dizocilpine-maleate and malonic-acid

Minocycline has been shown to exert neuroprotection against a wide variety of toxic insults both in vitro and in vivo. However, contradictory results have recently been reported. We now report that minocycline affords no protection against the neurotoxicity caused by malonate or N-methyl-d-aspartate (NMDA). Rats were treated with minocycline (45 mg/kg i.p. x 7) every 12 h. Thirty minutes after the second dose of minocycline, an intrastriatal stereotaxic injection of malonate (1.5 mumol) or NMDA (0.1 mumol) was administered. Seven days later, the rats were killed, and lesion volumes were quantified using two different methods [triphenyltetrazolium chloride (TTC) staining or cytochrome oxidase histochemistry]. Our results show that minocycline does not prevent the lesions caused by either malonate or by NMDA. On the contrary, the putative NMDA receptor antagonist, MK-801, blocked the toxicity caused by both toxins indicating that, although by different mechanisms, excitotoxicity is mediating neuronal death. We conclude that minocycline, at least under our experimental conditions, is not neuroprotective against excitotoxicity caused by either malonate or NMDA.

Topics: Animals; Dizocilpine Maleate; Drug Administration Routes; Drug Administration Schedule; Male; Malonates; Minocycline; N-Methylaspartate; Neostriatum; Neuroprotective Agents; Neurotoxicity Syndromes; Neurotoxins; Rats; Rats, Wistar; Treatment Outcome

There is growing evidence that mitochondrial dysfunction is an important factor in a cascade of neurotoxic events as observed during pathogenesis of various neurodegenerative diseases. In the neurodegenerative disease amyotrophic lateral sclerosis (ALS) both spinal and cortical motoneurons degenerate, but in experimental studies most attention so far has been focussed on the spinal motoneurons. In order to study the role of mitochondrial dysfunction in the pathways leading to cortical (upper) motoneuron (CMN) death, a long-term culture system of rat cortical explants was used. CMNs were visualized by immunocytochemical labeling with antibodies directed against nonphosphorylated neurofilament, SMI-32, and for their identification we also used their location in layer V of the explant, their size, and their morphological appearance. In this model the effect of mitochondrial inhibition was studied through chronic malonate treatment. For 2 weeks, low doses of complex II inhibitor malonate were added to the cultures twice a week. The malonate-induced chronic mitochondrial inhibition resulted in a dose-dependent increase of CMN death in the slices. Neuroprotection was achieved with the NMDA antagonist MK-801 and the non-NMDA antagonist CNQX indicating the involvement of glutamate in the malonate-induced CMN death. Furthermore, our data indicate that chronic mitochondrial inhibition results in CMN death, which is mediated by glutamate excitotoxicity via both non-NMDA and NMDA receptors. In this respect the present in vitro approach may act as a model for understanding mechanisms underlying CMN death in ALS.

Topics: Animals; Antigens, Differentiation; Cell Death; Cell Size; Cells, Cultured; Cerebral Cortex; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Glutamic Acid; Immunohistochemistry; In Vitro Techniques; Malonates; Mitochondria; Models, Biological; Motor Neurons; Neurodegenerative Diseases; Neurofilament Proteins; Neuroprotective Agents; Pyramidal Cells; Rats; Rats, Wistar; Time Factors

Transgenic Huntington's disease (HD) mice, expressing exon 1 of the HD gene with an expanded CAG repeat, are totally resistant to striatal lesion induced by excessive NMDA receptor activation. We now show that striatal lesions induced by the mitochondrial toxin malonate are reduced by 70-80% in transgenic HD mice compared with wild-type littermate controls. This occurred in 6- and 12-week-old HD mice with 150 CAG repeats (line R6/2) and in 18-week-old, but not 6-week-old, HD mice with 115 CAG repeats (line R6/1). Therefore, we show for the first time that the resistance to neurotoxin in transgenic HD mice is dependent on both the CAG repeat length and the age of the mice. Importantly, most HD patients develop symptoms in adulthood and exhibit an inverse relationship between CAG repeat length and age of onset. Transgenic mice expressing a normal CAG repeat (18 CAG) were not resistant to malonate. Although endogenous glutamate release has been implicated in malonate-induced cell death, glutamate release from striatal synaptosomes was not decreased in HD mice. Malonate-induced striatal cell death was reduced by 50-60% in wild-type mice when they were treated with either the NMDA receptor antagonist MK-801 or the caspase inhibitor zVAD-fmk. These two compounds did not reduce lesion size in transgenic R6/1 mice. This might suggest that NMDA receptor- and caspase-mediated cell death pathways are inhibited and that the limited malonate-induced cell death still occurring in HD mice is independent of these pathways. There were no changes in striatal levels of the two anti cell death proteins Bcl-X(L) and X-linked inhibitor of apoptosis protein (XIAP), before or after the lesion in transgenic HD mice. We propose that mutant huntingtin causes a sublethal grade of metabolic stress which is CAG repeat length-dependent and results in up-regulation over time of cellular defense mechanisms against impaired energy metabolism and excitotoxicity.

