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Presynaptic group I metabotropic glutamate receptors modulate synaptic transmission in the rat superior colliculus via 4‐AP sensitive K + channels
Author(s) -
White AnneMarie,
Kylänpää Risto A,
Christie Louisa A,
McIntosh Simon J,
Irving Andrew J,
Platt Bettina
Publication year - 2003
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0705570
Subject(s) - metabotropic glutamate receptor , neurotransmission , bicuculline , excitatory postsynaptic potential , agonist , metabotropic receptor , pharmacology , postsynaptic potential , glutamate receptor , antagonist , metabotropic glutamate receptor 5 , chemistry , neuroscience , metabotropic glutamate receptor 1 , inhibitory postsynaptic potential , biology , receptor , biochemistry
Group I metabotropic glutamate receptors (mGluRs) are thought to be important modulators of neuronal function in the superior colliculus (SC). Here, we investigated the pharmacology and signalling mechanisms underlying group I mGluR‐mediated inhibition of neuronal excitability and synaptic transmission in the rat SC slice. The group I agonist (RS)‐3,5‐dihydroxyphenylglycine (DHPG) potently depressed synaptically evoked excitatory postsynaptic potentials (EPSPs), currents (EPSCs), and action potentials in a dose‐dependent manner (IC 50 : 6.3 μ M ). This was strongly reduced by the broad‐spectrum antagonist (+)‐alpha‐methyl‐4‐carboxyphenylglycine (MCPG, 1 m M , ∼95% reduction), by the mGluR1 antagonist LY367385 (100 μ M , ∼80% reduction) but not by the mGluR5 antagonist 6‐methyl‐2‐(phenylethynyl)‐pyridine (MPEP, 1–100 μ M ). The putative mGluR5‐specific agonist (RS)‐2‐chloro‐5‐hydroxyphenylglycine (CHPG, 500 μ M ) also inhibited EPSPs. Interestingly, CHPG's actions were not blocked by MPEP, but LY367385 (100 μ M ) reduced the effect of CHPG by 50%. Inhibition induced by DHPG was independent of phospholipase C (PLC)/protein kinase C pathways, and did not require intact intracellular Ca 2+ stores. It was not abolished but enhanced by the GABA A antagonist bicuculline (5 μ M ), suggesting that DHPG's action was not due to facilitated inhibition or changes in neuronal network activity. The K + channel antagonist 4‐aminopyridine (4‐AP, 50–100 μ M ) converted the inhibitory effect of DHPG into facilitation. Paired‐pulse depression was strongly reduced by DHPG, an effect that was also prevented by 4‐AP. Our data indicate that group I agonists regulate transmitter release, presumably via an autoreceptor in the SC. This receptor may be involved in adaptation to repetitive stimulation via a non‐PLC mediated pathway.British Journal of Pharmacology (2003) 140 , 1421–1433. doi: 10.1038/sj.bjp.0705570