Glutamate Receptor mGluR1 Research Articles

SYNAPTIC MECHANISMS OF EPILEPSY: CONTEMPORARY VIEW

The purpose of the paper is to analyze possible mechanisms of ictal activity at the synaptic level in epilepsy. Materials and Methods. The search for literature sources was carried out in Pubmed, CyberLeninka, and Google Scholar. Results. The diversity of pathophysiological mechanisms of epilepsy makes it difficult to treat approximately one third of patients, whose ictal activity is not suppressed by traditional pharmacological agents. The increased glutamate effect may be a consequence of its increased concentration in the intercellular space due to impaired reuptake caused by dysfunction of the EAATs transporters. Excitatory influences can also be enhanced by reduced connexin 43 (Cx43) expression in the synaptic cleft and downregulation of Kir4.1 inward rectifying potassium channel, which increases the extracellular concentration of K+ and glutamate causing neuron hyperexcitability. Disturbances in neuronal, glial or neuronal-glial interactions have a similar effect. This is caused by malfunctioning of ionotropic or metabotropic receptors due to abnormal expression of astrocytic glutamate transporters and/or malfunction of neuronal or astrocytic enzymes. One of the proteins involved in epileptogenesis is aquaporin (AQP4). Altered AQP4 expression potentially affects potassium reuptake by Kir 4.1 and glutamate reuptake and reduces glutamate transporter EAAT2 expression. AQP4 can also interact with glutamate receptor mGluR5. Decreased GABAergic signaling may result from decreased numbers of GABAergic neurons in glial diseases and tumors. Besides, due to a decrease in plasmalemmal expression of the chloride cotransporter KCC2 and an increase in the expression of NKCC1 (Na-K-2Cl cotransporter), the intracellular concentration of CI– ions increases. As a result, GABA performs a depolarizing, excitatory role. Conclusion. The pathophysiological mechanisms of epilepsy may become a target in the development of new drugs with anticonvulsant effects.

Analysis of single nucleotide polymorphisms of the metabotropic glutamate receptors in a transgender population.

Gender incongruence (GI) is characterized by a marked incongruence between an individual's experienced/expressed gender and the assigned sex at birth. It includes strong displeasure about his or her sexual anatomy and secondary sex characteristics. In some people, this condition produces a strong distress with anxiety and depression named gender dysphoria (GD). This condition appears to be associated with genetic, epigenetics, hormonal as well as social factors. Given that L-glutamate is the major excitatory neurotransmitter in the central nervous system, also associated with male sexual behavior as well as depression, we aimed to determine whether metabotropic glutamate receptors are involved in GD. We analyzed 74 single nucleotide polymorphisms located at the metabotropic glutamate receptors (mGluR1, mGluR3, mGluR4, mGluR5, mGluR7 and mGluR8) in 94 transgender versus 94 cisgender people. The allele and genotype frequencies were analyzed by c2 test contrasting male and female cisgender and transgender populations. The strength of the associations was measured by binary logistic regression, estimating the odds ratio (OR) for each genotype. Measurement of linkage disequilibrium, and subsequent measurement of haplotype frequencies were also performed considering three levels of significance: P ≤ 0.05, P ≤ 0.005 and P ≤ 0.0005. Furthermore, false positives were controlled with the Bonferroni correction (P ≤ 0.05/74 = 0.00067). After analysis of allele and genotypic frequencies, we found twenty-five polymorphisms with significant differences at level P ≤ 0.05, five at P ≤ 0.005 and two at P ≤ 0.0005. Furthermore, the only two polymorphisms (rs9838094 and rs1818033) that passed the Bonferroni correction were both related to the metabotropic glutamate receptor 7 (mGluR7) and showed significant differences for multiple patterns of inheritance. Moreover, the haplotype T/G [OR=0.34 (0.19-0.62); P<0.0004] had a lower representation in the transgender population than in the cisgender population, with no evidence of sex cross-interaction. We provide genetic evidence that the mGluR7, and therefore glutamatergic neurotransmission, may be involved in GI and GD.

Modulation of Type 5 Metabotropic Glutamate Receptor-Mediated Intracellular Calcium Mobilization by Regulator of G Protein Signaling 4 (RGS4) in Cultured Astrocytes.

