Influence of Inflammatory Pain and Dopamine on Synaptic Transmission in the Mouse ACC.

Dopamine (DA) inhibits excitatory synaptic transmission in the anterior cingulate cortex (ACC), a brain region involved in the sensory and affective processing of pain. However, the DA modulation of inhibitory synaptic transmission in the ACC and its alteration of the excitatory/inhibitory (E/I) balance remains relatively understudied. Using patch-clamp recordings, we demonstrate that neither DA applied directly to the tissue slice nor complete Freund's adjuvant (CFA) injected into the hind paw significantly impacted excitatory currents (eEPSCs) in the ACC, when recorded without pharmacological isolation. However, individual neurons exhibited varied responses to DA, with some showing inhibition, potentiation, or no response. The degree of eEPSC inhibition by DA was higher in naïve slices compared to that in the CFA condition. The baseline inhibitory currents (eIPSCs) were greater in the CFA-treated slices, and DA specifically inhibited eIPSCs in the CFA-treated, but not naïve group. DA and CFA treatment did not alter the balance between excitatory and inhibitory currents. Spontaneous synaptic activity revealed that DA reduced the frequency of the excitatory currents in CFA-treated mice and decreased the amplitude of the inhibitory currents, specifically in CFA-treated mice. However, the overall synaptic drive remained similar between the naïve and CFA-treated mice. Additionally, GABAergic currents were pharmacologically isolated and found to be robustly inhibited by DA through postsynaptic D2 receptors and G-protein activity. Overall, the study suggests that CFA-induced inflammation and DA do not significantly affect the balance between excitatory and inhibitory currents in ACC neurons, but activity-dependent changes may be observed in the DA modulation of presynaptic glutamate release in the presence of inflammation.

Photobiomodulation Therapy Ameliorates Glutamatergic Dysfunction in Mice with Chronic Unpredictable Mild Stress-Induced Depression.

Accumulating evidence indicates that dysfunction of the glutamatergic neurotransmission has been widely involved in the pathophysiology and treatment of depression. Photobiomodulation therapy (PBMT) has been demonstrated to regulate neuronal function both in vitro and in vivo. Herein, we aim to investigate whether the antidepressant phenotype of PBMT is associated with the improvement of glutamatergic dysfunction and to explore the mechanisms involved. Results showed that PBMT decreased extracellular glutamate levels via upregulation of glutamate transporter-1 (GLT-1) and rescued astrocyte loss in the cerebral cortex and hippocampus, which also alleviated dendritic atrophy and upregulated the expression of AMPA receptors on the postsynaptic membrane, ultimately exhibiting behaviorally significant antidepressant effects in mice exposed to chronic unpredictable mild stress (CUMS). Notably, PBMT also obtained similar antidepressant effects in a depressive mouse model subcutaneously injected with corticosterone (CORT). Evidence from in vitro mechanistic experiments demonstrated that PBMT treatment significantly increased both the GLT-1 mRNA and protein levels via the Akt/NF-κB signaling pathway. NF-κB-regulated transcription was in an Akt-dependent manner, while inhibition of Akt attenuated the DNA-binding efficiency of NF-κB to the GLT-1 promoter. Importantly, in vitro, we further found that PKA activation was responsible for phosphorylation and surface levels of AMPA receptors induced by PBMT, which is likely to rescue excitatory synaptic transmission. Taken together, our research suggests that PBMT as a feasible therapeutic approach has great potential value to control the progression of depression.

Cytotoxic and anti-excitotoxic effects of selected plant and algal extracts using COMET and cell viability assays.

Excess glutamate in the central nervous system may be a major cause of neurodegenerative diseases with gradual loss and dysfunction of neurons. Primary or secondary metabolites from medicinal plants and algae show potential for treatment of glutamate-induced excitotoxicity. Three plant extracts were evaluated for impact on glutamate excitotoxicity-induced in primary cultures of retinal ganglion cells (RGC). These cells were treated separately in seven groups: control; Plicosepalus. curviflorus treated; Saussurea lappa treated; Cladophora glomerate treated. Cells were treated independently with 5, 10, 50, or 100 µg/ml of extracts of plant or alga material, respectively, for 2 h. Glutamate-treated cells (48 h with 5, 10, 50, or 100 µM glutamate); and P. curviflorus/glutamate; S. lappa/glutamate; C. glomerata/glutamate [pretreatment with extract for 2 h (50 and 100 µg/ml) before glutamate treatment with 100 µM for 48 h]. Comet and MTT assays were used to assess cell damage and cell viability. The number of viable cells fell significantly after glutamate exposure. Exposure to plant extracts caused no notable effect of viability. All tested plants extracts showed a protective effect against glutamate excitotoxicity-induced RGC death. Use of these extracts for neurological conditions related to excitotoxicity and oxidative stress might prove beneficial.

