Effects of intrastriatal injection of quinolinic acid on electrical activity and extracellular ion concentrations in rat striatum in vivo

Effects of different chronic restraint stress periods on anxiety- and depression-like behaviors and tryptophan-kynurenine metabolism along the brain-gut axis in C57BL/6N mice

Chronic restraint stress (CRS) is a widely used stimulus to induce anxiety- and depression-like behaviors, linked to alterations in tryptophan-kynurenine (TRP-KYN) metabolism in animals. This study assessed the effects of different CRS periods on anxiety- or depression-like behaviors and TRP-KYN metabolism along brain-gut axis in C57BL/6N mice. Results showed that one-week CRS decreased the open arm entries of mice in elevated plus maze and delayed latency of feeding in novelty suppressed feeding test. Four-week CRS reduced sucrose preference, increases forced swimming immobility time, and also induced anxiety-like behaviors of mice. UPLC-MS/MS analysis revealed decreased levels of the neurotoxic 3-hydroxykynurenine (3-HK) and quinolinic acid (QA), and an increase in the neuroprotective kynurenic acid (KA) in the hippocampus of one-week CRS mice; meanwhile, four-week CRS mice displayed a reduction in KA and increases in 3-HK and QA. In the colon, both one-week and four-week CRS mice exhibited significant reductions in 3-HK and QA, with a marked increase of KA exclusively in four-week CRS mice. Briefly, one-week CRS only induced anxiety-like behaviors with hippocampal neuroprotection in TRP-KYN metabolism, whereas four-week CRS caused anxiety- and depression-like behaviors with neurotoxicity. In the colon, during both CRS periods, KYN was metabolized in the direction of NAD+ production. However, four-week CRS triggered intestinal inflammation risk with increased KA. Summarily, slightly short-term stress has beneficial effects on mice, while prolonged chronic stress can lead to pathological changes. This study offers valuable insights into stress-induced emotional disturbances.

Kynurenines and Neurofilament Light Chain in Multiple Sclerosis

Multiple sclerosis is an autoimmune, demyelinating, and neurodegenerative disease of the central nervous system. In recent years, it has been proven that the kynurenine system plays a significant role in the development of several nervous system disorders, including multiple sclerosis. Kynurenine pathway metabolites have both neurotoxic and neuroprotective effects. Moreover, the enzymes of the kynurenine pathway play an important role in immunomodulation processes, among others, as well as interacting with neuronal energy balance and various redox reactions. Dysregulation of many of the enzymatic steps in kynurenine pathway and upregulated levels of these metabolites locally in the central nervous system, contribute to the progression of multiple sclerosis pathology. This process can initiate a pathogenic cascade, including microglia activation, glutamate excitotoxicity, chronic oxidative stress or accumulated mitochondrial damage in the axons, that finally disrupt the homeostasis of neurons, leads to destabilization of neuronal cell cytoskeleton, contributes to neuro-axonal damage and neurodegeneration. Neurofilaments are good biomarkers of the neuro-axonal damage and their level reliably indicates the severity of multiple sclerosis and the treatment response. There is increasing evidence that connections exist between the molecules generated in the kynurenine metabolic pathway and the change in neurofilament concentrations. Thus the alterations in the kynurenine pathway may be an important biomarker of the course of multiple sclerosis. In our present review, we report the possible relationship and connection between neurofilaments and the kynurenine system in multiple sclerosis based on the available evidences.

Quinolinic acid: an endogenous neurotoxin with multiple targets

Quinolinic acid (QUIN), a neuroactive metabolite of the kynurenine pathway, is normally presented in nanomolar concentrations in human brain and cerebrospinal fluid (CSF) and is often implicated in the pathogenesis of a variety of human neurological diseases. QUIN is an agonist of N-methyl-D-aspartate (NMDA) receptor, and it has a high in vivo potency as an excitotoxin. In fact, although QUIN has an uptake system, its neuronal degradation enzyme is rapidly saturated, and the rest of extracellular QUIN can continue stimulating the NMDA receptor. However, its toxicity cannot be fully explained by its activation of NMDA receptors it is likely that additional mechanisms may also be involved. In this review we describe some of the most relevant targets of QUIN neurotoxicity which involves presynaptic receptors, energetic dysfunction, oxidative stress, transcription factors, cytoskeletal disruption, behavior alterations, and cell death.