Acting as GTPase activating proteins promoting the silencing of activated G-proteins, regulators of G protein signaling (RGSs) are generally considered negative modulators of cell signaling. In the CNS, the expression of RGS4 is altered in diverse pathologies and its upregulation was reported in astrocytes exposed to an inflammatory environment. In a model of cultured cortical astrocytes, we herein investigate the influence of RGS4 on intracellular calcium signaling mediated by type 5 metabotropic glutamate receptor (mGluR5), which is known to support the bidirectional communication between neurons and glial cells. RGS4 activity was manipulated by exposure to the inhibitor CCG 63802 or by infecting the cells with lentiviruses designed to achieve the silencing or overexpression of RGS4. The pharmacological inhibition or silencing of RGS4 resulted in a decrease in the percentage of cells responding to the mGluR5 agonist DHPG and in the proportion of cells showing typical calcium oscillations. Conversely, RGS4-lentivirus infection increased the percentage of cells showing calcium oscillations. While the physiological implication of cytosolic calcium oscillations in astrocytes is still under investigation, the fine-tuning of calcium signaling likely determines the coding of diverse biological events. Indirect signaling modulators such as RGS4 inhibitors, used in combination with receptor ligands, could pave the way for new therapeutic approaches for diverse neurological disorders with improved efficacy and selectivity.

Effects of Chronic Hydrocodone Exposure and Ceftriaxone on the Expression of Astrocytic Glutamate Transporters in Mesocorticolimbic Brain Regions of C57/BL Mice.

Exposure to opioids can lead to the alteration of several neurotransmitters. Among these neurotransmitters, glutamate is thought to be involved in opioid dependence. Glutamate neurotransmission is mainly regulated by astrocytic glutamate transporters such as glutamate transporter 1 (GLT-1) and cystine/glutamate antiporter (xCT). Our laboratory has shown that exposure to lower doses of hydrocodone reduced the expression of xCT in the nucleus accumbens (NAc) and the hippocampus. In the present study, we investigated the effects of chronic exposure to hydrocodone, and tested ceftriaxone as a GLT-1 upregulator in mesocorticolimbic brain regions such as the NAc, the amygdala (AMY), and the dorsomedial prefrontal cortex (dmPFC). Eight-week-old male mice were divided into three groups: (1) the saline vehicle control group; (2) the hydrocodone group; and (3) the hydrocodone + ceftriaxone group. Mice were injected with hydrocodone (10 mg/kg, i.p.) or saline for 14 days. On day seven, the hydrocodone/ceftriaxone group was injected with ceftriaxone (200 mg/kg, i.p.) for last seven days. Chronic exposure to hydrocodone reduced the expression of GLT-1, xCT, protein kinase B (AKT), extracellular signal-regulated kinases (ERK), and c-Jun N-terminal Kinase (JNK) in NAc, AMY, and dmPFC. However, hydrocodone exposure increased the expression of G-protein-coupled metabotropic glutamate receptors (mGluR5) in the NAc, AMY, and dmPFC. Importantly, ceftriaxone treatment normalized the expression of mGluR5, GLT-1, and xCT in all these brain regions, except for xCT in the AMY. Importantly, ceftriaxone treatment attenuated hydrocodone-induced downregulation of signaling pathways such as AKT, ERK, and JNK expression in the NAc, AMY, and dmPFC. These findings demonstrate that ceftriaxone has potential therapeutic effects in reversing hydrocodone-induced downregulation of GLT-1 and xCT in selected reward brain regions, and this might be mediated through the downstream kinase signaling pathways such as AKT, ERK, and JNK.

Inhibiting metabotropic glutamate receptor 5 after stroke restores brain function and connectivity.

Stroke results in local neural disconnection and brain-wide neuronal network dysfunction leading to neurological deficits. Beyond the hyper-acute phase of ischaemic stroke, there is no clinically-approved pharmacological treatment that alleviates sensorimotor impairments. Functional recovery after stroke involves the formation of new or alternative neuronal circuits including existing neural connections. The type-5 metabotropic glutamate receptor (mGluR5) has been shown to modulate brain plasticity and function and is a therapeutic target in neurological diseases outside of stroke. We investigated whether mGluR5 influences functional recovery and network reorganization rodent models of focal ischaemia. Using multiple behavioural tests, we observed that treatment with negative allosteric modulators (NAMs) of mGluR5 (MTEP, fenobam and AFQ056) for 12 days, starting 2 or 10 days after stroke, restored lost sensorimotor functions, without diminishing infarct size. Recovery was evident within hours after initiation of treatment and progressed over the subsequent 12 days. Recovery was prevented by activation of mGluR5 with the positive allosteric modulator VU0360172 and accelerated in mGluR5 knock-out mice compared with wild-type mice. After stroke, multisensory stimulation by enriched environments enhanced recovery, a result prevented by VU0360172, implying a role of mGluR5 in enriched environment-mediated recovery. Additionally, MTEP treatment in conjunction with enriched environment housing provided an additive recovery enhancement compared to either MTEP or enriched environment alone. Using optical intrinsic signal imaging, we observed brain-wide disruptions in resting-state functional connectivity after stroke that were prevented by mGluR5 inhibition in distinct areas of contralesional sensorimotor and bilateral visual cortices. The levels of mGluR5 protein in mice and in tissue samples of stroke patients were unchanged after stroke. We conclude that neuronal circuitry subserving sensorimotor function after stroke is depressed by a mGluR5-dependent maladaptive plasticity mechanism that can be restored by mGluR5 inhibition. Post-acute stroke treatment with mGluR5 NAMs combined with rehabilitative training may represent a novel post-acute stroke therapy.

