• The Korean Journal of Physiology and Pharmacology
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• v.20 no.4
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• pp.425-432
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• 2016

In addition to classical synaptic transmission, information is transmitted between cells via the activation of extrasynaptic receptors that generate persistent tonic current in the brain. While growing evidence supports the presence of tonic NMDA current ($I_{NMDA}$) generated by extrasynaptic NMDA receptors (eNMDARs), the functional significance of tonic $I_{NMDA}$ in various brain regions remains poorly understood. Here, we demonstrate that activation of eNMDARs that generate INMDA facilitates the ${\alpha}$-amino-3-hydroxy-5-methylisoxazole-4-proprionate receptor (AMPAR)-mediated steady-state current in supraoptic nucleus (SON) magnocellular neurosecretory cells (MNCs). In $low-Mg^{2+}$ artificial cerebrospinal fluid (aCSF), glutamate induced an inward shift in $I_{holding}$ ($I_{GLU}$) at a holding potential ($V_{holding}$) of -70 mV which was partly blocked by an AMPAR antagonist, NBQX. NBQX-sensitive $I_{GLU}$ was observed even in normal aCSF at $V_{holding}$ of -40 mV or -20 mV. $I_{GLU}$ was completely abolished by pretreatment with an NMDAR blocker, AP5, under all tested conditions. AMPA induced a reproducible inward shift in $I_{holding}$ ($I_{AMPA}$) in SON MNCs. Pretreatment with AP5 attenuated $I_{AMPA}$ amplitudes to ~60% of the control levels in $low-Mg^{2+}$ aCSF, but not in normal aCSF at $V_{holding}$ of -70 mV. $I_{AMPA}$ attenuation by AP5 was also prominent in normal aCSF at depolarized holding potentials. Memantine, an eNMDAR blocker, mimicked the AP5-induced $I_{AMPA}$ attenuation in SON MNCs. Finally, chronic dehydration did not affect $I_{AMPA}$ attenuation by AP5 in the neurons. These results suggest that tonic $I_{NMDA}$, mediated by eNMDAR, facilitates AMPAR function, changing the postsynaptic response to its agonists in normal and osmotically challenged SON MNCs.

• The Korean Journal of Physiology and Pharmacology
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• v.15 no.5
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• pp.285-289
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• 2011

Shilajit, a medicine herb commonly used in Ayurveda, has been reported to contain at least 85 minerals in ionic form that act on a variety of chemical, biological, and physical stressors. The substantia gelatinosa (SG) neurons of the trigeminal subnucleus caudalis (Vc) are involved in orofacial nociceptive processing. Shilajit has been reported to be an injury and muscular pain reliever but there have been few functional studies of the effect of Shilajit on the SG neurons of the Vc. Therefore, whole cell and gramicidin-perfotrated patch clamp studies were performed to examine the action mechanism of Shilajit on the SG neurons of Vc from mouse brainstem slices. In the whole cell patch clamp mode, Shilajit induced short-lived and repeatable inward currents under the condition of a high chloride pipette solution on all the SG neurons tested. The Shilajit-induced inward currents were concentration dependent and maintained in the presence of tetrodotoxin (TTX), a voltage gated $Na^+$ channel blocker, CNQX, a non-NMDA glutamate receptor antagonist, and AP5, an NMDA receptor antagonist. The Shilajit-induced responses were partially suppressed by picrotoxin, a $GABA_A$ receptor antagonist, and totally blocked in the presence of strychnine, a glycine receptor antagonist, however not affected by mecamylamine hydrochloride (MCH), a nicotinic acetylcholine receptor antagonist. Under the potassium gluconate pipette solution at holding potential 0 mV, Shilajit induced repeatable outward current. These results show that Shilajit has inhibitory effects on the SG neurons of Vc through chloride ion channels by activation of the glycine receptor and $GABA_A$ receptor, indicating that Shilajit contains sedating ingredients for the central nervous system. These results also suggest that Shilajit may be a potential target for modulating orofacial pain processing.