Effects of caffeic acid, rofecoxib, and their combination against quinolinic acid-induced behavioral alterations and disruption in glutathione redox status

OBJECTIVE

The neuroprotective roles of cyclooxygenase (COX) and lipooxygenase (LOX) inhibitors have been well documented. Quinolinic acid (QA) is a well-known excitotoxic agent that could induce behavioral, morphological and biochemical alterations similar with symptoms of Huntington's disease (HD), by stimulating NMDA receptors. However, the exact roles of COX and LOX inhibitors in HD have not yet been explained. The present study aims to elucidate the effects of caffeic acid (a specific inhibitor for LOX), rofecoxib (a specific inhibitor for COX-2), and their combination in ameliorating QA-induced neurotoxicity in rats.

METHODS

QA was injected into the right striatum of rats to induce neurotoxicity. Caffeic acid and rofecoxib were then orally administered separately. In the combination study, caffeic acid and rofecoxib were administered together. After that, a series of behavioral assessments were conducted to determine the effects of caffeic acid and rofecoxib, respectively, and the co-effect of caffeic acid and rofecoxib, against QA-induced neurotoxicity.

RESULTS

Intrastriatal QA administration (300 nmol) not only induced a significant reduction in body weight and motor incoordination, but also altered the redox status (decreased glutathione and increased oxidized glutathione level) in striatum, as compared to the sham group. Moreover, chronic treatment with caffeic acid (5 mg/kg and 10 mg/kg, respectively, p.o.) or rofecoxib (10 mg/kg, p.o.) could significantly attenuate QA-induced behavioral alterations and restore the redox status in striatum. However, at the dose of 2.5 mg/kg, caffeic acid did not show any significant effects on these parameters in QA-treated rats. Furthermore, the combination of rofecoxib (10 mg/kg) and caffeic acid (5 mg/kg) could significantly protect against QA neurotoxicity.

CONCLUSION

The in vivo study indicates that excitotoxic injury to the brain might affect oxidant/antioxidant equilibrium by eliciting changes in glutathione. Moreover, the LOX and the COX pathways may be both involved in quinolinic-induced neurotoxicity, which provides a promising target for HD treatment.

Simultaneous two-voxel localized (1)H-observed (13)C-edited spectroscopy for in vivo MRS on rat brain at 9.4T: Application to the investigation of excitotoxic lesions

(13)C spectroscopy combined with the injection of (13)C-labeled substrates is a powerful method for the study of brain metabolism in vivo. Since highly localized measurements are required in a heterogeneous organ such as the brain, it is of interest to augment the sensitivity of (13)C spectroscopy by proton acquisition. Furthermore, as focal cerebral lesions are often encountered in animal models of disorders in which the two brain hemispheres are compared, we wished to develop a bi-voxel localized sequence for the simultaneous bilateral investigation of rat brain metabolism, with no need for external additional references. Two sequences were developed at 9.4T: a bi-voxel (1)H-((13)C) STEAM-POCE (Proton Observed Carbon Edited) sequence and a bi-voxel (1)H-((13)C) PRESS-POCE adiabatically decoupled sequence with Hadamard encoding. Hadamard encoding allows both voxels to be recorded simultaneously, with the same acquisition time as that required for a single voxel. The method was validated in a biological investigation into the neuronal damage and the effect on the Tri Carboxylic Acid cycle in localized excitotoxic lesions. Following an excitotoxic quinolinate-induced localized lesion in the rat cortex and the infusion of U-(13)C glucose, two (1)H-((13)C) spectra of distinct (4x4x4mm(3)) voxels, one centred on the injured hemisphere and the other on the contralateral hemisphere, were recorded simultaneously. Two (1)H bi-voxel spectra were also recorded and showed a significant decrease in N-acetyl aspartate, and an accumulation of lactate in the ipsilateral hemisphere. The (1)H-((13)C) spectra could be recorded dynamically as a function of time, and showed a fall in the glutamate/glutamine ratio and the presence of a stable glutamine pool, with a permanent increase of lactate in the ipsilateral hemisphere. This bi-voxel (1)H-((13)C) method can be used to investigate simultaneously both brain hemispheres, and to perform dynamic studies. We report here the neuronal damage and the effect on the Tri Carboxylic Acid cycle in localized excitotoxic lesions.

