Role Of mGluR5 Research Articles

Blockade of mGluR5 in nucleus accumbens modulates calcium sensor proteins, facilitates extinction, and attenuates reinstated morphine place preference in rats

Numerous findings confirm that the metabotropic glutamate receptors (mGluRs) are involved in the conditioned place preference (CPP) induced by morphine. Here we focused on the role of mGluR5 in the nucleus accumbens (NAc) as a main site of glutamate action on the rewarding effects of morphine. Firstly, we investigated the effects of intra-NAc administrating mGluR5 antagonist 3-((2-Methyl-1,3-thiazol-4-yl) ethynyl) pyridine hydrochloride (MTEP; 1, 3, and 10 μg/μl saline) on the extinction and the reinstatement phase of morphine CPP. Moreover, to determine the downstream signaling cascades of mGluR5 in morphine CPP, the protein levels of stromal interaction molecules (STIM1 and 2) in the NAc and hippocampus (HPC) were measured by western blotting. The behavioral data indicated that the mGluR5 blockade by MTEP at the high doses of 3 and 10 μg facilitated the extinction of morphine-induced CPP and attenuated the reinstatement to morphine in extinguished rats. Molecular results showed that the morphine led to increased levels of STIM proteins in the HPC and increased the level of STIM1 without affecting STIM2 in the NAc. Furthermore, intra-NAc microinjection of MTEP (10 μg) in the reinstatement phase decreased STIM1 in the NAc and HPC and reduced the STIM2 in the HPC. Collectively, our data show that morphine could facilitate brain reward function in part by increasing glutamate-mediated transmission through activation of mGluR5 and modulation of STIM proteins. Therefore, these results highlight the therapeutic potential of mGluR5 antagonists in morphine use disorder.

Metabotropic glutamate receptor 5-mediated inhibition of inward-rectifying K+ channel 4.1 contributes to orofacial ectopic mechanical allodynia following inferior alveolar nerve transection in male mice.

Inward-rectifying K+ channel 4.1 (Kir4.1), which regulates the electrophysiological properties of neurons and glia by affecting K+ homeostasis, plays a critical role in neuropathic pain. Metabotropic glutamate receptor 5 (mGluR5) regulates the expression of Kir4.1 in retinal Müller cells. However, the role of Kir4.1 and its expressional regulatory mechanisms underlying orofacial ectopic allodynia remain unclear. This study aimed to investigate the biological roles of Kir4.1 and mGluR5 in the trigeminal ganglion (TG) in orofacial ectopic mechanical allodynia and the role of mGluR5 in Kir4.1 regulation. An animal model of nerve injury was established via inferior alveolar nerve transection (IANX) in male C57BL/6J mice. Behavioral tests indicated that mechanical allodynia in the ipsilateral whisker pad lasted at least 14 days after IANX surgery and was alleviated by the overexpression of Kir4.1 in the TG, as well as intraganglionic injection of an mGluR5 antagonist (MPEP hydrochloride) or a protein kinase C (PKC) inhibitor (chelerythrine chloride); Conditional knockdown of the Kir4.1 gene downregulated mechanical thresholds in the whisker pad. Double immunostaining revealed that Kir4.1 and mGluR5 were co-expressed in satellite glial cells in the TG. IANX downregulated Kir4.1 and upregulated mGluR5 and phosphorylated PKC (p-PKC) in the TG; Inhibition of mGluR5 reversed the changes in Kir4.1 and p-PKC that were induced by IANX; Inhibition of PKC activation reversed the downregulation of Kir4.1 expression caused by IANX (p < .05). In conclusion, activation of mGluR5 in the TG after IANX contributed to orofacial ectopic mechanical allodynia by suppressing Kir4.1 via the PKC signaling pathway.

The selective blockade of metabotropic glutamate receptor-5 attenuates fat accumulation in an in vitro model of benign steatosis.

It has been previously found that the blockade of metabotropic glutamate receptor type 5 (mGluR5) protects against hepatic ischemia/reperfusion injury and acetaminophen toxicity. The role of mGluR5 in NAFLD has not yet been elucidated. Here, we evaluated the effects of mGluR5 blockade in an in vitro model of steatosis. HepG2 cells were pre-incubated for 12 h with an mGluR5 agonist, a negative allosteric modulator (DHPG and MPEP, respectively) or vehicle, then treated with 1.5 mM oleate/palmitate (O/P) for another 12 h. Cell viability was evaluated with the MTT assay; fat accumulation was measured using the fluorescent dye Nile red; SREBP- 1, PPAR-α, iNOS and Caspase-3 protein expression were evaluated by Western blot; NFkB activity was evaluated as pNFkB/NFkB ratio. mGluR5 modulation did not alter cell viability in O/P-incubated cells; MPEP prevented intracellular lipid accumulation in O/P treated cells; MPEP administration was also associated with a reversion of O/P-induced changes in SREBP-1 and PPAR-α expression, involved in free fatty acid metabolism and uptake. No changes were observed in iNOS and caspase-3 expression, or in NFkB activity. In conclusion, mGluR5 pharmacological blockade reduced fat accumulation in HepG2 cells incubated with O/P, probably by modulating the expression of SREBP-1 and PPAR-α.

