Nicotine prevents glutamate-induced proteolysis of the microtubule-associated protein MAP-2 and glutamate neurotoxicity in primary cultures of cerebellar neurons

The aim of this work was to assess whether nicotine prevents glutamate neurotoxicity in primary cultures of cerebellar neurons, to try to identify the receptor mediating the protective effect and to shed light on the step of the neurotoxic process which is prevented by nicotine. It is shown that nicotine prevents glutamate and NMDA neurotoxicity in primary cultures of cerebellar neurons. The protective effect of nicotine is not prevented by atropine, mecamylamine or dihydro-beta-erythroidine, but is slightly prevented by hexamethonium and completely prevented by tubocurarine and alpha-bungarotoxin, indicating that the protective effect is mediated by activation of alpha7 neuronal nicotinic receptors. Moreover, alpha-bungarotoxin potentiates glutamate neurotoxicity, suggesting a tonic prevention of glutamate neurotoxicity by basal activation of nicotinic receptors. Nicotine did not prevent glutamate-induced rise of free intracellular calcium nor depletion of ATP. Nicotine prevents glutamate-induced proteolysis of the microtubule-associated protein MAP-2 and disaggregation of the neuronal microtubular network. The possible mechanism responsible for this prevention is discussed.     

BDNF prevents NO mediated glutamate cytotoxicity in cultured cortical neurons

The effects of brain-derived neurotrophic factor (BDNF) on glutamate-induced cytotoxicity were examined using primary cultures of rat cortical neurons. BDNF induced TrkB tyrosine phosphorylation in rat cultured cortical neurons. The cell viability was significantly reduced when cultures were briefly exposed to glutamate and incubated with normal medium for 24 h. Glutamate cytotoxicity was prevented by MK-801, which is a non-competitive blocker of N-methyl-D-aspartate and N(omega)-nitro-L-arginine, which is a blocker of nitric oxide synthetase. Delayed neurotoxicity was also induced by ionomycin, a calcium ionophore, and nitric oxide (NO) donors such as S-nitrosocysteine (SNOC) and 3-morpholinosydnonimine (SIN-1). Incubating cultures with BDNF for 10 min to 24 h protected cortical neurons against glutamate neurotoxicity. The protective effects of BDNF against glutamate cytotoxicity were dependent on both its concentrations and incubation time. BDNF also prevented the ionomycin-, SNOC-, and SIN-1 induced cytotoxicity. These results indicate that BDNF protects cultured cortical neurons from NMDA receptor-mediated glutamate neurotoxicity by reducing cytotoxic action of NO.     

Ifenprodil prevents glutamate cytotoxicity via polyamine modulatory sites of N-methyl-D-aspartate receptors in cultured cortical neurons

Neuroprotective effects of ifenprodil, a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, against glutamate cytotoxicity were examined in cultured rat cortical neurons. The viability of the cultures was markedly reduced by a 10-min exposure to glutamate followed by incubation with glutamate-free medium for 60 min. Ifenprodil and its derivative SL 82.0715 dose-dependently prevented cell death induced by glutamate. The NMDA antagonists MK-801 and 3-[(+/-)-2-carboxypiperazin-4-yl]propyl-1-phosphonic acid also prevented glutamate cytotoxicity with a potency similar to that of ifenprodil. Ifenprodil as well as MK-801 prevented NMDA-induced cytotoxicity, but did not affect kainate-induced cytotoxicity. Glutamate cytotoxicity was inhibited by removing extracellular Ca++ during and immediately after glutamate exposure. Ifenprodil and MK-801 reduced NMDA-induced Ca++ influx measured with rhod-2. Either spermidine, a polyamine modulatory site agonist, or glycine, a strychnine-insensitive glycine site agonist, potentiated NMDA- and glutamate-induced cytotoxicity. The protective effects of ifenprodil against NMDA- and glutamate-induced cytotoxicity were significantly reduced by spermidine, but not by glycine. These findings indicate that ifenprodil protects cortical neurons against glutamate cytotoxicity by selective antagonism of the polyamine modulatory site of the NMDA receptor complex.     