AAV-mediated expression of Bcl-xL or XIAP fails to induce neuronal resistance against quinolinic acid-induced striatal lesioning

Apoptotic mechanisms have been proposed to contribute to the selective loss of medium spiny striatal projection neurons in Huntington's disease (HD). This raises the question as to whether enhancing the expression of anti-apoptotic factors in vulnerable striatal projection neurons can reduce their susceptibility to neurotoxic processes occurring in the HD brain. In this study AAV 1/2 vectors encoding either the anti-apoptotic factor Bcl-xL or XIAP were used to transduce striatal neurons prior to an intrastriatal injection of the excitotoxic glutamate analogue quinolinic acid (QA). AAV 1/2 vector treated rats were observed in behavioural tests undertaken to assess whether anti-apoptotic factor expression provided amelioration of motor function impairment following unilateral QA-induced striatal lesioning. AAV-XIAP treated rats displayed complete amelioration of an ipsilateral forelimb use bias relative to control animals. However, neither AAV-XIAP nor AAV-Bcl-xL treated rats demonstrated an improvement in sensorimotor neglect compared to control animals. Furthermore, we did not observe a significant reduction of QA-induced pathology in assessed neuronal populations of the basal ganglia. These results indicate that sole enhancement of XIAP or Bcl-xL is not sufficient to counteract QA-induced excitotoxic insult of striatal neurons.

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.

In vitro effect of quinolinic acid on energy metabolism in brain of young rats

Quinolinic acid (QA) is found at increased concentrations in brain of patients affected by various common neurodegenerative disorders, including Huntington's and Alzheimer's diseases. Considering that the neuropathology of these disorders has been recently attributed at least in part to energy deficit, in the present study we investigated the in vitro effect of QA (0.1-100 microM) on various parameters of energy metabolism, such as glucose uptake, (14)CO(2) production and lactate production, as well as on the activities of the respiratory chain complexes I-V, the citric acid cycle (CAC) enzymes, creatine kinase (CK), lactate dehydrogenase (LDH) and Na(+),K(+)-ATPase and finally the rate of oxygen consumption in brain of 30-day-old rats. We initially observed that QA significantly increased glucose uptake (55%), whereas (14)CO(2) generation from glucose, acetate and citrate was inhibited (up to 60%). Furthermore, QA-induced increase of brain glucose uptake was prevented by the NMDA receptor antagonist MK-801. Complex II activity was also inhibited (up to 35%) by QA, whereas the other activities of the respiratory chain complexes, CAC enzymes, CK and Na(+),K(+)-ATPase were not affected by the acid. Furthermore, inhibition of complex II activity was fully prevented by pre-incubating cortical homogenates with catalase plus superoxide dismutase, indicating that this effect was probably mediated by reactive oxygen species. In addition, lactate production was also not altered by QA, in contrast to the conversion of pyruvate to lactate catalyzed by LDH, which was significantly decreased (17%) by this neurotoxin. We also observed that QA did not change state III, state IV and the respiratory control ratio in the presence of glutamate/malate or succinate, suggesting that its effect on cellular respiration was rather weak. The data provide evidence that QA provokes a mild impairment of brain energy metabolism in vitro and does not support the view that the brain energy deficiency associated to certain neurodegenerative disorders could be solely endorsed to QA accumulation.