• The Korean Journal of Pain
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• v.23 no.1
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• pp.1-10
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• 2010

Background: Recent studies indicate that reactive oxygen species (ROS) are involved in persistent pain, including neuropathic and inflammatory pain. Since the data suggest that ROS are involved in central sensitization, the present study examines the levels of activated N-methyl-D-aspartate (NMDA) receptors in the dorsal horn after an exogenous supply of three antioxidants in rats with chronic post-ischemia pain (CPIP). This serves as an animal model of complex regional pain syndrome type-I induced by hindpaw ischemia/reperfusion injury. Methods: The application of tight-fitting O-rings for a period of three hours produced CPIP in male Sprague-Dawley rats. Allopurinol 4 mg/kg, allopurinol 40 mg/kg, superoxide dismutase (SOD) 4,000 U/kg, N-nitro-L-arginine methyl ester (L-NAME) 10 mg/kg and SOD 4,000 U/kg plus L-NAME 10 mg/kg were administered intraperitoneally just after O-ring application and on the first and second days after reperfusion. Mechanical allodynia was measured, and activation of the NMDA receptor subunit 1 (pNR1) of the lumbar spinal cord (L4-L6) was analyzed by the Western blot three days after reperfusion. Results: Allopurinol reduced mechanical allodynia and attenuated the enhancement of spinal pNR1 expression in CPIP rats. SOD and L-NAME also blocked spinal pNR1 in accordance with the reduced mechanical allodynia in rats with CPIP. Conclusions: The present data suggest the contribution of superoxide, produced via xanthine oxidase, and the participation of superoxide and nitric oxide as a precursor of peroxynitrite in NMDA mediated central sensitization. Finally, the findings support a therapeutic potential for the manipulation of superoxide and nitric oxide in ischemia/reperfusion related pain conditions.

• Journal of Life Science
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• v.15 no.3 s.70
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• pp.505-512
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• 2005

Excitotoxicity and epileptogenesis have often been associated with glutamate receptor activation. Accumulating evidences indicates that topiramate (TPM), an antiepileptic drug with multiple mechanisms of action has neuroprotective activity. We explored the neuroprotective effect of TPM on the status epilepticus (SE)-induced hippocampal neuronal death. After development of SE by kainite injection (15 mg/Kg), rats were treated with TPM (10mg/kg) for 1 week. The neuronal death was detected by Apop tag in situ detection kit, and the expression levels of glutamate receptors were semi-quantitatively analyzed by immunoblot. Kainate-induced SE caused a significant neuronal death and cell loss in CAI and CA3 regions of hippocampus at 1 week. However, treatment of TPM for 1 week after SE markedly reduced hippocampal neuronal death. The expression of N-methyl-D-aspartate (NMDA) receptor subunit 1, was increased by SE, but was not affected by 1 week treatment of TPM. The expressions of NMDA receptor subunit 2a and 2b were not changed by either SE or TPM. As for ${\alpha}-amino-3-hydroxy-5-methyl-4-isoxazole-propionate$ (AMPA) glutamate receptors (GluR), kainate-induced SE markedly up-regulated GluR1 expression but down-regulated GluR2 expression, leading to increased formation of $Ca^{2+}$ permeable GluR2- lacking AMPA receptors. TPM administration for 1 week attenuated SE-induced expression of both the up-regulation of GluR1 and down-regulation of GluR2, reversing the ratio of GluR1/GluR2 to the control value. In conclusion, TPM protects neuronal cell death against glutamate induced excitotoxicity in kainate-induced SE model, supporting the potential of TPM as a neuroprotective agent.

• The Journal of Korean Medicine
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• v.25 no.4
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• pp.51-60
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• 2004

Objective : The effect Saenggitang (GT), which has been used for amnesia, in Oriental Medicine, on memory and learning ability, was investigated. Methods : Hot water extracts (HWE) of SGT were used for the studies. In passive avoidance performances (step through test), active avoidance performances (lever press test), Motor activity, pentobarbital-induced sleep, 20 and 50 mg/100g of SGT-HWE ameliorated the memory retrieval deficit induced by 40% ethanol. Results : The SGT-HWE did not affect the ambulatory activity of normal mice in normal condition. 20 and 50 mg/100g of SGT-HWE enhanced contextual fear memory, but not cued fear memory in a fear conditioning task, which requires the activation of the NMDA (N-methyl-D-aspartase) receptor. SGT-HWE did not affect the motor activity measured by the titling type ambulometer test performed immediately and 24 hr after the administration. SGT-HWE prolonged the sleeping time induced by 50 mg/kg pentobarbital in mice and decreased SMA (spontaneous motor activity) in active avoidance performances (lever press test). Conclusion : These results indicate that the SGT-HWE have an improving effect on the memory retrieval disability induced by ethanol and may act as a stimulating factor for activating the NMDA receptor. and the SGT-HWE has a tranquilizing and anti-anxiety action.

