• The Korean Journal of Physiology and Pharmacology
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• v.28 no.5
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• pp.413-422
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• 2024

Group I metabotropic glutamate receptors (mGluRs) modulate postsynaptic neuronal excitability and epileptogenesis. We investigated roles of group I mGluRs on low extracellular Mg²⁺ concentration ([Mg²⁺]_o)-induced epileptiform activity and neuronal cell death in the CA1 regions of isolated rat hippocampal slices without the entorhinal cortex using extracellular recording and propidium iodide staining. Exposure to Mg²⁺-free artificial cerebrospinal fluid can induce interictal epileptiform activity in the CA1 regions of rat hippocampal slices. MPEP, a mGluR 5 antagonist, significantly inhibited the spike firing of the low [Mg²⁺]_o-induced epileptiform activity, whereas LY367385, a mGluR1 antagonist, did not. DHPG, a group 1 mGluR agonist, significantly increased the spike firing of the epileptiform activity. U73122, a PLC inhibitor, inhibited the spike firing. Thapsigargin, an ER Ca²⁺-ATPase antagonist, significantly inhibited the spike firing and amplitude of the epileptiform activity. Both the IP₃ receptor antagonist 2-APB and the ryanodine receptor antagonist dantrolene significantly inhibited the spike firing. The PKC inhibitors such as chelerythrine and GF109203X, significantly increased the spike firing. Flufenamic acid, a relatively specific TRPC 1, 4, 5 channel antagonist, significantly inhibited the spike firing, whereas SKF96365, a relatively non-specific TRPC channel antagonist, did not. MPEP significantly decreased low [Mg²⁺]_o DMEM-induced neuronal cell death in the CA1 regions, but LY367385 did not. We suggest that mGluR 5 is involved in low [Mg²⁺]_o-induced interictal epileptiform activity in the CA1 regions of rat hippocampal slices through PLC, release of Ca²⁺ from intracellular stores and PKC and TRPC channels, which could be involved in neuronal cell death.

• The Korean Journal of Physiology and Pharmacology
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• v.26 no.6
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• pp.531-540
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• 2022

Group 1 metabotropic glutamate receptors (mGluRs) can positively affect postsynaptic neuronal excitability and epileptogenesis. The objective of the present study was to determine whether group 1 mGluRs might be involved in synaptically-induced intracellular free Ca²⁺ concentration ([Ca²⁺]_i) spikes and neuronal cell death induced by 0.1 mM Mg²⁺ and 10 µM glycine in cultured rat hippocampal neurons from embryonic day 17 fetal Sprague-Dawley rats using imaging methods for Ca²⁺ and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays for cell survival. Reduction of extracellular Mg²⁺ concentration ([Mg²⁺]_o) to 0.1 mM induced repetitive [Ca²⁺]_i spikes within 30 sec at day 11.5. The mGluR5 antagonist 6-Methyl2-(phenylethynyl) pyridine (MPEP) almost completely inhibited the [Ca²⁺]_i spikes, but the mGluR1 antagonist LY367385 did not. The group 1 mGluRs agonist, 3,5-dihydroxyphenylglycine (DHPG), significantly increased the [Ca²⁺]_i spikes. The phospholipase C inhibitor U73122 significantly inhibited the [Ca²⁺]_i spikes in the absence or presence of DHPG. The IP₃ receptor antagonist 2-aminoethoxydiphenyl borate or the ryanodine receptor antagonist 8-(diethylamino)octyl 3,4,5-trimethoxybenzoate also significantly inhibited the [Ca²⁺]_i spikes in the absence or presence of DHPG. The TRPC channel inhibitors SKF96365 and flufenamic acid significantly inhibited the [Ca²⁺]_i spikes in the absence or presence of DHPG. The mGluR5 antagonist MPEP significantly increased the neuronal cell survival, but mGluR1 antagonist LY367385 did not. These results suggest a possibility that mGluR5 is involved in synaptically-induced [Ca²⁺]_i spikes and neuronal cell death in cultured rat hippocampal neurons by releasing Ca²⁺ from IP₃ and ryanodine-sensitive intracellular stores and activating TRPC channels.