4395 alpha-Synuclein Induced Reactive Gliosis

OBJECTIVES/GOALS: Reactive gliosis is a hallmark of neurodegenerative disease and is characterized by the release of pro-inflammatory cytokines and physiologic changes to glial cells. Our work identifies a novel inflammatory glial-glial cell interaction and role for mGluR5 that has the potential to provide novel insight into the mechanisms of neurodegeneration. METHODS/STUDY POPULATION: Cell Culture: Mouse primary astrocytes and microglia were isolated from P0-P3 C57BL/6 or Cx3cr1GFP/+ mice.1Treatment: Glia were treated with oligomeric α-synuclein 1μg/mL or mGluR5 agonist CHPG 100 μM.2,3ELISA: Glia culture media was collected and analyzed according to the manufacturer. qRT-PCR: TaqMan™ probes were used according to manufacturer on extracted glia mRNA. ICC: Microglia were labeled with 1:750 Rb x Iba1 (Wako) and 1:500 Alexa Fluor 488 Gt x Rb. Phagocytosis Assay: Primary glia were treated with α-synuclein or astrocyte-conditioned culture media for 24-48hrs. For treatment of microglia with conditioned media, astrocytes were washed with PBS and fresh media was added to prevent carry over of α-synuclein to microglia. The number of fluorescent microbeads per microglia was quantified. RESULTS/ANTICIPATED RESULTS: Mouse primary cortical astrocytes simulated with α-synuclein aggregates adopt a reactive A1 phenotype independent of microglial stimulation. This A1 phenotype is characterized by release of pro-inflammatory cytokines including Complement Component 3 and the monocyte chemoattractant CCL2. Reactive astrocyte media induces a phagocytic phenotype in primary mouse microglia. Along with this, α-synuclein-directed microglial phagocytosis was attenuated with the addition of the mGluR5 agonist CHPG. DISCUSSION/SIGNIFICANCE OF IMPACT: Our findings suggest that oligomeric α-synuclein is capable of inducing a reactive phenotype in astrocytes independent of microglia and implicate crosstalk between glia as an important mediator of inflammation and microglial phagocytosis in synucleinopathies.

Role of mGluR 1 in synaptic plasticity impairment induced by maltol aluminium in rats

The main symptoms of Alzheimer's disease (AD) is the loss of learning and memory ability, of which biological basis is synaptic plasticity. Aluminium has been found to cause changes in synaptic plasticity, but its molecular mechanism was unclear. In this study, Sprague-Dawley rats were injected with aluminium maltol (Al(mal)3) through the lateral ventricle to establish an AD-like model. Y-maze, electrophysiological measurements, Golgi staining, scanning electron microscopy, quantitative real-time polymerase chain reaction, and western blot techniques were used to investigate regulation of the metabolic glutamate receptor 1 (mGluR1) in synaptic plasticity impairment induced by Al(mal)3. The results showed that Al(mal)3 inhibited the induction and maintenance of long-term potentiation in the hippocampal CA1 region. During this process, the expression of mGluR1 was up-regulated and it inhibited the expression and phosphorylation of the N-methyl-D-aspartic acid receptors (NMDARs). This mainly affected NMDAR1 and NMDAR2B but did not affect protein kinase C expression.

PD24-03 ACTIVATION OF GROUP I AND III METABOTROPIC GLUTAMATE RECEPTORS INFLUENCES THE MICTURITION REFLEX IN URETHANE-ANESTHETIZED RATS