Topics: Aging; Amino Acid Chloromethyl Ketones; Animals; bcl-X Protein; Blood Glucose; Cell Death; Corpus Striatum; Disease Models, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Female; Glutamic Acid; Humans; Huntingtin Protein; Huntington Disease; Immunoblotting; Immunohistochemistry; Male; Malonates; Mice; Mice, Inbred C57BL; Mice, Inbred CBA; Mice, Transgenic; Nerve Tissue Proteins; Neurons; Neuroprotective Agents; Nuclear Proteins; Proteins; Proto-Oncogene Proteins c-bcl-2; Succinate Dehydrogenase; Synaptosomes; Trinucleotide Repeats; X-Linked Inhibitor of Apoptosis Protein

Intrastriatal injection of the reversible succinate dehydrogenase inhibitor malonate results in both chemically induced hypoxia and striatal lesions that are similar to those seen in Huntington's disease and cerebral ischaemia. The mechanisms leading to neuronal death involve secondary excitotoxicity, the release of dopamine from nigrostriatal fibres and the generation of reactive oxygen species (ROS) including nitric oxide (NO) and hydroxyl radicals. Here, we further investigated the contribution and mechanism of dopamine on malonate-induced striatal lesions. Prior lesions of the nigrostriatal pathway with 6-OHDA or the depletion of striatal dopamine stores by pretreatment with reserpine, an inhibitor or the vesicular monoamine transporter type-2 (VMAT2), in combination with alpha-methyl-p-tyrosine resulted in a significant reduction of malonate-induced striatal lesion volumes. This was paralleled by block or reduction of the malonate-induced generation of ROS, as measured by the conversions of salicylate to 2,3-dihydroxybenzoic acid (2,3-DHBA) using microdialysis. Systemic or intrastriatal application of L-DOPA or dopamine, respectively, reconstituted malonate toxicity and the generation of ROS in 6-OHDA-lesioned rats. Block of the dopamine transporter by GBR12909 did not result in a reduction of malonate-induced dopamine release, but significantly reduced the generation of hydroxyl radicals. The D2 receptor agonist lisuride and the mixed D1 and D2 receptor agonist apomorphine, but not the D1 receptor agonist SKF38393, partially restored malonate toxicity in 6-OHDA-lesioned rats without increasing the generation of ROS. In line with these results sulpiride, an inhibitor of D2 receptors, reduced the malonate-induced lesion volume, whereas SCH23390, an inhbitor of D1 receptors, was ineffective. Our data suggest that malonate-induced dopamine toxicity to energetically impaired neurons is mediated by two independent pathways: (i) dopamine transporter uptake-dependent, dopamine receptor-independent generation of ROS, and (ii) excessive stimulation of D2 receptors.

Topics: 3,4-Dihydroxyphenylacetic Acid; alpha-Methyltyrosine; Animals; Benzazepines; Brain Diseases; Carbidopa; Carrier Proteins; Corpus Striatum; Dizocilpine Maleate; Dopamine; Dopamine D2 Receptor Antagonists; Dopamine Plasma Membrane Transport Proteins; Enzyme Inhibitors; Homovanillic Acid; Levodopa; Male; Malonates; Membrane Glycoproteins; Membrane Transport Proteins; Nerve Tissue Proteins; Neuropeptides; Oxidopamine; Rats; Rats, Wistar; Reactive Oxygen Species; Receptors, Dopamine; Receptors, Dopamine D1; Receptors, Dopamine D2; Receptors, N-Methyl-D-Aspartate; Reserpine; Succinate Dehydrogenase; Sulpiride; Vesicular Biogenic Amine Transport Proteins; Vesicular Monoamine Transport Proteins