Unravelling Contributions of Astrocytic Connexin 43 to the Functional Activity of Brain Neuron-Glial Networks under Hypoxic State In Vitro.

Brain hypoxia remains an Achilles’ heel for public health that must be urgently addressed. Hypoxic damage affects both neurons and glial cells, particularly astrocytes, which are in close dynamic bi-directional communication, and are organized in plastic and tightly regulated networks. However, astroglial networks have received limited attention regarding their influence on the adaptive functional rearrangements of neural networks to oxygen deficiency. Herein, against the background of astrocytic Cx43 gap junction blockade by the selective blocker Gap19, we evaluated the features of spontaneous calcium activity and network characteristics of cells in primary cultures of the cerebral cortex, as well as the expression levels of metabotropic glutamate receptors 2 (mGluR2) and 5 (mGluR5) in the early and late periods after simulated hypoxia in vitro. We showed that, under normoxic conditions, blockade of Cx43 leads to an increase in the expression of metabotropic glutamate receptors mGluR2 and mGluR5 and long-term modulation of spontaneous calcium activity in primary cortical cultures, primarily expressed in the restructuring of the functional architectonics of neuron–glial networks through reducing the level of correlation between cells in the network and the percentage of existing correlated connections between cells. Blocking Cx43 during hypoxic injury has a pronounced neuroprotective effect. Together with the increased expression of mGluR5 receptors, a decrease in mGluR2 expression to the physiological level was found, which suggests the triggering of alternative molecular mechanisms of cell adaptation to hypoxia. Importantly, the blockade of Cx43 in hypoxic damage contributed to the maintenance of both the main parameters of the spontaneous calcium activity of primary cortical cultures and the functional architectonics of neuron–glial networks while maintaining the profile of calcium oscillations and calcium signal communications between cells at a highly correlated level. Our results demonstrate the crucial importance of astrocytic networks in functional brain adaptation to hypoxic damage and could be a promising target for the development of rational anti-hypoxic therapy.

Prions induce an early Arc response and a subsequent reduction in mGluR5 in the hippocampus

Synapse dysfunction and loss are central features of neurodegenerative diseases, caused in part by the accumulation of protein oligomers. Amyloid-β, tau, prion, and α-synuclein oligomers bind to the cellular prion protein (PrPC), resulting in the activation of macromolecular complexes and signaling at the post-synapse, yet the early signaling events are unclear. Here we sought to determine the early transcript and protein alterations in the hippocampus during the pre-clinical stages of prion disease. We used a transcriptomic approach focused on the early-stage, prion-infected hippocampus of male wild-type mice, and identify immediate early genes, including the synaptic activity response gene, Arc/Arg3.1, as significantly upregulated. In a longitudinal study of male, prion-infected mice, Arc/Arg-3.1 protein was increased early (40% of the incubation period), and by mid-disease (pre-clinical), phosphorylated AMPA receptors (pGluA1-S845) were increased and metabotropic glutamate receptors (mGluR5 dimers) were markedly reduced in the hippocampus. Notably, sporadic Creutzfeldt-Jakob disease (sCJD) post-mortem cortical samples also showed low levels of mGluR5 dimers. Together, these findings suggest that prions trigger an early Arc response, followed by an increase in phosphorylated GluA1 and a reduction in mGluR5 receptors.