Dihydrokainate-sensitive neuronal glutamate transport is required for protection of rat cortical neurons in culture against synaptically released glutamate

Glutamate transport in nearly pure rat cortical neurons in culture (less than 0.2% astrocytes) is potently inhibited by dihydrokainate, l-serine-O-sulphate, but not by l-alpha-amino-adipate. This system allows for a test of the hypothesis that glutamate transport is important for protecting neurons against the toxicity of endogenous synaptically released glutamate. In support of this hypothesis, a 20-24 h exposure to 1 mm dihydrokainate reduced cell survival to only 14.8 +/- 9.8% in neuronal cultures (P < 0.001; n = 3), although it had no effect on neuronal survival in astrocyte-rich cultures (P > 0.05; n = 3). Dihydrokainate also significantly caused accumulation of glutamate in the extracellular medium of cortical neuronal cultures (6.6 +/- 4.9 micrometer, compared to 1.2 +/- 0.3 micrometer in control, n = 14, P < 0.01). The neurotoxicity of dihydrokainate was blocked by 10 micrometer MK-801, 10 micrometer tetrodotoxin, and an enzyme system that degrades extracellular glutamate. The latter two also abolished the accumulation of glutamate in the extracellular medium. Dihydrokainate (1 mm) inhibited the 45calcium uptake stimulated by 30 micrometer N-methyl-d-aspartate (NMDA), but not by higher concentrations consistent with a weak antagonist action of dihydrokainate at the NMDA receptor. Whole cell recordings showed that 1 mm dihydrokainate produced approximately 25% inhibition of 30 micrometer NMDA-induced current in cortical neurons. Dihydrokainate (1 mm) alone generated a small current (17% of the current produced by 30 micrometer NMDA) that was blocked by 30 micrometer 5,7-dichlorokynurenate and only weakly by 10 micrometer cyano-7-nitroquinoxaline-2,3-dione (CNQX). These results suggest that the toxicity of dihydrokainate in neuronal cultures is due to its ability to block glutamate transport in these cultures, and that dihydrokainate-sensitive neuronal glutamate transport may be important in protecting neurons against the toxicity of synaptically released glutamate.     

Antagonists for group I mGluRs attenuate excitotoxic neuronal death in cortical cultures

Activation of ion channel-linked glutamate receptors, especially N-methyl-D-aspartate (NMDA) receptors, mediates the excitotoxic effects of glutamate upon central neurons. We examined the hypothesis that activation of group I metabotropic glutamate receptors (mGluRs) would increase NMDA receptor-mediated cortical neuronal death. Addition of the selective group I mGluR agonists, dihydroxyphenylglycine (DHPG) or trans-azetidine-2,4-dicarboxylic acid (t-ADA) potentiated NMDA-induced neuronal death, and application of the group I mGluR-selective antagonist, aminoindan-1,5-dicarboxylic acid (AIDA), as well as the non-selective antagonists methyl-4-carboxyphenylglycine (MCPG) or 4-carboxyphenylglycine (4CPG) reduced NMDA- and kainate-induced neuronal death in murine cortical cultures. The pro-excitotoxic effect of group I mGluR activation may be mediated largely by enhancement of glutamate release, as DHPG potentiated high potassium-stimulated glutamate release, and the protective effects of both AIDA and MCPG were abolished when NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) receptors were blocked immediately after toxic NMDA receptor overstimulation. The present data support the possibility that antagonizing group I mGluRs may be a useful strategy for attenuating excitotoxic neuronal death in certain disease states.     