You have accessJournal of UrologyBladder & Urethra: Anatomy, Physiology & Pharmacology II (PD24)1 Apr 2020PD24-03 ACTIVATION OF GROUP I AND III METABOTROPIC GLUTAMATE RECEPTORS INFLUENCES THE MICTURITION REFLEX IN URETHANE-ANESTHETIZED RATS Masashi Honda*, Ryutaro Shimizu, Shogo Teraoka, Ryoma Nishikawa, Yusuke Kimura, Panagiota Tsounapi, Hideto Iwamoto, Shuichi Morizane, Katsuya Hikita, and Atsushi Takenaka Masashi Honda*Masashi Honda* More articles by this author , Ryutaro ShimizuRyutaro Shimizu More articles by this author , Shogo TeraokaShogo Teraoka More articles by this author , Ryoma NishikawaRyoma Nishikawa More articles by this author , Yusuke KimuraYusuke Kimura More articles by this author , Panagiota TsounapiPanagiota Tsounapi More articles by this author , Hideto IwamotoHideto Iwamoto More articles by this author , Shuichi MorizaneShuichi Morizane More articles by this author , Katsuya HikitaKatsuya Hikita More articles by this author , and Atsushi TakenakaAtsushi Takenaka More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000000881.03AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: The modulatory effects of glutamate are mediated by activation of metabotropic glutamate receptors (mGluRs). Eight mGluRs (mGluR1−8) have been classified into three groups (I−III) according to their sequence homology. Group I (mGluRI; mGluR1 and mGluR5), group II (mGluRII; mGluR2 and mGluR3), and group III (mGluRIII; mGluR4, mGluR6, mGluR7, and mGluR8) mGluRs are widely distributed throughout the central nervous system. However, the role of mGluRs in the regulation of neural mechanisms controlling the micturition reflex remains unknown. Therefore, we assessed whether RS-3,5-dihydroxyphenylglycine (RS-3,5-DHPG), a selective mGluRI agonist, 2R,4R-4-aminopyrrolidine-2,4-dicarboxylate (2R,4R-APDC), a selective mGluRII agonist, and L-(+)-2-amino-4-phosphonobutyric acid (L-AP4), a selective mGluRIII agonist, affect the micturition reflex in urethane-anesthetized rats. METHODS: Adult female Sprague-Dawley rats weighing 242 to 268 g were used. Continuous cystometrograms were performed for two groups of urethane-anesthetized rats. The first group of 54 rats was used for intracerebroventricular administration of 1−10 µg of RS-3,5-DHPG, 2R,4R-APDC, or L-AP4 via a catheter inserted into the lateral ventricle. In the second group of 54 rats, 1−10 μg of RS-3,5-DHPG, 2R,4R-APDC, or L-AP4 was administered via an intrathecal catheter. Cystometric parameters were recorded and compared before and after drug administration. RESULTS: Intracerebroventricular administration of RS-3,5-DHPG at doses of 1, 3, and 10 µg (n = 6 per dose) increased the intercontraction interval in a dose-dependent manner to 111.8 ± 9.4%, 121.8 ± 8.7%, and 129.2 ± 10.7% of the control value, respectively (p < 0.01). Intracerebroventricular administration of L-AP4 at doses of 1, 3, and 10 µg (n = 6 per dose) showed similar effects, with the intercontraction interval increasing to 115.3 ± 11.5%, 128.6 ± 9.5%, and 132.2 ± 13.6% of the control value, respectively (p < 0.01). Intrathecal administration of RS-3,5-DHPG and L-AP4 at doses of 1, 3, and 10 µg (n = 6 per dose) also increased the intercontraction interval in a dose-dependent manner. However, intracerebroventricular or intrathecal administration of 2R,4R-APDC did not affect the intercontraction interval, maximum voiding pressure, or baseline pressure at any tested dose. CONCLUSIONS: These results indicate that activation of mGluRI and mGluRIII could inhibit the spinal and supraspinal micturition reflexes in urethane-anesthetized rats. Source of Funding: None © 2020 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 203Issue Supplement 4April 2020Page: e533-e533 Advertisement Copyright & Permissions© 2020 by American Urological Association Education and Research, Inc.MetricsAuthor Information Masashi Honda* More articles by this author Ryutaro Shimizu More articles by this author Shogo Teraoka More articles by this author Ryoma Nishikawa More articles by this author Yusuke Kimura More articles by this author Panagiota Tsounapi More articles by this author Hideto Iwamoto More articles by this author Shuichi Morizane More articles by this author Katsuya Hikita More articles by this author Atsushi Takenaka More articles by this author Expand All Advertisement PDF downloadLoading ...

Role of mGluR5 in laterocapcular division of central nucleus of amygdala in fentanyl-induced hyperalgesia in rats

