Quinolinic Acid Lesions Research Articles

Immediate-early gene response to methamphetamine, haloperidol, and quinolinic acid is not impaired in Huntington's disease transgenic mice.

Striatal neurons in symptomatic Huntington's disease (HD) transgenic mice are resistant to a variety of toxic insults, including quinolinic acid (QA), kainic acid and 3-nitropropionic acid. The basis for this resistance is currently unknown. To investigate the possibility that the immediate-early gene (IEG) response is defective in symptomatic HD mice leading to a lack of response to these compounds, we examined the expression of c-Fos and Krox 24 after administration of the indirect dopamine agonist methamphetamine, the dopamine D(2) receptor antagonist haloperidol and the neurotoxin QA in 5- and 10-week-old R6/2 transgenic HD and wild-type mice. Unlike wild-type and pre-symptomatic R6/2 transgenic HD mice, 10-week-old symptomatic HD mice were resistant to methamphetamine-induced gliosis and QA lesion. There was, however, no difference in the number or distribution of c-Fos-immunoreactive nuclei 2 hr after single injections of methamphetamine or haloperidol among 5- and 10-week-old wild-type mice and 5- and 10-week-old R6/2 HD mice. Similarly, despite their resistance to QA-induced lesioning and lower basal levels of krox-24 mRNA, the symptomatic R6/2 mice had equivalent increases in the amount of c-fos and krox-24 mRNA compared to wild-type and pre-symptomatic R6/2 HD mice as determined by in situ hybridization and densitometry 2 hr after QA administration. These data demonstrate that the c-Fos and Krox 24 IEG response to dopamine agonists, dopamine antagonists and neurotoxic insult is functional in symptomatic R6/2 HD mice. Resistance to toxic insult in R6/2 mice may be conferred by interactions of mutant huntingtin with proteins or transcriptional processes further along the toxic cascade.

The Effects of Prelimbic and Infralimbic Lesions on Working Memory for Visual Objects in Rats

The present experiment investigated the effects of quinolinic acid (90 mM) lesions of the prelimbic-infralimbic cortices on working memory for visual objects and on acquisition of a visual object discrimination. In both tests a GO/NO-GO procedure was used. In the working memory task, rats were tested before and after surgery. A continuous recognition procedure was used to assess working memory, which involved successive exposure to different three-dimensional objects that could be displaced to receive a cereal reinforcement. Of the 12 object presentations/session, 4 objects were presented for a second time in which displacing the object did not result in a reinforcement. The number of trials between the first and second presentations of an object ranged from 0 to 3 (lags). Memory was assessed by the latency to displace an object during the second presentation. In the visual object discrimination, rats had successive exposure to two different objects. Displacement of one object resulted in a cereal reinforcement, while displacement of the other did not. The findings indicated that prelimbic-infralimbic lesions significantly impaired memory for visual objects across all lags. Prelimbic-infralimbic lesions did not impair acquisition of the visual object discrimination. The results suggest that the prelimbic-infralimbic areas are part of neural system important in the short-term memory for visual objects.

The role of rat dorsomedial prefrontal cortex in working memory for egocentric responses

The present experiment studied the effects of quinolinic acid (90 mM) lesions of the medial precentral and anterior cingulate on working memory for egocentric responses. Rats were trained on a delayed match-to-sample task that involved memory for a 90° right or left turn. The results indicated that lesioned rats had significantly decreased scores during the 10 s delay condition compared to presurgery levels. An increase in the delay to 20 s significantly reduced working memory performance in the lesioned rats compared to that of controls. These findings suggest that the rat medial precentral and/or anterior cingulate area play an important role in working memory for egocentric responses.

Role of the Medial and Lateral Caudate-Putamen in Mediating an Auditory Conditional Response Association

Rats with quinolinic acid lesions of the medial or lateral caudate-putamen (CPu) and controls were tested for performance of a previously learned auditory conditional response association task. The task involved the selection of two possible responses when presented with one of two different tones. Results indicated that lesions of either the medial or the lateral CPu produced a sustained deficit in the auditory conditional response association task. Only the lateral CPu lesioned rats exhibited transient motor problems immediately following surgery, but these problems did not interfere with the execution of the appropriate responses. It is suggested that both the medial and the lateral CPu are involved in response selection and response separation within egocentric space.