beta-Amyloid neurotoxicity in human cortical culture is not mediated by excitotoxins

beta-Amyloid is a metabolic product of the amyloid precursor protein, which accumulates abnormally in senile plaques in the brains of patients with Alzheimer's disease. The neurotoxicity of beta-amyloid has been observed in cell culture and in vivo, but the mechanism of this effect is unclear. In this report, we describe the direct neurotoxicity of beta-amyloid in high-density primary cultures of human fetal cortex. In 36-day-old cortical cultures, beta-amyloid neurotoxicity was not inhibited by the broad-spectrum excitatory amino acid receptor antagonist kynurenate or the NMDA receptor antagonist D-2-amino-5-phosphonovaleric acid under conditions that inhibited glutamate and NMDA neurotoxicity. In 8-day-old cortical cultures, neurons were resistant to glutamate and NMDA toxicity but were still susceptible to beta-amyloid neurotoxicity, which was unaffected by excitatory amino acid receptor antagonists. Treatment with beta-amyloid caused chronic neurodegenerative changes, including neuronal clumping and dystrophic neurites, whereas glutamate treatment caused rapid neuronal swelling and neurite fragmentation. These results suggest that beta-amyloid is directly neurotoxic to primary human cortical neurons by a mechanism that does not involve excitatory amino acid receptors.     

Neuroprotective effects of NMDA receptor glycine recognition site antagonism: dependence on glycine concentration

High-affinity NMDA receptor glycine recognition site antagonists protect brain tissue from ischemic damage. The neuroprotective effect of 5-nitro-6,7-dichloro-2,3-quinoxalinedione (ACEA 1021), a selective NMDA receptor antagonist with nanomolar affinity for the glycine binding site, was examined in rat cortical mixed neuronal/glial cultures. ACEA 1021 alone did not alter spontaneous lactate dehydrogenase (LDH) release. Treatment with ACEA 1021 (0.1-10 microM) before 500 microM glutamate, 30 microM NMDA, or 300 microM kainate exposure was found to reduce LDH release in a concentration-dependent fashion. These effects were altered by adding glycine to the medium. Glycine (1 mM) partially reversed the effect of ACEA 1021 on kainate cytotoxicity. Glycine (100 microM-1 mM) completely blocked the effects of ACEA 1021 on glutamate and NMDA cytotoxicity. The glycine concentration that produced a half-maximal potentiation of excitotoxin-induced LDH release in the presence of 1.0 microM ACEA 1021 was similar for glutamate and NMDA (18 +/- 3 and 29 +/- 9 microM, respectively). ACEA 1021 also reduced kainate toxicity in cultures treated with MK-801. The effects of glycine and ACEA 1021 on glutamate-induced LDH release were consistent with a model of simple competitive interaction for the strychnine-insensitive NMDA receptor glycine recognition site, although nonspecific effects at the kainate receptor may be of lesser importance.     

Neuroprotective activity of a new class of steroidal inhibitors of the N-methyl-D-aspartate receptor

Release of the excitatory neurotransmitter glutamate and the excessive stimulation of N-methyl-D-aspartate (NMDA)-type glutamate receptors is thought to be responsible for much of the neuronal death that occurs following focal hypoxia-ischemia in the central nervous system. Our laboratory has identified endogenous sulfated steroids that potentiate or inhibit NMDA-induced currents. Here we report that 3alpha-ol-5beta-pregnan-20-one hemisuccinate (3alpha5betaHS), a synthetic homologue of naturally occurring pregnanolone sulfate, inhibits NMDA-induced currents and cell death in primary cultures of rat hippocampal neurons. 3alpha5betaHS exhibits sedative, anticonvulsant, and analgesic properties consistent with an action at NMDA-type glutamate receptors. Intravenous administration of 3alpha5betaHS to rats (at a nonsedating dose) following focal cerebral ischemia induced by middle cerebral artery occlusion significantly reduces cortical and subcortical infarct size. The in vitro and in vivo neuroprotective effects of 3alpha5betaHS demonstrate that this steroid represents a new class of potentially useful therapeutic agents for the treatment of stroke and certain neurodegenerative diseases that involve over activation of NMDA receptors.     