Intrastriatal injection of the reversible succinate dehydrogenase inhibitor malonate produces both energy depletion and striatal lesions similar to that seen in cerebral ischemia and Huntington's disease. The mechanisms of neuronal cell death involve secondary excitotoxicity and the generation of reactive oxygen species. Here, we investigated the effects of dopamine on malonate-induced generation of hydroxyl radicals and striatal lesion volumes. Using in vivo microdialysis, we found that malonate induced a 94-fold increase in extracellular striatal dopamine concentrations. This was paralleled by an increase in the generation of hydroxyl radicals. Prior unilateral lesioning of the nigrostriatal dopaminergic pathway by focal injection of 6-hydroxydopamine blocked the malonate-induced increase in dopamine concentrations and the generation of hydroxyl radicals and attenuated the lesion volume. In contrast, the NMDA receptor antagonist MK-801 attenuated malonate-induced lesion volumes but did not block the generation of hydroxyl radicals. Thus, the dopaminergic and glutamatergic pathways are essential in the pathogenesis of malonate-induced striatal lesions. Our results suggest that the malonate-induced release of dopamine but not NMDA receptor activation mediates hydroxyl radical formation.

Topics: Animals; Dizocilpine Maleate; Dopamine; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Hydroxyl Radical; Male; Malonates; Microdialysis; Neostriatum; Oxidopamine; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Substantia Nigra; Succinate Dehydrogenase

In rats, striatal histotoxic hypoxic lesions produced by the mitochondrial toxin malonate resemble those of focal cerebral ischemia. Intrastriatal injections of malonate induced cleavage of caspase-2 beginning at 6 h, and caspase-3-like activity as identified by DEVD biotin affinity-labeling within 12 h. DEVD affinity-labeling was prevented and lesion volume reduced in transgenic mice overexpressing BCL-2 in neuronal cells. Intrastriatal injection of the tripeptide, N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD-fmk), a caspase inhibitor, at 3 h, 6 h, or 9 h after malonate injections reduced the lesion volume produced by malonate. A combination of pretreatment with the NMDA antagonist, dizocilpine (MK-801), and delayed treatment with zVAD-fmk provided synergistic protection compared with either treatment alone and extended the therapeutic window for caspase inhibition to 12 h. Treatment with cycloheximide and zVAD-fmk, but not with MK-801, blocked the malonate-induced cleavage of caspase-2. NMDA injections alone resulted in a weak caspase-2 cleavage. These results suggest that malonate toxicity induces neuronal death by more than one pathway. They strongly implicate early excitotoxicity and delayed caspase activation in neuronal loss after focal ischemic lesions and offer a new strategy for the treatment of stroke.

Topics: Amino Acid Chloromethyl Ketones; Animals; Apoptosis; Brain; Caspase 2; Caspase 3; Caspase Inhibitors; Caspases; Corpus Striatum; Cycloheximide; Cysteine Proteinase Inhibitors; Dizocilpine Maleate; Drug Synergism; Genes, bcl-2; Humans; Hypoxia, Brain; In Situ Nick-End Labeling; Male; Malonates; Mice; Mice, Transgenic; Neuroprotective Agents; Proto-Oncogene Proteins c-bcl-2; Rats; Rats, Sprague-Dawley