• International Journal of Oral Biology
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• v.34 no.4
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• pp.215-222
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• 2009

Medial vestibular nucleus (MVN) neurons are involved in the reflex control of the head and eyes, and in the recovery of vestibular function after the formation of peripheral vestibular lesions. In our present study, whole cell patch clamp recordings were carried out on MVN neurons in brainstem slices from neonatal rats to investigate the actions of a group I metabotropic glutamate receptor (mGluR) agonist upon synaptic transmission and ionic currents. Application of the mGluR I agonist (S)-3,5- dihydroxyphenylglycine (DHPG) increased the frequency of miniature inhibitory postsynaptic currents (mIPSCs) but had no effect upon amplitude distributions. To then identify which of mGluR subtypes is responsible for the actions of DHPG in the MVN, we employed two novel subtype selective antagonists. (S)-(+)-$\alpha$-amino-a-methylbenzeneacetic acid (LY367385) is a potent competitive antagonist that is selective for mGluR1, whereas 2-methyl-6-(phenylethynyl)-pyridine (MPEP) is a potent noncompetitive antagonist of mGluR5. Both LY367385 and MPEP antagonized the DHPG-induced increase of mIPSCs, with the former being more potent. DHPG was also found to induce an inward current, which can be enhanced under depolarized conditions. This DHPG-induced current was reduced by both LY367385 and MPEP. The DHPG-induced inward current was also suppressed by the PLC blocker U-73122, the $IP_3$ receptor antagonist 2-APB, and following the depletion of the intracellular $Ca^{2+}$ pool by thapsigargin. These data suggest that the DHPG-induced inward current may be mainly regulated by the intracellular $Ca^{2+}$ store via the PLC-$IP_3$ pathway. In conclusion, mGluR I, via pre- and postsynaptic actions, may modulate the excitability of the MVN neurons.

• 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.

• International Journal of Oral Biology
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• v.33 no.3
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• pp.97-103
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• 2008

The present study investigated the role of peripheral group I, II, and III metabotropic glutamate receptors (mGluRs) in mustard oil (MO)-induced nociceptive response in the masseter muscles of lightly anesthetized rats. Experiments were carried out on male Sprague-Dawley rats weighing 300-350 gm. After initial anesthesia with sodium pentobarbital (40 mg/kg, i.p.), one femoral vein was cannulated and connected to an infusion pump for intravenous infusion of sodium pentobarbital. The rate of infusion was adjusted to provide a constant level of anesthesia. MO (30 ${\mu}L$) was injected into the mid-region of the left masseter muscle via a 30-gauge needle over 10 seconds. After 30 mL injection of 5, 10, 15, or 20% MO into the masseter muscle, total number of hindpaw-shaking behavior was monitored. Intramuscular administration of MO significantly produced hindpawshaking behavior in a dose-dependent manner, as compared with the vehicle (mineral oil)-treated group. Intramuscular pretreatment with 10 or 100 ng DHPG, a group I mGluRs agonist, enhanced MO-induced hindpaw-shaking behavior, while APDC (20 or 200 ${\mu}g$), a group II mGluRs agonist, or L-AP4 (2 ${\mu}g$), a group III mGluRs agonist, significantly reduced MO-induced nociceptive behavior. The antinociception, produced by group II or III mGluRs agonists, was abolished by pretreatment with LY341495, a group II mGluRs antagonist, or CPPG, a group III mGluRs antagonist, res-pectively. Based on these observations, peripheral mGluRs differentially modulated MO-induced nociceptive behavior response in the craniofacial muscle pain and peripheral group II and III mGluRs agonists could be used in treatment of craniofacial muscle nociception.