Domoic acid neurotoxicity in cultured cerebellar granule neurons is mediated predominantly by NMDA receptors that are activated as a consequence of excitatory amino acid release

The participation of NMDA and non-NMDA receptors in domoic acid-induced neurotoxicity was investigated in cultured rat cerebellar granule cells (CGCs). Neurons were exposed to 300 microM L-glutamate or 10 microM domoate for 2 h in physiologic buffer at 22 degrees C followed by a 22-h incubation in 37 degrees C conditioned growth media. Excitotoxic injury was monitored as a function of time by measurement of lactate dehydrogenase (LDH) activity in both the exposure buffer and the conditioned media. Glutamate and domoate evoked, respectively, 50 and 65% of the total 24-h increment in LDH efflux after 2 h. Hyperosmolar conditions prevented this early response but did not significantly alter the extent of neuronal injury observed at 24 h. The competitive NMDA receptor antagonist D(-)-2-amino-5-phosphonopentanoic acid and the non-NMDA receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)quinoxaline (NBQX) reduced glutamate-induced LDH efflux totals by 73 and 27%, respectively, whereas, together, these glutamate receptor antagonists completely prevented neuronal injury. Domoate toxicity was reduced 65-77% when CGCs were treated with competitive and noncompetitive NMDA receptor antagonists. Unlike the effect on glutamate toxicity, NBQX completely prevented domoate-mediated injury. HPLC analysis of the exposure buffer revealed that domoate stimulates the release of excitatory amino acids (EAAs) and adenosine from neurons. Domoate-stimulated EAA release occurred almost exclusively through mechanisms related to cell swelling and reversal of the glutamate transporter. Thus, whereas glutamate-induced injury is mediated primarily through NMDA receptors, the full extent of neurodegeneration is produced by the coactivation of both NMDA and non-NMDA receptors. Domoate-induced neuronal injury is also mediated primarily through NMDA receptors, which are activated secondarily as a consequence of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)/kainate receptor-mediated stimulation of EAA efflux.     

Exposure to prenatal nicotine transiently increases neuronal nicotinic receptor subunit alpha7, alpha4 and beta2 messenger RNAs in the postnatal rat brain

This study determined the effects of prenatal nicotine exposure (2 mg/kg/day) in Sprague Dawley CD rats via subcutaneously implanted osmotic minipumps, during gestational days 7-21, on postnatal levels of neuronal nicotinic receptor alpha4, alpha7 and beta2 subunit messenger RNAs. Northern analysis of postnatal day 1, 7, 14 and 28 hippocampal/septal and cortical total RNA using alpha-[32P]dCTP-labeled alpha4, alpha7 and beta2 complementary DNA probes identified a single (5.7-kb) alpha7 messenger RNA, three (2.4-, 3.8- and 8.0-kb) alpha4 messenger RNAs and four (3.7-, 5.0-, 7.5- and 10.0-kb) beta2 messenger RNAs. In comparison to prenatal saline, prenatal nicotine produced several significantly higher messenger RNA levels (cortical: 5.7-kb alpha7, 2.4-, 3.8- and 8.0-kb alpha4, 10.0-kb beta2; hippocampal/septal: 2.4- and 8.0-kb alpha4); these increases occurred predominantly on, but were not restricted to, postnatal day 14. Effects of nicotine were generally resolved by postnatal day 28. Collapsing the data across sex and age, a significant treatment effect indicated that hippocampal/septal and cortical 8.0-kb alpha4 messenger RNA levels and 10.0-kb beta2 messenger RNA levels were significantly higher following prenatal nicotine exposure. This is the first study indicating that prenatal nicotine produces alterations in developing postnatal rat neuronal nicotinic receptor messenger RNA levels, possibly by premature stimulation of neuronal nicotinic receptors. These results further implicate the teratogenic potential of nicotine in postnatal neuronal development.     