Neuroprotective effects of oolong tea extracts against glutamate-induced toxicity in cultured neuronal cells and ß-amyloid-induced toxicity in Caenorhabditis elegans.

Oolong tea, a traditional Chinese tea, is especially popular in south China and has a variety of health benefits. However, studies about its neuroprotective and neuroregenerative properties are still limited. This study explored the neuroprotective and neurite outgrowth-promoting properties of oolong tea in cultured neuronal cells (Neuro-2a and HT22) and Caenorhabditis elegans models. Ultra performance liquid chromatography was applied to identify the main natural bioactive compounds in oolong tea. Using Neuro-2a and HT22 cells, we found that oolong tea extracts had a protective effect against glutamate-induced cell death. The extracts reduced intracellular reactive oxygen species accumulation and induced gene expression of cellular antioxidant enzymes such as GPx, GSTs and SODs. These extracts also increased the average neurite length, and GAP-43 and Ten-4 mRNA expression in Neuro-2a cells. Moreover, they had protective effects against Aß-induced paralysis, chemotaxis deficiency and α-synuclein aggregation in C. elegans. This is the first study showing the neuroregenerative and neuroprotective potential of the oolong tea extracts against glutamate/Aß/α-synuclein-induced toxicity in vitro and in vivo. Our study may support oolong tea extracts as potential candidates for the prevention of neurodegenerative diseases.

Tetrastigma hemsleyanum Vine Flavone Ameliorates Glutamic Acid-Induced Neurotoxicity via MAPK Pathways.

Glutamic acid (Glu) is a worldwide flavor enhancer with various positive effects. However, Glu-induced neurotoxicity has been reported less. Tetrastigma hemsleyanum (TH), a rare herbal plant in China, possesses high medicinal value. More studies paid attention to tuber of TH whereas vine part (THV) attracts fewer focus. In this study, we extracted and purified flavones from THV (THVF), and UPLC-TOF/MS showed THVF was consisted of 3-caffeoylquinic acid, 5-caffeoylquinic acid, quercetin-3-O-rutinoside, and kaempferol-3-O-rutinoside. In vitro, Glu caused severe cytotoxicity, genotoxicity, mitochondrial dysfunction, and oxidative damage to rat phaeochromocytoma (PC12) cells. Conversely, THVF attenuated Glu-induced toxicity via MAPK pathways. In vivo, the neurotoxicity triggered by Glu restrained the athletic ability in Caenorhabditis elegans (C. elegans). The treatment of THVF reversed the situation induced by Glu. In a word, Glu could cause neurotoxicity and THVF owns potential neuroprotective effects both in vitro and in vivo via MAPK pathways.

The Effect of Protein-Rich Extract from Bombyx Batryticatus against Glutamate-Damaged PC12 Cells Via Regulating γ-Aminobutyric Acid Signaling Pathway.

Bombyx Batryticatus (BB) is a known traditional Chinese medicine (TCM) utilized to treat convulsions, epilepsy, cough, asthma, headaches, etc. in China for thousands of years. This study is aimed at investigating optimum extraction of protein-rich extracts from BB (BBPs) using response surface methodology (RSM) and exploring the protective effects of BBPs against nerve growth factor (NGF)-induced PC12 cells injured by glutamate (Glu) and their underlying mechanisms. The results indicated optimum process of extraction was as follows: extraction time 1.00 h, ratio of liquid to the raw material 3.80 mL/g and ultrasonic power 230.0 W. The cell viability of PC12 cells stimulated by Glu was determined by CCK-8 assay. The levels of γ-aminobutyric (GABA), interleukin-1ß (IL-1ß), interleukin-4 (IL-4), tumor necrosis factor-α (TNF-α), 5-hydroxytryptamine (5-HT) and glucocorticoid receptor alpha (GR) in PC12 cells were assayed by ELISA. Furthermore, the Ca2+ levels in PC12 cells were determined by flow cytometry analysis. Protein and mRNA expressions of GABAA-Rα1, NMDAR1, GAD 65, GAD 67, GAT 1 and GAT 3 in PC12 cells were evaluated by real-time polymerase chain reaction (RT-PCR) and Western blotting assays. Results revealed that BBPs decreased toxic effects due to Glu treatment and decreased Ca2+ levels in PC12 cells. After BBPs treatments, levels of GABA and 5-HT were increased and contents of TNF-α, IL-4 and IL-1ß were decreased in NGF-induced PC12 cells injured by Glu. Moreover, BBPs up-regulated the expressions of GABAA-Rα1, GAD 65 and GAD 67, whereas down-regulated that of NMDAR1 GAT 1 and GAT 3. These findings suggested that BBPs possessed protective effects on NGF-induced PC12 cells injured by Glu via γ-Aminobutyric Acid (GABA) signaling pathways, which demonstrated that BBPs has potential anti-epileptic effect in vitro. These findings may be useful in the development of novel medicine for the treatment of epilepsy.