CRISPR-mediated activation of autism gene Itgb3 restores cortical network excitability via mGluR5 signaling

Many mutations in autism spectrum disorder (ASD) affect a single allele, indicating a key role for gene dosage in ASD susceptibility. Recently, haplo-insufficiency of ITGB3, the gene encoding the extracellular matrix receptor β3 integrin, was associated with ASD. Accordingly, Itgb3 knockout (KO) mice exhibit autism-like phenotypes. The pathophysiological mechanisms of Itgb3 remain, however, unknown, and the potential of targeting this gene for developing ASD therapies uninvestigated. By combining molecular, biochemical, imaging, and pharmacological analyses, we establish that Itgb3 haplo-insufficiency impairs cortical network excitability by promoting extra-synaptic over synaptic signaling of the metabotropic glutamate receptor mGluR5, which is similarly dysregulated in fragile X syndrome, the most frequent monogenic form of ASD. To assess the therapeutic potential of regulating Itgb3 gene dosage, we implemented CRISPR activation and compared its efficacy with that of a pharmacological rescue strategy for fragile X syndrome. Correction of neuronal Itgb3 haplo-insufficiency by CRISPR activation rebalanced network excitability as effectively as blockade of mGluR5 with the selective antagonist MPEP. Our findings reveal an unexpected functional interaction between two ASD genes, thereby validating the pathogenicity of ITGB3 haplo-insufficiency. Further, they pave the way for exploiting CRISPR activation as gene therapy for normalizing gene dosage and network excitability in ASD.

MTORC1 function in hippocampal parvalbumin interneurons: regulation of firing and long-term potentiation of intrinsic excitability but not long-term contextual fear memory and context discrimination

Hippocampal CA1 parvalbumin-expressing interneurons (PV INs) play a central role in controlling principal cell activity and orchestrating network oscillations. PV INs receive excitatory inputs from CA3 Schaffer collaterals and local CA1 pyramidal cells, and they provide perisomatic inhibition. Schaffer collateral excitatory synapses onto PV INs express Hebbian and anti-Hebbian types of long-term potentiation (LTP), as well as elicit LTP of intrinsic excitability (LTPIE). LTPIE requires the activation of type 5 metabotropic glutamate receptors (mGluR5) and is mediated by downregulation of potassium channels Kv1.1. It is sensitive to rapamycin and thus may involve activation of the mammalian target of rapamycin complex 1 (mTORC1). LTPIE facilitates PV INs recruitment in CA1 and maintains an excitatory-inhibitory balance. Impaired CA1 PV INs activity or LTP affects network oscillations and memory. However, whether LTPIE in PV INs plays a role in hippocampus-dependent memory remains unknown. Here, we used conditional deletion of the obligatory component of mTORC1, the Regulatory-Associated Protein of mTOR (Raptor), to directly manipulate mTORC1 in PV INs. We found that homozygous, but not heterozygous, conditional knock-out of Rptor resulted in a decrease in CA1 PV INs of mTORC1 signaling via its downstream effector S6 phosphorylation assessed by immunofluorescence. In whole-cell recordings from hippocampal slices, repetitive firing of CA1 PV INs was impaired in mice with either homozygous or heterozygous conditional knock-out of Rptor. High frequency stimulation of Schaffer collateral inputs that induce LTPIE in PV INs of control mice failed to do so in mice with either heterozygous or homozygous conditional knock-out of Rptor in PV INs. At the behavioral level, mice with homozygous or heterozygous conditional knock-out of Rptor showed similar long-term contextual fear memory or contextual fear memory discrimination relative to control mice. Thus, mTORC1 activity in CA1 PV INs regulates repetitive firing and LTPIE but not consolidation of long-term contextual fear memory and context discrimination. Our results indicate that mTORC1 plays cell-specific roles in synaptic plasticity of hippocampal inhibitory interneurons that are differentially involved in hippocampus-dependent learning and memory.

VGLUT3 Ablation Differentially Modulates Glutamate Receptor Densities in Mouse Brain.

