectant than MK-801 (ED 500.8mg/kg i.p) when administered systemically, but was dramatically more potent following coinjection with quinolinic acid (Ed 50'S 0.2 and 117 nmol, respectively). When injected intrastriatally 0.5–2 h post-quinolinic acid, CGP 37849 was protective over the entire period studied, whereas MK-801 was less effective at all post-quinolinic acid injection times. The finding that CGP 37849 is neuroprotective when administered intrastriatally 1–2 h post-quinolinic acid supports the hypothesis that a period exists following excitotoxic insult in which neurons are not committed to die, and can be rescued by blockade of ongoing. N-methyl- d-aspartate receptor activation. Competition studies indicated that, when coinjected with 100–400 nmol quinolinic acid into the striatum, CGP 37849 exhibited kinetics predicted of a competitive N-methyl- d-aspartate receptor antagonist (declining neuroprotective potency with increasing doses of agonist), whereas MK-801 displayed a complex picture, with weak protective activity at low doses of quinolinic acid. Following systemic administration, neither antagonist was markedly affected by the dose of excitotoxin. When given i.p. at up to 6 h post-quinolinic acid, CGP 37849 and MK-801 showed essentially identical profiles of post-insult protection; degeneration of cholinergic neurons was reduced significantly throughout the entire post-insult period, whereas GABAergic neurons were protected only when drugs were administered 2 h or earlier post-quinolinic acid. The data indicate that competitive and uncompetitive N-methyl- d-aspartate receptor antagonists are effective neuroprotectants in vivo, and that parameters such as drug lipophilicity or mechanism of action at the receptor do not impinge upon their properties as systemically active cerebroprotectants.

Striatal implants of fetal striatum or gelfoam protect against quinolinic acid lesions of the striatum

Previous studies in our laboratory have shown that intrastriatal implants of fetal striatum significantly attenuate excitotoxic damage resulting from a 240 nmol quinolinic acid (QA) challenge delivered 7 days later. In contrast, animals with intrastriatal implants of other tissue types (adipose tissue, peripheral nerve or adrenal medulla) demonstrate a more limited, but consistent trend in protection from QA excitotoxicity. The present study was designed to test the hypothesis that partial striatal protection found in animals receiving peripheral tissue grafts is due to the transplantation procedure eliciting a host response which attenuates excitotoxicity. Adult female Long-Evans rats received either cellular (fetal striatum) or acellular (gelfoam) implants followed 1 week later by a unilateral injection of 240 nmol QA into the grafted striatum. Animals were tested for rotational asymmetries before grafting, post-implantation, and after lesioning. Compared to baseline rotational behavior, rats which received implants did not show changes in ipsilateral turning after QA lesions. This protective effect was not limited to rotational behavior since improvements in spontaneous locomotor activity were evident. In addition, the adipsia and aphagia often associated with striatal lesions were ameliorated in both groups of grafted animals. Morphometric analysis demonstrated that endogenous dopaminergic, cholinergic and enkephalinergic systems in the two transplanted groups sustained less excitotoxic damage than in the QA lesioned, non-grafted animals. These results are consistent with the hypothesis that a host generated response activated by the implantation provides a protective effect against QA excitotoxicity.

Chronic Intrastriatal Dialytic Administration of Quinolinic Acid Produces Selective Neural Degeneration

The excitotoxic hypothesis of Huntington's disease pathogenesis suggests that selective striatal neuronal loss results from excessive activation of striatal excitatory amino acid receptors. Using a microdialysis probe mated to an Alzet 2002 mini-osmotic pump three different concentrations of quinolinic acid or vehicle were administered to the striata of rats over a 3-week period. Animals that received a total of 3.3 μmol of quinolinic acid had significant striatal atrophy that could be attributed to two distinct areas of neuronal loss. First, an area of necrosis surrounding the probe was marked by inflammatory infiltrate and a lack of neurons. In the second region, surrounding the necrotic area, there was a significant reduction in nissl-stained cells, with relative sparing of NADPH-diaphorase-staining neurons. In addition, there was a reduction in cytochrome oxidase staining throughout both of the areas of cell loss. Beyond the area of cell loss, the striatum appeared normal in all respects. The striata of animals that received 880 nmol quinolinic acid appeared identical to those that received vehicle. The striata of animals that received 8.8 μmol quinolinic acid showed severe nonselective atrophy of the striatum and some surrounding structures. We conclude that dialytic delivery of 3.3 μmol quinolinic acid produces an area of neuronal destruction that resembles the selective neuronal loss seen in Huntington's disease. This selective neurodegeneration produced by chronic exposure to quinolinic acid simulates more closely the course of Huntington's disease than previously described methods.

