6-methyl-2-(phenylethynyl)pyridine and Nerve-Degeneration

Gene expression of mGluR2, mGluR3 and mGluR5 was evaluated in the hippocampus and frontal cortex in Wistar rats in 1 and 4 weeks after bilateral microinjection of kainic acid into the dorsal hippocampus. The time-course of the receptors' expression suggested their adaptive role in response on the induction of excitotoxicity. It was assumed that the decrease of kainate-induced neurodegeneration could be achieved through simultaneous activation of presynaptic mGluRs and inhibition of mGlu postsynaptic receptors. Both negative allosteric modulator of mGluR5, MPEP, and agonist of mGluR2, LY354740, were administered intraperitoneally 5 days after microinjection of kainic acid. As shown by histochemical studies with cresyl violet and Fluoro-Jade, kainate induced significant damage of hippocampal neurons in the CA3 and CA1 fields. Pharmacological treatment with the negative modulator of mGlu5 receptors in common with the agonist of mGluR2 decreased kainate-induced neurodegeneration in dorsal hippocampus.

Topics: Animals; Bridged Bicyclo Compounds; Hippocampus; Kainic Acid; Microinjections; Nerve Degeneration; Pyridines; Rats, Wistar; Receptors, Metabotropic Glutamate; Time Factors

Group I mGluRs (metabotropic glutamate receptors), including mGluR1 and mGluR5, are GPCRs (G-protein coupled receptors) and play important roles in physiology and pathology. Studies on their role in cerebral ischaemia have provided controversial results. In this study, we used a PT (photothrombosis)-induced ischaemia model to investigate whether antagonists to the group I mGluRs may offer acute and long-term protective effects in adult mice. Our results demonstrated that administration with mGluR5 antagonist MPEP [2-methyl-6-(phenylethynyl)-pyridine] or mGluR1 antagonist LY367385 by intraperitoneal injection at 3 h after PT decreased brain infarct volume evaluated one day after ischaemia. Additive effects on infarct volume were observed upon co-injection with MPEP and LY367385. These antagonists also significantly alleviated neurodegeneration and apoptosis in the penumbra. In addition, when evaluated 2 weeks after PT, they reduced infarct volume and tissue loss, attenuated glial scar formation, and inhibited cell proliferation in the penumbra. Importantly, co-injection with MPEP and LY367385 reduced the expression levels of calpain, a Ca2+-activated protease known to mediate ischaemia-induced neuronal death. Injection of calpeptin, a calpain inhibitor, could inhibit neuronal death and brain damage after PT but injection of calpeptin together with MPEP and LY367385 did not further improve the protective effects mediated by MPEP and LY367385. These results suggest that inhibition of group I mGluRs is sufficient to protect ischaemic damage through the calpain pathway. Taken together, our results demonstrate that inhibition of group I mGluRs can mitigate PT-induced brain damage through attenuating the effects of calpain, and improve long-term histological outcomes.

Topics: Animals; Antimetabolites, Antineoplastic; Astrocytes; Benzoates; Blotting, Western; Brain; Brain Ischemia; Bromodeoxyuridine; Cell Death; Cell Proliferation; Cerebral Infarction; Excitatory Amino Acid Antagonists; Glycine; Immunohistochemistry; In Situ Nick-End Labeling; Intracranial Thrombosis; Male; Mice; Mice, Inbred C57BL; Nerve Degeneration; Neuroglia; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate

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

Degeneration of dopaminergic neurons of the substantia nigra pars compacta is a cardinal feature of Parkinson's disease (PD). Although uncertain, the pathology has been suggested to derive from a malfunction of the complex interaction between dopaminergic and metabotropic glutamate receptors (mGluRs). To further address this issue, we investigated the imaging profile and expression of dopamine D(2) receptors and mGluRs in a classic parkinsonian rodent model induced by the toxin 6-hydroxydopamine.. Adult male Sprague-Dawley rats (250-300 g) received a stereotaxic injection of 8 mug/2 muL of 6-hydroxydopamine (n = 6) or saline solution (n = 4) in the right medial forebrain bundle. Small-animal PET was performed on all rats 4 wk after the surgical procedure to assess dopamine transporter (DAT) status using (11)C-2beta-carbomethoxy-3beta-(4-fluorophenyl)-tropane (CFT), as well as dopamine D(2) receptor and mGluR(5) modulation using (11)C-raclopride and 2-(11)C-methyl-6-(2-phenylethynyl)-pyridine ((11)C-MPEP), respectively. Behavioral studies were also conducted 6 wk after lesioning by d-amphetamine challenge. Immunohistochemistry and Western blotting were carried out at 8 wk after lesioning to confirm dopamine fiber, neuronal loss, and level of striatal mGluR(5) expression.. PET images showed decreased (11)C-CFT binding on the lesioned side, including the structures of the striatum, hippocampus, and cortex, compared with the contralateral intact side. Interestingly, dopamine D(2) receptors and mGluR(5) upregulation were observed in the right striatum, hippocampus, and cortex, using (11)C-raclopride and (11)C-MPEP, respectively. A negative correlation was also found between the percentage change in mGluR(5) expression and DAT function. Finally, tyrosine hydroxylase immunoreactivity confirmed both dopamine fiber loss (t test, P < 0.01) and neuronal loss (t test, P < 0.01) on the lesioned side. These changes were accompanied by a strongly enhanced mGluR(5) expression in the right striatum of the lesioned side analyzed by Western plot.. These findings support the existence of compensatory mechanisms in nigrostriatal dopamine degeneration and provide new insights that help further dissect some of the pathways underlying neurodegeneration. In addition, these results reconfirm that PET is a valuable tool for multilevel receptor studies, significantly contributing to the understanding of pathogenic mechanisms and ultimately opening new avenues in the study of neuroprotective approaches toward PD.

Topics: Animals; Carbon Radioisotopes; Cocaine; Corpus Striatum; Dopamine Plasma Membrane Transport Proteins; Hippocampus; Immunohistochemistry; Male; Nerve Degeneration; Neurons; Oxidopamine; Parkinsonian Disorders; Positron-Emission Tomography; Pyridines; Raclopride; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Dopamine D2; Receptors, Metabotropic Glutamate; Substantia Nigra; Tyrosine 3-Monooxygenase

Evidence suggests that increased glutamatergic input to the substantia nigra pars compacta as a result of hyperactivity of subthalalmic nucleus output pathways may contribute to the progressive degeneration of nigral dopaminergic neurones in Parkinson's disease (PD), a debilitating neurodegenerative disorder which affects approximately 1% of people aged over 65. Substantial electrophysiological evidence suggests that the excitation of nigral dopaminergic neurones is regulated by the activation of Group I metabotropic glutamate receptors (mGluR), comprising mGluR1 and mGluR5 subtypes. As activation of these receptors by endogenous glutamate may promote multiple cascades leading to excitotoxic neuronal death, it may be hypothesised that functional antagonism of Group I mGluR should be neuroprotective and could form the basis of a novel neuroprotective treatment for PD. To investigate this hypothesis, the neuroprotective potential of the selective competitive mGlu1 antagonist (+)-2-methyl-4-carboxyphenylglycine ((S)-(+)-alpha-amino-4-carboxy-2-methlybenzeneacetic acid; LY367385) and the selective allosteric mGlu5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) was tested in a rodent 6-hydroxydopamine (6-OHDA) model of PD in vivo. Both acute and subchronic intranigral administration of either LY367385 or MPEP resulted in significant neuroprotection of nigral tyrosine hydroxylase immunoreactive cell bodies, which correlated closely with prevention of striatal monoamine depletion following 6-OHDA lesioning. This neuroprotective action of LY367385 and MPEP displayed a clear concentration-dependent effect, suggesting a receptor-mediated mechanism of action. LY367385 produced robust neuroprotection at all concentrations tested (40, 200 and 1000 nmol in 4 microL), whilst MPEP displayed a bell-shaped neuroprotective profile with significant neuroprotection at low concentrations (2 and 10 nmol in 4 microL) but not at higher concentrations (50 nmol). Importantly, subchronic intranigral administration of MPEP and LY367385 appeared to slow the degeneration of remaining nigral dopaminergic neurones and prevented further striatal dopamine depletion in animals with established 6-OHDA induced nigrostriatal lesions, suggesting that these compounds may significantly influence disease progression in this model.

Topics: Animals; Benzoates; Corpus Striatum; Dopamine; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Glutamic Acid; Glycine; Male; Molecular Structure; Nerve Degeneration; Neural Pathways; Neuroprotective Agents; Neurotoxins; Oxidopamine; Parkinsonian Disorders; Pyridines; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; Substantia Nigra; Treatment Outcome; Tyrosine 3-Monooxygenase

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