Type 3 vesicular glutamate transporter (VGLUT3) represents a unique modulator of glutamate release from both nonglutamatergic and glutamatergic varicosities within the brain. Despite its limited abundance, VGLUT3 is vital for the regulation of glutamate signaling and, therefore, modulates the activity of various brain microcircuits. However, little is known about how glutamate receptors are regulated by VGLUT3 across different brain regions. Here, we used VGLUT3 constitutive knock-out (VGLUT3–/–) mice and explored how VGLUT3 deletion influences total and cell surface expression of different ionotropic and metabotropic glutamate receptors. VGLUT3 deletion upregulated the overall expression of metabotropic glutamate receptors mGluR5 and mGluR2/3 in the cerebral cortex. In contrast, no change in the total expression of ionotropic NMDAR glutamate receptors were observed in the cerebral cortex of VGLUT3–/– mice. We noted significant reduction in cell surface levels of mGluR5, NMDAR2A, NMDAR2B, as well as reductions in dopaminergic D1 receptors and muscarinic M1 acetylcholine receptors in the hippocampus of VGLUT3–/– mice. Furthermore, mGluR2/3 total expression and mGluR5 cell surface levels were elevated in the striatum of VGLUT3–/– mice. Last, AMPAR subunit GluA1 was significantly upregulated throughout cortical, hippocampal, and striatal brain regions of VGLUT3–/– mice. Together, these findings complement and further support the evidence that VGLUT3 dynamically regulates glutamate receptor densities in several brain regions. These results suggest that VGLUT3 may play an intricate role in shaping glutamatergic signaling and plasticity in several brain areas.

N-Acetylcysteine Mitigates Social Dysfunction in a Rat Model of Autism Normalizing Glutathione Imbalance and the Altered Expression of Genes Related to Synaptic Function in Specific Brain Areas.

Prenatal exposure to valproic acid (VPA) is a risk factor for autism spectrum disorder (ASD) in humans and it induces autistic-like behaviors in rodents. Imbalances between GABAergic and glutamatergic neurotransmission and increased oxidative stress together with altered glutathione (GSH) metabolism have been hypothesized to play a role in both VPA-induced embriotoxicity and in human ASD. N-acetylcysteine (NAC) is an antioxidant precursor of glutathione and a modulator of glutamatergic neurotransmission that has been tested in ASD, although the clinical studies currently available provided controversial results. Here, we explored the effects of repeated NAC (150 mg/kg) administration on core autistic-like features and altered brain GSH metabolism in the VPA (500 mg/kg) rat model of ASD. Furthermore, we measured the mRNA expression of genes encoding for scaffolding and transcription regulation proteins, as well as the subunits of NMDA and AMPA receptors and metabotropic glutamate receptors mGLUR1 and mGLUR5 in brain areas that are relevant to ASD. NAC administration ameliorated the social deficit displayed by VPA-exposed rats in the three-chamber test, but not their stereotypic behavior in the hole board test. Furthermore, NAC normalized the altered GSH levels displayed by these animals in the hippocampus and nucleus accumbens, and it partially rescued the altered expression of post-synaptic terminal network genes found in VPA-exposed rats, such as NR2a, MGLUR5, GLUR1, and GLUR2 in nucleus accumbens, and CAMK2, NR1, and GLUR2 in cerebellum. These data indicate that NAC treatment selectively mitigates the social dysfunction displayed by VPA-exposed rats normalizing GSH imbalance and reestablishing the expression of genes related to synaptic function in a brain region-specific manner. Taken together, these data contribute to clarify the behavioral impact of NAC in ASD and the molecular mechanisms that underlie its effects.

TRPC3 Channel Activity and Viability of Purkinje Neurons can be Regulated by a Local Signalosome.

Canonical transient receptor potential channels (TRPC3) may play a pivotal role in the development and viability of dendritic arbor in Purkinje neurons. This is a novel postsynaptic channel for glutamatergic synaptic transmission. In the cerebellum, TRPC3 appears to regulate functions relating to motor coordination in a highly specific manner. Gain of TRPC3 function is linked to significant alterations in the density and connectivity of dendritic arbor in Purkinje neurons. TRPC3 signals downstream of class I metabotropic glutamate receptors (mGluR1). Moreover, diacylglycerol (DAG) can directly bind and activate TRPC3 molecules. Here, we investigate a key question: How can the activity of the TRPC3 channel be regulated in Purkinje neurons? We also explore how mGluR1 activation, Ca2+ influx, and DAG homeostasis in Purkinje neurons can be linked to TRPC3 activity modulation. Through systems biology approach, we show that TRPC3 activity can be modulated by a Purkinje cell (PC)–specific local signalosome. The assembly of this signalosome is coordinated by DAG generation after mGluR1 activation. Our results also suggest that purinergic receptor activation leads to the spatial and temporal organization of the TRPC3 signaling module and integration of its key effector molecules such as DAG, PKCγ, DGKγ, and Ca2+ into an organized local signalosome. This signaling machine can regulate the TRPC3 cycling between active, inactive, and desensitized states. Precise activity of the TRPC3 channel is essential for tightly regulating the Ca2+ entry into PCs and thus the balance of lipid and Ca2+ signaling in Purkinje neurons and hence their viability. Cell-type–specific understanding of mechanisms regulating TRPC3 channel activity could be key in identifying therapeutic targeting opportunities.