To investigate the role of metabotropic glutamate receptor 5 (mGluR5) in laterocapcular division of the central nucleus of amygdala (CeLC) in fentanyl-induced hyperalgesia in rats. Methods: A total of 12 Sprague-Dawley male rats (60-100 g) were randomly divided into a normal group 1 (n=6) and an opioid-induced hyperalgesia (OIH) group 1 (n=6). The OIH group 1 was injected with fentanyl through the lower neck skin to build OIH model, and the normal group 1 was given the same volume of saline. After 6.5 h, paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL) were tested to verify the success of the induction of OIH. Then rats were sacrificed and the right CeLC tissue were taken for detection of the mGluR5 by Western blotting. Forty SD male rats were randomly divided into 4 groups (n=10 each): an OIH+DMSO, an OIH+MTEP (3.0 μg), an OIH+MTEP (7.5 μg) and an OIH+MTEP (15.0 μg) group. MTEP was a selective antagonist of mGluR5. Catheterization in the right CeLC was first performed. After one-week recovery, OIH was induced. Then 0.5 μL DMSO, MTEP 3.0 μg, MTEP 7.5 μg and MTEP 15.0 μg were administrated through the CeLC catheter accordingly. PWMT and PWTL were tested at pre-OIH, 6 h after OIH and post-drug. Then the expression levels of mGluR5 of CeLC tissue were analyzed by Western blotting. Another 8 SD male rats were randomly divided into a normal group 2 and an OIH group 2 (n=4 each). The rats were induced OIH by injecting of fentanyl while rats in the normal group 2 were injected with same volume of saline. The miniature excitatory postsynaptic currents (mEPSCs) of the 2 groups' neurons in the right CeLC region were recorded by whole cell voltage-clamp before and after the administration of MTEP in brain slice. Results: Compared with the normal group 1, the PWTL and PWMT were significantly decreased and the expression of mGluR5 was apparently increased in the OIH group 1 (P<0.05). The PWMT and PWTL were significantly decreased in each group and indicated success of OIH model (P<0.05). The expression of mGluR5 in the CeLC was increased. MTEP reversed these changes in a dose-dependent way (P<0.05). Compared with the normal group 2, the amplitude and frequency of mEPSCs in the OIH group 2 were significantly increased (P<0.05) and they were reversed by MTEP (P<0.05). Conclusion: mGluR5 in the CeLC may be involved in the maintenance of OIH. Inhibition of the activity of mGluR5 in the CeLC may alleviate the symptoms of fentanyl-induced hyperalgesia.

Unchanged type 1 metabotropic glutamate receptor availability in patients with Alzheimer's disease: A study using 11C-ITMM positron emission tomography.

Imaging of type 1 metabotropic glutamate receptor (mGluR1) has recently become possible using positron emission tomography (PET). To date, little evidence exists on the role of mGluR1 in the pathophysiology of Alzheimer's disease (AD). We aimed to examine mGluR1 availability in patients with AD. Ten patients with AD (78.9 ± 5.9 years) and 12 age-matched volunteers (74.6 ± 2.6 years) underwent PET using an mGluR1 radiotracer. All patients were anti-dementia drug-naive. Volumes-of-interest were placed on the anterior and posterior lobes and vermis in the cerebellum and frontal, parietal, and temporal cortices. The binding potential (BPND) was calculated to estimate mGluR1 availability, and partial volume correction was applied to the BPND values. Mini Mental State Examination (MMSE) scores were also obtained (22.0 ± 4.8). No significant difference was observed in BPND between the AD and control groups in the anterior lobe (p = .30), posterior lobe (p = .95), vermis (p = .96), frontal cortex (p = .61), parietal cortex (p = .59), or temporal cortex (p = .27). No significant correlation was observed between BPND and MMSE scores in the anterior lobe (p = .59), posterior lobe (p = .35), vermis (p = .92), frontal cortex (p = .78), parietal cortex (p = .83), or temporal cortex (p = .82). In conclusions, this study suggests that mGluR1 availability is unchanged in the relatively early stage of AD. However, because regional mGluR1 availability may change with the progression of AD, further longitudinal follow-up is necessary.

Endocannabinoid Signaling in Embryonic Neuronal Motility and Cell–Cell Contact – Role of mGluR5 and TRPC3 Channels

Cell–cell communication plays a central role in the guidance of migrating neuronal precursor cells during the development of the cerebral cortex. Endocannabinoids (eCBs) have previously been shown to be one of the central factors regulating neuronal migration. In this study the effects of eCBs on different parameters, expected to affect embryonic cortical neuronal motility have been analyzed in neurosphere-derived neuroblasts using time-lapse microscopy. Increased endogenous production of the endocannabinoid 2-arachidonyl glycerol (2-AG) causes bursts of neuroblast motility. The neuroblasts move longer distances and show a low frequency of turning, and the number of neuron–neuron contacts are reduced. Similar changes occur interfering with the function of the metabotropic glutamate receptor 5 (mGluR5) or its transducer canonical transient receptor potential channel 3 (TRPC3) or the neuregulin receptor ErbB4. Blocking of 2-AG production reverses these effects. The data suggest that eCB-regulated neuronal motility is controlled by mGluR5/TRPC3 activity possibly via NRG/ErbB4 signaling.