• The Korean Journal of Pain
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• v.19 no.2
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• pp.131-136
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• 2006

Background: The aim of this study was to clarify the role of spinal groups II and III metabotropic glutamate receptors (mGluRs) with respect to postoperative pain at the spinal level. In addition, the nature of the pharmacological interaction between groups II and III mGluRs agonists and morphine was determined. Methods: Catheters were inserted into the intrathecal space of male SD rats. To induce postoperative pain, an incision was made in the plantar surface of the hind paw. A pharmacological characteristic for the interaction between groups II and III mGluRs agonists and morphine was evaluated using a fixed-dose analysis. Results: None of intrathecal group II and III mGluRs agonists modified the withdrawal threshold of the incisional pain. The administration of intrathecal morphine resulted in an increase of a dose dependent withdrawal threshold. A fixed-dose analysis revealed that the group III mGluRs agonist, ACPT-III, increased the antinociceptive action of morphine, while the group II mGluRs agonist, APDC, had no effect the antinociception of morphine. Conclusions: These results suggest that group II and III mGluRs may not play a direct modulatory role in the processing of postoperative pain at the spinal level. However, agonizing group III mGluRs may indirectly contributable to the potentiation of morphines antinociception in the spinal cord. Thus, the combination of morphine and a group III mGluRs agonist may be useful in the management of spinal postoperative pain.

• Proceedings of the Korean Society of Applied Pharmacology
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• 2008.04a
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• pp.33-45
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• 2008

Auditory fear memory is thought to be maintained by fear conditioning-induced potentiation of synaptic efficacy. The conditioning-induced potentiation has been shown to be maintained, at least in part, by enhanced expression of surface AMPA receptor (AMPAR) at excitatory synapses in the lateral amygdala (LA). Depotentiation, reversal of conditioning-induced potentiation, has been proposed as a cellular mechanism for fear extinction. However, a direct link between depotentiation and extinction has not yet been tested. To address this, we applied both ex vivo and in vivo approaches to rats in which fear memory had been consolidated. We found a novel form of ex vivo depotentiation; the depotentiation reversed conditioning-induced potentiation at thalamic input synapses onto the LA (T-LA synapses) ex vivo, and it could be induced only when both NMDA and metabotropic glutamate receptors were co-activated. Extinction returned the enhanced T-LA synaptic efficacy observed in conditioned rats to baseline and occluded the depotentiation. Consistently, extinction reversed conditioning-induced enhancement of surface expression of AMPAR subunits in LA synaptosomal preparations. A GluR2-derived peptide that blocks regulated AMPAR endocytosis inhibited depotentiation, and microinjection of a cell-permeable form of the peptide into the LA attenuated extinction. Our results are consistent with the use of depotentiation to weaken potentiated synaptic inputs onto the LA during extinction, and they provide strong evidence that AMPAR removal at excitatory synapses in the LA underlies extinction. The results described here are in line with previous findings. Neural activity in the LA has been shown to decrease after extinction in the rat and human. The NMDAR dependency of the depotentiation fits nicely with a large body of evidence that fear extinction depends upon amygdala NMDARs. Similarly, blockade of metabotropic glutamate recepotrs in the LA has recently been shown to attenuate fear extinction.

• Proceedings of the Korean Society of Veterinary Pathology Conference
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• 2005.11a
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• pp.95-96
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• 2005

• Proceedings of the Korean Society of Veterinary Pathology Conference
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• 2004.10a
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• pp.13-13
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• 2004

• Archives of Pharmacal Research
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• v.24 no.6
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• pp.613-617
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• 2001

The present study examined the hypothesis that NMDA, AMPA/Kainate, and metabotropic (mGlu) glutamate receptors contribute to a behavioral stimulation induced by activation of dopamine receptors by comparing responses in apomorphine-induced cage climbing behaviors in mice. MK-801, CNQX, and MCPG were served as the NMDA receptor, AMPA/Kainate receptor, and mGlu receptor antagonist, respectively, to elucidate the glutamatergic modulation in apomorphine-induced eopaminergic activation in mice. Drugs were administered intracerebroventricularly (i.c.v.) into the mouse brain 15 min before the apomorphine treatment (2 mg/kg, s.c.). 1.c.v. injection of MK-801 inhibited the apomorphine-induced cage climbing behavior dose-dependently. However, treatments with CNQX and MCPG did not any significant change in apomorphine-induced cage climbing behavior in mice. These results suggest that stimulation of NMDA type of glutamate receptors could contribute to the dopaminergic sti mutation, but not AMPA/Kainate and mGlu type glutamate receptors.