6-methyl-2-(phenylethynyl)pyridine and Disease-Models--Animal

Topics: Animals; Child Development Disorders, Pervasive; Child, Preschool; Communication; Curriculum; Disease Models, Animal; Double-Blind Method; Early Intervention, Educational; Follow-Up Studies; Grooming; Humans; Infant; Mice; Motor Skills; Personality Assessment; Pyridines; Randomized Controlled Trials as Topic; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Socialization; Stereotyped Behavior

When Zika virus emerged as a public health emergency there were no drugs or vaccines approved for its prevention or treatment. We used a high-throughput screen for Zika virus protease inhibitors to identify several inhibitors of Zika virus infection. We expressed the NS2B-NS3 Zika virus protease and conducted a biochemical screen for small-molecule inhibitors. A quantitative structure-activity relationship model was employed to virtually screen ∼138,000 compounds, which increased the identification of active compounds, while decreasing screening time and resources. Candidate inhibitors were validated in several viral infection assays. Small molecules with favorable clinical profiles, especially the five-lipoxygenase-activating protein inhibitor, MK-591, inhibited the Zika virus protease and infection in neural stem cells. Members of the tetracycline family of antibiotics were more potent inhibitors of Zika virus infection than the protease, suggesting they may have multiple mechanisms of action. The most potent tetracycline, methacycline, reduced the amount of Zika virus present in the brain and the severity of Zika virus-induced motor deficits in an immunocompetent mouse model. As Food and Drug Administration-approved drugs, the tetracyclines could be quickly translated to the clinic. The compounds identified through our screening paradigm have the potential to be used as prophylactics for patients traveling to endemic regions or for the treatment of the neurological complications of Zika virus infection.

Topics: Animals; Antiviral Agents; Artificial Intelligence; Chlorocebus aethiops; Disease Models, Animal; Drug Evaluation, Preclinical; High-Throughput Screening Assays; Immunocompetence; Inhibitory Concentration 50; Methacycline; Mice, Inbred C57BL; Protease Inhibitors; Quantitative Structure-Activity Relationship; Small Molecule Libraries; Vero Cells; Zika Virus; Zika Virus Infection

There is a major clinical need for new therapies for the treatment of chronic itch. Many of the molecular components involved in itch neurotransmission are known, including the neuropeptide NPPB, a transmitter required for normal itch responses to multiple pruritogens in mice. Here, we investigated the potential for a novel strategy for the treatment of itch that involves the inhibition of the NPPB receptor NPR1 (natriuretic peptide receptor 1). Because there are no available effective human NPR1 (hNPR1) antagonists, we performed a high-throughput cell-based screen and identified 15 small-molecule hNPR1 inhibitors. Using in vitro assays, we demonstrated that these compounds specifically inhibit hNPR1 and murine NPR1 (mNPR1). In vivo, NPR1 antagonism attenuated behavioral responses to both acute itch- and chronic itch-challenged mice. Together, our results suggest that inhibiting NPR1 might be an effective strategy for treating acute and chronic itch.

Topics: Animals; Behavior, Animal; Cell-Free System; Dermatitis, Contact; Disease Models, Animal; Ganglia, Spinal; Humans; Mice, Inbred C57BL; Mice, Knockout; Neurons; Pruritus; Receptors, Atrial Natriuretic Factor; Reproducibility of Results; Signal Transduction; Small Molecule Libraries

This study investigated whether metabotropic glutamate receptor (mGluR) 5 and 8 are involved in the effect of ultramicronizedpalmitoylethanolamide (um-PEA) on the cognitive behavior and long term potentiation (LTP) at entorhinal cortex (LEC)-dentate gyrus (DG) pathway in mice rendered neuropathic by the spare nerve injury (SNI). SNI reduced discriminative memory and LTP. Um-PEA treatment started after the development of neuropathic pain had no effects in sham mice, whereas it restored cognitive behavior and LTP in SNI mice. 2-Methyl-6-(phenylethynyl) pyridine (MPEP), a selective mGluR5 antagonist, improved cognition in SNI mice and produced a chemical long term depression of the field excitatory postsynaptic potentials (fEPSPs) in sham and SNI mice. After theta burst stimulation (TBS) MPEP restored LTP in SNI mice. In combination with PEA, MPEP antagonized the PEA effect on discriminative memory and decreased LTP in SNI mice. The (RS)-4-(1-amino-1-carboxyethyl)phthalic acid (MDCPG), a selective mGluR8 antagonist, did not affect discriminative memory, but it induced a chemical LTP and prevented the enhancement of fEPSPs after TBS in SNI mice which were treated or not treated with PEA. The effect of PEA on LTP and cognitive behavior was modulated by mGluR5 and mGluR8. In particular in the SNI conditions, the mGluR5 blockade facilitated memory and LTP, but prevented the beneficial effects of PEA on discriminative memory while the mGluR8 blockade, which was ineffective in itself, prevented the favorable action of the PEA on LTP. Thus, although their opposite roles (excitatory/inhibitory of the two receptor subtypes on the glutamatergic system), they appeared to be required for the neuroprotective effect of PEA in conditions of neuropathic pain.

Topics: Amides; Animals; Dentate Gyrus; Disease Models, Animal; Ethanolamines; Excitatory Postsynaptic Potentials; Humans; Long-Term Potentiation; Male; Memory; Mice; Neuralgia; Olfactory Cortex; Palmitic Acids; Peripheral Nerve Injuries; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate

2-Methyl-6-(phenylethynyl)pyridine (MPEP), a negative allosteric modulator of the metabotropic glutamate receptor (mGluR) 5, protects hepatocytes from ischemic injury. In astrocytes and microglia, MPEP depletes ATP. These findings seem to be self-contradictory, since ATP depletion is a fundamental stressor in ischemia. This study attempted to reconstruct the mechanism of MPEP-mediated ATP depletion and the consequences of ATP depletion on protection against ischemic injury. We compared the effects of MPEP and other mGluR5 negative modulators on ATP concentration when measured in rat hepatocytes and acellular solutions. We also evaluated the effects of mGluR5 blockade on viability in rat hepatocytes exposed to hypoxia. Furthermore, we studied the effects of MPEP treatment on mouse livers subjected to cold ischemia and warm ischemia reperfusion. We found that MPEP and 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) deplete ATP in hepatocytes and acellular solutions, unlike fenobam. This finding suggests that mGluR5s may not be involved, contrary to previous reports. MPEP, as well as MTEP and fenobam, improved hypoxic hepatocyte viability, suggesting that protection against ischemic injury is independent of ATP depletion. Significantly, MPEP protected mouse livers in two different ex vivo models of ischemia reperfusion injury, suggesting its possible protective deployment in the treatment of hepatic inflammatory conditions.

Topics: Adenosine Triphosphate; Animals; Cell Hypoxia; Disease Models, Animal; Hepatocytes; Imidazoles; Liver; Mice; Mitochondria, Liver; Piperidines; Pyridines; Rats; Receptor, Metabotropic Glutamate 5; Reperfusion Injury; Thiazoles; Tumor Necrosis Factor-alpha

The purinergic receptor P2X

Topics: Animals; Astrocytes; Brain Stem; Disease Models, Animal; Facial Pain; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Hyperalgesia; Male; Microscopy, Electron; Pyridines; Rats; Rats, Sprague-Dawley; Receptors, Purinergic P2X3

Disrupted metabotropic glutamate receptor 5 (mGluR5) signaling is implicated in many neuropsychiatric disorders, including autism spectrum disorder, found in fragile X syndrome (FXS). Here we report that intracellular calcium responses to the group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG) are augmented, and calcium-dependent mGluR5-mediated mechanisms alter the differentiation of neural progenitors in neurospheres derived from human induced pluripotent FXS stem cells and the brains of mouse model of FXS. Treatment with the mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) prevents an abnormal clustering of DHPG-responsive cells that are responsive to activation of ionotropic receptors in mouse FXS neurospheres. MPEP also corrects morphological defects of differentiated cells and enhanced migration of neuron-like cells in mouse FXS neurospheres. Unlike in mouse neurospheres, MPEP increases the differentiation of DHPG-responsive radial glial cells as well as the subpopulation of cells responsive to both DHPG and activation of ionotropic receptors in human neurospheres. However, MPEP normalizes the FXS-specific increase in the differentiation of cells responsive only to N-methyl-d-aspartate (NMDA) present in human neurospheres. Exposure to MPEP prevents the accumulation of intermediate basal progenitors in embryonic FXS mouse brain suggesting that rescue effects of GluR5 antagonist are progenitor type-dependent and species-specific differences of basal progenitors may modify effects of MPEP on the cortical development. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 419-437, 2017.

Topics: Animals; Cell Differentiation; Cerebral Cortex; Disease Models, Animal; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Female; Fragile X Syndrome; Humans; Male; Methoxyhydroxyphenylglycol; Mice; Mice, Inbred C57BL; Mice, Knockout; N-Methylaspartate; Neural Stem Cells; Pyridines; Receptor, Metabotropic Glutamate 5

The most common inherited monogenetic cause of intellectual disability is Fragile X syndrome (FXS). The clinical symptoms of FXS evolve with age during adulthood; however, neurophysiological data exploring this phenomenon are limited. The Fmr1 knockout (Fmr1KO) mouse models FXS, but studies in these mice of prefrontal cortex (PFC) function are underrepresented, and aging linked data are absent. We studied synaptic physiology and activity-dependent synaptic plasticity in the medial PFC of Fmr1KO mice from 2 to 12 months. In young adult Fmr1KO mice, NMDA receptor (NMDAR)-mediated long-term potentiation (LTP) is intact; however, in 12-month-old mice this LTP is impaired. In parallel, there was an increase in the AMPAR/NMDAR ratio and a concomitant decrease of synaptic NMDAR currents in 12-month-old Fmr1KO mice. We found that acute pharmacological blockade of mGlu5 receptor in 12-month-old Fmr1KO mice restored a normal AMPAR/NMDAR ratio and LTP. Taken together, the data reveal an age-dependent deficit in LTP in Fmr1KO mice, which may correlate to some of the complex age-related deficits in FXS.

Topics: Action Potentials; Animals; Disease Models, Animal; Electric Stimulation; Excitatory Postsynaptic Potentials; Fragile X Mental Retardation Protein; Fragile X Syndrome; Long-Term Potentiation; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Neurons; Prefrontal Cortex; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate

The aim of this study was to determine the effects of 2-methyl-6-(phenylethynyl)pyridine (MPEP - a selective antagonist for the glutamate metabotropic receptor subtype mGluR5) on the protective action of some novel antiepileptic drugs (lamotrigine, oxcarbazepine, pregabalin and topiramate) against maximal electroshock-induced seizures in mice. Brain concentrations of antiepileptic drugs were measured to determine whether MPEP altered pharmacokinetics of antiepileptic drugs. Intraperitoneal injection of 1.5 and 2mg/kg of MPEP significantly elevated the threshold for electroconvulsions in mice, whereas MPEP at a dose of 1mg/kg considerably enhanced the anticonvulsant activity of pregabalin and topiramate, but not that of lamotrigine or oxcarbazepine in the maximal electroshock-induced seizures in mice. Pharmacokinetic results revealed that MPEP (1mg/kg) did not alter total brain concentrations of pregabalin and topiramate, and the observed effect in the mouse maximal electroshock seizure model was pharmacodynamic in nature. Collectively, our preclinical data suggest that MPEP may be a safe and beneficial adjunct to the therapeutic effects of antiepileptic drugs in human patients.

Topics: Animals; Anticonvulsants; Brain; Carbamazepine; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Drug Therapy, Combination; Electroshock; Excitatory Amino Acid Antagonists; Fructose; Lamotrigine; Male; Mice; Oxcarbazepine; Pregabalin; Pyridines; Random Allocation; Receptor, Metabotropic Glutamate 5; Seizures; Topiramate; Triazines

The present study examined whether a single or multiple episode(s) of status epilepticus induced with kainic acid (KA) during the first 3 weeks of postnatal (P) development would aberrantly stimulate proliferation zones that alters migration to potentially injured areas and whether they would be blocked by selective Group I mGluR antagonists. mGluR1α (LY367385) and mGluR5 (MPEP) antagonists were administered 2h following KA-induced status epilepticus and animals were examined after 7days. Proliferating cells of the subventricular zone (SVZ), third ventricle, hippocampus, amygdala cortical complex were analyzed with the proliferative marker, Ki67; and two complementary retrograde dye tracers. Proliferation increased in extrahippocampal limbic structures when KA was administered on P13 or P20 which correlated with number of injured cells at the older age. LY367385 post-treatment caused striking decreases in proliferation in all limbic structures in the presence and absence of injury, whereas a reduction with MPEP was observed only within the amygdala cortical complex (Amg/ERcx) in the presence of multiple seizures (3×KA). After 3×KA and LY367385 post-treatments, diminished co-staining of dye tracers with Ki67 was observed within the Amg/ERcx despite high levels of progenitors marked by the retrograde tracers in this region. This indicates that not only was local proliferation within the SVZ and distant structures inhibited, but also that migration itself was reduced indirectly since there were less cells to migrate from the SVZ. Co-labeling with biomarkers provided evidence for neuronal differentiation suggesting potential aberrant integration may occur in distant locations, and that targeting of mGluR1α receptors may be a potential therapeutic strategy for future development.

Topics: Age Factors; Animals; Animals, Newborn; Benzoates; Brain; Cell Cycle; Cell Movement; Cell Proliferation; Disease Models, Animal; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Female; Gene Expression Regulation, Developmental; Glycine; Kainic Acid; Lateral Ventricles; Male; Pregnancy; Pyridines; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; Rhodamines; Status Epilepticus; Time Factors

This Letter describes the identification of a series of novel non-acetylenic mGluR5 negative allosteric modulators based on the alpha-substituted acylamine structure. An initial structure-activity relationship study suggested that (R)-19b and (R)-19j might have good in vitro activity. When administered orally, these compounds were found to have an anxiolytic-like effect in a mouse model of stress-induced hyperthermia.

Topics: Administration, Oral; Allosteric Regulation; Amines; Animals; Anti-Anxiety Agents; Crystallography, X-Ray; Disease Models, Animal; Hyperthermia, Induced; Mice; Molecular Conformation; Receptor, Metabotropic Glutamate 5; Rectum; Stereoisomerism; Structure-Activity Relationship; Temperature

In Parkinson's disease (PD) and l-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesias (LIDs), overactivity of brain glutamate neurotransmission is documented and antiglutamatergic drugs decrease LID. Serotonin (5-HT) receptors and transporter (SERT) are also implicated in LID and we hypothesize that antiglutamatergic drugs can also regulate brain serotoninergic activity. Our aim was to investigate the long-term effect of the prototypal metabotropic glutamate 5 (mGlu5) receptor antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP) with L-DOPA on basal ganglia SERT, 5-HT(1A) and 5-HT(2A) receptor levels in monkeys lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP monkeys were treated for one month with L-DOPA and developed LID while those treated with L-DOPA and MPEP (10 mg/kg) developed significantly less LID. Normal controls and saline-treated MPTP monkeys were included for biochemical analysis. The MPTP lesion and experimental treatments left unchanged striatal 5-HT concentrations. MPTP lesion induced an increase of striatal 5-HIAA concentrations similar in all MPTP monkeys as compared to controls. [(3)H]-8-OH-DPAT and [(3)H]-citalopram specific binding levels to 5-HT(1A) receptors and SERT respectively remained unchanged in the striatum and globus pallidus of all MPTP monkeys compared to controls and no difference was observed between groups of MPTP monkeys. [(3)H]-ketanserin specific binding to striatal and pallidal 5-HT2A receptors was increased in L-DOPA-treated MPTP monkeys as compared to controls, saline and L-DOPA+MPEP MPTP monkeys and no difference between the latter groups was observed; dyskinesia scores correlated positively with this binding. In conclusion, reduction of development of LID with MPEP was associated with lower striatal and pallidal 5-HT2A receptors showing that glutamate activity also affects serotoninergic markers.

Topics: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; 3,4-Dihydroxyphenylacetic Acid; Animals; Benserazide; Brain; Disease Models, Animal; Dopamine; Dopamine Agents; Dose-Response Relationship, Drug; Drug Combinations; Dyskinesia, Drug-Induced; Excitatory Amino Acid Antagonists; Female; Homovanillic Acid; Levodopa; Macaca fascicularis; Ovariectomy; Parkinsonian Disorders; Protein Binding; Pyridines; Serotonin

The marble burying test is used to measure repetitive and anxiety-related behaviour in rodents. The number of marbles that animals bury are count data (non-negative integers), which are bounded below by zero and above by the number of marbles present. Count data are often analysed using normal linear models, which include the t-test and analysis of variance (ANOVA) as special cases. Linear models assume that the data are unbounded and that the variance is constant across groups. These requirements are rarely met with count data, leading to 95% confidence intervals that include impossible values (less than zero or greater than the number of marbles present), misleading p-values, and impossible predictions. Transforming the data or using nonparametric methods are common alternatives but transformations do not perform well when many zero values are present and nonparametric methods have several drawbacks.. The problems with using normal linear models to analyse marble burying data are demonstrated and generalised linear models (GLMs) are introduced as more appropriate alternatives.. GLMs have been specifically developed to deal with count and other types of non-Gaussian data, are straightforward to use and interpret, and will lead to more sensible inferences.