Selective resistance of tachykinin-responsive cholinergic neurons in the quinolinic acid lesioned neostriatum

We have studied changes on endogenous acetylcholine (ACh) release evoked by different agents from rat neostriatal slices after quinolinic acid (QA) injections. QA lesions induced a biphasic decrease on ACh release evoked by 1 μM glutamate and 50 mM KCl. ACh release evoked by selective tachykinin agonists was only significantly decreased by 250 nmol QA. These results suggest the presence of different functional cholinergic cell populations, with tachykinin-responsive cholinergic neurons selectively spared.

Kynurenic Acid in the Quinolinate‐lesioned Rat Hippocampus: Studies In Vitro and In Vivo

The present study was designed to examine the cellular localization and biosynthetic machinery of the broad-spectrum excitatory amino acid receptor antagonist kynurenic acid in the lesioned rat hippocampus. Seven days after an intrahippocampal injection of 120 nmol quinolinic acid, which causes massive neurodegeneration in the dorsal hippocampus, kynurenic acid tissue levels and the activity of kynurenic acid's anabolic enzyme, kynurenine aminotransferase, were increased by 92% and 67%, respectively, as compared to controls. The steady-state levels of extracellular kynurenic acid, examined by microdialysis in unanaesthetized rats, were also increased in the lesioned tissue (from 93.6 +/- 10.2 to 207.6 +/- 18.6 fmol/30 microl dialysate). Using microdialysis, three compounds which are known to decrease kynurenic acid production from its bioprecursor l-kynurenine in brain slices and in vivo were tested for their ability to reduce the levels of endogenous kynurenic acid. In unlesioned tissue, aminooxyacetic acid (300 microM), veratridine (50 microM) and glutamate (5 mM), all administered through the dialysis probe, decreased extracellular kynurenic acid concentrations by 30 - 40%, i.e. to a lesser degree than in previous experiments in which kynurenine was used as a bioprecursor. Only the effect of veratridine was abolished in the quinolinate-lesioned hippocampus. These data indicate that kynurenic acid is produced in and liberated from astrocytes, and that aminooxyacetic acid and glutamate (but not veratridine) exert their action by directly affecting glial kynurenic acid biosynthesis. The results also suggest the existence of two distinct intracellular kynurenic acid pools, which are responsible for kynurenic acid storage and rapid kynurenic acid mobilization, respectively. Taken together, these features of kynurenic acid neurobiology may be of relevance in the control of excitatory amino acid receptor function under physiological and pathological conditions.

Effects of quinolinic acid on messenger RNAs encoding somatostatin and glutamic acid decarboxylases in the striatum of adult rats

The level of expression of mRNAs encoding somatostatin and two isoforms of glutamic acid decarboxylase ( M r 65,000, GAD65 and 67,000, GAD67) was examined by quantitative in situ hybridization histochemistry in the striatum of adult rats after local injections of quinolinic acid. After a 2-week survival period, Nissl stains showed a profound loss of neurons in the injected striata. With a dose of 120 nmol quinolinic acid, the lesioned area was completely devoid of somatostatin mRNA-positive neurons but contained cells expressing nicotinamide adenine dinucleotide-diaphorase activity (a marker of somatostatinergic interneurons in striatum). After 60 nmol of quinolinic acid, the number of neurons expressing somatostatin mRNA in the lesioned area was similar to controls but the level of labeling per neuron was increased. In the lesioned area, labeling for GAD65 mRNA was abolished and labeling for GAD67 mRNA markedly reduced. However, scattered neurons expressing GAD67 mRNA could still be detected. The majority of surviving GABA-ergic neurons expressed immunoreactivity to parvalbumin, a marker for striatal GABA-ergic interneurons. The results show that quinolinic acid induces dose-dependent alterations in the expression of striatal somatostatin mRNA and reveal a relative sparing of GABA-ergic interneurons in the quinolinic acid-lesioned rat striatum.