Neuroprotective Effects of Dammarane-Type Saponins from Panax notoginseng on Glutamate-Induced Cell Damage in PC12 Cells.

Dammarane-type saponins, the main active ingredients of Panax notoginseng, have substantial neuroprotective effects in different animal models of neurodegenerative diseases. However, because these compounds have different structures, the level of protection provided by individual compounds varies, and highly active compounds can be selected based on structure-activity relationships. Glutamate is a major excitatory neurotransmitter that plays an important role in synaptic response development. However, excessive extracellular glutamate levels lead to neuronal dysfunctions in the central nervous system. Herein, we investigated the neuroprotective effects of nine saponins (compounds 1:  - 9: ) on glutamate-treated PC12 cells in the concentration range of 0.1 - 10 µM. The MTT assay revealed that these compounds increased cell viability to 65.6, 69.8, 76.9, 91.7, 74.4, 63.3, 59.9, 64.7, and 59.9%, respectively, compared with the glutamate-treated cells (44.6%). Protopanaxatriol (compound 4: ) was the most neuroprotective compound, and subsequent experiments revealed that pretreatment with compound 4: significantly reverses mitochondrial membrane potential collapse, increases superoxide dismutase activity, and decreases lactate dehydrogenase leakage, malondiadehyde levels, reactive oxygen species generation, and cell apoptosis. Compound 4: also decreased the Bax/Bcl-2 ratio, cleaved caspase-3, N-methyl-D-aspartic receptor 1, and Ca2+-/calmodulin-dependent protein kinase II expression, and inhibited glutamate-induced cytochrome C release and phosphorylation of apoptosis signal-regulating kinase 1, c-Jun N-terminal kinase, and p38. Overall, the results indicate that protopanaxatriol has significant neuroprotective effects, and might be a promising neuroprotective agent for preventing and treating neurodegenerative diseases.

Echinacoside, an Active Constituent of Cistanche Herba, Exerts a Neuroprotective Effect in a Kainic Acid Rat Model by Inhibiting Inflammatory Processes and Activating the Akt/GSK3ß Pathway.

Echinacoside is a major compound of Cistanche Herb and has glutamate release-inhibiting activity in the brain. Given the involvement of excitotoxicity caused by massive glutamate in the pathophysiology of epilepsy, we explored the antiepileptic effect of echinacoside on kainic acid-induced seizures in rats. The rats were intraperitoneally administrated echinacoside for 30 min prior to intraperitoneal injection with kainic acid. The results showed that kainic acid induced seizure-like behavioral patterns, increased glutamate concentrations, caused neuronal loss and microglial activation, and stimulated proinflammatory cytokine gene expression in the hippocampus. These kainic acid-induced alternations were found to be attenuated by echinacoside pretreatment. Furthermore, decreased Akt and glycogen synthase kinase 3ß (GSK3ß) phosphorylation as well as Bcl-2 expression in the hippocampus was reversed by the echinacoside pretreatment. These results demonstrate that echinacoside exert its antiepileptic and neuroprotective actions in a kainic acid rat model through suppressing inflammatory response and activating the Akt/GSK3ß signaling. Therefore, the present study suggests that echinacoside is the potentially useful in the prevention of epilepsy.

Neuroprotective effect of Aronia melanocarpa extract against glutamate-induced oxidative stress in HT22 cells.