Topics: Analysis of Variance; Animals; Anxiety; Autistic Disorder; Behavior, Animal; Calcium Carbonate; Disease Models, Animal; Linear Models; Mice; Obsessive-Compulsive Disorder; Pyridines; Statistical Distributions; Valproic Acid

Fragile X syndrome (FXS) is the most common genetic cause for intellectual disability. Fmr1 knockout (KO) mice are an established model of FXS. Chronic pharmacological inhibition of metabotropic glutamate receptor 5 (mGlu5) in these mice corrects multiple molecular, physiological, and behavioral phenotypes related to patients' symptoms. To better understand the pathophysiology of FXS and the effect of treatment, brain activity was analyzed using functional magnetic resonance imaging in relation to learning and memory performance.. Wild-type (WT) and Fmr1 KO animals receiving chronic treatment with the mGlu5 inhibitor CTEP or vehicle were evaluated consecutively for 1) learning and memory performance in the inhibitory avoidance and extinction test, and 2) for the levels of brain activity using continuous arterial spin labeling based functional magnetic resonance imaging. Neural activity patterns were correlated with cognitive performance using a multivariate regression analysis. Furthermore, mGlu5 receptor expression in brains of untreated mice was analyzed by autoradiography and saturation analysis using [(3)H]-ABP688.. Chronic CTEP treatment corrected the learning deficit observed in Fmr1 KO mice in the inhibitory avoidance and extinction test and prevented memory extinction in WT and Fmr1 KO animals. Chronic CTEP treatment normalized perfusion in the amygdala and the lateral hypothalamus in Fmr1 KO mice and furthermore decreased perfusion in the hippocampus and increased perfusion in primary sensorimotor cortical areas. No significant differences in mGlu5 receptor expression levels between Fmr1 WT and KO mice were detected.. Chronic mGlu5 inhibition corrected the learning deficits and partially normalized the altered brain activity pattern in Fmr1 KO mice.

Topics: Animals; Avoidance Learning; Brain; Cognition; Disease Models, Animal; Electroshock; Excitatory Amino Acid Antagonists; Extinction, Psychological; Fragile X Mental Retardation Protein; Fragile X Syndrome; Imidazoles; Mice; Mice, Knockout; Oximes; Oxygen; Pyridines; Receptor, Metabotropic Glutamate 5; Tritium

A significant proportion of patients with autism exhibit some degree of intellectual disability. The BTBR T(+) Itpr3(tf)/J mouse strain exhibits behaviors that align with the major diagnostic criteria of autism. To further evaluate the BTBR strain's cognitive impairments, we quantified hippocampus-dependent object location memory (OLM) and found that one-third of the BTBR mice exhibited robust memory, whereas the remainder did not. Fluorescence deconvolution tomography was used to test whether synaptic levels of activated extracellular signal-regulated kinase 1/2 (ERK1/2), a protein that contributes importantly to plasticity, correlate with OLM scores in individual mice. In hippocampal field CA1, the BTBRs had fewer post-synaptic densities associated with high levels of phosphorylated (p-) ERK1/2 as compared with C57BL/6 mice. Although counts of p-ERK1/2 immunoreactive synapses did not correlate with OLM performance, the intensity of synaptic p-ERK1/2 immunolabeling was negatively correlated with OLM scores across BTBRs. Metabotropic glutamate receptor (mGluR) 5 signaling activates ERK1/2. Therefore, we tested whether treatment with the mGluR5 antagonist MPEP normalizes synaptic and learning measures in BTBR mice: MPEP facilitated OLM and decreased synaptic p-ERK1/2 immunolabeling intensity without affecting numbers of p-ERK1/2+ synapses. In contrast, semi-chronic ampakine treatment, which facilitates memory in other models of cognitive impairment, had no effect on OLM in BTBRs. These results suggest that intellectual disabilities associated with different neurodevelopmental disorders on the autism spectrum require distinct therapeutic strategies based on underlying synaptic pathology.

Topics: Animals; Autistic Disorder; CREB-Binding Protein; Cyclodextrins; Disease Models, Animal; Disks Large Homolog 4 Protein; Excitatory Amino Acid Antagonists; Female; Fragile X Mental Retardation Protein; Guanylate Kinases; Hippocampus; Male; MAP Kinase Signaling System; Maze Learning; Membrane Proteins; Memory Disorders; Memory, Long-Term; Mice; Mice, Inbred Strains; Pyridines; Stereotyped Behavior; Synapses

NMDA-receptor (NMDAR) hypofunction is strongly implicated in the pathophysiology of schizophrenia. Several convergent lines of evidence suggest that net excitation propagated by impaired NMDAR signaling on GABAergic interneurons may be of particular interest in mediating several aspects of schizophrenia. However, it is unclear which behavioral domains are governed by a net increase of excitation and whether modulating downstream GABAergic signaling can reverse neural and thus behavioral deficits. The current study determines the selective contributions of NMDAR dysfunction on PV-containing interneurons to electrophysiological, cognitive, and negative-symptom-related behavioral phenotypes of schizophrenia using mice with a PVcre-NR1flox-driven ablation of NR1 on PV-containing interneurons. In addition, we assessed the efficacy of one agent that directly modulates GABAergic signaling (baclofen) and one agent that indirectly modifies NMDAR-mediated signaling through antagonism of mGluR5 receptors (2-methyl-6-(phenylethynyl) pyridine (MPEP)). The data indicate that loss of NMDAR function on PV interneurons impairs self-care and sociability while increasing N1 latency and baseline gamma power, and reducing induction and maintenance of long-term potentiation. Baclofen normalized baseline gamma power without corresponding effects on behavior. MPEP further increased N1 latency and reduced social behavior in PVcre/NR1+/+ mice. These two indices were negatively correlated before and following MPEP such that as N1 latency increases, sociability decreases. This finding suggests a predictive role for N1 latency with respect to social function. Although previous data suggest that MPEP may be beneficial for core features of autism spectrum disorders, current data suggest that such effects require intact function of NMDAR on PV interneurons.

Topics: Animals; Baclofen; Brain; Disease Models, Animal; Evoked Potentials; Excitatory Amino Acid Antagonists; Exploratory Behavior; GABA Agonists; Interpersonal Relations; Maze Learning; Mice; Mice, Inbred C57BL; Mice, Transgenic; Nerve Tissue Proteins; Neurons; Parvalbumins; Pyridines; Receptors, N-Methyl-D-Aspartate; Rest; Self Care; Social Behavior Disorders

Angelman syndrome (AS) is caused by the loss of Ube3A, an ubiquitin ligase that commits specific proteins to proteasomal degradation. How this defect causes autism and other pathological phenotypes associated with AS is unknown. Long-term depression (LTD) of excitatory synaptic transmission mediated by type 5 metabotropic glutamate (mGlu5) receptors was enhanced in hippocampal slices of Ube3A(m-/p+) mice, which model AS. No changes were found in NMDA-dependent LTD induced by low-frequency stimulation. mGlu5 receptor-dependent LTD in AS mice was sensitive to the protein synthesis inhibitor anisomycin, and relied on the same signaling pathways as in wild-type mice, e.g., the mitogen-activated protein kinase (MAPK) pathway, the phosphatidylinositol-3-kinase (PI3K)/mammalian target of rapamycine pathway, and protein tyrosine phosphatase. Neither the stimulation of MAPK and PI3K nor the increase in Arc (activity-regulated cytoskeleton-associated protein) levels in response to mGlu5 receptor activation were abnormal in hippocampal slices from AS mice compared with wild-type mice. mGlu5 receptor expression and mGlu1/5 receptor-mediated polyphosphoinositide hydrolysis were also unchanged in the hippocampus of AS mice. In contrast, AS mice showed a reduced expression of the short Homer protein isoform Homer 1a, and an increased coupling of mGlu5 receptors to Homer 1b/c proteins in the hippocampus. These findings support the link between Homer proteins and monogenic autism, and lay the groundwork for the use of mGlu5 receptor antagonists in AS.

Topics: Angelman Syndrome; Animals; Carrier Proteins; Disease Models, Animal; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Hemizygote; Hippocampus; Homer Scaffolding Proteins; Immunosuppressive Agents; In Vitro Techniques; Long-Term Synaptic Depression; Methoxyhydroxyphenylglycol; Mice; Mice, Inbred C57BL; Mice, Transgenic; Mitogen-Activated Protein Kinase Kinases; Pyridines; Receptor, Metabotropic Glutamate 5; Signal Transduction; Sirolimus; Ubiquitin-Protein Ligases

Peripheral neuropathy is a common adverse effect of bortezomib-based chemotherapy. In this study we have investigated the role played by subtype 5 of metabotropic receptors in bortezomib induced peripheral neuropathy. Rats were administered with bortezomib three times weekly at 0.20 mg/kg for a total of 4 weeks in presence or absence of mGluR5 antagonist MPEP. The animals were submitted to paw-pressure test and tail sensory nerve conduction measurement more times during the treatment and follow-up. Bortezomib treatment induced a progressively increasing hyperalgesia in rat which was accompanied by a significant reduction in sensory nerve conduction velocity (SNCV). MPEP prevented the emergence of bortezomib-induced pain and counteracted SNCV reduction when co-administered with bortezomib treatment. Spinal extracellular glutamate levels increased in rats treated with bortezomib. Bortezomib-induced onset of the hyperalgesia and SNCV decrease could be prevented by agents that promote the reuptake of glutamate maintaining spinal glutamate at basal level. Our data support the manipulation of the glutamatergic system through the mGluR5 receptor in bortezomib induced peripheral neuropathy. The use of antagonists at the mGluR5, initiated at the same time as bortezomib-chemotherapy, might reduce the number of patients who develop painful peripheral chemo-neuropathy.

Topics: Analgesics; Animals; Boronic Acids; Bortezomib; Ceftriaxone; Cell Line, Tumor; Cell Survival; Central Nervous System Agents; Disease Models, Animal; Excitatory Amino Acid Antagonists; Glutamic Acid; Humans; Hyperalgesia; Injections, Spinal; Male; Neural Conduction; Neuralgia; Peripheral Nervous System Diseases; Pyrazines; Pyridines; Random Allocation; Rats; Receptor, Metabotropic Glutamate 5

Expression of dynorphin, an endogenous opioid peptide, increases with age and has been associated with memory impairments in rats. In human, prodynorphin (Pdyn) gene polymorphisms might be linked to cognitive function in the elderly. Moreover, elevated dynorphin levels have been reported in postmortem samples from Alzheimer's disease patients. However, the cellular and molecular processes affected by higher dynorphin levels during aging remain unknown. Using Pdyn(-/-) mice, we observed significant changes in the function and expression of Group 1 metabotropic glutamate receptor (mGluR). Compared with age-matched wild-type (WT) littermates, we found increased expression of mGluR1α and mGluR5 in the hippocampus and cortex of old, but not young, Pdyn(-/-) mice. Increased Group 1 mGluR expression in aged Pdyn(-/-) mice was associated with enhanced mGluR-mediated long-term depression, a form of synaptic plasticity. Notably, whereas aged WT mice developed spatial and recognition memory deficits, aged Pdyn(-/-) mice performed similarly as young mice. Pharmacological treatments with 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide, a positive modulator of mGlu5 receptors, or norbinaltorphimine, an antagonist for dynorphin-targeted κ-opioid receptor, rescued memory in old WT mice. Conversely, mGlu5 receptor antagonist 2-methyl-6-(phenylethynyl)pyridine hydrochloride impaired spatial memory of old Pdyn(-/-) mice. Intact cognition in aged Pdyn(-/-) mice paralleled with increased expression of Group 1 mGluR-related genes Homer 1a and Arc. Finally, aged Pdyn(-/-) mice displayed less anxiety-related behaviors than age-matched WT mice. Together, our results suggest that elevated Pdyn expression during normal aging reduces mGluR expression and signaling, which in turn impairs cognitive functions and increases anxiety.

Topics: Aging; Animals; Anxiety; Benzamides; Benzphetamine; Central Nervous System Stimulants; Cerebral Cortex; Cognition Disorders; Disease Models, Animal; Enkephalins; Excitatory Amino Acid Antagonists; Exploratory Behavior; Gene Expression Regulation; Hippocampus; In Vitro Techniques; Long-Term Synaptic Depression; Memory Disorders; Mice; Mice, Inbred C57BL; Mice, Knockout; Protein Precursors; Pyrazoles; Pyridines; Receptors, Metabotropic Glutamate; Recognition, Psychology

Fragile X syndrome, the most common form of heritable mental retardation, is a developmental disorder with known effects within sensory systems. Altered developmental plasticity has been reported in the visual and somatosensory systems in Fmr1 knock-out (KO) mice. Behavioral studies have revealed maladaptive auditory responses in fragile X syndrome patients and Fmr1 KO mice, suggesting that adaptive plasticity may also be impaired in the auditory system. Here we show that, whereas tonotopic frequency representation develops normally in Fmr1 KO mice, developmental plasticity in primary auditory cortex is grossly impaired. This deficit can be rescued by pharmacological blockade of mGluR5 receptors. These results support the mGluR hypothesis of fragile X mental retardation and suggest that deficient developmental plasticity may contribute to maladaptive auditory processing in fragile X syndrome.

Topics: Animals; Auditory Cortex; Critical Period, Psychological; Disease Models, Animal; Excitatory Amino Acid Antagonists; Fragile X Mental Retardation Protein; Fragile X Syndrome; Mice; Mice, Knockout; Neuronal Plasticity; Neurons; Pyridines; Receptor, Metabotropic Glutamate 5

Fragile X syndrome (FXS) is a leading cause of intellectual disability. FXS is caused by loss of function of the FMR1 gene, and mice in which Fmr1 has been inactivated have been used extensively as a preclinical model for FXS. We investigated the behavioral pharmacology of drugs acting through dopaminergic, glutamatergic, and cholinergic systems in fragile X (Fmr1 (-/Y)) mice with intracranial self-stimulation (ICSS) and locomotor activity measurements. We also measured brain expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine biosynthesis. Fmr1 (-/Y) mice were more sensitive than wild type mice to the rewarding effects of cocaine, but less sensitive to its locomotor stimulating effects. Anhedonic but not motor depressant effects of the atypical neuroleptic, aripiprazole, were reduced in Fmr1 (-/Y) mice. The mGluR5-selective antagonist, 6-methyl-2-(phenylethynyl)pyridine (MPEP), was more rewarding and the preferential M1 antagonist, trihexyphenidyl, was less rewarding in Fmr1 (-/Y) than wild type mice. Motor stimulation by MPEP was unchanged, but stimulation by trihexyphenidyl was markedly increased, in Fmr1 (-/Y) mice. Numbers of midbrain TH+ neurons in the ventral tegmental area were unchanged, but were lower in the substantia nigra of Fmr1 (-/Y) mice, although no changes in TH levels were found in their forebrain targets. The data are discussed in the context of known changes in the synaptic physiology and pharmacology of limbic motor systems in the Fmr1 (-/Y) mouse model. Preclinical findings suggest that drugs acting through multiple neurotransmitter systems may be necessary to fully address abnormal behaviors in individuals with FXS.

Topics: Animals; Antipsychotic Agents; Aripiprazole; Behavior, Animal; Blotting, Western; Cocaine; Disease Models, Animal; Dopamine Uptake Inhibitors; Excitatory Amino Acid Antagonists; Fragile X Mental Retardation Protein; Fragile X Syndrome; Immunoenzyme Techniques; Male; Mice; Mice, Knockout; Motor Activity; Muscarinic Antagonists; Piperazines; Pyridines; Quinolones; Receptor, Metabotropic Glutamate 5; Reward; Trihexyphenidyl; Tyrosine 3-Monooxygenase

We have demonstrated that blocking CXCR4 may be a potent anti-metastatic therapy for CXCR4-related oral cancer. However, as CXCR4 antagonists are currently in clinical use to induce the mobilization of hematopoietic stem cells, continuous administration as an inhibitor for the metastasis may lead to persistent leukocytosis. In this study, we investigated the novel therapeutic downstream target(s) of the SDF-1/CXCR4 system, using B88-SDF-1 cells, which have an autocrine SDF-1/CXCR4 system and exhibit distant metastatic potential in vivo. Microarray analysis revealed that 418 genes were upregulated in B88-SDF-1 cells. We identified a gene that is highly upregulated in B88-SDF-1 cells, metabotropic glutamate receptor 5 (mGluR5), which was downregulated following treatment with 1,1' -[1,4-Phenylenebis(methylene)]bis-1,4,8,11-tetraazacyclotetradecane octahydrochloride (AMD3100), a CXCR4 antagonist. The upregulation of mGluR5 mRNA in the SDF-1/CXCR4 system was predominately regulated by the Ras-extracellular signal-regulated kinase (ERK)1/2 pathway. Additionally, the growth of B88-SDF-1 cells was not affected by the mGluR5 agonist (S)-3,5-DHPG (DHPG) or the mGluR5 antagonists 2-Methyl-6-(phenylethynyl)pyridine (MPEP) and 3-((2-Methyl-1,3-thiazol-4-yl)ethynyl)pyridine (MTEP). However, we observed that DHPG promoted B88-SDF-1 cell migration, whereas both MPEP and MTEP inhibited B88-SDF-1 cell migration. To assess drug toxicity, the antagonists were intraperitoneally injected into immunocompetent mice for 4 weeks. Mice injected with MPEP (5 mg/kg) and MTEP (5 mg/kg) did not exhibit any side effects, such as hematotoxicity, allergic reactions or weight loss. The administration of antagonists significantly inhibited the metastasis of B88-SDF-1 cells to the lungs of nude mice. These results suggest that blocking mGluR5 with antagonists such as MPEP and MTEP could prevent metastasis in CXCR4-related oral cancer without causing side effects.