Role of the striatum and nucleus accumbens in paced copulatory behavior in the female rat

Female rats engage in a series of approach and avoidance behaviors (pacing behavior) directed at the male in order to achieve a preferred rate of intromissions that make pregnancy more likely to occur with insemination. The striatum and nucleus accumbens have been implicated in the modulation of pacing behavior. It is unclear, however, whether these areas of the brain are necessary for the display of pacing behavior. To address this question, ovariectomized female rats received either bilateral quinolinic acid lesions of the striatum or nucleus accumbens or sham surgeries. After hormone priming, rats were allowed to engage in mating behaviors in an apparatus in which they could pace the rate of the copulatory bout. There was a significant reduction in pacing efficiency after striatal lesions, in that females were less likely to leave the male's side of the chamber after a contact. Animals with lesions of the nucleus accumbens that included the shell were more likely to avoid sexual interaction altogether than animals with control lesions. Therefore, it is concluded that the striatum and nucleus accumbens modulate specific aspects of pacing behavior in the female rat.

Deficits in Striatal Dopamine D2 Receptors and Energy Metabolism Detected by in Vivo MicroPET Imaging in a Rat Model of Huntington's Disease

Functional imaging by repeated noninvasive scans of specific 18F tracer distribution using a high-resolution small-animal PET scanner, the microPET, assessed the time course of alterations in energy utilization and dopamine receptors in rats with unilateral striatal quinolinic acid lesions. Energy utilization ipsilateral to the lesion, determined using scans of 2-deoxy-2-[18F]fluoro-d-glucose uptake, was compromised severely 1 week after intrastriatal excitotoxin injections. When the same rats were imaged 5 and 7 weeks postlesion, decrements in energy metabolism were even more prominent. In contrast, lesion-induced effects on dopamine D2 receptor binding were more progressive, with an initial upregulation of [3-(2′-18F]fluoroethyl)spiperone binding apparent 1 week postlesion followed by a decline 5 and 7 weeks thereafter. Additional experiments revealed that marked upregulation of dopamine D2 receptors consequent to quinolinic acid injections could be detected as early as 3 days after the initial insult. Postmortem markers of striatal GABAergic neurons were assessed in the same rats 7 weeks after the lesion: expression of glutamic acid decarboxylase and dopamine D1 receptor mRNA, as well as [3H]SCH-23,390 and [3H]spiperone binding to dopamine D1 and D2 receptors, respectively, detected prominent decrements consequent to the lesion. In contrast, by 7 weeks postlesion [3H]WIN-35,428 binding to dopamine transport sites within the striatum appeared to be enhanced proximal to the quinolinic acid injection sites. The results demonstrate that functional imaging using the microPET is a useful technique to explore not only the progressive neurodegeneration that occurs in response to excitotoxic insults, but also to examine more closely the intricacies of neurotransmitter activity in a small animal model of HD.

Complex motor disturbances in a sequential double lesion rat model of striatonigral degeneration (multiple system atrophy)

This study characterizes paw reaching, stepping and balance abnormalities in a double lesion rat model of striatonigral degeneration, the core pathology underlying levodopa unresponsive parkinsonism associated with multiple system atrophy. Extensive unilateral nigral or striatal lesions induced by 6-hydroxydopamine or quinolinic acid, respectively, produced a similarly marked contralateral paw reaching deficit without further deterioration following a secondary (complementary) lesion of ipsilateral striatum or substantia nigra. Contralateral stepping rates were reduced by unilateral 6-hydroxydopamine lesions without further deterioration following the secondary striatal lesion. In contrast, initial unilateral striatal quinolinic acid injections induced bilateral stepping deficits that significantly worsened contralaterally following the secondary nigral lesion. Contralateral sidefalling rates were significantly increased following primary nigral and striatal lesions. Secondary nigral but not secondary striatal lesions worsened contralateral sidefalling rates. Histological studies revealed subtotal (>90%) depletion of dopaminergic neurons in substantia nigra pars compacta and variable degrees of striatal degeneration depending on the lesion sequence. Animals pre-lesioned with 6-hydroxydopamine showed significantly larger residual striatal surface areas following the secondary striatal quinolinic acid lesion compared to animals with primary striatal quinolinic acid lesions ( P<0.001). These findings are in line with previous experimental studies demonstrating that striatal dopamine depletion confers neuroprotection against subsequent excitotoxic injury. Whether loss of dopaminergic neurons protects against the striatal disease process occurring in multiple system atrophy (Parkinson-type) remains to be elucidated. In summary, this is the first experimental study to investigate spontaneous motor behaviour in a unilateral double lesion rat model. Our observations are consistent with a complex interaction of nigral and striatal lesions producing distinct behavioural and histological changes depending on the lesion sequence. Tests of forelimb akinesia and complex motor behaviour appear to provide a reliable tool that will be helpful for monitoring the effects of interventional strategies such as embryonic neuronal transplantation in the rat model of striatonigral degeneration.