• The Korean Journal of Physiology and Pharmacology
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• v.7 no.2
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• pp.53-57
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• 2003

The glutamate receptors (GluRs) are key receptors for modulatory synaptic events in the central nervous system. It has been reported that glutamate increases the intracellular $Ca^{2+}$ concentration ($[Ca^{2+}]_i$) and induces cytotoxicity. In the present study, we investigated whether the glutamate-induced $[Ca^{2+}]_i$ increase was associated with the activation of ionotropic (iGluR) and metabotropic GluRs (mGluR) in substantia gelatinosa neurons, using spinal cord slice of juvenile rats (10${\sim}21 day). $[Ca^{2+}]_i$ was measured using conventional imaging techniques, which was combined with whole-cell patch clamp recording by incorporating fura-2 in the patch pipette. At physiological concentration of extracellular $Ca^{2+}$, the inward current and $[Ca^{2+}]_i$ increase were induced by membrane depolarization and application of glutamate. Dose-response relationship with glutamate was observed in both $Ca^{2+}$ signal and inward current. The glutamate-induced $[Ca^{2+}]_i$ increase at holding potential of -70 mV was blocked by CNQX, an AMPA receptor blocker, but not by AP-5, a NMDA receptor blocker. The glutamate-induced $[Ca^{2+}]_i$ increase in $Ca^{2+}$ free condition was not affected by iGluR blockers. A selective mGluR (group I) agonist, RS-3,5-dihydroxyphenylglycine (DHPG), induced $[Ca^{2+}]_i$ increase at holding potential of -70 mV in SG neurons. These findings suggest that the glutamate-induced $[Ca^{2+}]_i$ increase is associated with AMPA-sensitive iGluR and group I mGluR in SG neurons of rats.

• Biomolecules & Therapeutics
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• v.20 no.1
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• pp.1-18
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• 2012

Schizophrenia is a devastating psychiatric illness that afflicts 1% of the population worldwide, resulting in substantial impact to patients, their families, and health care delivery systems. For many years, schizophrenia has been felt to be associated with dysregulated dopaminergic neurotransmission as a key feature of the pathophysiology of the illness. Although numerous studies point to dopaminergic abnormalities in schizophrenia, dopamine dysfunction cannot completely account for all of the symptoms seen in schizophrenia, and dopamine-based treatments are often inadequate and can be associated with serious side effects. More recently, converging lines of evidence have suggested that there are abnormalities of glutamate transmission in schizophrenia. Glutamatergic neurotransmission involves numerous molecules that facilitate glutamate release, receptor activation, glutamate reuptake, and other synaptic activities. Evidence for glutamatergic abnormalities in schizophrenia primarily has implicated the NMDA and AMPA subtypes of the glutamate receptor. The expression of these receptors and other molecules associated with glutamate neurotransmission has been systematically studied in the brain in schizophrenia. These studies have generally revealed region- and molecule-specifi c changes in glutamate receptor transcript and protein expression in this illness. Given that glutamatergic neurotransmission has been implicated in the pathophysiology of schizophrenia, recent drug development efforts have targeted the glutamate system. Much effort to date has focused on modulation of the NMDA receptor, although more recently other glutamate receptors and transporters have been the targets of drug development. These efforts have been promising thus far, and ongoing efforts to develop additional drugs that modulate glutamatergic neurotransmission are underway that may hold the potential for novel classes of more effective treatments for this serious psychiatric illness.