BACKGROUND: Glutamate (an endogenous excitatory neurotransmitter) at high concentrations contributes to the development of neurodegenerative diseases. Aronia melanocarpa (A. melanocarpa) berries contain anthocyanins and have high antioxidant activities. In this study, we evaluated whether A. melanocarpa berries could protect neuronal cells against glutamate-induced oxidative stress. METHOD: A. melanocarpa berries exerted a protective effect against cytotoxicity in HT22 mouse hippocampal cells by MTT assay. We evaluated oxidative stress parameters including ROS level, intracellular Ca2+ level, glutathione level and antioxidant enzyme activity in HT22 cells to elucidate the mechanism of its neuroprotective effect. RESULTS: A. melanocarpa berries decreased glutamate-induced death of HT22 cells. In addition, A. melanocarpa berries reduced ROS and intracellular Ca2+ levels. Glutathione level, antioxidant enzymes, glutathione reductase and glutathione peroxide activities and mitochondrial membrane potential were also increased in HT22 cells. CONCLUSION: These results suggested that A. melanocarpa berries protected HT22 cells by exerting an antioxidant effect.

Cleistocalyx nervosum var. paniala berry fruit protects neurotoxicity against endoplasmic reticulum stress-induced apoptosis.

Oxidative and endoplasmic reticulum (ER) stresses cause neuronal damage leading to neurodegenerative disorders. Cleistocalyx nervosum var. paniala (CNP) berry fruit has been shown to possess powerful antioxidant properties. Here, we investigated the neuroprotective effect of CNP extract against glutamate-mediated oxidative/ER stress-induced cell death in mouse hippocampal neuronal HT22 cells. CNP extract was clarified for its radical scavenging activities, total phenolic and anthocyanin contents. The key anthocyanin cyanidin-3-glucoside was used as a marker to standardize the extract used in the study. We found that pretreated cells with CNP extract (0.05-1 µg/ml) prevented neuronal cell death in response to 5 mM glutamate evaluated by cell viability MTT, LDH and apoptosis/necrosis Annexin V/propidium iodide co-staining assays. For mechanistic approach, glutamate-induced cell death through reactive oxygen species (ROS)-mediated ER stress pathways, indicating the increase of ROS and ER stress signature molecules including calpain, caspases-12 and C/EBP homologous proteins (CHOP). CNP extract inhibited ROS production. Moreover, the extract also suppressed the specific-ER stress apoptotic proteins level in glutamate-induced cells by upregulating the gene expression of cellular antioxidant enzymes (SODs, CAT, GPx and GSTs). Taken together, our results provide information about and the molecular mechanism of CNP extract as a promising neuroprotectant and antioxidant.

Protective effects of cycloartane triterpenoides from Passiflora edulis Sims against glutamate-induced neurotoxicity in PC12 cell.

Four new cycloartane triterpenoids, 1α,3ß-dihydroxy-16-keto-24(31)-en-cycloartane (1), 31-methoxyl-passifloic acid (2), cyclopassifloside XIV (3), and cyclopassifloside XV (4), together with six known compounds (5-10) were isolated from Passiflora edulis Sims. Their structures were elucidated on the basis of extensive spectroscopic analysis. All the compounds were evaluated for protective effects against damage of PC12 cell induced by glutamate according to traditional usage of the herbal medicine, and the results indicated that cycloartane triterpenoids maybe one of the active compositions of P. edulis Sims for the treatment of neurodegenerative disease.

Synthesis and Evaluation of 3-(furo[2,3-b]pyridin-3-yl)-4-(1H-indol-3-yl)-maleimides as Novel GSK-3ß Inhibitors and Anti-Ischemic Agents.

A series of novel 3-(furo[2,3-b]pyridin-3-yl)-4-(1H-indol-3-yl)-maleimides were designed, synthesized, and biologically evaluated for their GSK-3ß inhibitory activities. Most compounds showed favorable inhibitory activities against GSK-3ß protein. Among them, compounds 5n, 5o, and 5p significantly reduced GSK-3ß substrate tau phosphorylation at Ser396 in primary neurons, indicating inhibition of cellular GSK-3ß activity. In the in vitro neuronal injury models, compounds 5n, 5o, and 5p prevented neuronal death against glutamate, oxygen-glucose deprivation, and nutrient serum deprivation which are closely associated with cerebral ischemic stroke. In the in vivo cerebral ischemia animal model, compound 5o reduced infarct size by 10% and improved the neurological deficit. The results may provide new insights into the development of novel GSK-3ß inhibitors with potential neuroprotective activity against brain ischemic stroke.

Neuroprotective effect of prenylated arylbenzofuran and flavonoids from morus alba fruits on glutamate-induced oxidative injury in HT22 hippocampal cells.

