6-methyl-2-(phenylethynyl)pyridine and 2-amino-4-phosphonobutyric-acid

Metabotropic glutamate (mGlu) receptors modulate pain from within the midbrain periaqueductal grey (PAG). In the present study, the postsynaptic mGlu receptor mediated effects on rat PAG neurons were examined using whole-cell patch-clamp recordings in brain slices. The selective group I agonist DHPG (10 μM) produced an inward current in all PAG neurons tested which was associated with a near parallel shift in the current-voltage relationship. By contrast, the group II and III mGlu receptor agonists DCG-IV (1 μM) and l-AP4 (3 μM) produced an outward current in only 10-20% of PAG neurons tested. The DHPG induced current was concentration dependent (EC(50) = 1.4 μM), was reduced by the mGlu1 antagonist CPCCOEt (100 μM), and was further reduced by CPCCOEt in combination with the mGlu5 antagonist MPEP (10 μM). The glutamate transport blocker TBOA (30 μM) also produced an inward current, however, this was largely abolished by CNQX (10 μM) plus AP5 (25 μM). Slow EPSCs were evoked following train, but not single shock stimulation, which were enhanced by TBOA (30 μM). The TBOA enhancement of slow EPSCs was abolished by MPEP plus CPCCOEt. These findings indicate that endogenously released glutamate, under conditions in which neurotransmitter spill-over is enhanced, activates group I mGlu receptors to produce excitatory currents within PAG. Thus, postsynaptic group I mGlu receptors have the potential to directly modulate the analgesic, behavioural and autonomic functions of the PAG. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Aminobutyrates; Animals; Aspartic Acid; Chromones; Cyclopropanes; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Female; Glycine; Male; Membrane Potentials; Methoxyhydroxyphenylglycol; Neurons; Periaqueductal Gray; Pyridines; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate

Mouse embryonic stem (ES) cells were stimulated to differentiate either as adherent monolayer cultures in DMEM/F12 supplemented with N2/B27, or as floating embryoid bodies (EBs) exposed to 1 microM retinoic acid (RA) for 4 days, starting from 4 DIV, and subsequently re-plated in DMEM/F12 medium. Adherent monolayer cultures of ES cells expressed mGlu5 receptors throughout the entire differentiation period. Selective pharmacological blockade of mGlu5 receptors with methyl-6-(phenylethynyl)-pyridine (MPEP) (1 microM, added once a day) accelerated the appearance of the neuronal marker, beta-tubulin. In addition, treatment with MPEP increased the number of cells expressing glutamate decarboxylase-65/67 (GAD(65/67)), a marker of GABAergic neurons. In floating EBs, mGlu5 receptors are progressively replaced by mGlu4 receptors. The orthosteric mGlu4/6/7/8 receptor agonist, L-2-amino-4-phosphonobutanoate (L-AP4), or the selective mGlu4 receptor enhancer, PHCCC,--both combined with RA at concentrations of 30 microM--increased the expression of both beta-tubulin and GAD(65/67), inducing the appearance of fully differentiated neurons that released GABA in response to membrane depolarization. We conclude that mGlu receptor subtypes regulate neuronal differentiation of ES cells in a context-dependent manner, and that subtype-selective ligands of these receptors might be used for the optimization of in vitro protocols aimed at producing GABAergic neurons from ES cells.

Topics: Aminobutyrates; Animals; Benzopyrans; Cell Adhesion; Cell Differentiation; Cell Line; Embryonic Stem Cells; Excitatory Amino Acid Antagonists; gamma-Aminobutyric Acid; Glutamate Decarboxylase; Membrane Potentials; Mice; Neurons; Phenotype; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Time Factors; Tretinoin; Tubulin

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