Immune response associated with nonmelanoma skin cancer

The effect of antioxidants and reducing agents on glutamate-induced cytotoxicity was examined using PC12 cells. The antioxidants vitamin E, idebenone, and selegiline protected cells against the cytotoxicity observed 24 h after exposure to 0.5 or 10 mM glutamate, as determined by lactate dehydrogenase leakage, even when added 3 h after glutamate. The reducing agents, glutathione (GSH) and dithiothreitol (DTT), also provided protection against the cytotoxicity of glutamate. Preincubation of PC12 cells with the antioxidants mentioned above, or the incubation with those antioxidants after exposure to glutamate for 3 h, prevented the reduction of viability caused by glutamate. Cystine uptake was inhibited by exposure of cells to glutamate, as determined by L-[35S]-cystine uptake. Incubation of cells with 0.5 or 10 mM glutamate caused a marked decrease in cellular GSH levels, not prevented by antioxidants. The activity of GSSG reductase was decreased by glutamate and this inhibition was reverted in the presence of the reducing agents GSH and DTT. These results indicate that glutamate toxicity on PC12 cells results from the inhibition of cystine uptake with consequent GSH depletion and oxidative stress, suggesting that antioxidants may reduce the cellular damage in pathologic conditions associated with excessive glutamate release.     

Tissue specific distribution of the herpes simplex virus type 1 latency-associated transcripts on polyribosomes during latent infection

Certain natural products and Asian herbal remedies have been used in Asia to attenuate neurodegenerative diseases, including senile dementia. We have examined derivatives of several natural products for potential neuroprotective activity in an in vitro test system. In the present study, we assayed a number of compounds that were isolated from Panax ginseng C.A. Meyer (Araliaceae) for an ability to protect rat cortical cell cultures from the deleterious effects of the neurotoxicant, glutamate. We found that ginsenosides Rb1 and Rg3 significantly attenuated glutamate-induced neurotoxicity. Brief exposure of cultures to excess glutamate caused extensive neuronal death. Glutamate-induced neuronal cell damage was reduced significantly by pretreatment with Rb1 and Rg3. Ginsenosides Rb1 and Rg3 inhibited the overproduction of nitric oxide, which routinely follows glutamate neurotoxicity, and preserved the level of superoxide dismutase in glutamate-treated cells. Furthermore, in cultures treated with glutamate, these ginsenosides inhibited the formation of malondialdehyde, a compound that is produced during lipid peroxidation, and diminished the influx of calcium. These results show that ginsenosides Rb1 and Rg3 exerted significant neuroprotective effects on cultured cortical cells. Therefore, these compounds may be efficacious in protecting neurons from oxidative damage that is produced by exposure to excess glutamate.     

Nicotinic acetylcholine receptors in rat cochlear nucleus: [125I]-alpha-bungarotoxin receptor autoradiography and in situ hybridization of alpha 7 nAChR subunit mRNA