Previously, we have reported that intranigral infusions of malonate, an inhibitor of mitochondrial function, lead to the degeneration of the dopaminergic neurons of the nigrostriatal pathway that is mediated, at least in part, through NMDA receptor activation and nitric oxide formation. In the present study, unilateral focal infusions of malonate into the nucleus basalis magnocellularis (nbM) of male Sprague-Dawley rats (weighing 250-300 g) resulted in a dose-related depletion in ipsilateral cortical and amygdaloid choline acetyltransferase (ChAT) activity. Infusion of a 3 mumol dose of malonate into the nbM of vehicle-treated animals resulted in a 41 and 54% decrease in cortical and amygdaloid ChAT activity, respectively. Systemic pretreatment with lamotrigine (16 mg/kg, i.p.) and MK-801 (5 mg/kg, i.p.) attenuated the depletions in cortical and amygdaloid ChAT activity that resulted from an infusion of this dose of malonate into the nbM. Acetylcholinesterase (AChE) histochemistry of the nbM following focal infusion of malonate (3 mumol) showed a marked decrease in the number of AChE-positive neurons that was partially prevented by MK-801 pretreatment. Before examining the role of nitric oxide formation in malonate-induced toxicity, the ability of systemic administration of N omega-nitro-L-arginine (L-NA) to inhibit nitric oxide synthase (NOS) activity in the nbM and cerebellum was investigated. L-NA (2, 10, and 20 mg/kg, i.p.) produced a dose-related inhibition of nbM and cerebellar NOS activity that was maximal following a dose of 10 mg/kg L-NA. This level of NOS inhibition persisted for at least 13 h following L-NA (10 mg/kg) administration. Subsequently, the effect of L-NA pretreatment on malonate toxicity was evaluated. Following pretreatment with L-NA (2 and 10 mg/kg, i.p.), the toxic action of malonate on cortical and amygdaloid ChAT activity was not altered. In addition, infusion of a lower dose of malonate (2 mumol) into the nbM resulted in decreases in cortical and amygdaloid ChAT activity that were not altered by pretreatment with L-NA (2 and 10 mg/kg, i.p.). In 7-nitroindazole (7-NI; 25 and 50 mg/kg, i.p.)-pretreated animals, malonate (3 mumol) produced decreases in cortical and amygdaloid ChAT activity that were attenuated by both doses of 7-NI. Thus, malonate-induced destruction of the basal forebrain cholinergic neurons was attenuated by systemic pretreatment with lamotrigine, MK-801, and 7-NI but not by L-NA.

Topics: Animals; Dizocilpine Maleate; Enzyme Inhibitors; Indazoles; Lamotrigine; Male; Malonates; Nerve Degeneration; Neurons; Neuroprotective Agents; Nitric Oxide Synthase; Nitroarginine; Parasympathetic Nervous System; Prosencephalon; Rats; Rats, Sprague-Dawley; Triazines

Impaired energy metabolism may contribute to the pathogenesis of late-onset neurodegenerative disorders such as Alzheimer's disease by increasing neuronal vulnerability to excitotoxic damage through the NMDA receptor. The effects of metabolic impairment on the striatum have been extensively examined, but relatively little is known regarding the vulnerability of the hippocampus. To examine the effect of metabolic impairment on the hippocampal formation, malonate (0.25-2.5 mumol), a reversible inhibitor of succinate dehydrogenase, was administered by stereotaxic injection into the hippocampus of male Sprague-Dawley rats. Neuronal loss was assessed by Nissl stain, and immunocytochemistry was used to examine cytoskeletal disruption. Malonate produced a dose-dependent lesion in which CA1 pyramidal neurons were most vulnerable, followed by CA3 and dentate gyrus. Cytoskeletal alterations included the loss of microtubule-associated protein 2 (MAP2) and dendritic MAP1B immunoreactivity, whereas axonal MAP1B and tau proteins were relatively spared. Spatially and temporally correlated with the loss of MAP2 was an increase in the immunoreactivity of calpain-cleaved spectrin. A similar pattern of neuronal damage and cytoskeletal disruption was produced by intrahippocampal injection of quinolinate (0.1 mumol), an NMDA agonist. Although these results are consistent with the hypothesis that metabolic impairment results in excitotoxic death, MK-801 (dizocilipine maleate), a noncompetitive NMDA receptor antagonist, did not attenuate the lesions produced by malonate but was effective against quinolinate. The results suggest that NMDA receptor activation is not required for malonate-induced damage in the hippocampal formation.

