6-cyano-7-nitroquinoxaline-2-3-dione and 4-carboxyphenylglycine

Metabotropic glutamate receptors (mGluRs) have been proposed to be involved in oscillatory rhythmic activity in the hippocampus. However, the subtypes of mGluRs involved and their precise distribution in different populations of interneurons is unclear. In this study, we combined functional analysis of mGluR-mediated inward currents in CA1 oriens-alveus interneurons with anatomical and immunocytochemical identification of these interneurons and expression analysis of group I mGluR using single-cell reverse transcription-PCR (RT-PCR). Four major interneuron subtypes could be distinguished based on the mGluR-mediated inward current induced by the application of 100 microm trans-(1S,3R)-1-aminocyclopentane-1, 3-dicarboxylic acid (ACPD) under voltage-clamp conditions and the action potential firing pattern under current-clamp conditions. Type I interneurons responded with a large inward current of approximately 224 pA, were positive for somatostatin, and the majority expressed both mGluR1 and mGluR5. Type II interneurons responded with an inward current of approximately 80 pA, contained calbindin, and expressed mainly mGluR1. Type III interneurons responded with an inward current of approximately 60 pA. These interneurons were fast-spiking, contained parvalbumin, and expressed mainly mGluR5. Type IV interneurons did not respond with an inward current upon application of ACPD, yet they expressed group I mGluRs. Activation of group I mGluRs under current-clamp conditions increased spike frequency and resulted in rhythmic firing activity in type I and II, but not in type III and IV, interneurons. RT-PCR results suggest that activation of mGluR1 in the subsets of GABAergic interneurons, classified here as type I and II, may play an important role in mediating synchronous activity.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Benzoates; Cycloleucine; Excitatory Amino Acid Antagonists; GABA Antagonists; Gene Expression; Glycine; Hippocampus; Interneurons; Neuroprotective Agents; Patch-Clamp Techniques; Periodicity; Picrotoxin; Rats; Rats, Wistar; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Reverse Transcriptase Polymerase Chain Reaction; Tetrodotoxin

We have used rats and mice with mutations in myosin-Va to evaluate the range and function of IP3-mediated Ca2+ signaling in dendritic spines. In these mutants, the endoplasmic reticulum and its attendant IP3 receptors do not enter the postsynaptic spines of parallel fiber synapses on cerebellar Purkinje cells. Long-term synaptic depression (LTD) is absent at the parallel fiber synapses of the mutants, even though the structure and function of these synapses otherwise appear normal. This loss of LTD is associated with selective changes in IP3-mediated Ca2+ signaling in spines and can be rescued by photolysis of a caged Ca2+ compound. Our results reveal that IP3 must release Ca2+ locally in the dendritic spines to produce LTD and indicate that one function of dendritic spines is to target IP3-mediated Ca2+ release to the proper subcellular domain.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Benzoates; Calcium Channels; Calcium Signaling; Cerebellum; Dendrites; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Glycine; In Vitro Techniques; Inositol 1,4,5-Trisphosphate Receptors; Intermediate Filament Proteins; Mice; Mice, Neurologic Mutants; Myosin Heavy Chains; Myosin Type V; Neural Inhibition; Patch-Clamp Techniques; Purkinje Cells; Rats; Rats, Mutant Strains; Receptors, Cytoplasmic and Nuclear; Synaptic Transmission; Time

We have studied the activation of phospholipase D (PLD) by glutamate in rat cultured astrocytes by measuring the PLD-catalyzed formation of [32P]phosphatidylbutanol in [32P]Pi-prelabeled cells, stimulated in the presence of butanol. Glutamate elicited the activation of PLD in cortical astrocytes but not in cortical neurons, whereas similar glutamate activation of phosphoinositide phospholipase C was found in both astrocytes and neurons. The extent of PLD stimulation by glutamate was similar in astrocytes from brain cortex and hippocampus, but no effect was found in cerebellar astrocytes. In cortical astrocytes, the glutamate response was insensitive to antagonists of ionotropic glutamate receptors and was reproduced by agonists of metabotropic glutamate receptors (mGluRs) with a rank order of agonist potency similar to that reported for group I mGluR-mediated phosphoinositide phospholipase activation [quisqualate > (S)-3,5-dihydroxyphenylglycine > (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid]. The response to (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid was inhibited by the mGluR antagonist (S)-alpha-methyl-4-carboxyphenylglycine and, less potently, by 1-aminoindan-1,5-dicarboxylic acid and 4-carboxyphenylglycine, two antagonists of group I mGluRs that display higher potency on mGluR1 than on mGluR5. The mGluR5-selective agonist (RS)-2-chloro-5-hydroxyphenylglycine also activated PLD in astrocytes. These findings indicate the involvement of group I mGluRs, most likely mGluR5, in the glutamate activation of PLD in cultured rat cortical astrocytes.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Astrocytes; Benzoates; Carcinogens; Cerebellum; Cerebral Cortex; Cycloleucine; Dose-Response Relationship, Drug; Enzyme Activation; Excitatory Amino Acid Antagonists; Glutamic Acid; Glycine; Hippocampus; Neurons; Neuroprotective Agents; Norepinephrine; Phospholipase D; Phosphorus Radioisotopes; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; Sympathomimetics; Tetradecanoylphorbol Acetate; Type C Phospholipases