Metabotropic glutamate receptor 5 deficiency inhibits neutrophil infiltration after traumatic brain injury in mice

Both brain native inflammatory cells and infiltrated peripheral white blood cells (WBCs) are primary participants in the brain inflammatory damage post-TBI. Metabotropic glutamate receptor 5 (mGluR5) has been reported to regulate microglias and astrocytes to affect inflammation after TBI, but its effect on modulating infiltrated peripheral WBCs remains unclear. In a mouse moderate TBI model, we found that mGluR5 knockout (KO) significantly reduced neutrophil infiltration and inflammatory cytokine expression in the brain at 24 hours post TBI, which was accompanied by improved neurological dysfunction. Further investigation indicated that mGluR5 KO reduced the permeability of blood-brain barrier (BBB), the entrance for neutrophils to enter brain, and markedly decreased the mRNA levels of neutrophil-associated chemokines in brain tissue, including CXCL1, CXCL2, CCL2, CCL4 and CCL5. Using brain microvascular endothelial cells (BMECs), neutrophils and a BBB model in vitro, we confirmed the inhibitory effect of mGluR5 deficiency on neutrophil infiltration and demonstrated that blockade of protein kinase C (PKC) signaling was involved in it. These results provide insight into the role of mGluR5 in the regulation of inflammation in the acute phase of TBI, which may provide novel clues for TBI therapy.

Abstract 1886: mGluR1 drives invasion of proneural subtype of glioblastoma cells

Abstract A major cause for the therapeutic failure and subsequent morbidity and mortality of glioblastoma (GBM) is the aggressive invasion of malignant cells into the surrounding normal brain that effectively renders complete surgical resection impossible and virtually assures recurrent tumor growth. Multi-omic profiling of GBM led to their molecular sub-classification into two distinct molecular subtypes: proneural (PN) and mesenchymal (MES). However, very little is known about shared or distinct invasion processes of cells in these genomically different subtypes. Using Microarray gene expression profiles of microdissected paired stationary core and invasive rim samples from 19 patients, we demonstrated that invasive gene signature of MES subtypes differs from PN. Specifically, using three orthogonal but intersecting bioinformatic approaches, i.e. gene set variation analysis, causal network analysis, and iRegulon analysis; we discovered that genes differentially expressed between PN core and rim could, to a meaningful degree, be accounted for based on their annotation as “regulated by the transcription factor REST”. REST functions as a repressor of gene expression. Of the genes repressed by REST, mGluR1 (Metabotropic Glutamate Receptor 1) was significantly overexpressed at the rim of PN glioma cells as compared to the core. Finally, we also investigated the role of mGluR1 in glutamate induced glioma cell migration; our results show that glutamate stimulates migration of proneural-like glioma cells (A172) as compare to non-proneural-like glioma cell (T98G). mGluR1 activation by glutamate has shown to induce activation of Pyk2 and Src in astrocytes; knockout of mGluR1 is not embryonic lethal. In summary, our data demonstrate that glutamate-induced glioma cell migration of PN subtype of GBM is dependent on mGluR1 and thus raises the prospect that therapeutic targeting of mGluR1 may be a novel approach to controlling the invasion of this deadly disease. Citation Format: Alena Gladwin, Sen Peng, Jeff Kiefer, Seugchan Kim, Michael Berens, Harshil D. Dhruv. mGluR1 drives invasion of proneural subtype of glioblastoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1886. doi:10.1158/1538-7445.AM2017-1886

Increased Metabotropic Glutamate Receptor 5 Signaling Underlies Obsessive-Compulsive Disorder-like Behavioral and Striatal Circuit Abnormalities in Mice

BackgroundDevelopment of treatments for obsessive-compulsive disorder (OCD) is hampered by a lack of mechanistic understanding about this prevalent neuropsychiatric condition. Although circuit changes such as elevated frontostriatal activity are linked to OCD, the underlying molecular signaling that drives OCD-related behaviors remains largely unknown. Here, we examine the significance of type 5 metabotropic glutamate receptors (mGluR5s) for behavioral and circuit abnormalities relevant to OCD. MethodsSapap3 knockout (KO) mice treated acutely with an mGluR5 antagonist were evaluated for OCD-relevant phenotypes of self-grooming, anxiety-like behaviors, and increased striatal activity. The role of mGluR5 in the striatal circuit abnormalities of Sapap3 KO mice was further explored using two-photon calcium imaging to monitor striatal output from the direct and indirect pathways. A contribution of constitutive signaling to increased striatal mGluR5 activity in Sapap3 KO mice was investigated using pharmacologic and biochemical approaches. Finally, sufficiency of mGluR5 to drive OCD-like behavior in wild-type mice was tested by potentiating mGluR5 with a positive allosteric modulator. ResultsExcessive mGluR5 signaling underlies OCD-like behaviors and striatal circuit abnormalities in Sapap3 KO mice. Accordingly, enhancing mGluR5 activity acutely recapitulates these behavioral phenotypes in wild-type mice. In Sapap3 KO mice, elevated mGluR5 signaling is associated with constitutively active receptors and increased and imbalanced striatal output that is acutely corrected by antagonizing striatal mGluR5. ConclusionsThese findings demonstrate a causal role for increased mGluR5 signaling in driving striatal output abnormalities and behaviors with relevance to OCD and show the tractability of acute mGluR5 inhibition to remedy circuit and behavioral abnormalities.