Neuroprotection of nerve growth factor-loaded microspheres on the D2 dopaminergic receptor positive-striatal neurones in quinolinic acid-lesioned rats: a quantitative autoradiographic assessment with iodobenzamide

Huntington's disease (HD) results from the degeneration of striatal neurones, mainly γ-aminobutyric acid (GABA)ergic projection neurones and lately cholinergic interneurones. The use of trophic factors as agents able to prevent such neural degeneration is a promising strategy. The aim of this study was to validate nerve growth factor-loaded (NGF-loaded) poly- d,l-lactide-co-glycolide (PLGA) microspheres for treatment of HD in a rat model with quinolinic acid lesion using autoradiographic study of D2 dopaminergic receptors (D2R). This target is expressed by about half of striatal neurones and its scintigraphic exploration has already been performed for the follow-up of this degenerative process. Ex vivo autoradiography of D2R performed with iodobenzamide, the widely used ligand for single photo emission computerized tomography, revealed slight neuroprotection. Moreover, tolerance of microspheres was demonstrated by in vitro autoradiography with the marker of gliosis, [ 3H]-PK 11195.

Imaging the rat brain on a 1.5 T clinical MR-scanner

Magnetic resonance imaging (MRI) offers a noninvasive technique for studying neurodegenerative events in the rat brain, however, most of the studies are performed on small bore purpose dedicated MR scanners of limited availability and at high cost. The present study explored the feasibility of using a clinical whole body MR-scanner to perform imaging in rat brain and specifically in models of Parkinson's (PD) and Huntington's disease (HD). For that purpose rats were placed into a specially designed PVC device equipped with a flexible surface coil-and T2-weighted spin echo sequences were acquired on a Siemens Magnetom Vision at 1.5 T. In the experimental protocols of PD and HD, animals underwent 6-hydroxydopamine (6-OHDA) and quinolinic acid (QA) injections, respectively and were subsequently grafted with fetal tissue. T2-weighted images showed a small hyperintense area at the 6-OHDA lesion site and a diffuse hyperintensity in the striata with QA lesions. Transplants were seen as a hypointense area surrounded by a hyperintense rim on T1-weighted images. Moreover, disturbances of the blood-brain-barrier and its time of restoration could be monitored. In conclusion, high-resolution in vivo imaging of small animals is feasible with clinical MR-scanners and hence allows the study of various experimental protocols.

Differential effects of quinolinic acid lesions of the medial prefrontal cortex on the expression of morphine- and dizocilpine- induced behavioural plasticity in the rat.

Development and expression of behavioural sensitization have been shown to be differentially affected by drugs and lesions. Here we assessed the effects of quinolinic acid lesions of the rat medial prefrontal cortex on the expression of enhanced locomotion and rearing that has been induced prior to the lesions by 14 daily injections of morphine (10 mg/kg), dizocilpine (MK-801) (0.3 mg/kg) or the combination of both drugs. Expression of tolerance to morphine-induced behavioural inhibition was blocked by the lesions while the expression of MK-801 -induced sensitization was not affected and the expression of the sensitization induced by the drug combination was only mildly attenuated. These results suggest that the expression of behavioural plasticity induced by different drugs is mediated at least in part by different neural substrates.

Changes in limbic dopamine metabolism following quinolinic acid lesions of the left entorhinal cortex in rats

To examine the effects of lesions of the entorhinal cortex on limbic dopamine (DA) metabolism, DA and its metabolites were assayed in five brain regions (the medial prefrontal cortex, anterior cingulate cortex, caudate-putamen, accumbens nucleus, and lateral amygdala), 14 and 28 days after quinolinic acid or sham lesions of the left entorhinal cortex in rats. Concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) on day 14 in the medial prefrontal cortex, accumbens nucleus, and lateral amygdala of the entorhinal cortex lesioned animals were significantly decreased compared with the controls, but they returned to control levels on day 28. The concentration of DA in the lateral amygdala and spontaneous locomotion to a novel environment were significantly increased on day 28 after the lesion. These results suggest that entorhinal cortex lesions alter mesolimbic dopamine metabolism, particularly in the amygdala.