Topics: Animals; Cell Line, Tumor; Cell Movement; Cell Proliferation; Chemokine CXCL12; Disease Models, Animal; Gene Expression; Gene Expression Regulation, Neoplastic; Glutamic Acid; Humans; Mice; Mouth Neoplasms; Neoplasm Metastasis; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, CXCR4; Thiazoles

The metabotropic glutamate type 1 (mGlu1) and type 5 (mGlu5) receptors, the only members of group I mGlu receptors, are implicated in synaptic plasticity and mechanisms of feedback control of glutamate release. They exhibit nearly complementary distributions throughout the central nervous system, well evident in the cerebellum, where mGlu1 receptor is most intensely expressed while mGlu5 receptor is not. Despite their different distribution, they show a similar subcellular localization and use common transducing pathways. We recently described the Grm1(crv4) mouse with motor coordination deficits and renal anomalies caused by a spontaneous mutation inactivating the mGlu1 receptor. To define the neuropathological mechanisms in these mice, we evaluated expression and function of the mGlu5 receptor in cerebral and cerebellar cortices. Western blot and immunofluorescence analyses showed mGlu5 receptor overexpression. Quantitative reverse transcriptase-polymerase chain reaction results indicated that the up-regulation is already evident at RNA level. Functional studies confirmed an enhanced glutamate release from cortical cerebral and cerebellar synaptosomes when compared with wild-type that is abolished by the mGlu5 receptor-specific inhibitor, 2-methyl-6-(phenylethynyl) pyridine hydrochloride (MPEP). Finally, acute MPEP treatment of Grm1(crv4/crv4) mice induced an evident although incomplete improvement of motor coordination, suggesting that mGlu5 receptors enhanced activity worsens, instead of improving, the motor-coordination defects in the Grm1(crv4/crv4) mice.

Topics: Animals; Brain; Disease Models, Animal; Excitatory Amino Acid Antagonists; Female; Glutamic Acid; Male; Mice; Mice, Inbred BALB C; Movement Disorders; Mutation; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Synaptosomes

Plastic changes in the amygdala and limbic cortex networks have been widely shown in chronic pain. We have here investigated the role of group I metabotropic glutamate receptors (mGluRs) in the basolateral amygdala (BLA) pre-infra-limbic (PL-IL) divisions of the medial prefrontal cortex (mPFC) neuron connections after carrageenan-induced inflammatory pain in the rat. Intra-plantar injection of carrageenan decreased either spontaneous or mechanically/electrically evoked activity of PL cortex pyramidal neurons which responded with excitation in a way prevented by CPCOOEt, a selective mGluR1 antagonist, though not by MPEP, a selective mGluR5 antagonist. Accordingly, intra-BLA microinjection of DHPG, a group I mGluR agonist, caused PL cortex neuron activity depression, antagonized by CPCCOEt. CPCOOEt, but not MPEP, reduced also carrageenan-induced mechanical allodynia. The PL cortex cell deactivation in inflammatory pain condition was associated with increased GABA (conversely glutamate was decreased) in the PL/IL cortex. The local application of bicuculline, a GABA(A) receptor selective antagonist, reduced mechanical allodynia. An over-expression of mGluR1, but not mGluR5, have been observed in the PL-IL cortex after inflammatory pain suggesting an increased mGluR1-dependent cross-talk among BLA and IL-PL cortex neurons in inflammatory pain conditions. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Topics: Action Potentials; Amygdala; Animals; Bicuculline; Carrageenan; Chromones; Disease Models, Animal; Electric Stimulation; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Formaldehyde; GABA Antagonists; Gene Expression; Glycine; Male; Neural Inhibition; Neural Pathways; Neuronal Plasticity; Pain; Physical Stimulation; Prefrontal Cortex; Pyramidal Cells; Pyridines; Rats; Rats, Wistar; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Resorcinols

L-3,4-Dihydroxyphenylalanine (l-DOPA), the gold standard therapy for Parkinson disease (PD), is associated with motor fluctuations and dyskinesias. This study sought to prevent the development of l-DOPA-induced dyskinesias (LID) with the metabotropic glutamate receptor type 5 (mGlu5 receptor) antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP) in the de novo treatment of monkeys lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as a PD model. MPTP-lesioned monkeys were treated once daily for one month with either l-DOPA or l-DOPA + MPEP (10 mg/kg). MPEP (administered 15 min before l-DOPA) plasma concentrations were elevated during all the l-DOPA motor activation and did not accumulate during a month. The antiparkinsonian effect was maintained throughout the treatment period in MPTP-lesioned monkeys treated with l-DOPA + MPEP, while the duration of this effect decreased over time in MPTP-lesioned monkeys treated with l-DOPA alone, suggesting wearing-off. Over the month-long treatment, the mean dyskinesia score increased in l-DOPA-treated monkeys; interestingly, this increase was reduced by overall 72% in the l-DOPA + MPEP group. Mean dyskinesia scores of monkeys correlated inversely with plasma MPEP concentrations. Normal control and saline-treated MPTP-lesioned monkeys were also included for biochemical analyses. All MPTP-lesioned monkeys were extensively and similarly denervated. [(3)H]ABP688 specific binding to mGlu5 receptors increased in the putamen of l-DOPA-treated monkeys compared to control, saline or l-DOPA + MPEP-treated monkeys. Mean dyskinesia scores of MPTP-lesioned monkeys correlated positively with [(3)H]ABP688 specific binding in the putamen. This study showed a beneficial chronic antidyskinetic effect of MPEP in de novol-DOPA-treated MPTP-lesioned monkeys, supporting the therapeutic use of mGlu5 receptor antagonists in PD to prevent LID. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Topics: Animals; Antiparkinson Agents; Disease Models, Animal; Dopamine; Dopamine Plasma Membrane Transport Proteins; Drug Administration Schedule; Dyskinesia, Drug-Induced; Excitatory Amino Acid Antagonists; Female; Levodopa; Macaca fascicularis; Oximes; Parkinsonian Disorders; Putamen; Pyridines; Radioligand Assay; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate

Microinfusion of anticonvulsants into the perirhinal cortex through 1 guide cannula in each hemisphere only invades a small area of this seizure controlling site in rats exposed to soman. The purpose of the present study was to examine whether infusions made through 2 cannulas in each perirhinal cortex may produce more efficacious anticonvulsant action against soman intoxication than the use of 1 cannula only in rats infused with the ionotropic antagonists procyclidine and caramiphen or the metabotropic glutamate modulators DCG-IV and MPEP. The results showed that the mere presence of indwelling double cannulas caused proconvulsant effect in response to subsequent systemic administration of soman. Both the control and caramiphen groups with double cannulas had significantly shorter latencies to seizure onset than the corresponding groups with single cannula. Procyclidine resulted in anticonvulsant efficacy, even in rats with double cannulas. In rats that received twin infusions of DCG-IV or MPEP, the anticonvulsant impact was very high, inasmuch as a majority of the rats in each group was protected against seizure activity. Drugs possessing powerful anticonvulsant potency can apparently counteract the proconvulsant effect of double cannulas, and some can even gain enhanced anticonvulsant capacity when invading a larger area of the perirhinal cortex. Perirhinal EEG recordings (electrodes in indwelling cannulas) in a separate set of rats not exposed to soman or drugs showed no differences in basal electrical activity (total power 0.5-25Hz or the theta band 4-12Hz) between groups with single or double cannulas. The intrinsic excitability and synaptic connectivity of the perirhinal cortex may be associated with the proconvulsant impact observed in rats with double cannulas when exposed to soman.

Topics: Animals; Anticonvulsants; Brain Waves; Catheters, Indwelling; Cerebral Cortex; Cyclopentanes; Cyclopropanes; Disease Models, Animal; Drug Delivery Systems; Electroencephalography; Glycine; Infusions, Parenteral; Male; Micromanipulation; Procyclidine; Pyridines; Rats; Rats, Wistar; Reaction Time; Seizures; Soman; Time Factors

This study analyzed the effect of intra-ventrolateral periaqueductal grey (VL PAG) cannabinoid receptor (CB) stimulation on pain responses and rostral ventromedial medulla (RVM) neural activity in the chronic constriction injury (CCI) model of neuropathic pain in rats. Interaction between CB1 and metabotropic glutamate 1 and 5 (mGlu(1)/mGlu(5)) receptors was also investigated together with the expression of the CB1 receptor associated Gαi3 and cannabinoid receptor interacting 1a (CRIP 1a) proteins and the endocannabinoid synthesising and hydrolysing enzymes. In rats not subjected to CCI-induced pain, intra-VL PAG (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl) pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate (WIN 55,212-2) (2-4-8 nmol), a CB receptor agonist, increased the tail flick latency and changed the ongoing activity of RVM OFF and the tail flick-related activity of the ON and OFF cells, accordingly. These effects were prevented by SR141716A and MPEP, selective CB(1) and mGlu(5) receptor antagonists, respectively, though not by CPCCOEt, a selective mGlu(1) receptor antagonist. A higher dose up to 16 nmol of WIN 55,212-2 was necessary to increase tail flick latency and change ON and OFF cell activity in CCI rats. Consistently, CCI rats showed a decrease in the expression of CB(1) receptors, NAPE-PLD, Gαi3 and CRIP 1a proteins;the expression of diacylglycerol lipase A (DAGLA) was increased while fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MGL) did not change. As in control rats, MPEP and SR141716A also blocked WIN 55,212-2- induced effects in CCI rats. These data demonstrate a down regulation of the endocannabinoid system and a functional interaction between mGlu(5) and CB(1) receptors for cannabinoid-mediated effect in the PAG-RVM pain circuitry in neuropathic pain inflicted rats.

Topics: Analgesics; Animals; Benzoxazines; Disease Models, Animal; Drug Interactions; Excitatory Amino Acid Antagonists; Male; Medulla Oblongata; Morpholines; Naphthalenes; Neuralgia; Periaqueductal Gray; Piperidines; Pyrazoles; Pyridines; Rats; Rats, Wistar; Receptor, Cannabinoid, CB1; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Rimonabant

Hyperactivity of the glutamatergic system is involved in excitotoxicity and neurodegeneration in Parkinson's disease (PD). Metabotropic glutamate receptor subtype 5 (mGluR5) modulates glutamatergic transmission and thus has been proposed as a potential target for neuroprotective drugs. The aim of this study was to determine the effects of 2-methyl-6-(phenylethynyl)-pyridine (MPEP), an mGluR5 antagonist, on working memory, object recognition, and neurodegeneration in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD rat model. Male Wistar rats were stereotaxically injected with MPTP into the substantia nigra pars compacta (SNc). Starting 1 day after lesioning (day 1), the rats were treated daily with MPEP (2mg/kg/day, i.p.) for 14 days and rats underwent a T-maze test on days 8-10 and an object recognition test on days 12-14. MPTP-lesioned rats showed impairments of working memory in the T-maze test and of recognition function in the object recognition test and both effects were prevented by MPEP treatment. Furthermore, MPTP lesion-induced dopaminergic degeneration in the nigrostriatal system, microglial activation in the SNc, and cell loss in the hippocampal CA1 area were all inhibited by MPEP treatment. These data provide support for a role of mGluR5s in the pathophysiology of PD and suggest that MPEP is a promising pharmacological tool for the development of new treatments for dementia associated with PD.

Topics: Animals; Cognition Disorders; Disease Models, Animal; Male; Neurodegenerative Diseases; Parkinsonian Disorders; Pyridines; Random Allocation; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate

Recent studies highlight that the brain glutamate system is involved in the etiology of depression and glutamatergic-targeting drugs are currently being explored as novel antidepressant medications. Previous studies reveal that the selective metabotropic glutamate receptor 5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP) produces antidepressant-like effects in behavioral despair and olfactory bulbectomy models. The current study aimed to further explore its behavioral actions in additional animal models of depression (forced swimming test (FST) and learned helplessness (LH) test) and its underlying neurobiological mechanisms. The results demonstrated that acute treatment of MPEP at 30 but not 10mg/kg significantly reduced immobility in FST without affecting locomotor activities. Sub-chronic, five-day treatment of MPEP (30 mg/kg) decreased escape failures in animals that had developed LH symptoms. This sub-chronic treatment also increased hippocampal brain-derived neurotrophic factor (BDNF) protein levels in both non-stressed and stressed animals and restored the stress-induced down-regulation of BDNF expression. Current findings provide strong evidence for further studies of MPEP as a tool to explore novel antidepressants.

Topics: Analysis of Variance; Animals; Antidepressive Agents; Brain-Derived Neurotrophic Factor; Depression; Disease Models, Animal; Dose-Response Relationship, Drug; Down-Regulation; Escape Reaction; Helplessness, Learned; Immobility Response, Tonic; Male; Motor Activity; Olfactory Bulb; Pyridines; Rats; Rats, Sprague-Dawley; Swimming

Accumulated evidence indicates that metabotropic glutamate 5 (mGlu5) receptor blockade exerts antidepressant-like and anxiolytic-like effects in several animal models. The novelty-suppressed feeding (NSF) test is used to measure anxiety-induced hypophagia in rodents. Anxiogenic-like behavior can be counteracted by acute treatment with anxiolytics or chronic treatment with antidepressants. The objective of the present study was to investigate the effect of an mGlu5 receptor antagonist, 2-methyl-6-(phenylethynyl)-pyridine (MPEP), using the NSF test and to investigate the mechanisms underlying the effects of MPEP. The administration of MPEP at 1 h prior to testing significantly shortened the latency period until feed (an acute effect), and this effect lasted for 24 h (a sustained effect), similar to the results observed using the N-methyl-D-aspartate receptor antagonist ketamine. Pretreatment with a protein synthesis inhibitor, anisomycin, blocked the sustained, but not the acute, effects of MPEP, suggesting the involvement of new protein synthesis in the sustained effect of MPEP. In addition, the sustained effect of MPEP in the NSF test was partially abolished by pretreatment with a mammalian target of rapamycin (mTOR) antagonist, rapamycin. In contrast, a tropomyosin-related kinase, the tyrosine kinase inhibitor K252a, did not counteract the sustained effects of MPEP in this test. Taken together, these results are the first report to demonstrate that the blockade of the mGlu5 receptor exerted acute and sustained effects in the NSF test and that new protein synthesis may contribute to the sustained effects of MPEP, which may not mediate brain-derived neurotrophic factor-mTOR signaling.

Topics: Analysis of Variance; Animals; Anti-Anxiety Agents; Anxiety; Carbazoles; Diazepam; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Schedule; Enzyme Inhibitors; Exploratory Behavior; Feeding Behavior; Fluvoxamine; Immunosuppressive Agents; Indole Alkaloids; Inhibition, Psychological; Male; Mice; Mice, Inbred C57BL; Pyridines; Reaction Time; Sirolimus; Time Factors

Pharmaceutical treatments are being developed to correct specific behavioural and morphological aspects of neurodevelopmental disorders such as mental retardation. Fragile X syndrome is an X-linked mental retardation with abnormal dendritic protrusions from neurons in the brain. Increased signalling via excitatory metabotropic glutamate receptor (mGluR) pathways is hypothesised to contribute to this disorder. Targeting these receptors has shown improvements in both behaviour and morphology with the Fmr1-KO mouse model for the syndrome. It is not known whether similar changes occur in excitatory synaptic activity following treatment with mGluR antagonists. We tested the effects of prolonged mGluR blockade on excitatory synaptic activity at three developmental time points in hippocampal slices. We observed a rescue effect of the antagonist MPEP upon spontaneous EPSC amplitude and charge at 2 weeks but not 1 week or 8-10 weeks of development. These data support the role of mGluR antagonist treatment for functional synaptic correction at an early developmental stage in a model for fragile X syndrome.

Topics: Animals; Animals, Newborn; Disease Models, Animal; Excitatory Amino Acid Antagonists; Female; Fragile X Mental Retardation Protein; Fragile X Syndrome; Hippocampus; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Organ Culture Techniques; Pyridines; Receptors, Metabotropic Glutamate; Synaptic Transmission

Drinking to intoxication or binge drinking is a hallmark characteristic of alcohol abuse. Although hard to model in rodents, the scheduled high alcohol consumption (SHAC) procedure generates high, stable ethanol intake and blood ethanol concentrations in mice to levels consistent with definitions of binge drinking. The purpose of the present studies was to determine the effects of pharmacological manipulation of the opioidergic, glutamatergic, and γ-aminobutyric acid (GABA)ergic systems on binge drinking with the SHAC procedure. Parallel manipulations were conducted in mice trained in operant self-administration of either sucrose or ethanol. For the SHAC procedure, genetically heterogeneous Withdrawal Seizure Control mice were given varying periods of fluid access, with a 30-min ethanol session every third day (total of seven). Mice were pretreated intraperitoneally with naltrexone (0, 0.6, or 1.25 mg/kg), baclofen (0, 2.5, or 5.0 mg/kg), or 2-methyl-6-(phenylethynyl)-pyridine (MPEP; 0, 3.0, or 10.0 mg/kg) before each ethanol session. For the operant self-administration procedure, separate groups of C57BL/6 mice were trained to complete a single response requirement (16 presses on the active lever) to gain 30 min of access to an ethanol or a sucrose solution. Mice received pretreatments of the same doses of naltrexone, MPEP, or baclofen before the self-administration sessions, with saline injections on intervening days. Naltrexone produced a dose-dependent decrease in binge drinking, and the highest dose also significantly decreased operant self-administration of ethanol and sucrose. Both doses of baclofen significantly decreased binge alcohol consumption, but the higher dose also tended to decrease water intake. The highest dose of baclofen also significantly decreased operant self-administration of sucrose. MPEP (10 mg/kg) significantly decreased binge alcohol consumption and sucrose self-administration. These results indicate that manipulation of the opioidergic, glutamatergic, and GABAergic systems significantly decreased binge drinking.