A prenylated arylbenzofuran and six flavonoids were isolated from the fruits of Morus alba L. through silica gel, octadecyl silica gel, and Diaion HP-20 column chromatography. Based on the nuclear magnetic resonance, mass spectrometry, and infrared spectroscopic data, the chemical structures of the compounds were determined to be artoindonesianin O (1), isobavachalcone (2), morachalcone A (3), quercetin (4), astragalin (5), isoquercetin (6), and rutin (7). The isolated compounds were evaluated for protection of HT22-immortalized hippocampal cells against glutamate-induced oxidative stress. Compounds 1 and 3 exhibited protective effects with EC(50) values of 19.7±1.2 and 35.5±2.1 µM, respectively. The major compounds 1-3 and 7 were quantified using liquid chromatography/mass spectrometry analysis and were determined to be 1.88±2.1, 1.90±1.8, 0.78±1.5, and 37.29±2.2 mg/kg, respectively, in the ethanol extract of M. alba L. fruits.

Kaempferol attenuates the glutamate-induced oxidative stress in mouse-derived hippocampal neuronal HT22 cells.

It is thought that the neuronal cell loss caused by oxidative stress is the primary mechanism underlying the pathogenesis of several neurodegenerative disorders. Glutamate is an endogenous neurotransmitter, but at high concentrations it can act as a neurotoxicant by increasing the intracellular levels of reactive oxygen species (ROS). Therefore, the development of factors that can attenuate glutamate-induced oxidative stress in neuronal cells is a good strategy by which new drugs could be discovered that may treat or prevent neurodegenerative diseases. Here, the neuroprotective effects of kaempferol (KF) isolated from the stems of butterbur (Petasites japonicus) were examined in glutamate-treated hippocampal neuronal cells (HT22). The administration of KF (25 µM) resulted in a significant increase in cell viability (105.18 ± 7.48%) compared with the control (100.00 ± 3.05%), while glutamate (5 mM) reduced cell viability by 39.94 ± 1.61%. The glutamate-induced calcium (Ca(2+)) influx (1.93 ± 0.08-fold) was significantly reduced by 0.89 ± 0.02-fold following the administration of 25 µM KF. Additionally, when HT22 cells were stressed with excessive glutamate, there was a 3.70 ± 0.01-fold increase in intracellular ROS generation, even though this was effectively attenuated by KF (25 µM, 0.72 ± 0.01-fold). The protective effects of KF in HT22 cells were later confirmed using a lactate dehydrogenase (LDH) assay and a FITC-annexin V/propidium iodide double staining procedure. These findings also revealed that the neuroprotective effects of KF are a result of the regulation of the expression levels of proteins, such as Bcl-2, Bid, apoptosis-inducing factor (AIF), and mitogen-activated protein kinase (MAPK). This is the first report to investigate the neuroprotective influence of KF in glutamate-treated HT22 cells. These data demonstrate that KF may be a useful candidate for pharmacological therapies that can prevent and treat neurodegenerative diseases such as Alzheimer's disease (AD).

Aloysia gratissima prevents cellular damage induced by glutamatergic excitotoxicity.

OBJECTIVES: Aloysia gratissima aqueous extract (AE) was investigated as a putative protective agent against quinolinic acid (QA)-induced seizures in mice and hippocampal cell damage. Additionally, AE and ferulic acid (FA), the major compound of AE, were tested against neurotoxicity evoked by glutamate or its N-methyl-D-aspartate receptor (NMDAR) agonist, QA on hippocampal slices, in vitro. METHODS: Mice were treated with AE before QA infusion (36.8 nmol/site) and seizures were analysed. Cellular viability and modulation of excitatory amino acid transport were verified in hippocampal slices. In-vitro AE or FA was tested against neurotoxicity induced by glutamate or QA. KEY FINDINGS: AE did not prevent QA-induced seizures; however, it prevented cellular death and disruption of excitatory amino acid transport. In-vitro AE (0.1 or 1.0 mg/ml) or FA (1 or 10 µm), improved cell viability against citotoxicity exerted by glutamate or QA, respectively. Both AE and FA have protective effects depending on activation of the phosphatidylinositol-3 kinase (PI3K) signalling pathway. CONCLUSIONS: AE attenuated QA-induced cell damage possibly involving the glutamate transport modulation through NMDAR interaction. FA shows a similar profile of neuroprotection promoted by AE. Therefore, AE treatment might be a useful strategy in preventing brain damage caused by exacerbation of glutamatergic toxicity in nervous system disorders.

Neuroprotective action of deer bone extract against glutamate or Aß1₋42-induced oxidative stress in mouse hippocampal cells.