Brain mitochondrial defects amplify intracellular [Ca2+] rise and neurodegeneration but not Ca2+entry during NMDA receptor activation

According to the "indirect" excitotoxicity hypothesis, mitochondrial defects increase Ca2+ entry into neurons by rendering NMDA-R hypersensitive to glutamate. We tested this hypothesis by investigating in the rat striatum and cultured striatal cells how partial mitochondrial complex II inhibition produced by 3-nitropropionic acid (3NP) modifies the toxicity of the NMDA-R agonist quinolinate (QA). We showed that nontoxic 3NP treatment, leading to partial inhibition of complex II activity, greatly exacerbated striatal degeneration produced by slightly toxic QA treatment through an "all-or-nothing" process. The potentiation of QA-induced cell death by 3NP was associated with increased calpain activity and massive calpain-mediated cleavage of several postsynaptic proteins, suggesting major neuronal Ca2+ deregulation in the striatum. However, Ca2+ anomalies probably do not result from NMDA-R hypersensitivity. Indeed, brain imaging experiments using [(18)F]fluorodeoxyglucose indirectly showed that 3NP did not increase QA-induced ionic perturbations at the striatal glutamatergic synapses in vivo. Consistent with this, the exacerbation of QA toxicity by 3NP was not related to an increase in the QA-induced entry of 45Ca2+ into striatal neurons. The present results demonstrate that the potentiation of NMDA-R-mediated excitotoxicity by mitochondrial defects involves primarily intracellular Ca2+ deregulation, in the absence of NMDA-R hypersensitivity.

Kynurenines, Parkinson's disease and other neurodegenerative disorders: preclinical and clinical studies

The kynurenine pathway is the main pathway of tryptophan metabolism. L-kynurenine is a central compound of this pathway since it can change to the neuroprotective agent kynurenic acid or to the neurotoxic agent quinolinic acid. The break-up of these endogenous compounds' balance can be observable in many disorders. It can be occur in neurodegenerative disorders, such as Parkinson's disease, Huntington's and Alzheimer's disease, in stroke, in epilepsy, in multiple sclerosis, in amyotrophic lateral sclerosis, and in mental failures, such as schizophrenia and depression. The increase of QUIN concentration or decrease of KYNA concentration could enhance the symptoms of several diseases. According to numerous studies, lowered KYNA level was found in patients with Parkinson's disease. It can be also noticeable that KYNA-treatment prevents against the QUIN-induced lesion of rat striatum in animal experiments. Administrating of KYNA can be appear a promising therapeutic approach, but its use is limited because of its poorly transport across the blood-brain barrier. The solution may be the development of KYNA analogues (e.g. glucoseamine-kynurenic acid) which can pass across this barrier and disengaging in the brain, then KYNA can exert its neuroprotective effects binding at the excitatory glutamate receptors, in particular the NMDA receptors. Furthermore, it seems hopeful to use kynurenine derivatives (e.g. 4-chloro-kynurenine) or enzyme inhibitors (e.g. Ro-61-8048) to ensure an increased kynurenic acid concentration in the central nervous system.

Accumulation of Quinolinic Acid With Neuroinflammation: Does It Mean Excitotoxicity?

The quinolinic acid (QUIN) accumulation that is associated with neuroinflammation is often considered capable of promoting excitotoxic neuronal damage, but QUIN is a relatively weak agonist of N-methyl-D-aspartate (NMDA) receptors. Our study aimed to determine, in vivo, which extracellular concentrations of QUIN must be reached to initiate electrophysiological changes indicative of excitotoxic stress in the cerebral cortex of rats, under normal conditions and when superimposed to a challenge involving NMDA-receptor activation, i.e. repeated cortical spreading depression (CSD). Our experimental strategy relied on microdialysis probes incorporating an electrode, implanted in the brain of halothane-anaesthetised rats. These devices were used to apply QUIN or NMDA locally to the cortical area under study (with or without co-perfusion of high K+ for repetitive induction of CSD), and to record the associated changes in the extracellular DC potential (for information on the membrane polarisation of the cellular population surrounding the probe) and lactate (for the detection of increased local energy demand). The extracellular EC50 for induction of local depolarisation in the normal cortex was around 30 times higher than the extracellular QUIN levels measured in the immunoactivated brain of gerbils. Within the range of concentrations 0.03 to 0.3 mM in the perfusion medium, QUIN suppressed concentration-dependently the elicitation of CSD by K+, presumably because of NMDA-receptor desensitisation. Finally, on-line monitoring of changes in extracellular lactate with local application of QUIN indicated that extracellular concentration of QUIN in the low micromolar range are well tolerated by the brain parenchyma, at least in cortical regions. All these data do not support the notion that QUIN accumulation adds an excitotoxic component to neuroinflammation.