Topics: Alcohol Drinking; Animals; Baclofen; Disease Models, Animal; Ethanol; Excitatory Amino Acid Antagonists; GABA-B Receptor Agonists; Male; Mice; Mice, Inbred C57BL; Naltrexone; Narcotic Antagonists; Pyridines; Receptors, GABA-B; Receptors, Metabotropic Glutamate; Receptors, Opioid; Self Administration; Sucrose

Abnormal dendritic spine morphology is a significant neuroanatomical defect in fragile X mental retardation. It has been suggested that overactive group 1 metabotropic glutamate receptor (mGlu) signaling is associated with the spine dysmorphology occurring in fragile X syndrome (FXS). Thus, group 1 mGlu became a new therapeutic target for the treatment of FXS.. The purpose of this study was to identify the effect of inhibition of mGlu signaling in FXS.. We observed the changes in dendritic spines after pharmacological modulation of mGlu signaling in an Fmr1 knockout (KO) mouse model.. The activation of group 1 mGlu resulted in elongation of dendritic spines in the cultured neurons derived from Fmr1 KO mice and wild-type (WT) mice. Antagonism of group 1 mGlu reduced the average spine length of Fmr1 KO neurons. Furthermore, systemic administration of the selective group 1 mGlu5 antagonist 2-methyl-6-phenylethynyl pyridine (MPEP) reduced the average spine length and density in the cortical neurons of Fmr1 KO mice at developmental age. For the adult mice, MPEP administration was less effective for the restoration of spine length. The percentage of immature spines showed a similar reduction in parallel to the changes of spine length. Temporary MPEP intervention with single-dose treatment did not show any effect.. These results show that MPEP administration could partially rescue the morphological deficits of dendritic spines in Fmr1 KO mice at developmental age.

Topics: Age Factors; Analysis of Variance; Animals; Animals, Newborn; Benzopyrans; Cells, Cultured; Dendritic Spines; Disease Models, Animal; Fragile X Mental Retardation Protein; Fragile X Syndrome; Hippocampus; Methoxyhydroxyphenylglycol; Mice; Mice, Inbred C57BL; Mice, Knockout; Neural Inhibition; Neurons; Pyridines; Receptors, Metabotropic Glutamate; Signal Transduction; Silver Staining

To study the effects of chronic, systemic treatment with 2-methyl-6-(phenylethynyl)-pyridine (MPEP) on behavioral activity and neuroprotection in the rat with partial lesion of the nigrostriatal pathway.. A total of 37 male SD rats were randomly divided into sham (n=11), PD+ saline (n=15) and PD+MPEP group (n=11). Rat model of Parkinson's disease was established by injection of 6-OHDA into medial forebrain bundle. PD+vehicle rats and PD+MPEP rats were injected with NS (0.1 mL) and MPEP (3 mg/kg) per day respectively. Changes in the spontaneous and induced behaviors and the degree of dopamimnergic neurons loss in the substantia nigra pars compacta (SNpc) were observed by behavioral and immunocytochemical methods in partially lesioned and MPEP-treated rats.. Unilateral injection of 6-hydrodopamine (6-OHDA) into medial forebrain bundle resulted in the moderate loss (39%) of dopaminergic neurons in the SNpc, and MPEP treatment decreased the number of neurons loss compared with PD+saline rats (P < 0.01). In this model, the lesioned rats did not show obviously abnormal posture. However, apomorphine (APO) induced significant rotation behavior, which increases in a time-dependent manner. Chronic, systemic treatment with MPEP could against the toxicity of 6-OHDA, and reduced the loss of SNpc dopaminergic neurons. In addition, MPEP ameliorated significantly the rotation behaviour induced by APO, which is strengthened in a time-dependent manner.. MPEP treatment has anti-parkinsonian and neuroprotective effects in the rat with partial lesion of the nigrostriatal pathway, and the efficacy gradually increase with the treatment time.

Topics: Animals; Antiparkinson Agents; Behavior, Animal; Disease Models, Animal; Male; Neuroprotective Agents; Parkinson Disease; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate

The striatal glutamatergic hyperactivity is considered critical in the development of levodopa-induced dyskinesias (LID) in Parkinson's disease (PD). Pharmacological antagonism of the metabotropic glutamate receptors (mGluRs), in particular, the subtype mGluR5, can inhibit the expression of dyskinesia in both rodent and nonhuman primate models of PD. However, the exact mechanisms underlying the mGluR5 antagonism effects are not completely known. The vesicular glutamate transporters (VGluts) are localized in the synaptic vesicles of the striatal glutamatergic axonal terminals. The effects of mGluR5 antagonism modulating VGlut1 and VGlut2, as selective markers for the corticostriatal and thalamostriatal pathways, respectively, are still unknown. We investigated the effects of the mGluR5 antagonist, 2-methyl-6-(phenylethynyl) pyridine (MPEP) on the striatal expression of VGlut1 and VGlut2 in levodopa-treated hemiparkinsonian rats. Male Sprague-Dawley rats received a unilateral 6-hydroxydopamine (6-OHDA) administration in the nigrostriatal pathway. Rats were treated with: (a) levodopa (12 mg/kg/day with benserazide 15 mg/kg, ip) + vehicle; (b) MPEP (1.5 mg/kg/day, ip) + vehicle; (c) levodopa + MPEP, or (d) saline for 10 days. Levodopa treatment induced dyskinesias and did not modify the striatal expression of either VGlut1 or VGlut2. The administration of MPEP significantly attenuated LID and decreased the levels of VGlut2, but not the VGlut1, in the striatum ipsilateral to the lesion (P < 0.05). Our results suggest that the effects of MPEP on LID might be mediated by a modulating effect on VGlut 2 expression.

Topics: Animals; Antiparkinson Agents; Corpus Striatum; Disease Models, Animal; Down-Regulation; Dyskinesia, Drug-Induced; Excitatory Amino Acid Antagonists; Levodopa; Male; Parkinsonian Disorders; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Vesicular Glutamate Transport Protein 2

The present study examined the effects of the mGluR1 antagonist JNJ16259685 (JNJ) and the mGluR5 antagonist 2-methyl-6-phenylethynylpyridine (MPEP) alone and in combination with morphine in two acute pain models (hotplate, warm water tail-withdrawal), and a persistent, inflammatory pain model (capsaicin). In the hotplate and warm water tail-withdrawal procedures, JNJ and MPEP were ineffective when administered alone. In both procedures, JNJ potentiated morphine antinociception. In the hotplate procedure, MPEP potentiated morphine antinociception at the highest dose examined, whereas in the warm water tail-withdrawal procedure MPEP attenuated morphine antinociception at a moderate dose and potentiated morphine antinociception at a high dose. For both JNJ and MPEP, the magnitude of this morphine potentiation was considerably greater in the hotplate procedure. In the capsaicin procedure, the highest dose of MPEP produced intermediate levels of antihyperalgesia and also attenuated the effects of a dose of morphine that produced intermediate levels of antihyperalgesia. In contrast, JNJ had no effect when administered alone in the capsaicin procedure and did not alter morphine-induced antihyperalgesia. The present findings suggest that the effects produced by mGluR1 and mGluR5 antagonists alone and in combination with morphine can be differentiated in models of both acute and persistent pain.

Topics: Animals; Behavior, Animal; Capsaicin; Disease Models, Animal; Drug Therapy, Combination; Excitatory Amino Acid Antagonists; Inflammation; Male; Morphine; Narcotics; Pain; Pain Measurement; Pyridines; Quinolines; Rats; Rats, Inbred F344; Receptors, Metabotropic Glutamate

Autism spectrum disorders (ASD) are highly disabling developmental disorders with a population prevalence of 1-3%. Despite a strong genetic etiology, there are no current therapeutic options that target the core symptoms of ASD. Emerging evidence suggests that dysfunction of glutamatergic signaling, in particular through metabotropic glutamate receptor 5 (mGluR5) receptors, may contribute to phenotypic deficits and may be appropriate targets for pharmacologic intervention. This study assessed the therapeutic potential of 2-methyl-6-phenylethyl-pyrididine (MPEP), an mGluR5-receptor antagonist, on repetitive and anxiety-like behaviors in the valproic acid (VPA) mouse model of autism. Mice were exposed prenatally on day E13 to VPA and assessed for repetitive self-grooming and marble burying behaviors as adults. Anxiety-like behavior and locomotor activity were measured in an open-field. VPA-exposed mice displayed increased repetitive and anxiety-like behaviors, consistent with previously published results. Across both marble burying and self-grooming assays, MPEP significantly reduced repetitive behaviors in VPA-treated mice, but had no effect on locomotor activity. These results are consistent with emerging preclinical literature that mGluR5-antagonists may have therapeutic efficacy for core symptoms of autism.

Topics: Animals; Anti-Anxiety Agents; Autistic Disorder; Behavior, Animal; Disease Models, Animal; Female; Grooming; Mice; Motor Activity; Pregnancy; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Stereotyped Behavior; Valproic Acid

Both the GABA(B) receptor positive modulator GS39783 and the GABA(B) receptor antagonist CGP46381 exhibit anxiolytic-like properties in animal models. In the present studies, the effects of GS39783 and CGP46381 in the modified Geller-Seifter task were assessed. First, the predictive validity of the task was confirmed by assessing the effects of multiple anxiolytic and non-anxiolytic compounds on punished and unpunished responding.. Rats were trained in the modified Geller-Seifter task. After successful acquisition of the task, chlordiazepoxide, diazepam, MPEP, haloperidol, GS39783, 8-OH-DPAT, alprazolam and CGP46381 were tested consecutively. For each test compound, doses were administered in a randomized, counter-balanced, within-subjects design. Drug tests were performed only when rats exhibited baseline performance (the punished and time-out response rates were less than 10% of the unpunished response rate).. Chlordiazepoxide, diazepam, alprazolam and MPEP released punished responding with variable effects on unpunished responding. Haloperidol had a small but significant effect on punished responding at an intermediate dose, and decreased unpunished responding at the highest dose tested. In contrast, administration of the GABA(B) receptor positive modulator GS398783 or the GABA(B) receptor antagonist CGP46381 at doses up to 30 mg/kg had no effects on either punished or unpunished responding. The 5-HT(1A) agonist 8-OH-DPAT did not release punished responding, but significantly decreased unpunished responding at the highest dose tested.. The modified Geller-Seifter task generally exhibits good predictive validity for anxiolytic-like compounds. Neither GABA(B) receptor positive allosteric modulation nor blockade exhibited anxiolytic-like properties in the modified Geller-Seifter task. The 5-HT(1A) partial agonist buspirone was similarly ineffective.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Anxiety; Behavior, Animal; Conditioning, Operant; Conflict, Psychological; Disease Models, Animal; Dopamine Antagonists; Dose-Response Relationship, Drug; Electroshock; Excitatory Amino Acid Antagonists; GABA Agents; Haloperidol; Male; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT1A; Receptors, GABA-A; Reinforcement Schedule; Reproducibility of Results; Serotonin Receptor Agonists

Autism is a neurodevelopmental disorder characterized by abnormal reciprocal social interactions, communication deficits, and repetitive behaviors with restricted interests. BTBR T+tf/J (BTBR) is an inbred mouse strain that shows robust behavioral phenotypes with analogies to all three of the diagnostic symptoms of autism, including well-replicated deficits in reciprocal social interactions and social approach, unusual patterns of ultrasonic vocalization, and high levels of repetitive self-grooming. These phenotypes offer straightforward behavioral assays for translational investigations of pharmacological compounds. Two suggested treatments for autism were evaluated in the BTBR mouse model. Methyl-6-phenylethynyl-pyridine (MPEP), an antagonist of the mGluR5 metabotropic glutamate receptor, blocks aberrant phenotypes in the Fmr1 mouse model of Fragile X, a comorbid neurodevelopmental disorder with autistic features. Risperidone has been approved by the United States Food and Drug Administration for the treatment of irritability, tantrums, and self-injurious behavior in autistic individuals. We evaluated the actions of MPEP and risperidone on two BTBR phenotypes, low sociability and high repetitive self-grooming. Open field activity served as an independent control for non-social exploratory activity and motor functions. C57BL/6J (B6), an inbred strain with high sociability and low self-grooming, served as the strain control. MPEP significantly reduced repetitive self-grooming in BTBR, at doses that had no sedating effects on open field activity. Risperidone reduced repetitive self-grooming in BTBR, but only at doses that induced sedation in both strains. No overall improvements in sociability were detected in BTBR after treatment with either MPEP or risperidone. Our findings suggest that antagonists of mGluR5 receptors may have selective therapeutic efficacy in treating repetitive behaviors in autism.

Topics: Animals; Autistic Disorder; Disease Models, Animal; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Exploratory Behavior; Grooming; Interpersonal Relations; Mice; Mice, Inbred C57BL; Mice, Inbred Strains; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Statistics, Nonparametric; Stereotyped Behavior

The loss of nigrostriatal dopaminergic neurons that characterizes Parkinson's disease (PD) causes complex functional alterations in the basal ganglia circuit. Increased glutamatergic activity at crucial points of the circuit may be central to these alterations, thereby contributing to the onset of PD motor symptoms. Signs of neuroinflammation accompanying the neuronal loss have also been observed; also in this case, glutamate-mediated mechanisms may be involved. Glutamate may therefore intervene at multiple levels in PD pathophysiology, possibly through the modulation of metabotropic receptors. To address this issue, we evaluated the effects of systemic treatment with MPEP (2-methyl-6-(phenylethynyl)-pyridine), an antagonist of metabotropic receptor mGluR5, in a rodent model of progressive nigrostriatal degeneration based on the intrastriatal injection of 6-hydroxydopamine (6-OHDA). Following 6-OHDA injection, Sprague-Dawley rats underwent a 4-week, daily treatment with MPEP (1.5mg/kg, i.p.). To investigate whether the effects varied with the progression of the lesion, subgroups of lesioned animals started the treatment at different time-points: (1) immediately, (2) 1 week, or (3) 4 weeks after the neurotoxin injection. Akinesia, dopaminergic nigrostriatal damage and neuroinflammatory response (microglial and astroglial activation) were investigated. MPEP prompted immediate amelioration of 6-OHDA-induced akinesia, as measured by the Adjusting step test, in all subgroups, regardless of the degree of nigrostriatal damage. Conversely, MPEP did not modify neuronal survival or neuroinflammatory response in the nigrostriatal pathway. In conclusion, chronic treatment with MPEP exerted a pure symptomatic effect, further supporting that mGluR5 modulation may be a viable strategy to counteract the basal ganglia functional modifications underlying PD motor symptoms.

Topics: Animals; Behavior, Animal; Corpus Striatum; Disease Models, Animal; Dopamine; Excitatory Amino Acid Antagonists; Humans; Inflammation; Male; Motor Activity; Neurons; Oxidopamine; Parkinsonian Disorders; Pyridines; Random Allocation; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Substantia Nigra

Fragile X syndrome (FXS), a common inherited form of mental impairment and autism, is caused by transcriptional silencing of the fragile X mental retardation 1 (FMR1) gene. Earlier studies have identified a role for aberrant synaptic plasticity mediated by the metabotropic glutamate receptors (mGluRs) in FXS. However, many of these observations are derived primarily from studies in the hippocampus. The strong emotional symptoms of FXS, on the other hand, are likely to involve the amygdala. Unfortunately, little is known about how exactly FXS affects synaptic function in the amygdala. Here, using whole-cell recordings in brain slices from adult Fmr1 knockout mice, we find mGluR-dependent long-term potentiation to be impaired at thalamic inputs to principal neurons in the lateral amygdala. Consistent with this long-term potentiation deficit, surface expression of the AMPA receptor subunit, GluR1, is reduced in the lateral amygdala of knockout mice. In addition to these postsynaptic deficits, lower presynaptic release was manifested by a decrease in the frequency of spontaneous miniature excitatory postsynaptic currents (mEPSCs), increased paired-pulse ratio, and slower use-dependent block of NMDA receptor currents. Strikingly, pharmacological inactivation of mGluR5 with 2-methyl-6-phenylethynyl-pyridine (MPEP) fails to rescue either the deficit in long-term potentiation or surface GluR1. However, the same acute MPEP treatment reverses the decrease in mEPSC frequency, a finding of potential therapeutic relevance. Therefore, our results suggest that synaptic defects in the amygdala of knockout mice are still amenable to pharmacological interventions against mGluR5, albeit in a manner not envisioned in the original hippocampal framework.