Autoradiographic study of striatal dopamine re-uptake sites and dopamine D 1 and D 2 receptors in a 6-hydroxydopamine and quinolinic acid double-lesion rat model of striatonigral degeneration (multiple system atrophy) and effects of embryonic ventral mesencephalic, striatal or co-grafts

The influence of embryonic mesencephalic, striatal and mesencephalic/striatal co-grafts on amphetamine- and apomorphine-induced rotation behaviour was assessed in a rat model of multiple system atrophy/striatonigral degeneration type using dopamine D 1 ([ 3H]SCH23390) and D 2 ([ 3H]spiperone) receptor and dopamine re-uptake ([ 3H]mazindol) autoradiography. Male Wistar rats subjected to a sequential unilateral 6-hydroxydopamine lesion of the medial forebrain bundle followed by a quinolinic acid lesion of the ipsilateral striatum were divided into four treatment groups, receiving either mesencephalic, striatal, mesencephalic/striatal co-grafts or sham grafts. Amphetamine- and apomorphine-induced rotation behaviour was recorded prior to and up to 10 weeks following transplantation. 6-Hydroxydopamine-lesioned animals showed ipsiversive amphetamine-induced and contraversive apomorphine-induced rotation behaviour. Amphetamine-induced rotation rates persisted after the subsequent quinolinic acid lesion, whereas rotation induced by apomorphine was decreased. In 11 of 14 animals receiving mesencephalic or mesencephalic/striatal co-grafts, amphetamine-induced rotation scores were decreased by >50% at the 10-week post-grafting time-point. In contrast, only one of 12 animals receiving non-mesencephalic (striatal or sham) grafts exhibited diminished rotation rates at this time-point. Apomorphine-induced rotation rates were significantly increased following transplantation of mesencephalic, striatal or sham grafts. The largest increase of apomorphine-induced rotation rates approaching post-6-hydroxydopamine levels were observed in animals with striatal grafts. In contrast, in the co-graft group, there was no significant increase of apomorphine-induced rotation compared to the post-quinolinic acid time-point. Morphometric analysis revealed a 63–74% reduction of striatal surface areas across the treatment groups. Striatal [ 3H]mazindol binding on the lesioned side (excluding the demarcated graft area) revealed a marked loss of dopamine re-uptake sites across all treatment groups, indicating missing graft-induced dopaminergic re-innervation of the host. In eight (73%) of the 11 animals with mesencephalic grafts and reduced amphetamine-induced circling, discrete areas of [ 3H]mazindol binding (“hot spots”) were observed, indicating graft survival. Dopamine D 1 and D 2 receptor binding was preserved in the remaining lesioned striatum irrespective of treatment assignment, except for a significant reduction of D 2 receptor binding in animals receiving mesencephalic grafts. “Hot spots” of dopamine D 1 and D 2 receptor binding were observed in 10 (83%) and nine (75%) of 12 animals receiving striatal grafts or co-grafts, consistent with survival of embryonic primordial striatum grafted into a severely denervated and lesioned striatum. Our study confirms that functional improvement may be obtained from embryonic neuronal grafts in a double-lesion rat model of multiple system atrophy/striatonigral degeneration type. Co-grafts appear to be required for reversal of both amphetamine- and apomorphine-induced rotation behaviour in this model. We propose that the partial reversal of amphetamine-induced rotation asymmetry in double-lesioned rats receiving mesencephalic or mesencephalic/striatal co-grafts reflects non-synaptic graft-derived dopamine release. The changes of apomorphine-induced rotation following transplantation are likely to reflect a complex interaction of graft- and host-derived striatal projection pathways and basal ganglia output nuclei. Further studies in a larger number of animals are required to determine whether morphological parameters and behavioural improvement in the neurotransplantation multiple system atrophy rat model correlate.

Functional heterogeneity of the rat medial prefrontal cortex: effects of discrete subarea-specific lesions on drug-induced conditioned place preference and behavioural sensitization.