Metabolic changes in quinolinic acid-lesioned rat striatum detected non-invasively by in vivo (1)H NMR spectroscopy

Intrastriatal injection of quinolinic acid (QA) provides an animal model of Huntington disease. In vivo (1)H NMR spectroscopy was used to measure the neurochemical profile non-invasively in seven animals 5 days after unilateral injection of 150 nmol of QA. Concentration changes of 16 metabolites were measured from 22 microl volume at 9.4 T. The increase of glutamine ((+25 +/- 14)%, mean +/- SD, n = 7) and decrease of glutamate (-12 +/- 5)%, N-acetylaspartate (-17 +/- 6)%, taurine (-14 +/- 6)% and total creatine (-9 +/- 3%) were discernible in each individual animal (P < 0.005, paired t-test). Metabolite concentrations in control striata were in excellent agreement with biochemical literature. The change in glutamate plus glutamine was not significant, implying a shift in the glutamate-glutamine interconversion, consistent with a metabolic defect at the level of neuronal-glial metabolic trafficking. The most significant indicator of the lesion, however, were the changes in glutathione ((-19 +/- 9)%, P < 0.002)), consistent with oxidative stress. From a comparison with biochemical literature we conclude that high-resolution in vivo (1)H NMR spectroscopy accurately reflects the neurochemical changes induced by a relatively modest dose of QA, which permits one to longitudinally follow mitochondrial function, oxidative stress and glial-neuronal metabolic trafficking as well as the effects of treatment in this model of Huntington disease.

Quinolinic acid accumulation during neuroinflammation. Does it imply excitotoxicity?

It is often proposed that quinolinic acid (QUIN) contributes to the pathophysiology of neuroinflammation because this kynurenine pathway metabolite is a selective agonist of N-methyl-D-aspartate (NMDA) receptors, and both its brain tissue and cerebrospinal fluid concentrations increase markedly with inflammation. However, whether or not the extracellular levels of QUIN reached during neuroinflammation are high enough to promote excitotoxicity, remains unclear because QUIN is a weak NMDA receptor agonist. We have addressed this issue by evaluating the extracellular concentrations of QUIN that must be reached to initiate potentially excitotoxic changes in the cerebral cortex of rats, under normal conditions, and when superimposed on another insult. We have also examined the increase in extracellular lactate associated with the perfusion of increasing concentrations of QUIN through a microdialysis probe. The extracellular EC50 for induction of local depolarisation was 228 microM with QUIN alone; that is, about 30 times the levels of QUIN measured previously in immune activated brain. Furthermore, at least 20 microM extracellular QUIN needed to be reached to reduce K+ induced spreading depression, an unexpected effect since spreading depression is inhibited by NMDA receptor antagonists. Our data suggest that, although synthesis of QUIN from activated microglia and invading macrophages can increase its extracellular concentration 10-100-fold, the levels that are reached in these conditions remain far below the concentrations of QUIN that are necessary for excessive NMDA receptor activation. However, the possibility that QUIN accumulation may be a deleterious feature of neuroinflammation cannot be ruled out at this stage.