Effects of groupImetabotropic glutamate receptor on the synaptic transmission efficiency of the neurons in primary visual cortex of monocular form deprivated rats

Background The formation of amblyopia is closely associated with glutamate receptors of visual cortex, and researches determined that the expression of metabolic glutamate receptor 1 (mGluR1) in the visual cortex of amblyopic rats is down-regulated.However, the effect of mGluR1 on synaptic transmission of neurons in the visual cortex is unclear. Objective This study was to investigate the role of mGluR1 in the synaptic transmission efficiency of neurons in the primary visual cortex of monocular form-deprivated rats. Methods Sixteen 14-day-old SD rats were randomly divided into normal control group and form-deprivation group, with 8 rats in each group.The eyelids of the left eyes were sutured to establish the monocular form-deprivation models in the rats of the form-deprivation group, and the visual cortex slices were prepared until 31 days after modeling and incubated in artificial cerebrospinal fluid with 3, 5-dihydroxyphenylglycine (DHPG), LY367385+ DHPG, 2-methyl-6-(phenyl acetylene) pyridine hydrochloride(MPEP)+ DHPG and LY367385+ MPEP+ DHPG, respectively.The field excitatory postsynaptic potential (fEPSP) of neurons in the visual cortex of V1 area was detected by extracellular microelectrode recording.The use and care of the animals followed the statement for the Use of Animals in Ophthalmic and Vision Research. Results The slope value before drug treatment was set as 100%, the fEPSP-slopes of the normal control group and the form-deprivation group were increased to (136.4±17.3)% and (120.7±12.8)% after DHPG induction with significant difference between the two groups (t=2.280; P<0.05). The fEPSP-slopes of the normal control group were (114.9±9.3)% and (112.6±15.3)% after LY367385 and MPEP treatment, and those of the form-deprivation group were (107.3±6.0)% and (110.1±4.1)%, which were significantly lower than those after DHPG induction (normal control group: t=2.641, 2.915; both at P<0.05; form-deprivation group: t=2.410, 2.372; both at P<0.05). The fEPSP-slopes of the normal control group and the form-deprivation group were (104.5±2.2)% and (102.8±14.9)% after LY367385+ MPEP treatment, which were lower than that after DHPG induction (t=3.080, 2.306; both at P<0.05). Conclusions The effect of mGluR1 on the synaptic transmission of neurons in the visual cortex weakens after monocular form-deprivation in rats.Both mGluR1 and mGluR5 participate in the neuronic synaptic transmission on visual cortex area and appear to be equivalent contribution. Key words: Electrophysiology; Excitatory amino acid agonists/pharmacology; Excitatory amino acid antagonists/pharmacology; Phenylacetates/pharmacology; Receptors, metabotropic glutamate/physiology; Visual cortex/growth & development; Neuronic synaptic transmission/drug effect; Form deprivation; Rats, SD

Acute inhibition of mGluR5 disrupts behavioral flexibility

Conditioned cues can sometimes elicit maladaptive responses as seen in the post-traumatic stress disorder (PTSD). Lack of effective fear extinction, which involves a process of inhibitory learning, is hypothesized to associate with PTSD. In this study, we tested the effect of acute pharmacological inhibition of mGluR5 activity on the extinction of fear memory and spatial memory. Intraperitoneal injection of the mGluR5 (metabotropic glutamate receptor 5) antagonist MPEP [2-Methyl-6-(phenylethynyl) pyridine hydrochloride] allowed the retrieval but prevented the extinction of contextual fear memory in mice. Without altering locomotor activity, MPEP inhibited the acquisition but not the consolidation of contextual fear memory. Further, administration of MPEP blocked the extinction of spatial memory in the Morris water maze paradigm. Our data suggest a necessary role of mGluR5 in regulating certain aspects of behavioral flexibility.

Activation of mGluR5 Attenuates Microglial Activation and Neuronal Apoptosis in Early Brain Injury After Experimental Subarachnoid Hemorrhage in Rats.