Topics: Animals; Cell Death; Cytoskeleton; Dizocilpine Maleate; Dose-Response Relationship, Drug; Hippocampus; Injections; Male; Malonates; Neurons; Neuroprotective Agents; Quinolinic Acid; Rats; Rats, Sprague-Dawley; Succinate Dehydrogenase; Time Factors

Malonate is a reversible inhibitor of succinate dehydrogenase (SDH) that produces neurotoxicity by an N-methyl-D-aspartate (NMDA) receptor-dependent mechanism. We have examined the influence of pharmacological manipulation of membrane potential on striatal malonate toxicity in rats in vivo by analysis of lesion volume. Depolarization caused by coinjection of the Na+,K(+)-ATPase inhibitor ouabain or a high concentration of potassium greatly exacerbated malonate toxicity; this combined toxicity was blocked by the noncompetitive NMDA antagonist MK-801. The toxicity of NMDA was also exacerbated by ouabain. The overt toxicity of a high dose of ouabain (1 nmol) was largely prevented by MK-801. Coinjection of the K+ channel activator minoxidil (4 nmol) to reduce depolarization attenuated the toxicity of 1 mumol of malonate by approximately 60% without affecting malonate-induced ATP depletion. These results indicate that membrane depolarization exacerbates malonate neurotoxicity and that membrane hyperpolarization protects against malonate-induced neuronal damage. We hypothesize that the effects of membrane potential on malonate toxicity are mediated through the NMDA receptor as a result of its combined agonist- and voltage-dependent properties.

Topics: Adenosine Triphosphate; Animals; Corpus Striatum; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Synergism; Excitatory Amino Acid Antagonists; Male; Malonates; Membrane Potentials; Minoxidil; Ouabain; Potassium; Rats; Rats, Sprague-Dawley; Succinate Dehydrogenase

Neuronal death in neurodegenerative diseases may involve energy impairment leading to secondary excitotoxicity, and free radical generation. Potential therapies for the treatment of neurodegenerative diseases therefore include glutamate release blockers, excitatory amino acid receptor antagonists, agents that improve mitochondrial function, and free radical scavengers. In the present study we examined whether these strategies either alone or in combination had neuroprotective effects against striatal lesions produced by mitochondrial toxins. The glutamate release blockers lamotrigine and BW1003C87 significantly attenuated lesions produced by intrastriatal administration of 1-methyl-4-phenylpyridinium. Lamotrigine significantly attenuated lesions produced by systemic administration of 3-nitropropionic acid. Memantine, an N-methyl-D-aspartate antagonist, protected against malonate induced striatal lesions. We previously found that coenzyme Q10 and nicotinamide, and the free radical spin trap n-tert-butyl-alpha-(2-sulfophenyl)-nitrone (S-PBN) dose-dependently protect against lesions produced by intrastriatal injection of malonate. In the present study we found that the combination of MK-801 (dizocipiline) with coenzyme Q10 exerted additive neuroprotective effects against malonate. Lamotrigine with coenzyme Q10 was more effective than coenzyme Q10 alone. The combination of nicotinamide with S-PBN was more effective than nicotinamide alone. These results provide further evidence that glutamate release inhibitors and N-acetyl-D-aspartate antagonists can protect against secondary excitotoxic lesions in vivo. Furthermore, they show that combinations of agents which act at sequential steps in the neurodegenerative process can produce additive neuroprotective effects. These findings suggest that combinations of therapies to improve mitochondrial function, to block excitotoxicity and to scavenge free radicals may be useful in treating neurodegenerative diseases.

Topics: 1-Methyl-4-phenylpyridinium; Animals; Anticonvulsants; Coenzymes; Cyclic N-Oxides; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Free Radicals; Lamotrigine; Male; Malonates; Memantine; Mitochondria; Nervous System Diseases; Neuroprotective Agents; Neurotoxins; Niacinamide; Nitro Compounds; Nitrogen Oxides; Propionates; Pyrimidines; Rats; Rats, Sprague-Dawley; Spin Labels; Thallium; Triazines; Ubiquinone

Adult rats received chronic intrastriatal dialytic exposure to quinolinic acid (QUIN), malonate, or a combination of QUIN and malonate. The combination of subthreshold concentrations of QUIN (4 mM) and malonate (400 mM) produced lesions larger than did either QUIN or malonate alone. The neurotoxic effect of QUIN combined with malonate was subsequently blocked by co-administration of the NMDA receptor antagonist MK-801 (1 mM). These findings indicate that malonate synergistically enhances NMDA receptor mediated excitotoxicity.