Aquaporins in the central nervous system

In this review, we have tried to summarize most available data dealing with the aquaporin (AQP) family of water channels in the CNS. Two aquaporins have been identified so far in the CNS, AQP1 and AQP4. AQP1 is restricted to the choroid plexus of the lateral ventricles, which raises a role for this aquaporin in cerebrospinal fluid formation. AQP4 is the predominant water channel in the brain and it is more widely distributed than originally believed, with a marked prevalence over periventricular areas. In the first part of this review, we examine the complete distribution pattern of AQP4 in the CNS including its rostro-caudal localization to end with its subcellular location. After discussing scarce data dealing with regulation of aquaporins in the CNS, we focus in potential roles for aquaporins. Novel recent data highlights very important roles for this aquaporin in the normal and pathological brain including, among others, role in potassium buffering, body fluid homeostasis, central osmoreception and development and restoration of brain edema.

Morphology and compartmental location of cells exhibiting DNA damage after quinolinic acid injections into rat striatum

Although excitotoxic injury is thought to play a role in many pathologic conditions, the type of cell death induced by excitotoxins in vivo and the basis for the differential vulnerability of neurons to excitotoxic injury are still poorly understood. Morphologic alterations and the presence of DNA damage were examined in adult rat striatum after an intrastriatal injection of low doses of quinolinic acid, a N-methyl-D-aspartate receptor agonist. Rats were killed 6, 8, 10, or 12 hours after quinolinate or vehicle injection. Numerous neurons with necrotic morphologies were detected in the quinolinate-injected striata. In addition, few neurons with apoptotic morphologies were found in the dorsomedial striatum. DNA strand breaks were detected in tissue sections by in situ nick translation with (35)S-radiolabeled nucleotides and emulsion autoradiography. Labeled cells were first detected outside the needle track 10 hours after quinolinate injection and, on average, 20% of neurons exhibited DNA damage by 12 hours after surgery. DNA damage was found in cells with both apoptotic and necrotic morphologies. A marked differential vulnerability to DNA damage at this time was observed in two striatal compartments, the striosomes, identified as regions of dense [(3)H]naloxone binding, and the extrastriosomal matrix: the great majority of labeled cells were found in the extrastriosomal matrix and extremely few were seen in the striosomes. This preferential distribution was not due to premature cell death in the striosomes which contained numerous unlabeled neurons. The results suggest a greater vulnerability of neurons in the matrix, versus the striosomes, to early excitotoxin-induced DNA damage in rat striatum.

Early effects of intrastriatal injections of quinolinic acid on microtubule-associated protein-2 and neuropeptides in rat basal ganglia

The long-term effects of intrastriatal injections of the agonist of N-methyl-D-aspartate receptors, quinolinic acid, have been extensively characterized. Much less is known, however, about the early molecular and neurochemical changes which occur within a few hours of the toxin injection. In the present study, we have performed intrastriatal injections of low doses of quinolinic acid which induce DNA damage 10-12 h post-lesion, and selective death of striatal projection neurons two weeks later. We examined the time-course of alterations in the microtubule-associated protein 2, an early marker of cytoskeletal disruption, and enkephalin and substance P, two neuropeptides present in largely distinct subpopulations of striatal efferent neurons projecting to the globus pallidus and entopeduncular nucleus, respectively. Immunoreactivity for microtubule-associated protein 2 was decreased at the periphery of the lesion 10 h after quinolinate injection. Levels of enkephalin messenger RNA were markedly decreased as early as 6 h post-lesion; however, a significant decrease in enkephalin immunoreactivity was not observed in the globus pallidus (external pallidum) until 12 h post-injection. Levels of substance P messenger RNA were decreased 12 h post-injection in striatal neurons. However, in contrast to enkephalin immunoreactivity, immunolabeling for substance P was not significantly decreased at this time-point in the internal pallidum, a finding reminiscent of early grades of Huntington's disease. The results reveal the time-course of change in messenger RNA and peptide levels in striatal efferent neurons shortly after an excitotoxic insult. These data have implications for the interpretation of findings in post mortem brain and mouse models of Huntington's disease.