The cochlear nucleus (CN) is the first site in the central nervous system (CNS) for processing auditory information. Acetylcholine in the CN is primarily extrinsic and is an important neurotransmitter in efferent pathways thought to provide CNS modulation of afferent signal processing. Although muscarinic acetylcholine receptors have been studied in the CN, the role of nicotinic receptors has not. We examined the distribution of one nicotinic acetylcholine receptor subtype, the alpha-bungarotoxin receptor (alpha Bgt), in the CN. Quantitative autoradiography was used to localize receptors and in situ hybridization was used to localize alpha 7 mRNA in CN neurons that express the alpha Bgt receptor. Binding sites for alpha Bgt are abundant in the anterior ventral, posterior ventral, and dorsal divisions of the CN, and receptor density is low in the granule cell layer and interstitial nucleus. Heterogeneity in CN subregions is described. Four distinct patterns of alpha Bgt binding were observed: (1) binding over and around neuronal cell bodies, (2) receptors locally surrounding neurons, (3) dense punctate binding in the dorsal CN (DCN) not associated with neuronal cell bodies, and (4) diffuse fields of alpha Bgt receptors prominent in the DCN molecular layer, a field underlying the granule cell layer and in the medial sheet. The perikaryial receptors are abundant in the ventral CN (VCN) and are always associated with neurons expressing mRNA for the receptor. Other neurons in the VCN also express alpha 7 mRNA, but without alpha Bgt receptor expression associated with the cell body. In general, alpha Bgt receptor distribution parallels cholinergic terminal distribution, except in granule cell regions rich in cholinergic markers but low in alpha Bgt receptors. The findings indicate that alpha Bgt receptors are widespread in the CN but are selectively localized on somata, proximal dendrites, or distal dendrites depending on the specific CN subregion. The data are consistent with the hypothesis that descending cholinergic fibers modulate afferent auditory signals by regulating intracellular Ca2+ through alpha Bgt receptors.     

Ionspray ionization-mass spectrometric separation and determination of heptafluorobutyryl derivatives of polyamines

It has been reported that glutamate-induced neurotoxicity is related to an increase in nitric oxide (NO) concentration. An NO-sensitive electrode has been developed to measure NO concentration directly. Using this electrode, we examined NO concentration and neuronal survival after glutamate application in rat cultured cortical neurons. We also examined the effects of NMDA receptor antagonists, MK-801 and ketamine, and the NO synthetase inhibitor, L-NMMA on NO production and neuronal death. After 7 days in culture, application of glutamate (1 mM) or L-arginine (0.3 mM) to the cultured medium increased NO concentration, and decreased the number of anti-microtubule-associated protein 2 positive neurons. Both pretreatment with MK-801 (300 microns) and ketamine (300 microns) prevented glutamate-, but not L-arginine-induced increase in NO concentration and neuronal death. L-NMMA prevented both glutamate- and L-arginine-induced NO production and neuronal death. The nitric oxide donor, S-nitroso-N-acetyl-D,L-penicillamine (SNAP) also caused neuronal death, and MK-801, ketamine and L-NMMA did not prevent SNAP-induced toxicity. We have demonstrated excitatory amino acid-induced changes of NO concentration and the parallel relationship between changes of NO concentration and neuronal death. In conclusion, an increase in NO concentration does induce neuronal death, and the inhibition of the production of NO prevents glutamate-induced neuronal death.     

Phosphatidylcholine-specific phospholipase C regulates glutamate-induced nerve cell death

Phosphatidylcholine-specific phospholipase C (PC-PLC) is a necessary intermediate in transducing apoptotic signals for tumor necrosis factor and Fas/Apo-1 ligands in nonneuronal cells. The data presented here show that PC-PLC also is required in oxidative glutamate-induced programmed cell death of both immature cortical neurons and a hippocampal nerve cell line, HT22. In oxidative glutamate toxicity, which is distinct from excitotoxicity, glutamate interferes with cystine uptake by blocking the cystine/glutamate antiporter, indirectly causing a depletion of intracellular glutathione. A PC-PLC inhibitor blocks oxidative glutamate toxicity, and exogenous PC-PLC potentiates glutamate toxicity. The inhibition of PC-PLC uncouples the cystine uptake from glutamate inhibition, allowing the maintenance of glutathione synthesis and cell viability. These data suggest that PC-PLC modulates neuronal cell death through a mechanism that is distinct from that involved in nonneuronal apoptosis.     