Topics: Amygdala; Animals; Anti-Anxiety Agents; Autistic Disorder; Disease Models, Animal; Fragile X Mental Retardation Protein; Fragile X Syndrome; Male; Mice; Mice, Knockout; Neuronal Plasticity; Neurons; Pyridines; Receptors, AMPA; Receptors, Metabotropic Glutamate; Synapses

Fragile X syndrome (FXS) causes mental impairment and autism through transcriptional silencing of the Fmr1 gene, resulting in the loss of the RNA-binding protein fragile X mental retardation protein (FMRP). Cortical pyramidal neurons in affected individuals and Fmr1 knock-out (KO) mice have an increased density of dendritic spines. The mutant mice also show defects in synaptic and experience-dependent circuit plasticity, which are known to be mediated in part by dendritic spine dynamics. We used in vivo time-lapse imaging with two-photon microscopy through cranial windows in male and female neonatal mice to test the hypothesis that dynamics of dendritic protrusions are altered in KO mice during early postnatal development. We find that layer 2/3 neurons from wild-type mice exhibit a rapid decrease in dendritic spine dynamics during the first 2 postnatal weeks, as immature filopodia are replaced by mushroom spines. In contrast, KO mice show a developmental delay in the downregulation of spine turnover and in the transition from immature to mature spine subtypes. Blockade of metabotropic glutamate receptor (mGluR) signaling, which reverses some adult phenotypes of KO mice, accentuated this immature protrusion phenotype in KO mice. Thus, absence of FMRP delays spine stabilization and dysregulated mGluR signaling in FXS may partially normalize this early synaptic defect.

Topics: Animals; Animals, Newborn; Dendritic Spines; Disease Models, Animal; Excitatory Amino Acid Antagonists; Fragile X Mental Retardation Protein; Fragile X Syndrome; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Pseudopodia; Pyridines; Receptors, Metabotropic Glutamate

Fragile X syndrome (FXS) is caused by loss of the FMR1 gene product FMRP (fragile X mental retardation protein), a repressor of mRNA translation. According to the metabotropic glutamate receptor (mGluR) theory of FXS, excessive protein synthesis downstream of mGluR5 activation causes the synaptic pathophysiology that underlies multiple aspects of FXS. Here, we use an in vitro assay of protein synthesis in the hippocampus of male Fmr1 knock-out (KO) mice to explore the molecular mechanisms involved in this core biochemical phenotype under conditions where aberrant synaptic physiology has been observed. We find that elevated basal protein synthesis in Fmr1 KO mice is selectively reduced to wild-type levels by acute inhibition of mGluR5 or ERK1/2, but not by inhibition of mTOR (mammalian target of rapamycin). The mGluR5-ERK1/2 pathway is not constitutively overactive in the Fmr1 KO, however, suggesting that mRNA translation is hypersensitive to basal ERK1/2 activation in the absence of FMRP. We find that hypersensitivity to ERK1/2 pathway activation also contributes to audiogenic seizure susceptibility in the Fmr1 KO. These results suggest that the ERK1/2 pathway, and other neurotransmitter systems that stimulate protein synthesis via ERK1/2, represent additional therapeutic targets for FXS.

Topics: Animals; Disease Models, Animal; Fragile X Mental Retardation Protein; Fragile X Syndrome; Hippocampus; Isoenzymes; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Protein Biosynthesis; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Up-Regulation

Difficulty modeling complex behavioral phenotypes in rodents (e.g., language) has hindered pathophysiological investigation and treatment development for autism spectrum disorders. Recent human neuroimaging studies, however, have identified functional biomarkers that can be more directly related to the abnormal neural dynamics of autism spectrum disorders. This study assessed the translational potential of auditory evoked-response endophenotypes of autism in parallel mouse and human studies of autism.. Whole-cortex magnetoencephalography was recorded in 17 typically developing and 25 autistic children during auditory pure-tone presentation. Superior temporal gyrus activity was analyzed in time and frequency domains. Auditory evoked potentials were recorded in mice prenatally exposed to valproic acid (VPA) and analyzed with analogous methods.. The VPA-exposed mice demonstrated selective behavioral alterations related to autism, including reduced social interactions and ultrasonic vocalizations, increased repetitive self-grooming, and prepulse inhibition deficits. Autistic subjects and VPA-exposed mice showed a similar 10% latency delay in the N1/M100 evoked response and a reduction in γ frequency (30-50 Hz) phase-locking factor. Electrophysiological measures were associated with mouse behavioral deficits. In mice, γ phase-locking factor was correlated with expression of the autism risk gene neuroligin-3 and neural deficits were modulated by the mGluR5-receptor antagonist MPEP.. Results demonstrate a novel preclinical approach toward mechanistic understanding and treatment development for autism.

Topics: Animals; Animals, Newborn; Auditory Perception; Autistic Disorder; Behavior, Animal; Biomarkers; Brain Waves; Cell Adhesion Molecules, Neuronal; Cerebral Cortex; Child; Disease Models, Animal; Endophenotypes; Evoked Potentials, Auditory; Female; Humans; Magnetoencephalography; Male; Membrane Proteins; Mice; Mice, Inbred C57BL; Nerve Tissue Proteins; Pregnancy; Prenatal Exposure Delayed Effects; Pyridines; Temporal Lobe; Valproic Acid

Visuo-spatial deficits are the most consistently reported cognitive abnormalities in Parkinson's disease (PD), and they are frequently associated to motor symptoms in the early stages of the disease when dopamine loss is moderate and still restricted to the caudate-putamen. The metabotropic glutamate receptor 5 (mGluR5) antagonist, 2-methyl-6-(phenylethynyl)-pyridine (MPEP), has beneficial effects on motor symptoms in animal models of PD. However, the effects of MPEP on the cognitive deficits of the disease have never been investigated. Thus, the purpose of this study was to explore its therapeutic potentials by investigating its effects on the visuo-spatial deficits induced by 6-hydroxydopamine (6-OHDA) lesions of dorsal striatum in CD1 mice. The results demonstrated that systemic injections of MPEP (6, 12, and 24 mg/kg, i.p.) impair visuo-spatial discrimination in intact mice at high concentrations, whereas lower doses (1.5 and 3 mg/kg, i.p.) were void of effects. Nevertheless, when an ineffective dose (MPEP 3 mg/kg) was injected, either acutely or subchronically (8 days), it antagonized the visuo-spatial discrimination deficit induced by bilateral dopamine lesion of the striatum. Furthermore, the same treatment increased contralateral turning induced by L-DOPA in mice bearing unilateral 6-OHDA lesion. These results confirm the therapeutic potential of mGluR5 blockade on motor symptoms induced by reduced striatal dopamine function. Further, they demonstrate that mGluR5 blockade may also have beneficial effects on cognitive deficits induced by dopamine depletion.

Topics: Animals; Association Learning; Corpus Striatum; Disease Models, Animal; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Levodopa; Male; Memory Disorders; Mice; Movement; Oxidopamine; Parkinson Disease; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Space Perception; Vision Disorders

Significant advances have been made in understanding the underlying defects of and developing potential treatments for Fragile X syndrome (FXS), the most common heritable mental retardation. It has been shown that neuronal metabotropic glutamate receptor 5 (mGluR5)-mediated signaling is affected in FX animal models, with consequent alterations in activity-dependent protein translation and synaptic spine functionality. We demonstrate here that a central metabolic regulatory enzyme, glycogen synthase kinase-3 (GSK3) is present in a form indicating elevated activity in several regions of the FX mouse brain. Furthermore, we show that selective GSK3 inhibitors, as well as lithium, are able to revert mutant phenotypes of the FX mouse. Lithium, in particular, remained effective with chronic administration, although its effects were reversible even when given from birth. The combination of an mGluR5 antagonist and GSK3 inhibitors was not additive. Instead, it was discovered that mGluR5 signaling and GSK3 activation in the FX mouse are coordinately elevated, with inhibition of mGluR5 leading to inhibition of GSK3. These findings raise the possibility that GSK3 is a fundamental and central component of FXS pathology, with a substantial treatment potential.

Topics: Acoustic Stimulation; Analysis of Variance; Animals; Antimanic Agents; Brain; Citrates; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Routes; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Exploratory Behavior; Fragile X Mental Retardation Protein; Gene Expression Regulation; Glycogen Synthase Kinase 3; Indoles; Lithium Chloride; Male; Maleimides; Mice; Mice, Knockout; Pyridines; Seizures; Serine; Thiazoles; Urea

Cocaine addiction is characterized by an impaired ability to develop adaptive behaviors that can compete with cocaine seeking, implying a deficit in the ability to induce plasticity in cortico-accumbens circuitry crucial for regulating motivated behavior. We found that rats withdrawn from cocaine self-administration had a marked in vivo deficit in the ability to develop long-term potentiation (LTP) and long-term depression (LTD) in the nucleus accumbens core subregion after stimulation of the prefrontal cortex. N-acetylcysteine (NAC) treatment prevents relapse in animal models and craving in humans by activating cystine-glutamate exchange and thereby stimulating extrasynaptic metabotropic glutamate receptors (mGluR). NAC treatment of rats restored the ability to induce LTP and LTD by indirectly stimulating mGluR2/3 and mGluR5, respectively. Our findings show that cocaine self-administration induces metaplasticity that inhibits further induction of synaptic plasticity, and this impairment can be reversed by NAC, a drug that also prevents relapse.

Topics: Acetylcysteine; Animals; Behavior, Animal; Cocaine-Related Disorders; Disease Models, Animal; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Free Radical Scavengers; Long-Term Potentiation; Long-Term Synaptic Depression; Male; Neuronal Plasticity; Nucleus Accumbens; Prefrontal Cortex; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Secondary Prevention; Self Administration; Substance Withdrawal Syndrome

Systemic inhibition of complex I by rotenone in rats represents a model of Parkinson's disease (PD). The aim of this study was to elucidate whether neramexane (NMDA, nicotinic alpha9/alpha10 and 5-HT3 receptor antagonist), idazoxan (alpha2-adrenoceptor antagonist) or 2-methyl-6-(phenyl-ethyl)-pyrimidine (MPEP, metabotropic glutamate receptor 5 antagonist) prevents rotenone-induced parkinsonian-like behaviours and neurochemical changes in rats. Rotenone (2.5 mg/kg i.p. daily) was administered over 60 days together with saline, neramexane (5 mg/kg i.p., b.i.d.), idazoxan (2.5 mg/kg i.p., b.i.d.) or MPEP (2.5 mg/kg i.p., b.i.d.). The same doses of neramexane, idazoxan and MPEP were administered to rats treated with vehicle instead of rotenone. Treatment-related effects on parkinsonian-like behaviours, such as hypokinesia/rigidity and locomotor activity, were evaluated. Moreover, concentrations of dopamine, serotonin and their metabolites were measured in rats from each experimental group. Over the 60-day treatment period, the rotenone+saline treated animals developed hypokinesia, expressed as an increase in the bar and grid descent latencies in the catalepsy test, and a decrease in locomotor activity. Neramexane and idazoxan partially prevented the development of catalepsy in rotenone-treated rats. Co-administration of MPEP with rotenone resulted only in a decrease in descent latency in the grid test on day 60. Chronic rotenone treatment reduced concentrations of dopamine and serotonin in the anterior striatum, which was blocked by co-treatment with neramexane or idazoxan but not with MPEP. Only neramexane treatment blocked the rotenone-induced decrease in dopamine levels in the substantia nigra pars compacta. In conclusion, neramexane and idazoxan counteracted to some extent the development of parkinsonian symptoms and neurochemical alterations in the rotenone model of Parkinson's disease.

Topics: Adrenergic alpha-2 Receptor Antagonists; Adrenergic alpha-Antagonists; Animals; Basal Ganglia; Behavior, Animal; Catalepsy; Cyclopentanes; Disease Models, Animal; Dopamine; Excitatory Amino Acid Antagonists; Hypokinesia; Idazoxan; Male; Motor Activity; Muscle Rigidity; Neuroprotective Agents; Neurotoxicity Syndromes; Parkinsonian Disorders; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Adrenergic, alpha-2; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate; Rotenone; Serotonin; Substantia Nigra; Time Factors

Striatal glutamatergic hyperactivity through the metabotropic receptors and their intracellular signaling pathways is considered critical in the development of levodopa-induced dyskinesias in Parkinson's disease and in experimental parkinsonism.. We investigated whether the administration of the metabotropic glutamate antagonist, MPEP, modifies striatal expression of Homer family proteins which are involved in the intracellular mechanisms mediated by these receptors.. Sprague-Dawley rats were unilaterally lesioned in the nigrostriatal pathway with 6-hydroxydopamine (8 microg) and treated with: levodopa (12 mg/kg, i.p.) plus vehicle (n=10) divided in two daily injections; levodopa plus MPEP (1.5 and 3 mg/kg, i.p.; n=6-13) divided in two daily injections; or saline (n=7) for 10 consecutive days. Axial, limb, and orolingual dyskinesias were evaluated. Striatal expression of tyrosine hydroxylase (TH), Homer 1a, 1b/c, and deltaFosB were measured by Western Blot.. Animals treated with levodopa showed an increase of dyskinesia score (p<0.01) that was attenuated by the administration of MPEP (p<0.01). In the ipsilateral side of the lesion, striatal TH expression was decreased (p<0.01). No significant differences in striatal Homer 1a or b/c expression were observed between the groups of treatment. Striatal deltaFosB expression increased in the animals treated with levodopa (p<0.05) being attenuated after MPEP administration (p<0.05). MPEP effect was not paralleled by any modification of striatal Homer proteins expression.. These results suggest that Homer protein family is not causally involved in the development of dyskinetic movements induced by levodopa treatment in this animal model of parkinsonism.

Topics: Animals; Antiparkinson Agents; Carrier Proteins; Corpus Striatum; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Dyskinesia, Drug-Induced; Excitatory Amino Acid Antagonists; Gene Expression Regulation; Homer Scaffolding Proteins; Levodopa; Male; Oxidopamine; Parkinsonian Disorders; Proto-Oncogene Proteins c-fos; Pyridines; Rats; Rats, Sprague-Dawley; Tyrosine 3-Monooxygenase

Metabotropic glutamate (mGlu) receptors, which are present on neurons and glial cells, have been shown to play a role in neuropathic pain. The present study sought to investigate how the glial inhibitors minocycline and pentoxifylline alter the effect that chronic constriction injury (CCI) has on the expression of mGlu receptors and on their associated ligands. RT-PCR analysis revealed that seven days after CCI, the mRNA levels of glial markers C1q and GFAP, as well as those of mGlu5 and mGlu3, but not mGlu7, were elevated in the lumbar spinal cord - ipsilateral to the injury. The protein levels of the microglial marker OX42, the astroglial marker GFAP, and mGlu5 receptor protein were increased, whereas the levels of mGlu2/3 and mGlu7 receptor proteins were reduced. Preemptive and repeated intraperitoneal (i.p.) administration (16 and 1h before nerve injury and then twice daily for seven days) of minocycline (30mg/kg) and pentoxifylline (20mg/kg) prevented the injury-induced changes in the levels of mGlu3 and mGlu5 receptor mRNAs and the injury-induced changes in the protein levels of all the receptors. Repeated administration of minocycline and pentoxifylline significantly attenuated CCI-induced allodynia (von Frey test) and hyperalgesia (cold plate test) measured on day seven after injury and potentiated the antiallodynic and antihyperalgesic effects of single i.p. and intrathecal (i.t.) injections of mGlu receptor ligands: MPEP, LY379268 or AMN082. We conclude that attenuation of injury-induced glial activation can reduce glutamatergic activity, thereby contributing to regulation of pain sensation.

Topics: Amino Acids; Analysis of Variance; Animals; Benzhydryl Compounds; Bridged Bicyclo Compounds, Heterocyclic; CD11b Antigen; Complement C1q; Disease Models, Animal; Drug Administration Schedule; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Functional Laterality; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Hyperalgesia; Male; Mice; Minocycline; Pain Measurement; Pain Threshold; Pentoxifylline; Pyridines; Receptors, Metabotropic Glutamate; RNA, Messenger; Sciatica; Spinal Cord

Metabotropic glutamate receptor 5 (mGluR(5)) regulates the translation of amyloid precursor protein (APP) mRNA. Under resting conditions, mRNA is bound to and translationally repressed by the fragile X mental retardation protein (FMRP). Upon group 1 mGluR activation, FMRP dissociates from the mRNA and translation ensues. APP levels are elevated in the dendrites of primary neuronal cultures as well as in synaptoneurosomes (SN) prepared from embryonic and juvenile fmr-1 knockout (KO) mice, respectively. In order to study the effects of APP and its proteolytic product Abeta on Fragile X syndrome (FXS) phenotypes, we created a novel mouse model (FRAXAD) that over-expresses human APPSwe/Abeta in an fmr-1 KO background. Herein, we assess (1) human APP(Swe) and Abeta levels as a function of age in FRAXAD mice, and (2) seizure susceptibility to pentylenetetrazol (PTZ) after mGluR(5) blockade. PTZ-induced seizure severity is decreased in FRAXAD mice pre-treated with the mGluR(5) antagonist MPEP. These data suggest that Abeta contributes to seizure incidence and may be an appropriate therapeutic target to lessen seizure pathology in FXS, Alzheimer's disease (AD) and Down syndrome (DS) patients.