Topics: Animals; Dialysis; Dizocilpine Maleate; Drug Synergism; Electron Transport Complex IV; Excitatory Amino Acid Antagonists; Male; Malonates; N-Methylaspartate; NADPH Dehydrogenase; Neostriatum; Neurotoxins; Quinolinic Acids; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

We report that a subtoxic dose of the succinate dehydrogenase (SDH) inhibitor malonate greatly enhances the neurotoxicity of three different excitatory amino acid agonists: N-methyl-D-aspartate (NMDA), S-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (S-AMPA), and L-glutamate. In male Sprague-Dawley rats, intrastriatal stereotaxic injection of malonate alone (0.6 mumol), NMDA alone (15 nmol), S-AMPA alone (1 nmol), or glutamate alone (0.6 mumol) produced negligible toxicity as assessed by measurement of lesion volume. Coinjection of subtoxic malonate with NMDA produced a large lesion (15.2 +/- 1.4 mm3), as did coinjection of malonate with S-AMPA (11.0 +/- 1.0 mm3) or glutamate (12.8 +/- 0.7 mm3). Administration of the noncompetitive NMDA antagonist MK-801 (5 mg/kg i.p.) completely blocked the toxicity of malonate plus NMDA (0.5 +/- 0.3 mm3). This dose of MK-801 had little effect on the lesion produced by malonate plus S-AMPA (9.0 +/- 0.7 mm3), but it attenuated the toxicity of malonate plus glutamate by approximately 40% (7.5 +/- 0.9 mm3). Coinjection of the AMPA antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)-quinoxaline (NBQX; 2 nmol) had no effect on malonate plus NMDA or malonate plus glutamate toxicity (12.3 +/- 1.8 and 14.0 +/- 0.9 mm3, respectively) but greatly attenuated malonate plus S-AMPA toxicity (1.5 +/- 0.9 mm3). Combination of the two antagonists conferred no additional neuroprotection in any paradigm. These results indicate that metabolic inhibition exacerbates both NMDA receptor- and non-NMDA receptor-mediated excitotoxicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Brain; Brain Diseases; Dizocilpine Maleate; Drug Synergism; Glutamic Acid; Male; Malonates; N-Methylaspartate; Quinoxalines; Rats; Rats, Sprague-Dawley; Succinate Dehydrogenase

The effects of intrastriatal injections of a reversible inhibitor of succinate dehydrogenase, malonate, on the extracellular concentrations of amino acid neurotransmitters were examined using a microdialysis probe that was positioned a fixed distance from an injection cannula. Malonate (2 mumol) caused a 23 +/- 5-fold increase in extracellular glutamate (Glu), a 18 +/- 6-fold increase extracellular gamma-aminobutyric acid (GABA) and a modest increase in extracellular aspartate (Asp, 2.9 +/- 0.8-fold increase). Administration of the NMDA receptor antagonist MK-801 (5 mg/kg) prior to injection of malonate almost completely blocked these increases. This study provides direct evidence that inhibition of succinate dehydrogenase causes an increase in extracellular amino acid neurotransmitters and further evidence that bioenergetic defects may contribute to the pathogenesis of chronic neurodegenerative diseases through an excitotoxic mechanism.

Topics: Amino Acids; Animals; Dizocilpine Maleate; Glutamic Acid; Kinetics; Male; Malonates; Microdialysis; Rats; Rats, Sprague-Dawley; Succinate Dehydrogenase

The therapeutic time window for N-methyl-D-aspartate (NMDA) antagonists, non-NMDA antagonists, and glutamate release inhibitors in focal models of ischemia appears to be about 1-2 h. In contrast, a free radical spin trap was found to have an improved therapeutic window. We compared the therapeutic time windows of the NMDA antagonist dizolcilpine maleate (MK-801), the glutamate release inhibitor lamotrigine, and the free radical spin trap n-tert-butyl-alpha-(2-sulfophenyl)-nitrone (S-PBN) against striatal lesions produced by the mitochondrial toxin malonate, which produces histotoxic hypoxia. Lamotrigine exerted neuroprotective effects when administered at 1 h before malonate injections. MK-801 protected at 1 h before and 1 h after malonate injections, whereas S-PBN showed efficacy when administered up to 6 h after malonate injections. Striatal injections of malonate produced a rapid increase in lactate production and early changes in diffusion-weighted imaging as assessed by magnetic resonance imaging. Therefore, the time course to evolve a lesion in our model of histotoxic hypoxia is comparable with that of other models of focal ischemia. These findings provide direct evidence that a free radical spin trap has an improved therapeutic window compared to an NMDA antagonist and a glutamate release inhibitor. This could be a therapeutic advantage in the treatment of clinical stroke patients.