Water extracts of deer bone, called nokgol in Korean, and deer antlers have been traditionally used as anti-aging medicines. Deer antler extract is known to possess various activities, including anti-aging or anti-amnesic activity. However, there are no reports about the neuroprotective effect of deer bone extract (DBE). The objective of this study was to examine the neuroprotective effect of DBE on glutamate-induced cell death of mouse hippocampal cells (HT-22 cells) and to elucidate the mode of neuroprotective action of DBE. In this study, HT-22 cells was pretreated with DBE before stimulation with glutamate, and then, the effects of DBE on cell viability, oxidative stress markers, and MAP kinases were determined. Separately, the effect of DBE on H2O2 or amyloid beta peptide (1-42) (Aß1₋42)-induced cytotoxicity of HT-22 cells was evaluated. DBE protected HT-22 cells from glutamate-induced cell death and prevented the increase in lactate dehydrogenase leakage in HT-22 cells. DBE also prevented glutamate-induced oxidative stress, as indicated by increased reactive oxygen species and lipid peroxidation as well as by decreases in glutathione (GSH) levels and GSH peroxidase activity. In addition, DBE inhibited glutamate-induced activation of c-Jun N-terminal kinases (JNK), p38, and extracellular signal-regulated kinase, indicators of oxidative stress-induced cell death. Furthermore, DBE also protected against H2O2 and Aß1₋42-induced cytotoxicity. These results suggest that DBE may be a useful functional agent for the prevention against neurodegenerative disorders involving oxidative stress.

Neuroprotective effect of the proanthocyanidin-rich fraction in experimental model of spinal cord injury.

OBJECTIVES: In this study, we evaluated the effect of the proanthocyanidins-rich fraction (PRF) obtained from Croton celtidifolius bark in an experimental animal model of spinal cord injury and cell death induced by glutamate. METHODS: Experiments were conducted using adult male Wistar rats (10 weeks old and weighing 270-300g). Experimental groups were randomly allocated into the following groups: spinal cord injury (SCI) + vehicle group: rats were subjected to SCI plus intraperitoneal administration of vehicle (saline 10 ml/kg); SCI + PRF: rats were subjected to SCI plus intraperitoneal administration of PRF (10 mg/kg) at 1 and 6 h after injury and sham operated. KEY FINDINGS: The treatment with the proanthocyanidin-rich fraction significantly improved not only motor recovery and grip force but also H2 O2 or glutamate-induced cell death and reactive oxygen species generation induced by glutamate in dorsal root ganglion cells. In this study we demonstrate that the neuroprotective effect triggered by the proanthocyanidins-rich fraction appears to be mediated in part by the inhibition of N-methyl-D-aspartate-type glutamate receptors. CONCLUSIONS: Taken together, our results demonstrate that PRF treatment ameliorates spinal cord injury and glutamatergic excitotoxicity and could have a potential therapeutic use.

Neuroprotective effects of neolignans isolated from Magnoliae Cortex against glutamate-induced apoptotic stimuli in HT22 cells.

In the course of screening for neuroprotective natural products, Magnoliae Cortex showed potent inhibition of hippocampal neuronal HT22 cell death. Obovatol, honokiol, and magnolol were isolated from the ethanolic extract of Magnoliae Cortex. Isolated compounds obovatol, honokiol, and magnolol were protective against 5mM glutamate-induced cell death. When cells were stressed using glutamate, cell viability decreased to 16.98±4.58% over the control (100.00±10.15%). In contrast, 10 µM obovatol, 10 µM honokiol, and 50 µM magnolol increased cell viability to 91.80±1.70%, 93.59±1.93%, and 85.36±7.40%, respectively. The neuroprotective effects of obovatol and honokiol were attributable to the inhibition of intracellular reactive oxygen species production, followed by protection of the mitochondrial membrane potential (ΔΨm), recovery of Bcl-2 and Bid levels, inhibition of apoptosis-inducing factor expression, and phosphorylation of mitogen-activated protein kinases such as p38 kinases, extracellular signal-regulated kinases, and c-Jun N-terminal kinases. On the contrary, magnolol did not show any significant effect on the ΔΨm and apoptotic factors. Among three compounds, obovatol most strongly scavenged 2,2-diphenyl-1-picrylhydrazyl radicals and inhibited the elevation of intracellular reactive oxygen species levels in glutamate-stressed HT22 cells. These data suggest that obovatol and honokiol may have clinical applications for preventing neurodegenerative disorders.