Involvement of three glutamate receptor epsilon subunits in the formation of N-methyl-D-aspartate receptors mediating excitotoxicity in primary cultures of mouse cerebellar granule cells

The N-methyl-D-aspartate receptors have been implicated in neuronal plasticity and their overactivation leads to neurotoxicity. Molecular cloning and co-expression of various glutamate receptor zeta and epsilon complementary DNAs support a heteromeric structural organization for N-methyl-D-aspartate receptors. In this study, we show that cerebellar granular neurons in primary culture of mouse express glutamate receptor zeta1 and at least three glutamate receptor epsilon (epsilon1, epsilon2, and epsilon3) protein subunits. In vitro, the temporal patterns of glutamate receptor epsilon1, epsilon2, and epsilon3 subunit expression depend on culture stages. By day 9, a somatic and neuritic immunolocalization for all N-methyl-D-aspartate subunits was clearly identified in most neuronal, but not glial cells. The role of particular subunits in N-methyl-D-aspartate-mediated excitotoxicity was probed by exposing the cerebellar granule cells to antisense oligodeoxynucleotides generated against specific N-methyl-D-aspartate receptor subunits. Antisense oligodeoxynucleotide treatments significantly down-regulated the amounts of the corresponding N-methyl-D-aspartate subunits. The decrease in N-methyl-D-aspartate subunit protein correlated with a reduction in N-methyl-D-aspartate-induced calcium influx and N-methyl-D-aspartate-mediated excitotoxicity in cerebellar cultures. In contrast, antisense oligodeoxynucleotide treatment failed to protect neurons from 1-methyl-4-phenylpyridinium-induced metabolic cell toxicity. Antisense oligodeoxynucleotide treatment targeted at N-methyl-D-aspartate glutamate receptor epsilon subunits demonstrate that glutamate receptor epsilon1, epsilon2, and epsilon3 proteins form N-methyl-D-aspartate receptors responsible for neurotoxic effects on cerebellar neurons. This study provides direct evidence for the existence of distinct N-methyl-D-aspartate receptor subunit proteins in cerebellar granule cells developing in vitro that may trigger N-methyl-D-aspartate-dependent excitotoxicity.     

Selective activation of group-II metabotropic glutamate receptors is protective against excitotoxic neuronal death

Aminopyrrolidine-2R,4R-dicarboxylated (2R,4R-APDC) has recently been introduced as a potent and highly selective agonist of metabotropic glutamate (mGlu) receptor subtypes mGlu2 and -3. In murine cortical cultures containing both neurons and astrocytes, 2R,4R-APDC attenuated the delayed neuronal degeneration induced by a 10-min pulse of N-methyl-D-aspartate (NMDA). 2R,4R-APDC was maximally neuroprotective in a range of concentrations (0.1-1 microM) comparable to that reported for the activation of mGlu2 or -3 receptors in heterologous expression systems. The action of 2R,4R-APDC was sensitive to the mGlu2/3 receptor antagonists, (2S)-alpha-ethylglutamate and (2S,1S',2S',3R')-2-(2'-carboxy-3'-phenylcyclopropyl)glycine. These results indicate that activation of mGlu2 and/or -3 receptors is sufficient per se to protect neurons against excitotoxic degeneration, and encourage the search for potent, selective and systemically active mGlu2/3 receptor agonists as neuroprotective drugs.     

Chondroitin sulfate proteoglycans protect cultured rat's cortical and hippocampal neurons from delayed cell death induced by excitatory amino acids

Protective effects of chondroitin sulfate proteoglycans (CSPGs) from rat's brain against delayed cell death induced by excitatory amino acids were examined in cultured neurons of the rat. CSPGs reduced delayed neuronal death induced by 10 min exposure to glutamate at a concentration between 100 microM and 1 mM when lactate dehydrogenase activity of culture medium was assayed 24 h after the exposure. CSPGs also protected neuronal death induced by 200 microM N-methyl-D-aspartate (NMDA), kainate or 100 microM alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). CSPGs reduced death of cortical and hippocampal neurons even when they were administered at 2 h, but not 6 and 12 h, after the exposure to glutamate. These results indicate that CSPGs may have a neuroprotective action against acute noxious conditions in the brain.