Activation of metabotropic glutamate receptor 5 (mGluR5) provided neuroprotection in multiple central nervous system injury, but the roles of mGluR5 in subarachnoid hemorrhage (SAH) remain unclear. In present study, we aimed to evaluate whether activation of mGluR5 attenuates early brain injury (EBI) after experimental SAH in rats. We found that selective mGluR5 orthosteric agonist CHPG or positive allosteric modulator VU0360172 administration significantly improves neurological function and attenuates brain edema at 24 h after SAH. Furthermore, mGluR5 obviously expresses in activated microglia (ED-1 positive) after SAH. CHPG or VU0360172 administration significantly reduces the numbers of activated microglia and the protein and mRNA levels of pro-inflammatory cytokines IL-1β, IL-6 and TNF-α at 24 h after SAH. Moreover, CHPG or VU0360172 administration obviously reduces the number of TUNEL-positive cells and active caspase-3/NeuN-positive neurons in cortex at 24 h after SAH. CHPG or VU0360172 administration significantly up-regulates the expression of Bcl-2, and down-regulates the expression of Bax and active caspase-3, which in turn increases the ratio of Bcl-2/Bax. Our results indicate that activation of mGluR5 attenuates microglial activation and neuronal apoptosis, and improves neurological function in EBI after SAH.

MGluR5 in the nucleus accumbens shell regulates morphine-associated contextual memory through reactive oxygen species signaling.

Emerging evidence indicates that metabotropic glutamate receptor 5 (mGluR5) critically modulates drug and drug-related behaviors. However, the role of mGluR5 in the opiate-induced contextual memory remains unclear. Here, we found that microinfusion of the mGluR5 antagonist 3-((2-Methyl-1,3-thiazol-4-yl)ethynyl)pyridine (MTEP) into the nucleus accumbens (NAc) shell, but not into the core, significantly attenuated the expression of morphine conditioned place preference (CPP) in rats. Following the expression of morphine CPP, the protein level of membrane mGluR5 was selectively increased in the NAc shell. In primary striatal neurons, we observed that treatment with the mGluR5 agonist CHPG increased the phosphorylation level of extracellular signal-regulated kinase (ERK), which was dependent on the mGluR5-inositol-1,4,5-trisphosphate-reactive oxygen species (ROS) pathway. Moreover, the microinjection of the ROS scavenger Tempol into the NAc shell of rats blocked the expression of morphine CPP. Further, the administration of t-BOOH, a ROS donor, into the NAc shell rescued the retrieval impairment of morphine CPP produced by MTEP. Our previous study demonstrated that the expression of morphine CPP increased the phosphorylation of ERK selectively in the NAc shell. Thus, results of the present study suggest that mGluR5 in the NAc shell, but not in the core, is essential for the retrieval of morphine contextual memory, which is mediated at least in part, through the ROS/ERK signaling pathway. Uncovering the molecular basis of opiate contextual memory will benefit the development of new therapeutic approaches for the treatment of opiate addiction.

Microinjection of the mGluR5 antagonist MTEP into the nucleus accumbens attenuates the acquisition but not expression of morphine-induced conditioned place preference in rats

Previous studies suggest that metabotropic glutamate receptor type 5 (mGluR5) plays an important role in modulation of the rewarding properties of morphine. Little is known about the role of mGluR5 in the nucleus accumbens (NAc), as one of the important regions of the reward circuitry. In the present study, we investigated the effects of intra-accumbal injection of mGluR5 antagonist, 3-[(2-methyl-4-thiazolyl) ethynyl] pyridine, MTEP, on the acquisition and expression of morphine induced Conditioned Place Preference (CPP) in the rats. Eighty four adult male Wistar rats (220–260g) were bilaterally implanted with cannulae into the NAc. Subjects were tested in a CPP paradigm. Different doses of MTEP (0.3, 1 and 3μg/0.5μl per side) were delivered bilaterally into NAc during 3 conditioning days (Acquisition) or post-conditioning day (Expression).Results showed that bilateral intra accumbal administration of MTEP (1 and 3μg) significantly attenuated the acquisition but not expression of morphine-induced CPP in a dose-dependent manner.Our findings indicated that blockade of mGluR5 reduces rewarding properties of morphine. Further studies are needed to know the involved mechanisms.