While the principal components of the brain reward system, the nucleus accumbens septi and the ventral tegmental area have received much attention, their efferent and afferent structures have not been investigated to the same degree. One major input to this system originates from the medial prefrontal cortex (mPFC) which is not a homogenous structure but can be divided into different subareas that can be distinguished on anatomical and possibly functional grounds. We examined the effects of discrete bilateral quinolinic acid lesions (45 nmol/0.5 micro(L)) of each of the mPFC subareas, the infralimbic (il), prelimbic (pl) and the anterior cingulate (cg) mPFC, on the conditioned place preference (CPP) and psychomotor activation induced by several drugs. Lesions of the il mPFC blocked CPP induced by morphine (10 mg/kg) and CGP37849 [DL-(E)-2-amino-4-methyl-5-phosphono-3-pentic acid, a competitive N-methyl-D-aspartate receptor antagonist; 10 mg/kg]. Lesions of the pl mPFC blocked CPP induced by cocaine (15 mg/kg) and CGP37849, and lesions of the cg mPFC only blocked CGP37849-induced CPP. Lesions of the whole mPFC blocked morphine-, cocaine- and CGP37849-induced CPP. None of the lesions affected DL-amphetamine (4 mg/kg)-induced CPP. During the conditioning period, none of the lesions affected amphetamine-induced psychomotor activation and sensitization, whereas both phenomena were attenuated by pl and whole mPFC lesions in the case of cocaine, and by il and whole mPFC lesions in the case of morphine. These results show that the different mPFC subregions have distinct functional roles in the generation of behavioural effects produced by different classes of drugs. This heterogeneity should be taken into account in future studies addressing the role of the mPFC in drug reward and sensitization.

Chemical and anatomical changes in the striatum and substantia nigra following quinolinic acid lesions in the striatum of the rat: a detailed time course of the cellular and GABA(A) receptor changes.

The pattern and time-course of cellular, neurochemical and receptor changes in the striatum and substantia nigra were investigated following unilateral quinolinic acid lesions of the striatum in rats. The results showed that in the central region of the striatal lesion there was a major loss of Nissl staining of the small to medium sized cells within 2 h and a substantial loss of neuronal staining within 24 h after lesioning. Immunohistochemical studies showed a total loss of calbindin immunoreactivity, a known marker of GABAergic striatal projection neurons, throughout the full extent of the quinolinic acid lesion within 24 h. Similarly, within 24 h, there was a total loss of somatostatin/neuropeptide Y cells in the centre of the lesion but in the periphery of the lesion these cells remained unaltered at all survival times. Striatal GABA(A) receptors remained unchanged in the lesion for 7 days, and then declined in density over the remainder of the time course. Glial fibrillary acidic protein immunoreactive astrocytes were present in the periphery of the lesion at 7 days, occupied the full extent of the lesion by 4 weeks, and remained elevated for up to 2 months. In the substantia nigra, following placement of a striatal quinolinic acid lesion, there was: a loss of substance P immunoreactivity within 24 h; a marked astrocytosis evident from 1-4 weeks postlesion; and, a major increase in GABA(A) receptors in the substantia nigra which occurred within 2 h postlesion and was sustained for the remainder of the time course (15 months). This study shows that following quinolinic acid lesions of the striatum there is a major loss of calbindin and somatostatin/neuropeptide Y immunoreactive cells in the striatum within 24 h, and a marked increase in GABA(A) receptors in the substantia nigra within 2 h. These findings are similar to the changes in the basal ganglia in Huntington's disease and provide further evidence supporting the use of the quinolinic acid lesioned rat as an animal model of Huntington's disease.

Convection-enhanced selective excitotoxic ablation of the neurons of the globus pallidus internus for treatment of parkinsonism in nonhuman primates.