Topics: Age Factors; Amyloid beta-Protein Precursor; Animals; Anti-Anxiety Agents; Disease Models, Animal; Fragile X Mental Retardation Protein; Fragile X Syndrome; Gene Expression; Gene Silencing; Humans; Mice; Mice, Inbred C57BL; Mice, Knockout; Protease Nexins; Pyridines; Receptors, Cell Surface; RNA, Messenger; Seizures

Fragile X syndrome is caused by the functional loss of the fragile X mental retardation 1 (FMR1) gene. Deletion of the FMR1 ortholog in Drosophila melanogaster (Fmr1) recapitulates many phenotypes associated with fragile X syndrome. We have discovered that Fmr1 mutant Drosophila die during development when reared on food containing increased levels of glutamate, which is consistent with the theory that FMR1 loss results in excess glutamate signaling. Using this lethal phenotype, we screened a chemical library of 2,000 compounds and identified nine molecules that rescued the lethality, including three that implicate the GABAergic inhibitory pathway. Indeed, GABA treatment rescued several known Fmr1 mutant phenotypes in flies, including mushroom bodies defects, excess Futsch translation and abnormal male courtship behavior. These data are consistent with GABAergic inhibition of the enhanced excitatory pathway in fragile X syndrome. In addition, our screen reveals that the muscarinic cholinergic receptors may have a role in fragile X syndrome in parallel to the GABAergic pathway. These results point to potential therapeutic approaches for treating fragile X syndrome.

Topics: Animals; Disease Models, Animal; Drosophila; Drosophila Proteins; Drug Evaluation, Preclinical; Female; Fragile X Mental Retardation Protein; Fragile X Syndrome; gamma-Aminobutyric Acid; Glutamic Acid; Male; Molecular Weight; Mutation; Phenotype; Pyridines; RNA, Messenger; Small Molecule Libraries

Recent evidence suggests that changes in the expression of membrane receptors/ion channels in cerebellar Purkinje cells contribute to the onset of cerebellar motor symptoms in patients with multiple sclerosis (MS). We examined the expression of group-I metabotropic glutamate receptors (mGlu1 and mGlu5 receptors) in the cerebellum of mice developing experimental autoimmune encephalomyelitis (EAE) and in autoptic cerebellar samples of MS patients. EAE was induced in mice by immunization with the 35-55 fragment of MOG (myelin oligodendrocyte glycoprotein). EAE mice showed a progressive loss of mGlu1a receptors in the cerebellum, associated with an increased expression of mGlu5 receptors. These changes were restricted to Purkinje cells and their dendritic arborization, as shown by immunohistochemistry. A reduced expression of mGlu1a receptors in cerebellar Purkinje cells was also found in 7 of 9 MS patients. In addition, a light/moderate to very strong mGlu5 receptor immunoreactivity was detected in Purkinje cells of 8 MS patients, but was always absent in non-MS control patients. In EAE mice, an acute treatment with the mGlu1 receptor enhancer, 9H-xanthene-9-carboxylic acid (4-trifluoromethyl-oxazol-2-yl)-amide (RO0711401), significantly improved motor coordination, whereas treatment with the mGlu5 receptor antagonists, 2-methyl-6-(phenylethynyl)-pyridine (MPEP) and 6-methyl-2-(phenylazo)-3-pyridinol (SIB-1757), had no effect. We conclude that mGlu1 receptor enhancers improve motor symptoms associated with EAE and might be helpful as symptomatic drugs in patients with MS.

Topics: Aged; Animals; Behavior, Animal; Cerebellum; Disease Models, Animal; Encephalomyelitis, Autoimmune, Experimental; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Female; Gene Expression Regulation; Glycoproteins; Humans; Male; Mice; Mice, Inbred C57BL; Middle Aged; Multiple Sclerosis; Myelin-Oligodendrocyte Glycoprotein; Peptide Fragments; Purkinje Cells; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Time Factors

Non-dopaminergic drugs acting either on adenosine A2A or metabotropic glutamate (mGlu) receptors reduce motor impairment in animal models of Parkinson's disease (PD), suggesting a possible functional interaction between these receptors to regulate basal ganglia function. The present study therefore tested the behavioural effects of compounds acting selectively on A2A or on specific mGlu receptor subtypes, alone or in combination, in rodent models of PD. Acute administration of the adenosine A2A receptor antagonists CSC or MSX-3 at the highest doses tested (5 and 1.25mg/kg, respectively) significantly reduces haloperidol-induced catalepsy. Furthermore, the anticataleptic effect of MSX-3 was enhanced by a 3-week treatment. Acute administration of the selective group III mGlu agonist ACPT-I produces potent anticataleptic effects and prolongs time on rotarod of 6-OHDA-lesioned rats. In contrast, acute or chronic administration of MPEP (mGlu5 receptor antagonist) has no anticataleptic action. Furthermore, the acute co-administration of ACPT-I 1mg/kg, but not 5mg/kg, with CSC markedly reduces catalepsy. Opposite effects are observed after a 3-week co-administration. The co-administration of ACPT-I with MSX-3 has anticataleptic effects both after acute or chronic treatment. In contrast, acute combination of subthreshold doses of CSC and MPEP has no effect. After a 3-week treatment, however, the combination of CSC and MPEP was found to reduce haloperidol-induced catalepsy. Altogether, these results show for the first time that systemic activation of group III mGlu receptors with ACPT-I provides benefits in parkinsonian rats and underlie a possible interaction with A2A receptors to regulate basal ganglia motor function.

Topics: Adenosine A2 Receptor Antagonists; Animals; Behavior, Animal; Catalepsy; Cyclopentanes; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Schedule; Drug Combinations; Haloperidol; Male; Motor Activity; Oxidopamine; Parkinsonian Disorders; Pyridines; Rats; Rats, Wistar; Reaction Time; Receptors, Adenosine A2; Receptors, Metabotropic Glutamate; Tricarboxylic Acids; Xanthines

Recently, a simple procedure in mice, Drinking-in-the-Dark (DID), was hypothesized to have value for medication development for human alcoholism. In DID, mice are offered intermittent, limited access to ethanol over a series of days during the dark phase that results in rapid drinking to intoxication in predisposed genotypes.. We measured the effects of acamprosate or MPEP, metabotropic glutamate 5 receptor (mGluR5) antagonist, on intake of 20% ethanol, plain tap water or 10% sugar water using the DID procedure in male C57BL/6J mice.. Acamprosate (100, 200, 300, or 400 mg/kg) dose dependently decreased ethanol drinking with 300 mg/kg reducing ethanol intake by approximately 20% without affecting intake of plain water or 10% sugar water. MPEP (1, 3, 5, 10, 20, or 40 mg/kg) was more potent than acamprosate with 20 mg/kg reducing ethanol intake by approximately 20% and for longer duration without affecting intake of plain water or 10% sugar water.. These results support the hypothesis that mGluR5 signaling plays a role in excessive ethanol intake in DID and suggest DID may have value for screening novel compounds that reduce overactive glutamate signaling for potential pharmaceutical treatment of excessive ethanol drinking behavior.

Topics: Acamprosate; Alcohol Deterrents; Alcohol Drinking; Alcoholism; Animals; Darkness; Disease Models, Animal; Dose-Response Relationship, Drug; Food Deprivation; Male; Mice; Mice, Inbred C57BL; Pyridines; Receptors, Metabotropic Glutamate; Signal Transduction; Taurine

Altered glutamatergic neurotransmission is central to the expression of Parkinson's disease (PD) symptoms and may underlie l-DOPA-induced dyskinesias. Drugs acting on glutamate metabotropic receptors (mGluR) of group I can modulate subthalamic nucleus (STN) overactivity, which plays a pivotal role in these phenomena, and may counteract dyskinesias. To address these issues, we investigated the effects of a 3-week treatment with mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP), or of a subthalamic lesion, on abnormal involuntary movements (AIMs) and associated striatal expression of transcription factor FosB/Delta FosB caused by chronic l-DOPA administration, in rats with a nigrostriatal lesion. MPEP virtually abolished AIMs and reduced, dramatically, striatal expression of FosB/Delta FosB. Reduced FosB/Delta FosB expression, coupled with nonsignificant reduction of AIMs, was also observed in STN-lesioned rats. Our data confirm the role of glutamatergic neurotransmission in the pathogenesis of dyskinesias and the potential of mGluR5 antagonists in the treatment of l-DOPA-induced dyskinesias.

Topics: Adrenergic Agents; Analysis of Variance; Animals; Antiparkinson Agents; Behavior, Animal; Disease Models, Animal; Dyskinesia, Drug-Induced; Excitatory Amino Acid Antagonists; Levodopa; Male; Oxidopamine; Parkinson Disease; Proto-Oncogene Proteins c-fos; Pyridines; Rats; Subthalamic Nucleus; Time Factors; Tyrosine 3-Monooxygenase

Nicotine self-administration models typically evaluate the effects of smoking cessation aides on 'primary reinforcement' engendered by nicotine. However, the more recently described reinforcement enhancing effects of the drug are not always included in experimental analyses of potential therapeutics. We evaluated the effects of pretreatment with noncompetitive antagonists of the metabotropic glutamate 5 receptor (mGluR5) on each reinforcement-related effect of nicotine using a model in which a reinforcing visual stimulus (VS) and nicotine infusions were concurrently available. Five groups (2-lever, VS-only, NIC+VS, NIC-only, or SAL-only) were instrumented for self-administration. The 2-lever group could earn a nicotine infusion (0.06 mg/kg per infusion free base) for meeting the schedule on one lever (eg right), or VS for meeting the schedule on the other lever (eg left). The VS-only group could earn VS or saline under similar contingencies. Remaining rats could press one lever to earn both reinforcers (NIC+VS), nicotine infusions (NIC-only), or saline infusions (SAL-only); the other lever was 'inactive'. Responding on the VS lever in the 2-lever group was greater than that of the VS-only group, reflecting the reinforcement-enhancing effect of nicotine. Pretreatment with 2-methyl-6-(phenylethynyl)-pyridine (MPEP) or 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) decreased nicotine intake as well as the enhanced responding for the concurrently available VS. In follow-up studies, replacing nicotine via experimenter-administered infusions sustained the drugs reinforcement enhancing effect; neither MPEP nor MTEP decreased the enhancing effects of nicotine. These findings are consistent with other studies suggesting that mGlu5 receptors mediate nicotine seeking, but do not alter the reinforcement enhancing effects of nicotine.

Topics: Animals; Behavior, Animal; Conditioning, Operant; Disease Models, Animal; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Male; Nicotine; Nicotinic Agonists; Photic Stimulation; Pyridines; Rats; Rats, Sprague-Dawley; Reinforcement, Psychology; Self Administration; Thiazoles; Tobacco Use Disorder

This study was designed to verify the influence of MPEP (2-methyl-6-phenylethynyl pyridine hydrochloride), an antagonist of metabotropic glutamate receptor subtype 5 (mGluR5), in seizures and status epilepticus (SE) induced by pilocarpine in young rats. In order to investigate the protective effect of MPEP on pilocarpine-induced seizures, young male rats (21-day-old) were pretreated by intraperitoneal route (i.p.) with MPEP (1, 5 and 15 mg/kg) before of pilocarpine administration (400 mg/kg, i.p.). The animals were observed for 1 h after injection of pilocarpine (except pilocarpine group) to determine: number of peripheral cholinergic signs, tremors, stereotyped movements, seizures, SE, latency to the first seizure and number of deaths. Pretreatment with MPEP, at all doses, delayed the onset for the first seizure episode induced by pilocarpine in rats. MPEP abolished the mortality rate caused by administration of pilocarpine in rats. Pretreatment with MPEP (5 and 15 mg/kg) protected against the levels of RS (reactive species), CAT (catalase) and glutathione S-transferase (GST) activities in brain of rats altered by pilocarpine administration. MPEP, at all doses, protected acetylcholinsterase (AChE) activity inhibited by pilocarpine administration in rats. The results suggest that anticonvulsant action of MPEP can be attributed to its mGlu5 receptor antagonism. Therefore, blockade of mGlu5 receptors might represent a novel target for the treatment of seizures in young rats.

Topics: Acetylcholinesterase; Animals; Brain; Convulsants; Cytoprotection; Disease Models, Animal; Dose-Response Relationship, Drug; Epilepsy; Excitatory Amino Acid Antagonists; Glutamic Acid; Male; Muscarinic Agonists; Nerve Degeneration; Neuroprotective Agents; Oxidative Stress; Pilocarpine; Pyridines; Rats; Rats, Wistar; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Synaptic Transmission; Treatment Outcome

Pharmacological activation of group III metabotropic glutamate receptors (mGluR) or inhibition of group I mGluR by subtype-selective ligands is neuroprotective in experimental models of Parkinson's disease. The aim of this study was to investigate whether targeting both receptor subtypes simultaneously produces enhanced neuroprotection. Rodents bearing a 6-hydroxydopamine lesion were intranigrally administered either the group III mGluR agonist L-(+)-2-amino-4-phosphonobutyric acid or the group I mGluR antagonist 2-methyl-6-(phenylethynyl)pyridine, alone or in combination. Coadministration of L-(+)-2-amino-4-phosphonobutyric acid and 2-methyl-6-(phenylethynyl)pyridine resulted in robust nigrostriatal neuroprotection that was significantly increased compared with either compound alone. These data suggest that targeting multiple mGluR subtypes with low doses of selective ligands may provide an enhanced therapeutic response in experimental models of Parkinson's disease.

Topics: Aminobutyrates; Animals; Brain; Cytoprotection; Disease Models, Animal; Drug Therapy, Combination; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Ligands; Male; Neuroprotective Agents; Oxidopamine; Parkinson Disease; Parkinsonian Disorders; Pyridines; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; Treatment Outcome

This study used the metabotropic glutamate 5 (mGlu5) receptor subtype-selective antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP) to characterise the contribution of mGlu5 receptor activity to pain and hypersensitivity in an animal model of post-surgical pain. Adult female Wistar rats (200-250g) were anaesthetised with isoflurane (2%) and underwent a midline laparotomy with gentle manipulation of the viscera, and the effects of pre- (30min) or post- (5h) operative treatment with MPEP (1, 3 or 10mgkg(-1); i.p.) or drug-vehicle on hindpaw withdrawal latency (in seconds) to thermal stimulation (Hargreave's Test) and response threshold (in grams) to mechanical stimulation (using a dynamic plantar aesthesiometer) were measured. Animals that underwent surgery displayed significant hypersensitivity to mechanical stimulation of the hindpaws. Hypersensitivity was maximum at 6h post-surgery (44.5+/-2.4% decrease; p<0.01 vs. anaesthesia only controls) and persisted for 48h. Surgery had no effect on thermal withdrawal latency. Both pre-operative and post-operative administration of 10mgkg(-1)MPEP blocked mechanical hypersensitivity induced by surgery (p<0.01 vs. vehicle treatment). MPEP had no effect on acute nociceptive thresholds in naïve animals. These data suggest that activity at mGlu5 receptors contributes to development of pain and hypersensitivity following surgery.

Topics: Afferent Pathways; Animals; Disease Models, Animal; Excitatory Amino Acid Antagonists; Female; Glutamic Acid; Hyperalgesia; Laparotomy; Neurons, Afferent; Nociceptors; Pain Measurement; Pain Threshold; Pain, Postoperative; Presynaptic Terminals; Pyridines; Rats; Rats, Wistar; Reaction Time; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Synaptic Transmission

By intravenous administration of group I metabotropic glutamate receptor antagonists at 1 or 2h during pilocarpine induced status epilepticus (PISE), we showed that mGluR1 antagonists AIDA or LY367385 (at dosages ranging from 25 to 200mg/kg), mGluR5 antagonists SIB1757 (at dosages ranging from 25 to 200mg/kg), SIB1893 (from 25 to 100mg/kg), MPEP (from 25 to 100mg/kg) injected at 1 or 2h during PISE were ineffective in controlling status epilepticus (SE). However, when administered at 1h during PISE, MPEP at 200mg/kg, combination of MPEP (200mg/kg) with MK801 (0.1mg/kg) or with MK801 (0.1mg/kg) and diazepam (0.5mg/kg), combination of SIB1893 (200mg/kg) with MK801 (0.1mg/kg) could effectively control behavioral SE, and were neuroprotective. In particular, the combination of MPEP with MK801 and diazepam could stop both behavioral SE and electrical SE (under EEG monitoring) within a few minutes after the administration. HPLC study showed that a high level of MPEP was maintained in the blood and its metabolism rate was slow in experimental mice with PISE. We therefore concluded that the combination of MPEP (200mg/kg) with MK801 (0.1mg/kg) and diazepam (0.5mg/kg) could effectively stop SE and its subsequent neuronal loss in the hippocampus when administered 1h during PISE. It may provide a new approach to effectively control intractable SE.