Topics: Animals; Benzenesulfonates; Brain Ischemia; Corpus Striatum; Dizocilpine Maleate; Dose-Response Relationship, Drug; Free Radicals; Lamotrigine; Magnetic Resonance Imaging; Male; Malonates; Oxygen; Rats; Rats, Sprague-Dawley; Spin Trapping; Time Factors; Triazines

The CA1 region of hippocampus is selectively vulnerable to a variety of insults, including hypoxia-ischemia and Alzheimer's disease, but the basis of this regional susceptibility is poorly understood. We examined the regional hippocampal sensitivity to mitochondrial metabolic disruption induced by malonate, an inhibitor of succinate dehydrogenase. The CA1 region was exquisitely sensitive to malonate and the dentate gyrus was extremely resistant; the CA3 region had intermediate sensitivity. This pattern of vulnerability is reminiscent of hypoxic-ischemic damage. Malonate damage was blocked by the N-methyl-D-aspartic acid (NMDA) antagonist, MK-801, but regional susceptibility to malonate did not correlate with the density of NMDA receptors. Instead, malonate toxicity was inversely correlated with activity of succinate dehydrogenase. Our results suggest that regional metabolic capacity may help to determine sensitivity to metabolic/excitotoxic insults such as hypoxia-ischemia.

Topics: Animals; Autoradiography; Brain Ischemia; Dizocilpine Maleate; Hippocampus; Hypoxia; Hypoxia, Brain; Male; Malonates; N-Methylaspartate; Rats; Rats, Sprague-Dawley

We previously showed that local striatal injections of malonate produce age-dependent excitotoxic lesions. In the present study volumetric analysis confirmed that malonate produces age-dependent striatal lesions. Pretreatment with the non-competitive and competitive NMDA receptor antagonists, MK-801 and LY274614, and with lamotrigine resulted in significant protection in 4-month-old animals. In vivo magnetic resonance imaging of lesion area showed a significant correlation of increasing lesion size and lactate production in rats ranging from 1 to 12 months of age. Histological evaluation showed NADPH-diaphorase neurons were spared. The results provide further evidence that a subtle impairment of energy metabolism may play a role in neurodegenerative diseases.

Topics: Animals; Corpus Striatum; Dizocilpine Maleate; Isoquinolines; Magnetic Resonance Imaging; Male; Malonates; Oxidation-Reduction; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

Intrastriatal injection of malonate, a reversible inhibitor of succinate dehydrogenase (SDH), produced age-dependent striatal lesions, which were significantly greater in 4- and 12-month-old animals than in 1-month-old animals. Both histologic and neurochemical studies showed that the lesions were significantly attenuated by administration of the noncompetitive NMDA receptor antagonist MK-801. Water-suppressed chemical shift magnetic resonance imaging showed that malonate produces increased striatal lactate concentrations and striatal lesions on T2-weighted scans that were attenuated by MK-801. Neurochemical characterization of the lesions showed significant decreases in markers of medium-sized spiny neurons (GABA and substance P), whereas a marker of medium-sized aspiny neurons (somatostatin) was not different from control values, consistent with an NMDA receptor-mediated mechanism. The effects of intrastriatal injections of malonate on ATP concentrations were compared with those of the irreversible SDH inhibitor 3-nitropropionic acid (3-NP). The ATP depletions following an equimolar injection of malonate were less marked and more transient than those of 3-NP. These results show that the competitive SDH inhibitor malonate produces more transient and milder bioenergetic defects than 3-NP, which are associated with selective activation of NMDA receptors. The results strengthen the possibility that a subtle impairment of energy metabolism may play a role in the pathogenesis of Huntington's disease.

Topics: Adenosine Triphosphate; Aging; Animals; Corpus Striatum; Dizocilpine Maleate; gamma-Aminobutyric Acid; Lactates; Lactic Acid; Magnetic Resonance Imaging; Male; Malonates; Mitochondria; Neurotoxins; Oxidation-Reduction; Rats; Rats, Sprague-Dawley; Somatostatin; Substance P