Stabilization of Spine Synaptopodin by mGluR1 Is Required for mGluR-LTD.

Dendritic spines, actin-rich protrusions forming the postsynaptic sites of excitatory synapses, undergo activity-dependent molecular and structural remodeling. Activation of Group 1 metabotropic glutamate receptors (mGluR1 and mGluR5) by synaptic or pharmacological stimulation, induces LTD, but whether this is accompanied with spine elimination remains unresolved. A subset of telencephalic mushroom spines contains the spine apparatus (SA), an enigmatic organelle composed of stacks of smooth endoplasmic reticulum, whose formation depends on the expression of the actin-bundling protein Synaptopodin. Allocation of Synaptopodin to spines appears governed by cell-intrinsic mechanisms as the relative frequency of spines harboring Synaptopodin is conserved in vivo and in vitro Here we show that expression of Synaptopodin/SA in spines is required for induction of mGluR-LTD at Schaffer collateral-CA1 synapses of male mice. Post-mGluR-LTD, mushroom spines lacking Synaptopodin/SA are selectively lost, whereas spines harboring it are preserved. This process, dependent on activation of mGluR1 but not mGluR5, is conserved in mature mouse neurons and rat neurons of both sexes. Mechanistically, we find that mGluR1 supports physical retention of Synaptopodin within excitatory spine synapses during LTD while triggering lysosome-dependent degradation of the protein residing in dendritic shafts. Together, these results reveal a cellular mechanism, dependent on mGluR1, which enables selective preservation of stronger spines containing Synaptopodin/SA while eliminating weaker ones and potentially countering spurious strengthening by de novo recruitment of Synaptopodin. Overall, our results identify spines with Synaptopodin/SA as the locus of mGluR-LTD and underscore the importance of the molecular microanatomy of spines in synaptic plasticity.SIGNIFICANCE STATEMENT Long-term changes in functional synaptic strength are associated with modification of synaptic connectivity through stabilization or elimination of dendritic spines, the postsynaptic locus of excitatory synapses. How heterogeneous spine microanatomy instructs spine remodeling after long-term synaptic depression (LTD) remains unclear. Metabotropic glutamate receptors mGluR1 and mGluR5 induce a form of LTD critical to circuit function in physiological and disease conditions. Our results identify spines containing the protein Synaptopodin, which enables local assembly of a spine apparatus, as the locus of expression of mGluR-LTD and demonstrate a specific role of mGluR1 in promoting selective loss after mGluR-LTD of mature dendritic spines lacking Synaptopodin/spine apparatus. These findings highlight the fundamental contribution of spine microanatomy in selectively enabling functional and structural plasticity.

The mGluR6 ligand-binding domain, but not the C-terminal domain, is required for synaptic localization in retinal ON-bipolar cells

Signals from retinal photoreceptors are processed in two parallel channels—the ON channel responds to light increments, while the OFF channel responds to light decrements. The ON pathway is mediated by ON type bipolar cells (BCs), which receive glutamatergic synaptic input from photoreceptors via a G-protein-coupled receptor signaling cascade. The metabotropic glutamate receptor mGluR6 is located at the dendritic tips of all ON-BCs and is required for synaptic transmission. Thus, it is critically important for delivery of information from photoreceptors into the ON pathway. In addition to detecting glutamate, mGluR6 participates in interactions with other postsynaptic proteins, as well as trans-synaptic interactions with presynaptic ELFN proteins. Mechanisms of mGluR6 synaptic targeting and functional interaction with other synaptic proteins are unknown. Here, we show that multiple regions in the mGluR6 ligand-binding domain are necessary for both synaptic localization in BCs and ELFN1 binding in vitro. However, these regions were not required for plasma membrane localization in heterologous cells, indicating that secretory trafficking and synaptic localization are controlled by different mechanisms. In contrast, the mGluR6 C-terminus was dispensable for synaptic localization. In mGluR6 null mice, localization of the postsynaptic channel protein TRPM1 was compromised. Introducing WT mGluR6 rescued TRPM1 localization, while a C-terminal deletion mutant had significantly reduced rescue ability. We propose a model in which trans-synaptic ELFN1 binding is necessary for mGluR6 postsynaptic localization, whereas the C-terminus has a role in mediating TRPM1 trafficking. These findings reveal different sequence determinants of the multifunctional roles of mGluR6 in ON-BCs.