Topics: Animals; Behavior, Animal; Chromatography, High Pressure Liquid; Diazepam; Disease Models, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Therapy, Combination; Electroencephalography; Excitatory Amino Acid Antagonists; GABA Modulators; Male; Mice; Oxazines; Pilocarpine; Pyridines; Status Epilepticus

We compared the neuroprotective and metabolic effects of chronic treatment with ionotropic or metabotropic glutamate receptor antagonists, in rats bearing a unilateral nigrostriatal lesion induced by 6-hydroxydopamine (6-OHDA). The ionotropic, N-methyl-D-aspartate receptor antagonist MK-801 increased cell survival in the substantia nigra pars compacta (SNc) and corrected the metabolic hyperactivity (increased cytochrome oxidase activity) of the ipsilateral substantia nigra pars reticulata (SNr) associated with the lesion, but showed no effects on the 6-OHDA-induced hyperactivity of the subthalamic nucleus (STN). Significant-although less pronounced-protection of SNc neurons was also observed following treatment with the metabotropic glutamate receptor (mGluR5) antagonist 2-methyl-6-(phenylehtynyl)-pyridine (MPEP). As opposed to MK-801, MPEP abolished the STN metabolic hyperactivity associated with the nigrostriatal lesion, without affecting SNr activity. Specific modulation of STN hyperactivity obtained with mGluR5 blockade may, therefore, open interesting perspectives for the use of this class of compounds in the treatment of Parkinson's disease.

Topics: Animals; Cell Survival; Corpus Striatum; Disease Models, Animal; Dizocilpine Maleate; Electron Transport Complex IV; Energy Metabolism; Excitatory Amino Acid Antagonists; Male; Nerve Degeneration; Neural Pathways; Neuroprotective Agents; Oxidopamine; Parkinsonian Disorders; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Glutamate; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate; Substantia Nigra; Subthalamic Nucleus

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by a selective loss of motor neurones accompanied by intense gliosis in lesioned areas of the brain and spinal cord. Glutamate-mediated excitotoxicity resulting from impaired astroglial uptake constitutes one of the current pathophysiological hypotheses explaining the progression of the disease. In this study, we examined the regulation of glutamate transporters by type 5 metabotropic glutamate receptor (mGluR5) in activated astrocytes derived from transgenic rats carrying an ALS-related mutated human superoxide dismutase 1 (hSOD1(G93A)) transgene. Cells from transgenic animals and wild-type littermates showed similar expression of glutamate-aspartate transporter and glutamate transporter 1 (GLT-1) after in vitro activation, whereas cells carrying the hSOD1 mutation showed a three-fold higher expression of functional mGluR5, as observed in the spinal cord of end-stage animals. In cells from wild-type animals, (S)-3,5-dihydroxyphenylglycine (DHPG) caused an immediate protein kinase C (PKC)-dependent up-regulation of aspartate uptake that reflected the activation of GLT-1. Although this effect was mimicked in both cultures by direct activation of PKC using phorbol myristate acetate, DHPG failed to up-regulate aspartate uptake in cells derived from the transgenic rats. The failure of activated mGluR5 to increase glutamate uptake in astrocytes derived from this animal model of ALS supports the theory of glutamate excitotoxicity in the pathogenesis of the disease.

Topics: Amyotrophic Lateral Sclerosis; Animals; Animals, Genetically Modified; Aspartic Acid; Astrocytes; Blotting, Northern; Calcium; Carbachol; Cholinergic Agonists; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Antagonists; Excitatory Amino Acid Transporter 2; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Glutamic Acid; Humans; Immunohistochemistry; Male; Methoxyhydroxyphenylglycol; Protein Kinase C; Pyridines; Rats; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sodium; Superoxide Dismutase; Tritium

It has been suggested that Group I metabotropic glutamate receptor antagonists could have potential therapeutic value in the treatment of Parkinson's disease. There is evidence that when given systemically, 2-methyl-6-(phenylethynyl)-pyridine (MPEP), a metabotropic glutamate receptor type 5 (mGluR5) antagonist, produces anti-parkinsonian effects in animal models, but the site of action has not been directly established. In the present study, we examined whether the subthalamic nucleus (STN) and its output structures may mediate such an effect using a unilateral rat model of Parkinson's disease. A battery of simple behavioral tests, reliably sensitive to dopamine depletion, was applied consecutively: (i) prior to surgery; (ii) 3 weeks following a unilateral 6-hydroxydopamine lesion of the substantia nigra pars compacta; (iii) at 1 h, 24 h and 4 days following a microinjection of MPEP, via an indwelling cannula, into the STN, entopeduncular nucleus (EP) or substantia nigra zona reticulata. Unilaterally dopamine-depleted animals typically had severe motor and sensorimotor asymmetries 3 weeks following surgery. Microinjection of 25 nmol MPEP into the STN of these animals significantly attenuated these asymmetries relative to vehicle. Further microinjections of lower doses (5 and 10 nmol) revealed a dose-response effect. Microinjection of MPEP into either the EP or substantia nigra zona reticulata was without effect. These data suggest that MPEP may act at the level of the STN to reduce glutamatergic overactivity and thereby induce anti-parkinsonian effects.

Topics: Animals; Behavior, Animal; Disease Models, Animal; Dopamine; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Antagonists; Functional Laterality; Male; Motor Activity; Oxidopamine; Parkinson Disease; Parkinson Disease, Secondary; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Subthalamic Nucleus; Sympatholytics; Time Factors

The intercalated islands, clusters of dopamine D1-rich GABAergic neurons, are interposed between the basolateral and central nuclei of the amygdala, and control the traffic of nerve impulses between these two structures. Metabotropic glutamate receptor 5- (mGluR5)-like immunoreactivity was studied by immunohistochemistry in this part of the amygdala and was found to be mainly restricted to the central and basolateral nuclei and to a lesser extent to the medial paracapsular intercalated islands. The role of the metabotropic glutamate receptor 5 in the modulation of anxiety has been studied in this region by microinjection of small volumes of the mGluR5 antagonist 2-methyl-6(phenylethenyl) pyridine (MPEP), with restricted diffusion from its injection site, into the rostral amygdala near the basolateral and central amygdaloid nuclei and the intercalated islands, and the behavior of the animals was evaluated using three non-conditioned models of anxiety. Anxiolytic-like effects were observed after MPEP administration in all tests used. In the White and Black Box test, MPEP (2 nmol per side) significantly increased the time spent in the white compartment of the box. In line with these results, MPEP (8 nmol per side) increased the exploration of the open arms of the Elevated Plus-Maze. Burying behavior latency was increased and burying behavior itself was decreased in the Shock-Probe Burying test. It is suggested that anxiolytic effects of MPEP may be mediated by blockade of mGluR5 in the basolateral and/or central amygdaloid nuclei, reducing glutamate transmission in the basolateral amygdaloid nuclei and glutamate output from the central amygdala.

Topics: Amygdala; Animals; Anti-Anxiety Agents; Anxiety; Behavior, Animal; Conditioning, Classical; Disease Models, Animal; Immunohistochemistry; Injections, Intraventricular; Microinjections; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate

Fragile X Syndrome is a leading heritable cause of mental retardation that results from the loss of FMR1 gene function. Studies in mouse and Drosophila model organisms have been critical in understanding many aspects of the loss of function of the FMR1 gene in the human syndrome. Here, we establish that the zebrafish is a useful model organism for the study of the human fragile X syndrome and can be used to examine phenotypes that are difficult or inaccessible to observation in other model organisms. Using morpholino knockdown of the fmr1 gene, we observed abnormal axonal branching of Rohon-Beard and trigeminal ganglion neurons and guidance and defasciculation defects in the lateral longitudinal fasciculus. We demonstrate that this axonal branching defect can be rescued by treatment with MPEP [2-methyl-6-(phenylethynyl) pyridine]. This is consistent with an interaction between mGluR signalling and fmr1 function in neurite morphogenesis. We also describe novel findings of abnormalities in the abundance of trigeminal ganglion neurons and of craniofacial abnormalities apparently due to dysmorphic cartilage formation. These abnormalities may be related to a role for fmr1 in neural crest cell specification and possibly in migration.

Topics: Animals; Craniofacial Abnormalities; Disease Models, Animal; Excitatory Amino Acid Antagonists; Facial Bones; Fragile X Syndrome; Humans; Morphogenesis; Neural Crest; Neurites; Oligodeoxyribonucleotides, Antisense; Pyridines; Receptors, Metabotropic Glutamate; RNA-Binding Proteins; Zebrafish; Zebrafish Proteins

The discriminative stimulus properties of ethanol are mediated in part by positive modulation of GABA(A) receptors. Recent evidence indicates that metabotropic glutamate receptor subtype 5 (mGluR5) activity can influence GABA(A) receptor function. Therefore, the purpose of this work was to examine the potential involvement of mGluR5 in the discriminative stimulus effects of ethanol. In rats trained to discriminate ethanol (1 g/kg, intragastric gavage (i.g.)) from water, 2-methyl-6-(phenylethyl)-pyridine (MPEP) (1-50 mg/kg, i.p.) a selective noncompetitive antagonist of the mGlu5 receptor did not produce ethanol-like stimulus properties. However, pretreatment with MPEP (30 mg/kg) reduced the stimulus properties of ethanol as indicated by significant reductions in ethanol-appropriate responding, specifically at 0.5 and 1 g/kg ethanol, and a failure of ethanol test doses (1 and 2 g/kg) to fully substitute for the ethanol training dose. To test whether mGluR5 antagonism altered the GABA(A) receptor component of the ethanol stimulus, the ability of MPEP to modulate pentobarbital and diazepam substitution for ethanol was assessed. Pentobarbital substitution (1-10 mg/kg, i.p.) for ethanol was not altered by MPEP pretreatment. However, MPEP pretreatment inhibited the ethanol-like stimulus properties of diazepam (5 mg/kg, i.p.). To examine a potential anatomical basis for these pharmacological findings, expression patterns of mGluR5- and benzodiazepine-sensitive GABA(A) alpha1-containing receptors were examined by dual-label fluorescent immunohistochemistry with visualization by confocal microscopy. Results indicated that mGluR5- and GABA(A) alpha1-containing receptors were both coexpressed in limbic brain regions and colocalized on the same cells in specific brain regions including the amygdala, hippocampus, globus pallidus, and ventral pallidum. Together, these findings suggest an interaction between mGluR5- and benzodiazepine-sensitive GABA(A) receptors in mediating ethanol discrimination.

Topics: Alcoholism; Animals; Diazepam; Discrimination, Psychological; Disease Models, Animal; Drug Interactions; Ethanol; Excitatory Amino Acid Antagonists; GABA Modulators; gamma-Aminobutyric Acid; Glutamic Acid; Immunohistochemistry; Male; Neurons; Pentobarbital; Pyridines; Rats; Rats, Long-Evans; Receptor, Metabotropic Glutamate 5; Receptors, GABA-A; Receptors, Metabotropic Glutamate; Synaptic Transmission; Telencephalon

Pain has a strong emotional component. The amygdala plays a key role in emotionality and is also involved in pain processing and pain modulation. Our previous studies showed an important role of group I metabotropic glutamate receptors (mGluRs) in pain-related synaptic plasticity and sensitization of neurons in the central nucleus of the amygdala (CeA). Here we address the roles of mGluR1 and mGluR5 subtypes in the CeA in the modulation of supraspinally organized behavioral responses in a model of arthritic pain. Audible and ultrasonic (25+/-4 kHz) vocalizations were measured in awake rats during and after innocuous and noxious stimulation (15 s) of the knee joint. Vocalizations were recorded in the same animals before arthritis, 6 h after arthritis induction and during administration of antagonists selective for mGluR1 (CPCCOEt) and mGluR5 (MPEP) into the CeA through stereotaxically implanted microdialysis probes. The duration of audible and ultrasonic vocalizations increased in the arthritic pain state. The duration of vocalizations during stimulation (VDS), which are organized at the brainstem level, was significantly reduced by CPCCOEt but not by MPEP. Vocalizations that continued after stimulation (VAS), which are organized in the limbic forebrain, particularly the amygdala, were inhibited by CPCCOEt and MPEP. These findings suggest differential roles of mGluR1 and mGluR5 in the CeA in pain-related vocalizations. Both mGluR1 and mGluR5 contribute to vocalizations generated in the amygdala whereas mGluR1, but not mGluR5, is involved in the amygdala-mediated modulation of vocalizations originating from activity in the brainstem.

Topics: Amygdala; Analysis of Variance; Animals; Arthritis; Chondrus; Chromones; Disease Models, Animal; Excitatory Amino Acid Antagonists; Male; Microdialysis; Pain; Physical Stimulation; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Vocalization, Animal

Electrophysiological evidence suggests a synergistic relationship between metabotropic (mGlu) and ionotropic (iGlu) glutamate receptors. The functional consequences of these interactions have not been investigated in neurodegenerative diseases such as in Parkinson's disease.. The goals of this study are as follows: (1) to investigate the effects of 2-methyl-6-(phenylethynyl)-pyridine (MPEP) and dizocilpine (MK-801), antagonists at metabotropic glutamate 5 (mGlu5) and NMDA receptors, respectively, on the akinetic syndrome observed in bilateral 6-OHDA-lesioned rats; (2) to investigate if the effects of MPEP were potentiated by co-treatment with a behaviorally inactive dose of MK-801; and (3) to investigate the effects of L-DOPA alone and in combination with MPEP on the akinetic syndrome observed in 6-OHDA-lesioned rats.. The effects of the different treatments (single and co-treatment) administered for 3 weeks were measured in 6-OHDA-lesioned rats trained to release a lever rapidly after a visual stimulus onset in a simple reaction time task.. MPEP 0.75 mg/kg reversed the akinetic deficits produced by striatal dopamine depletion, while MPEP 0.375 mg/kg had no effect. Co-administration with MK-801 0.02 mg/kg, ineffective alone, failed to speed the recovery process of MPEP 0.75 mg/kg but revealed the anti-akinetic action of MPEP 0.375 mg/kg. L-DOPA 3 mg/kg alone had a potent anti-akinetic effect in 6-OHDA lesioned rats, and this effect was not potentiated by a subthreshold MPEP treatment.. These results support a critical role for mGlu5 receptor blockade in improving parkinsonian symptomatology either as a single treatment or in combination with low concentrations of L-DOPA and demonstrate an interaction between NMDA and mGluR5 in regulating these effects.

Topics: Animals; Disease Models, Animal; Dizocilpine Maleate; Drug Synergism; Levodopa; Male; Parkinsonian Disorders; Pyridines; Rats; Rats, Wistar; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate

Antagonists of type I of metabotropic glutamate receptors exhibit anticonvulsant action in adult as well as immature rodents. To know the anticonvulsant profile of a specific mGluR5 antagonist MPEP in developing rats, two models of epileptic seizures were used. MPEP (10, 20 or 40 mg/kg i.p.) suppressed in a dose-dependent manner epileptic afterdischarges induced by electrical stimulation of sensorimotor cortical area in three age groups (12, 18 and 25 days old). The anticonvulsant action was more expressed in the youngest group than in older animals so that in 25-day-old rats an additional dose of 80 mg/kg was used. In contrast to this marked anticonvulsant action, MPEP at a dose of 40 mg/kg i.p. in 18-day-old rat pups and at doses of 40 and 80 mg/kg in 25-day-old rat pups did not affect episodes of spike-and-wave rhythm elicited by low doses of pentetrazol. Our results delineate the profile of the anticonvulsant action of MPEP and confirm the higher efficacy of this antagonist at early developmental stages in comparison with prepubertal animals.

Topics: Age Factors; Analysis of Variance; Animals; Animals, Newborn; Anticonvulsants; Cerebral Cortex; Disease Models, Animal; Dose-Response Relationship, Drug; Electric Stimulation; Electroencephalography; Epilepsy; Epilepsy, Absence; Male; Pyridines; Rats; Rats, Wistar; Reaction Time; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate

We investigated whether the metabotropic glutamate receptor subtype 5 (mGluR5) selective antagonist, 2-methyl-6-(phenylethynyl)-pyridine (MPEP) has direct effects on primary afferent fiber responses to noxious mechanical stimulation following inflammation. Mechanosensory primary afferent fibers innervating the hind paw were recorded in naïve and complete Freunds adjuvant (CFA) inflamed rats. Following intraplantar injection of CFA, afferent fibers showed property changes including expanded receptive fields, burst firing with fast adaptive mechanical responses and a higher incidence of cold and/or heat sensitivities compared to naïve rats. In eight afferent fibers tested following i.v. administration of MPEP, seven fibers showed significantly reduced responses to noxious mechanical stimulation. At a cumulative dose of 10 mg/kg, MPEP inhibited afferent responses to 32.66+/-11.48% of control. The mean ID50 value of MPEP was 6.49+/-0.43 mg/kg. In contrast to its inhibitory action in the CFA model, i.v. administration of MPEP produced only a mild reduction of mechanical responses in 3 fibers out of 11 in naïve rats. These results provide direct functional evidence that blockade of peripheral mGluR5 receptors inhibits nociceptive transmission and support previous studies demonstrating a peripheral site of action associated with the antinociceptive effect of MPEP following inflammation.