Abstract 1993: The role of metabotropic glutamate receptor 5 on the lymph node metastases in oral cancer

Abstract We identified a metastasis-related gene, metabotropic glutamate receptor (mGluR)-5, as a target gene of stromal cell-derived factor (SDF)-1/CXCR4 system in oral cancer. In this study, we examined the role of mGluR5 on the lymph node metastasis of oral cancer. mGluR5-specific antagonists, 2-Methyl-6-(phenylethynyl)pyridine (MPEP) and 3-((2-Methyl-1,3-thiazol-4-yl)ethynyl)pyridine (MTEP) did not affect the growth of oral cancer cells, but did inhibit the SDF-1/CXCR4 dependent-migration of the cells. When the CXCR4 expressing-oral cancer cells were orthotopically transplanted into masseter muscle of nude mice, these antagonists significantly inhibited lymph node metastases of the cells. Immunohistochemical analysis revealed that there was a significant association between CXCR4 and mGluR5 protein expression. Furthermore, the mGluR5 protein expression in clinical specimen was significantly associated with the lymph node metastases and the modes of invasion. Moreover conditioned media derived from the oral cancer cells acquiring SDF-1/CXCR4 system enhanced the migration of lymphatic endothelial cells, which was significantly suppressed by the treatment with MPEP or MTEP. Although SDF-1/CXCR4 dependent-production of angiogenic factors, including interleukin-6, interleukin-8, and vascular endothelial growth factor (VEGF)-A were observed, mGluR5 antagonists did not affect the production of these factors. However, induction of a lymphangiogenic factor, VEGF-C was specifically impaired by the treatment with these mGluR5 antagonists. These results suggested that mGluR5 promotes the lymph node metastases of oral cancer cells by the SDF-1/CXCR4 system via enhancement of cancer cell migration and induction of lymphangiogenesis by VEGF-C. Citation Format: Nobuyuki Kuribayashi, Daisuke Uchida, Makoto Kinouchi, Tetsuya Tamatani, Hirokazu Nagai, Youji Miyamoto. The role of metabotropic glutamate receptor 5 on the lymph node metastases in oral cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1993. doi:10.1158/1538-7445.AM2014-1993

Investigating the expression of metabotropic glutamate receptors in trigeminal ganglion neurons and satellite glial cells: implications for craniofacial pain

Context/objective: Previous studies have demonstrated that various subtypes of the metabotropic glutamate receptors (mGluRs) are expressed in the dorsal root ganglion (DRG) of the peripheral nervous system (PNS), implicating that glutamate potentially contributes to sensory transmission through these receptors. While mGluR expression has been investigated largely in the DRG, the present study focused on mGluR expression on neurons and satellite glial cells (SGCs) of the trigeminal ganglion (TG). Materials and methods: To address the presence of mGluRs in rat TG neurons and their corresponding SGCs, the trigeminal ganglia from six adult male Wistar rats were isolated and immunohistochemistry and immunocytochemistry were performed. The expression of mGluR1α-, mGluR2/3- and mGluR8 on TG neurons and SGCs was investigated in tissue slices and isolated cells. Results: 35.1 ± 6.0% of the TG neurons were positive for mGluR1α, whereas 39.9 ± 7.7% and 55.5 ± 6.3% were positive for mGluR2/3 and mGluR8, respectively. Immunoreactive neurons expressing mGluRs were mainly medium- to large sized, with a smaller population of small-sized neurons showing immunoreactivity. The SGCs showed immunoreactivity toward mGluR1α and mGluR8, but not mGluR2/3, both in the tissue and in isolated cells. Conclusions: Findings from the present study showed that trigeminal neurons express mGluR1α, mGluR2/3 and mGluR8, while SGCs only express mGluR1α and mGluR8. This novel evidence may advance investigations on a possible role of mGluRs in relation to trigeminal pain transmission within the craniofacial region.

Supraspinal basis of analgesic and clinical effects of the metabotropic glutamate mGluR1 antagonist during colonic distension in sheep

We have previously demonstrated a differential role for metabotropic glutamate receptors (mGluRs) using behavioral evidence, the role of mGluRs in spinal nociception in normal sheep. It was confirmed that is particularly apparent in neuropathic, inflammatory hyperalgesia produced by unilateral intradermal injection of carrageenan into the lower forelimb and mechanical hypersensitivity following abdominal surgery in sheep intrathecal blockade of mGluRs group I antagonists inhibits this phenomenon.The present study examined contribution of group I mGluRs to development and maintenance changes in behavioural and clinical symptoms, cortisol and catecholamines blood plasma concentrations caused by visceral pain evoked by colonic distension (CD) in sheep. Intracerebroventricular (icv) administration of the group I mGluRs antagonist racemic mixture of DL-AP3 blocked development of visceral pain symptoms and neuroendocrinological changes in the blood plasma of sheep. This data clearly demonstrated that development and maintenance of visceral pain symptoms of CD is dependent on activation of group I mGluRs in supraspinal level and that these types of mGluR play a crucial role in modulating of acute colonic pain (colic). What is more, this is the first record of supraspinal analgesic effects of mGluR1 antagonist in sheep.