Effects of Oleuropein on Depression Caused by Chronic Stress in Mice

Background and Objectives: Depression is still one of challenging, and widely encountered disorders with complex etiology. Recently the role of healthy diet and olive oil in ameliorating depression has been claimed. This study was designed to explore the effects of oleuropein on depression induced by chronic stress in mice. Methods: To induce chronic stress Chronic Restraint Stress (CRS) mice immobilizated in restrainer 2 hours; for 2 weeks then an foot electric shock (2 minutes 0.5mA) were used. Mice under chronic stress were randomly divided into 5 groups; including control group (under chronic stress receiving normal saline), intervention groups (under acute stress receiving oleuropein at doses of 7.5, 15 and 30 mg/kg and positive control (under chronic stress receiving diazepam). Then the expression of 6-interleukin (6- IL) and Metabotropic Glutamate Receptor (mGluR1) were measured, Forced Swimming Test (FST) and Tail Suspension Test (TST) were recorded. Results: In CRS mice,at the dose of oleuropein at 15 mg/kg, the duration of immobility significantly reduced in tail suspension test and doses of 15 and 30 mg/kg of oleuropein significantly decreased the immobility time in forced swimming test (P&lt;0.05) Oleuropein also decreased the expression of 6- IL and mGluR1. Conclusion: According to our results, it seems that reducing the expression of 6- IL and mGluR1 may induce the effect of oleuropein on depressive-like behaviors in mice under chronic stress disorder.

Homodimerization of a proximal region within the C-terminus of the orphan G-protein coupled receptor GPR179

G-protein coupled receptors exhibit numerous biological functions. The orphan G-protein coupled receptor GPR179 is a central component of a 1 Megadalton large signalling complex in the ON-pathway of the mammalian retina that assembles multiple proteins, including the metabotropic glutamate receptor mGluR6. Dimer formation is a hallmark of G-protein coupled receptors and some use intracellular C-termini for dimerization. Here we tested the dimerization properties of the intracellular C-terminal domains of mGluR6 and GPR179. While the C-termini of GPR179 and mGluR6 did not interact, we detected a robust homodimerization of a proximal region in the GPR179 C-terminus. Mapping studies defined a linear stretch of 64 amino acids as dimerization region. Bioinformatic analysis indicated that this dimerization region might adopt an α-helical structure that is predicted to dimerize by forming a coiled-coil. Based on these data, we speculate that homodimerization of GPR179 might contribute to the formation of large signalling complexes in the mammalian retina.

An Alzheimer's drug target only for men

Pharmacology β-Amyloid deposits in the brain are a hallmark of Alzheimer's disease. The binding of β-amyloid to the metabotropic glutamate receptor mGluR5 contributes to disease progression. Abd-Elrahman et al. found that β-amyloid was bound to mGluR5 in brain tissue samples only from male Alzheimer's disease model mice or male patients. Blocking the activity of mGluR5 reversed cognitive decline in male mice but not in their female counterparts, suggesting that mGluR5 inhibitors may be therapeutically beneficial only for male Alzheimer's disease patients. Sci. Signal. 13 , eabd2494 (2020).

Activation of tyrosine phosphatase PTP1B in pyramidal neurons impairs endocannabinoid signaling by tyrosine receptor kinase trkB and causes schizophrenia-like behaviors in mice.

Schizophrenia is a debilitating disorder affecting young adults displaying symptoms of cognitive impairment, anxiety, and early social isolation prior to episodes of auditory hallucinations. Cannabis use has been tied to schizophrenia-like symptoms, indicating that dysregulated endogenous cannabinoid signaling may be causally linked to schizophrenia. Previously, we reported that glutamatergic neuron-selective ablation of Lmo4, an endogenous inhibitor of the tyrosine phosphatase PTP1B, impairs endocannabinoid (eCB) production from the metabotropic glutamate receptor mGluR5. These Lmo4-deficient mice display anxiety-like behaviors that are alleviated by local shRNA knockdown or pharmacological inhibition of PTP1B that restores mGluR5-dependent eCB production in the amygdala. Here, we report that these Lmo4-deficient mice also display schizophrenia-like behaviors: impaired working memory assessed in the Y maze and defective sensory gating by prepulse inhibition of the acoustic startle response. Modulation of inhibitory inputs onto layer 2/3 pyramidal neurons of the prefrontal cortex relies on eCB signaling from the brain-derived neurotrophic factor receptor trkB, rather than mGluR5, and this mechanism was defective in Lmo4-deficient mice. Genetic ablation of PTP1B in the glutamatergic neurons lacking Lmo4 restored tyrosine phosphorylation of trkB, trkB-mediated eCB signaling, and ameliorated schizophrenia-like behaviors. Pharmacological inhibition of PTP1B with trodusquemine also restored trkB phosphorylation and improved schizophrenia-like behaviors by restoring eCB signaling, since the CB1 receptor antagonist 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide blocked this effect. Thus, activation of PTP1B in pyramidal neurons contributes to schizophrenia-like behaviors in Lmo4-deficient mice and genetic or pharmacological intervention targeting PTP1B ameliorates schizophrenia-related deficits.