Selective treatment of central nervous system (CNS) structures holds therapeutic promise for many neurological disorders, including Parkinson's disease (PD). The ability to inhibit or augment specific neuronal populations within the CNS reliably by using present therapeutic techniques is limited. To overcome this problem, the authors modeled and developed a method in which convection was used to deliver compounds to deep brain nuclei in a reproducible, homogeneous, and targeted manner. To determine the feasibility and clinical efficacy of convective drug delivery for treatment of a neurological disorder, the investigators selectively ablated globus pallidus internus (GPi) neurons with quinolinic acid (QA), an excitotoxin, in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced model of primate parkinsonism. After the parameters of convective distribution to the GPi were confirmed by infusion of biotinylated albumin into the GPi of a primate (Macaca mulatta), seven adult monkeys of this species were rendered either fully parkinsonian by intravenous injections of MPTP (five animals) or hemiparkinsonian by a right-sided intracarotid injection of this agent (two monkeys). Using convection-enhanced delivery to the GPi, animals were infused with either QA (three fully parkinsonian, two hemiparkinsonian) or saline (two fully parkinsonian). The three fully parkinsonian animals that underwent GPi lesioning with QA had substantial improvement of PD symptoms, manifested by a marked increase in activity (34 +/- 2.5%; mean +/- standard deviation) and dramatic improvement of parkinsonian clinical scores. In contrast, the control animals did not improve (activity monitor change = -1.5 +/- 0.5%). The two hemiparkinsonian animals that underwent QA lesioning of the GPi had dramatic recovery of extremity use. Histological examination revealed selective neural ablation of GPi neurons (mean loss 87%) with sparing of surrounding gray and white matter structures. No animal developed worsening signs of PD or neurological deficits after infusion. Convection-enhanced delivery of QA permits selective, region-specific (GPi), and safe lesioning of neuronal subpopulations, resulting in dramatic improvement in parkinsonian symptomatology. The properties of convection-enhanced delivery indicate that this method could be used for chemical neurosurgery for medically refractory PD and that it may be ideal for cell-specific therapeutic ablation or trophic treatment of other targeted structures associated with CNS disorders.

Cerebral glucose metabolism in unilateral entorhinal cortex-lesioned rats: an animal PET study.

To evaluate the effect of entorhinal cortical lesion on cerebral cortical function, we studied cerebral glucose utilization (CMRGlc) using a high resolution PET scanner after quinolinic acid lesion of the unilateral entorhinal cortex in rats. [18F]Fluorodeoxyglucose PET was performed at 4 days and 4 weeks after surgery, and CMRGlc in the bilateral frontal, parietal and temporal regions were analyzed. At 4 days, the entorhinal lesion induced a 12-15% decrease in CMRGlc of frontal, parietal and temporal regions ipsilateral to the lesion. The hypometabolism continued at 4 weeks in the temporal region. These findings suggest that entorhinal lesion induces cerebral cortical hypometabolism, which implies a pathogenetic role of entorhinal area on the cortical hypometabolism in Alzheimer's disease.

Administration of recombinant human activin-A has powerful neurotrophic effects on select striatal phenotypes in the quinolinic acid lesion model of Huntington's disease

Huntington disease is characterized by the selective loss of striatal neurons, particularly of medium-sized spiny glutamate decarboxylase 67 staining/GABAergic projection neurons which co-contain the calcium binding protein calbindin. Lesioning of the adult rat striatum by intrastriatal injection of the N-methyl- d-aspartate receptor agonist quinolinic acid (100 nmol) results in a pattern of striatal neuropathology seven days later that resembles that seen in the Huntington brain. Using this animal model of human Huntington's disease we investigated the effect of daily intrastriatal infusion of the nerve cell survival molecule ActivinA (single bolus dose of 0.73 μg daily for seven days) on the quinolinic acid-induced degeneration of various striatal neuronal phenotypes. By seven days, unilateral intrastriatal infusion of quinolinic acid produced a partial but significant loss ( P<0.01) in the number of striatal neurons immunoreactive for glutamate decarboxylase (to 51.0±5.8% of unlesioned levels), calbindin (to 58.7±5.1%), choline acetyltransferase (to 68.6±6.1%), NADPH-diaphorase (to 47.4±5.4%), parvalbumin (to 58.8±4.1%) and calretinin (to 60.6±8.6%) in adult rats that were administered intrastriatal phosphate-buffered saline for seven days following quinolinic acid. In contrast, in rats that received intrastriatal recombinant human ActivinA once daily for seven days following quinolinic acid, phenotypic degeneration was significantly attenuated in several populations of striatal neurons. Treatment with ActivinA had the most potent protective effect on the striatal cholinergic interneuron population almost completely preventing the lesion induced decline in choline acetyltransferase expression (to 95.1±5.8% of unlesioned levels, P<0.01). ActivinA also conferred a significant protective effect on parvalbumin (to 87.5±7.7%, P<0.01) and NADPH-diaphorase (to 77.5±7.5%, P<0.01) interneuron populations but failed to prevent the phenotypic degeneration of calretinin neurons (to 56.6±5.5%). Glutamate decarboxylase 67 and calbindin-staining nerve cells represent largely overlapping populations and both identify striatal GABAergic projection neurons. We found that ActivinA significantly attenuated the loss in the numbers of neurons staining for calbindin (to 79.7±6.6%, P<0.05) but not glutamate decarboxylase 67 (to 61.1±5.9%) at seven days following quinolinic acid lesioning. Taken together these results suggest that exogenous administration of ActivinA can rescue both striatal interneurons (labelled with choline acetyltransferase, parvalbumin, NADPH-diaphorase) and striatal projection neurons (labelled by calbindin) from excitotoxic lesioning with quinolinic acid. Longer-term studies will be required to determine whether these surviving calbindin-expressing projection neurons recover their ability to express the glutamate decarboxylase 67/GABAergic phenotype. These results therefore suggest that treatment with ActivinA may help to prevent the degeneration of vulnerable striatal neuronal populations in Huntington's disease.