• Journal of Life Science
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• v.29 no.5
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• pp.564-569
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• 2019

Heavy drinking disrupts the nervous system by activation of GABA receptors and inhibition of glutamate receptors, thereby preventing short-term memory formation. Degradation of cognition by alcohol induces blackouts, and it can lead to alcoholic dementia if repeated. Therefore, drugs need to be developed to prevent alcohol-induced blackout. In this study, we confirmed the effect of an ethanol extract of Cassia obtusifolia seeds (COE) on alcohol-induced memory impairment. The effects of COE and ethanol on cognitive functions mice were examined using the passive avoidance and Y-maze tests. The manner in which alcohol affects long-term potentiation (LTP) in relation to the learning and memory was confirmed by electrophysiology performed on mouse hippocampal slices. We also measured N-methyl-D-aspartate (NMDA) receptor-mediated field excitatory synapses (fEPSPs), which have a known association with cognitive impairment caused by ethanol. Ethanol caused memory impairments in passive avoidance and Y-maze tests. COE prevented these ethanol-induced memory impairments in these tests. Ethanol also blocked LTP induction in the mouse hippocampus, and COE prevented this ethanol-induced LTP deficit. Ethanol decreased NMDA receptor-mediated fEPSPs in the mouse hippocampus, and this decrease was prevented by COE. These results suggest that COE might be useful in preventing alcohol-induced neurological dysfunctions, including blackouts.

• The Korean Journal of Physiology and Pharmacology
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• v.20 no.4
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• pp.399-406
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• 2016

Early life neuronal exposure to environmental toxicants has been suggested to be an important etiology of neurodegenerative disease development. Perfluorohexanesulfonate (PFHxS), one of the major perfluoroalkyl compounds, is widely distributed environmental contaminants. We have reported that PFHxS induces neuronal apoptosis via ERK-mediated pathway. Imperatorin is a furanocoumarin found in various edible plants and has a wide range of pharmacological effects including neuroprotection. In this study, the effects of imperatorin on PFHxS-induced neuronal apoptosis and the underlying mechanisms are examined using cerebellar granule cells (CGC). CGC were isolated from seven-day old rats and were grown in culture for seven days. Caspase-3 activity and TUNEL staining were used to determine neuronal apoptosis. PFHxS-induced apoptosis of CGC was significantly reduced by imperatorin and PD98059, an ERK pathway inhibitor. PFHxS induced a persistent increase in intracellular calcium, which was significantly blocked by imperatorin, NMDA receptor antagonist, MK801 and the L-type voltage-dependent calcium channel blockers, diltiazem and nifedipine. The activation of caspase-3 by PFHxS was also inhibited by MK801, diltiazem and nifedipine. PFHxS-increased ERK activation was inhibited by imperatorin, MK801, diltiazem and nifedipine. Taken together, imperatorin protects CGC against PFHxS-induced apoptosis via inhibition of NMDA receptor/intracellular calcium-mediated ERK pathway.

• The Korean Journal of Physiology and Pharmacology
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• v.5 no.1
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• pp.19-25
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• 2001

We have studied the effects of excitatory amino acids on the expression of the c-fos and c-jun mRNA in rat C6 glioma cells. The glutamate, $N-methyl-_D-aspartate$ (NMDA), and kainic acid (KA) increased c-fos mRNA level in a concentration-dependent manner. However, they did not affect c-jun mRNA level. In addition, forskolin and phorbol 12-myristate 13-acetate (PMA) increased c-fos mRNA level. Furthermore, PMA increased c-jun mRNA level whereas forskolin downregulated c-jun mRNA level. The glutamate, NMDA and KA, at a concentration of 0.25 mM, did not affect the basal c-fos and c-jun mRNA levels, and also did not affect forskolin- and PMA-induced responses. Furthermore, both forskolin and PMA itself increased the phosphorylation of ERK (extracellular signal regulated kinase) and CREB (cyclicAMP responsible element binding protein) proteins. The KA, NMDA, and glutamate did not affect forskolin- induced increase of ERK and CREB phosphorylation. The KA decreased PMA-induced increase of phosphorylation of ERK and CREB proteins, whereas glutamate and NMDA did not affect the phosphorylation of ERK and CREB proteins induced by PMA. These findings suggest that, in C6 glioma cells, c-fos mRNA induction induced by EAAs is not mediated by phosphorylation of ERK and CREB proteins.