Transcriptional corepressor SIN3A regulates hippocampal synaptic plasticity via Homer1/mGluR5 signaling.

Long-term memory depends on the control of activity-dependent neuronal gene expression, which is regulated by epigenetic modifications. The epigenetic modification of histones is orchestrated by the opposing activities of 2 classes of regulatory complexes: permissive coactivators and silencing corepressors. Much work has focused on coactivator complexes, but little is known about the corepressor complexes that suppress the expression of plasticity-related genes. Here, we define a critical role for the corepressor SIN3A in memory and synaptic plasticity, showing that postnatal neuronal deletion of Sin3a enhances hippocampal long-term potentiation and long-term contextual fear memory. SIN3A regulates the expression of genes encoding proteins in the postsynaptic density. Loss of SIN3A increases expression of the synaptic scaffold Homer1, alters the metabotropic glutamate receptor 1α (mGluR1α) and mGluR5 dependence of long-term potentiation, and increases activation of ERK in the hippocampus after learning. Our studies define a critical role for corepressors in modulating neural plasticity and memory consolidation and reveal that Homer1/mGluR signaling pathways may be central molecular mechanisms for memory enhancement.

Alterations in sleep, sleep spindle, and EEG power in mGluR5 knockout mice.

The type 5 metabotropic glutamate receptor (mGluR5) represents a novel therapeutic target for schizophrenia and other disorders. Schizophrenia is associated with progressive abnormalities in cortical oscillatory processes including reduced spindles (8-15 Hz) during sleep and increased delta (0.5-4 Hz)- and gamma-band activity (30-80 Hz) during wakefulness. mGluR5 knockout (KO) mice demonstrate many schizophrenia-like behaviors, including abnormal sleep. To examine the effects of mGluR5 on the maintenance of the neocortical circuitry responsible for such neural oscillations, we analyzed sleep/wake electroencephalographic (EEG) activity of mGluR5 KO mice at baseline, after 6 h of sleep deprivation, and during a visual method of cortical entrainment (visual steady state response). We hypothesized mGluR5-KO mice would exhibit translationally relevant abnormalities in sleep and neural oscillations that mimic schizophrenia. Power spectral and spindle density analyses were performed across 24-h EEG recordings in mGluR5-KO mice and wild-type (WT) controls. Novel findings in mGluR5 KO mice include deficits in sleep spindle density, wake alpha power, and 40-Hz visual task-evoked gamma power and phase locking. Sigma power (10-15 Hz), an approximation of spindle activity, was also reduced during non-rapid eye movement sleep transitions. Our observations on abnormal sleep/wake are generally in agreement with previous reports, although we did not replicate changes in rapid eye movement sleep. The timing of these phenotypes may suggest an impaired circadian process in mGluR5 KO mice. In conclusion, EEG phenotypes in mGluR5 KO mice resemble deficits observed in patients with schizophrenia. These findings implicate mGluR5-mediated pathways in several translationally relevant phenotypes associated with schizophrenia, and suggest that agents targeting this receptor may have harmful consequences on sleep health and daily patterns of EEG power.NEW & NOTEWORTHY Metabotropic glutamate receptor type 5 (mGluR5) knockout (KO) mice show several translationally relevant abnormalities in neural oscillatory activity associated with schizophrenia. These include deficits in sleep spindle density, sigma and alpha power, and 40-Hz task-evoked gamma power. The timing of these phenotypes suggests an impaired circadian process in these mice. Previously reported rapid eye movement sleep deficits in this model were not observed. These findings suggest mGluR5-enhancing drugs may improve sleep stability and sleep spindle density, which could impact memory and cognition.