Topics: Action Potentials; Afferent Pathways; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Freund's Adjuvant; Hindlimb; Inflammation; Mechanoreceptors; Pain; Pain Measurement; Physical Stimulation; Pyridines; Rats

Transient lower esophageal sphincter relaxation (TLESR) is the major mechanism of gastroesophageal acid reflux. TLESR is mediated via vagal pathways, which may be modulated by metabotropic glutamate receptors (mGluRs). Group I mGluRs (mGluR1 and 5) have excitatory effects on neurons, whereas group II (mGluR2 and 3) and group III (mGluR4, 6, 7, and 8) are inhibitory. This study determined the effect of mGluRs on triggering of TLESR and reflux in an established conscious ferret model.. Esophageal manometric/pH studies were performed in ferrets with chronic esophagostomies. TLESR were induced by a gastric load of 25 mL glucose (pH 3.5) and 30 mL air.. In control treated animals, gastric load induced 3.52 +/- 0.46 TLESRs per 47-minute study, 89.7% of which were associated with reflux episodes (n = 16). The mGluR5 antagonist MPEP inhibited TLESR dose dependently, with maximal 71% +/- 7% inhibition at 35 micromol/kg (n = 9; P < .0001). MPEP also significantly reduced reflux episodes (P < .001) and increased basal lower esophageal sphincter pressure (P < .05). MPEP inhibited swallowing dose dependently, suggesting a common action on trigger mechanisms for swallowing and TLESR. The more selective analogue, MTEP, had more potent effects (90% +/- 6% inhibition TLESR at 40 micromol/kg; n = 8; P < .0001). In contrast, the group I agonist DHPG tended to increase TLESR. The group II agonist (2R, 4R)-APDC was ineffective, whereas the group III agonist L-(AP4 slightly reduced TLESR (33% at 11 micromol/kg; P < .05). The selective mGluR8 agonist (S)-3, 4-DCPG inhibited TLESR by 54% at 15 micromol/kg (P < .01).. mGluR5 antagonists potently inhibit TLESR and reflux in ferrets, implicating mGluR5 in the mechanism of TLESR. mGluR5 antagonists are therefore promising as therapy for patients with GERD.

Topics: Animals; Deglutition; Disease Models, Animal; Esophagus; Female; Ferrets; Gastroesophageal Reflux; Ligands; Muscle Relaxation; Muscle, Smooth; Pressure; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Thiazoles

Evidence for heteromeric receptor complexes comprising adenosine A2A and metabotropic glutamate 5 (mGlu5) receptors in striatum has raised the possibility of synergistic interactions between striatal A2A and mGlu5 receptors. We investigated the role of striatal A2A receptors in the locomotor stimulant and antiparkinsonian properties of mGlu5 antagonists using complementary pharmacologic and genetic approaches. Locomotion acutely stimulated by the mGlu5 antagonist [2-methyl-6-(phenylethynyl)-pyridine (MPEP)] was absent in mGlu5 knock-out (KO) mice and was potentiated by an A2A antagonist KW-6002 [(E)-1,3-diethyl-8-(3,4-dimethoxystyryl)-7-methylxanthine], both in normal and in dopamine-depleted (reserpinized) mice. Conversely, the MPEP-induced motor response was markedly attenuated in single and double A2A and D2 receptor KO mice. In contrast, motor stimulation by a D1 dopamine agonist was not attenuated in the KO mice. The A2A receptor dependence of MPEP-induced motor stimulation was investigated further using a postnatal forebrain-specific conditional (Cre/loxP system) KO of the A2A receptor. MPEP loses the ability to stimulate locomotion in conditional KO mice, suggesting that this mGlu5 antagonist effect requires the postdevelopmental action of striatal A2A receptors. The potentiation of mGlu5 antagonist-induced motor stimulation by an A2A antagonist and its dependence on both D2 and forebrain A2A receptors highlight the functional interdependence of these receptors. These data also strengthen a rationale for pursuing a combinational drug strategy for enhancing the antiparkinsonian effects of A2A and mGlu5 antagonists.

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; Analysis of Variance; Animals; Animals, Newborn; Behavior, Animal; Blotting, Western; Disease Models, Animal; Dopamine Agonists; Dose-Response Relationship, Drug; Drug Synergism; Excitatory Amino Acid Antagonists; Locomotion; Mice; Mice, Inbred C57BL; Mice, Knockout; Motor Activity; Parkinson Disease; Purines; Pyridines; Receptor, Adenosine A2A; Receptor, Metabotropic Glutamate 5; Receptors, Dopamine D2; Receptors, Metabotropic Glutamate; Time Factors

Structure-activity relationship studies leading to the discovery of a new, orally active mGlu5 receptor antagonist are described. The title compound, 5-[(2-methyl-1,3-thiazol-4-yl)ethynyl]-2,3'-bipyridine, is highly potent in vitro, has good in vivo receptor occupancy, and is efficacious in the rat fear-potentiated startle model of anxiety following oral dosing.

Topics: Animals; Anti-Anxiety Agents; Anxiety; Disease Models, Animal; Excitatory Amino Acid Antagonists; Kinetics; Models, Molecular; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Structure-Activity Relationship; Thiazoles

We combined the use of knock-out mice and subtype-selective antagonists [2-methyl-6-(phenylethynyl)pyridine (MPEP) and (E)-2-methyl-6-(2-phenylethenyl)-pyridine (SIB1893)] to examine whether endogenous activation of mGlu5 metabotropic glutamate receptors contributes to the pathophysiology of nigro-striatal damage in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of parkinsonism. High doses of MPTP (four injections of 20 mg/kg, i.p., every 2 hr) induced a high mortality rate and a nearly total degeneration of the nigro-striatal pathway in wild-type mice. mGlu5 knock-out mice were less sensitive to MPTP toxicity, as shown by a higher survival and a milder nigro-striatal damage. Protection against MPTP (80 mg/kg) toxicity was also observed after MPEP injections (four injections of 5 mg/kg, i.p., 30 min before each MPTP injection). MPEP treatment did not further increase neuroprotection against 80 mg/kg of MPTP in mGlu5 knock-out mice, indicating that the drug acted by inhibiting mGlu5 receptors. In wild-type mice, MPEP was also neuroprotective when challenged against lower doses of MPTP (either 30 mg/kg, single injection, or four of 10 mg/kg injections). The action of MPEP was mimicked by SIB1893 but not by the mGlu1 receptor antagonist 7-hydroxyiminocyclopropan[b]chromen-1a-carboxylic acid ethyl ester. MPEP did not change the kinetics of 1-methyl-4-phenylpyridinium ion formation in the striatum of mice injected with MPTP. We conclude that mGlu5 receptors act as amplifiers of MPTP toxicity and that mGlu5 receptor antagonists may limit the extent of nigro-striatal damage in experimental models of parkinsonism.

Topics: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; 1-Methyl-4-phenylpyridinium; 3,4-Dihydroxyphenylacetic Acid; Animals; Corpus Striatum; Disease Models, Animal; Dopamine; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Homovanillic Acid; Mice; Mice, Knockout; MPTP Poisoning; Neuroprotective Agents; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Substantia Nigra; Survival Rate; Synaptosomes

The effects of several metabotropic receptor (mGluR) ligands on baseline hippocampal glutamate and GABA overflow in conscious rats and the modulation of limbic seizure activity by these ligands were investigated. Intrahippocampal mGluR group I agonist perfusion via a microdialysis probe [1 mm (R,S)-3,5-dihydroxyphenylglycine] induced seizures and concomitant augmentations in amino acid dialysate levels. The mGlu1a receptor antagonist LY367385 (1 mm) decreased baseline glutamate but not GABA concentrations, suggesting that mGlu1a receptors, which regulate hippocampal glutamate levels, are tonically activated by endogenous glutamate. This decrease in glutamate may contribute to the reported LY367385-mediated anticonvulsant effect. The mGlu5 receptor antagonist 2-methyl-6-(phenylethynyl)-pyridine (50 mg/kg) also clearly abolished pilocarpine-induced seizures. Agonist-mediated actions at mGlu2/3 receptors by LY379268 (100 microm, 10 mg/kg intraperitoneally) decreased basal hippocampal GABA but not glutamate levels. This may partly explain the increased excitation following systemic LY379268 administration and the lack of complete anticonvulsant protection within our epilepsy model with the mGlu2/3 receptor agonist. Group II selective mGluR receptor blockade with LY341495 (1-10 microm) did not alter the rats' behaviour or hippocampal amino acid levels. These data provide a neurochemical basis for the full anticonvulsant effects of mGlu1a and mGlu5 antagonists and the partial effects observed with mGlu2/3 agonists in vivo.

Topics: Amino Acids; Animals; Anticonvulsants; Benzoates; Bridged Bicyclo Compounds, Heterocyclic; Cyclopropanes; Disease Models, Animal; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Extracellular Fluid; gamma-Aminobutyric Acid; Glutamic Acid; Glycine; Hippocampus; Ligands; Limbic System; Male; Microdialysis; Pilocarpine; Pyridines; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; Seizures

Metabotropic glutamate receptor 5 (mGluR5) is densely expressed in medium-sized spiny projection neurons of the rat striatum. Activation of mGluR5 increases intracellular Ca2+, resulting in Ca(2+)-dependent cellular responses. Acute administration of the psychostimulant amphetamine (AMPH) induces immediate early gene (IEG) expression in the striatum, which is considered an important molecular event for the development of striatal neuroplasticity related to the addictive properties of drugs of abuse. This study investigated the role of mGluR5 in the mediation of IEG expression in the rat striatum induced by a single dose of AMPH (4 mg/kg, i.p.) in vivo. We found that systemic administration of the mGluR5-selective antagonist 2-methyl-6-(phenylethynyl) pyridine hydrochloride (MPEP) at a dose of 10 mg/kg, i.p. reduced AMPH-stimulated c-fos mRNA levels in the dorsal (caudoputamen) and ventral (nucleus accumbens) striatum as revealed by quantitative in situ hybridization. Similar results were observed in the three areas of cerebral cortex (cingulate, sensory, and piriform cortex). In contrast to c-fos mRNAs, AMPH-stimulated mRNA expression of another IEG, zif/268, was not significantly altered by the blockade of mGluR5 with MPEP in the entire striatum and the three areas of cortex. Treatment with MPEP alone had no effect on basal levels of c-fos and zif/268 mRNAs in the striatal and cortical areas. These results indicate that an mGluR5-dependent mechanism selectively contributes to c-fos expression in the striatum and cortex in response to acute exposure to AMPH.

Topics: Amphetamine; Amphetamine-Related Disorders; Animals; Cerebral Cortex; Corpus Striatum; Disease Models, Animal; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Genes, Immediate-Early; Male; Proto-Oncogene Proteins c-fos; Pyridines; Rats; Rats, Wistar; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; RNA, Messenger; Up-Regulation

Chronic glutamate mediated excitotoxicity has been suggested to contribute to the pathogenesis of Huntington's disease (HD). Both, inhibition of glutamate release through stimulation of presynaptic metabotropic glutamate receptor (mGluR) 2 and blockade of postsynaptic mGluR5 have been demonstrated to be neuroprotective against excitotoxicity. R6/2 HD transgenic mice which express an expanded CAG triplet repeat serve as a well-characterized mouse model for HD with progressing neurological abnormalities and limited survival. We treated R6/2 HD transgenic mice with either the mGluR2 agonist LY379268 (1.2 mg/kg) or with the mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) (100 mg/kg) orally from a presymptomatic stage until death to investigate their potential disease modifying effects. We found that survival time in both the MPEP treated mice and the LY379268 treated mice was significantly increased in comparison to placebo treated transgenic controls (14.87+/-0.14 and 14.22+/-0.11 weeks versus 12.87+/-0.11 weeks, respectively). Additionally, the progressive decline in motor coordination of HD transgenic mice as tested with the rotarod test was significantly attenuated in MPEP- but not in LY379268-treated mice. Early pathological hyperactivity, which can be found in placebo treated HD transgenic mice, was significantly attenuated by both MPEP and LY379268 treatment. Immunohistologial examination of HD characteristic neuronal intranuclear inclusion (NII), however, demonstrated no effect on NII formation by either of the treatments applied. These data suggest that inhibition of glutamate neurotransmission via specific interaction with mGluRs might be interesting for both inhibition of disease progression as well as early symptomatic treatment in HD.

Topics: Amino Acids; Animals; Bridged Bicyclo Compounds, Heterocyclic; Disease Models, Animal; Disease Progression; Female; Huntington Disease; Male; Mice; Mice, Inbred C57BL; Mice, Inbred CBA; Mice, Transgenic; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate

Glutamate overactivity within the basal ganglia has been shown to be central to the expression of motor symptoms in advanced stages of Parkinson's disease, and metabotropic glutamate receptors (mGluRs) represent promising targets for new therapeutic strategies in this pathology. Little is known, however, about the cellular and behavioral changes occurring in the early stages of the disease when dopamine depletion is moderate. Here, we report that rats with partial bilateral dopamine lesions exhibit akinetic deficits associated with dramatically increased neuronal metabolic activity in selective structures of the basal ganglia such as the subthalamic nucleus and the substantia nigra pars reticulata, but not in the entopeduncular nucleus. Furthermore, chronic treatment with the mGluR5 antagonist 2-methyl-6-(phenylethylnyl)-pyridine alleviated the akinesia and was associated with a normalization of the activity of these two overactive structures. These data stress the therapeutic potential of mGluR5 antagonists in the treatment of parkinsonian patients in the early stages of the disease.

Topics: Animals; Basal Ganglia; Behavior, Animal; Corpus Striatum; Disease Models, Animal; Electron Transport Complex IV; Excitatory Amino Acid Antagonists; Gene Expression; Glutamate Decarboxylase; In Situ Hybridization; Isoenzymes; Male; Motor Activity; Neurons; Oxidopamine; Parkinsonian Disorders; Pyridines; Rats; Rats, Wistar; Reaction Time; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; RNA, Messenger; Substantia Nigra; Subthalamic Nucleus

Metabotropic glutamate receptor 5 (mGluR5) protein increased after sciatic nerve section in ipsilateral L4 and L5 DRG neuronal profiles, with most of the increase occurring in myelinated A-fiber somata. mGluR5 also increased in lamina II of the ipsilateral spinal cord and the proximal sciatic nerve stump in this model. After L5 spinal nerve ligation, mGluR5 immunoreactivity increased dramatically not only in damaged L5 but also in the neighboring undamaged L4. Interestingly, after partial sciatic nerve section, mGluR5 expression did not change in either L4 or L5 DRG neuronal profiles. Both spinal nerve ligation and sciatic nerve partial section produced significant mechanical and thermal hyperalgesia and tactile allodynia. After partial sciatic nerve section, the mGluR5-specific antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) had no effect on any of these behaviors. However, after L5 spinal nerve ligation, although MPEP failed to alter the induced tactile allodynia or mechanical hyperalgesia, it dose dependently reversed the developed thermal hyperalgesia. Therefore, reversal of thermal hyperalgesia by MPEP correlates with increased mGluR5 in lumbar DRG A-fiber somata after nerve injury. Furthermore, A-fibers in the uninjured L4 DRG after L5 spinal nerve ligation that have increased mGluR5 are the same A-fibers that newly express vanilloid receptor 1 after such injury. Together, these results suggest that, after L5 spinal nerve injury, mGluR5 expression on A-fibers is essential to the development of thermal hyperalgesia. After partial nerve section, however, it is unlikely that thermal responses are mediated through mGluR5 because no such increase in mGluR5 is detected in this model and MPEP is ineffective.

Topics: Animals; Behavior, Animal; Disease Models, Animal; Ganglia, Spinal; Hyperalgesia; Immunohistochemistry; Ligation; Lumbosacral Region; Male; Nerve Fibers, Myelinated; Neurons; Pain Measurement; Pyridines; Rats; Rats, Wistar; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Sciatic Nerve; Spinal Nerves; Up-Regulation

Activation of group I metabotropic glutamate receptors (mGluR) has been implicated in the pathophysiology of acute central nervous system injury. However, the relative roles of the two group I subtypes, mGluR1 or mGluR5, in such injury has not been well examined. We compared the effects of treatment with the newly developed, selective mGluR5 antagonist 2-methyl-6-phenylethynylpyridine (MPEP) and the selective mGluR5 agonist (R,S)-2-chloro-5-hydroxyphenylglycine (CHPG) in a rat intraluminal filament model of temporary middle cerebral artery occlusion (MCAo). Rats were administered MPEP or CHPG i.c.v. beginning 15 or 135 min after induction of ischemia for 2 h. Infarct size was measured after either 22 or 70 h of reperfusion, and neurological function was quantified at 2, 24, 48 and 72 h. Treatment with MPEP or CHPG at 15 min reduced 24 h infarct volume by 61 and 44%, respectively. The neuroprotective effects were dose dependent. Delaying MPEP treatment until 135 min eliminated the neuroprotective effects. In other studies, using early MPEP treatment (15 min) at optimal doses, infarct volume was reduced by 44% at 72 h and this was correlated with significant neurological recovery. These data suggest that both MPEP and CHPG are neuroprotective when administered after focal cerebral ischemia. In separate, recent studies we found that although MPEP does act as an mGluR5 antagonist and blocks agonist induced phosphoinositide hydrolysis, it also serves as a non-competitive NMDA antagonist; in contrast, other results indicate that CHPG mediated neuroprotection may reflect anti-apoptotic activity. Therefore, both types of compounds may prove to have therapeutic potential for the treatment of stroke.

Topics: Animals; Body Temperature; Body Weight; Brain Ischemia; Cell Survival; Cerebral Cortex; Disease Models, Animal; Dose-Response Relationship, Drug; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Glycine; Infarction, Middle Cerebral Artery; Male; Neurons; Neuroprotective Agents; Phenylacetates; Pyridines; Rats; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Reperfusion Injury