A peptidase-resistant cyclic octapeptide analogue of somatostatin (SMS 201–995) modulates seizures induced by quinolinic and kainic acids differently in the rat hippocampus

Electroencephalographic (EEG) seizures were measured in rats after intrahippocampal injection of 120 nmol quinolinic acid into the stratum radiatum CA1 or 0.19 nmol kainic acid in the dentate gyrus or in the stratum radiatum. Injection of 5 μg SMS 201–995, a peptidase-resistant cyclic octapeptide analogue of somatostatin, into the stratum radiatum, 15 min before quinolinic acid, did not significantly modify the number of seizures and the total time in seizures. Five μg SMS 201–995 injected into the stratum radiatum reduced the number of seizures induced by kainic acid in the same area and the total time spent in seizures by 58% and 75%, respectively (Student's t-test; P < 0.01). In both instances the latency to the first ictal episode was not significantly modified. Lesions of the medial septum, which reduced the activity of choline-o-acetyl-transferase (CAT) in the dorsal hippocampus by >90% after one week did not significantly affect seizures induced by quinolinic acid. In rats lesioned in the medial septum, 5 μg SMS 201–995 reduced the total time spent in seizures by 43%, without changing the number of ictal episodes and raised the latency to the first quinolinic acid-induced seizure by 53% (ANOVA 2 × 2, P < 0.05) but had no effect on these measures in the corresponding sham-operated group. A significant, 50% reduction of the total time spent in seizures and a 20% increase in the latency to the first quinolinic acid-induced seizure, with no changes in the number of ictal episodes, were observed when 5 μg SMS 201–995 was injected intrahippocampally with 10 μg atropine (ANOVA 2 × 2, P < 0.05), a muscarinic receptor antagonist, which per se did not significantly change seizures caused by quinolinic acid. Five μg of the peptide into the dentate gyrus reduced the total time spent in seizures induced by kainic acid, in the same area by about 60% and significantly reduced the number of seizures by 33% (Dunnett's test; P < 0.05). Picrotoxin (2 mg/kg, i.p. or 1.5 nmol into the dentate gyrus), a GABA A receptor antagonist, did not alter the EEG pattern induced by kainic acid in the dentate gyrus or modify the anticonvulsant effect of SMS 201–995 on seizures induced by kainic acid.

Female rats are more sensitive to the locomotor alterations following quinolinic acid-induced striatal lesions: Effects of striatal transplants

The effects of sex differences and hormonal factors on the locomotor alterations following intrastriatal injections of quinolinic acid (QA) and the ability of fetal striatal transplants to reverse those effects were examined. Male, female, or ovariectomized female rats received bilateral injections of 150 nmol QA or vehicle into the striatum. Using a multidimensional analysis of spontaneous nocturnal locomotor behavior, a significant increase in locomotion was observed in female but not male or ovariectomized female rats. The increases in activity observed in the lesioned females were attenuated at 6 and 10 weeks following transplantation of rat fetal (E17) striatal tissue into the lesioned striata. Transplanted striatal tissue had no effect on locomotion in male or ovariectomized female rats. Cytochrome oxidase histochemistry revealed that QA produced a marked loss of metabolic activity in regions exhibiting cell loss. Within these areas there was a marked loss of striatal neurons including those reactive for NADPH diaphorase. Despite the sex-related differences in QA-induced locomotion, there were no apparent differences in the extent of striatal pathology or survival of the grafts in any of the groups receiving QA. These experiments demonstrate a sex-dependent dissociation between the behavioral and neurobiological consequences of QA and suggest that sex and hormonal variables play an important role in the locomotor changes following excitotoxic-induced striatal damage.