Immunohistochemical localization of subtype 4a metabotropic glutamate receptors in the rat and mouse basal ganglia

Recent studies suggest that metabotropic glutamate receptors (mGluRs) may play a significant role in regulating basal ganglia functions. In this study, we investigated the localization of mGluR4a protein in the mouse and rat basal ganglia. Polyclonal antibodies that specifically react with the metabotropic glutamate receptor subtype mGluR4a were produced and characterized by Western blot analysis. These antibodies recognized a native protein in wild-type mouse brain with a molecular weight similar to the molecular weight of the band from a mGluR4a-transfected cell line. The immunoreactivity was absent in brains of knockout mice deficient in mGluR4. mGluR4a immunoreactivity was most intense in the molecular layer of the cerebellum. We also found a striking mGluR4a immunoreactivity in globus pallidus, and moderate staining in substantia nigra pars reticulata and entopeduncular nucleus. Moderate to low mGluR4a immunoreactivity was present in striatum and other brain regions, including hippocampus, neocortex, and thalamus. Double labeling with mGluR4a antibodies and antibodies to either a dendritic marker or a marker of presynaptic terminals suggest a localization of mGluR4a on presynaptic terminals. Immunocytochemistry at electron microscopy level confirmed these results, revealing that in the globus pallidus, mGluR4a is mainly localized in presynaptic sites in axonal elements. Finally, quinolinic acid lesion of striatal projection neurons decreased mGluR4a immunoreactivity in globus pallidus, suggesting a localization of mGluR4a on striatopallidal terminals. These data support the hypothesis that mGluR4a serves as a presynaptic heteroreceptor in the globus pallidus, where it may play an important role in regulating g-amino-n-butyric acid (GABA) release from striatopallidal terminals.

Quinolinic acid lesion of the nigrostriatal pathway: effect on turning behaviour and protection by elevation of endogenous kynurenic acid in rattus norvegicus

Endogenous excitotoxins have been implicated in degeneration of nigral dopaminergic neurons in Parkinson's disease. It may be possible to reduce neurodegeneration by blocking the effects of these endogenous agents. The present study shows that contralateral turning seen following quinolinic acid-induced lesions of the nigrostriatal dopaminergic pathway was reversed by a treatment that increased brain levels of kynurenic acid, an endogenous excitatory amino acid antagonist. The treatment consisted of nicotinylalanine (5.6 nmol/5 μl i.c.v.), an inhibitor of kynureninase and kynurenine hydroxylase plus the precursor kynurenine (450 mg/kg i.p.) plus probenencid (200 mg/kg i.p.), an inhibitor of organic acid transport. Thus, neuroprotection by increasing brain kynurenic acid in vivo may be useful in retarding cell loss in Parkinson's and other neurodegenerative diseases involving excitotoxicity.

The role of the agranular insular cortex in working memory for food reward value and allocentric space in rats

The present experiment examined the effects of quinolinic acid (125 mM) lesions of the agranular insular area on working memory for food reward value and working memory for spatial locations. In both tasks a go/no-go procedure was used. Working memory for food reward value was assessed using a delayed conditional discrimination in which either a 20% or 45% sugar content cereal was associated with a reinforcement and the other cereal was not. In the spatial locations task, rats were allowed to enter 12 arms in a radial maze for a food reinforcement. Of the 12 arm presentations, three or four arms were presented for a second time in a session which did not contain a reinforcement. The number of trials between the 1st and 2nd presentation of an arm ranged from 0 to 6 (lags). Working memory was assessed by the latency to enter an arm during the 2nd presentation. In the food reward value task, agranular insular lesions produced memory deficits in a delay-dependent manner. In contrast, agranular insular lesions did not impair working memory for spatial locations. These results add to accumulating evidence suggesting that different types of working memory are distributed across separate prefrontal subregions.