title: Unexpected inhibitory regulation of glutamate release from rat cerebrocortical nerve terminals by presynaptic 5-hydroxytryptamine-2A receptors.
abstract: Presynaptic 5-HT(2A) receptor modulation of glutamate release from rat cerebrocortical nerve terminals (synaptosomes) was investigated by using the 5-HT(2A/2C) receptor agonist (+/-)-1-[2,5-dimethoxy-4-iodophenyl]-2-aminopropane (DOI). DOI potently inhibited 4-aminopyridine (4AP)-evoked glutamate release. Involvement of presynaptic 5-HT(2A) receptors in this modulation of 4AP-evoked release was confirmed by blockade of the DOI-mediated inhibition by the 5-HT(2A) receptor antagonist ketanserin but not by the 5-HT(2C) receptor antagonist RS102221. Inhibition of glutamate release by DOI was associated with a reduction of 4AP-evoked depolarization and downstream elevation of cytoplasmic free calcium concentration ([Ca(2+)](C)) mediated via P/Q- and N-type voltage-dependent Ca(2+) channels (VDCCs). In contrast to the DOI effect on 4AP-evoked release, the agonist had no effect on high external [K(+)] (30 mM)-induced (KCl) stimulation of VDCCs or glutamate release. Likewise, release mediated by direct Ca(2+) entry with Ca(2+) ionophore (ionomycin) or by hypertonic sucrose was unaffected by DOI. Mechanistically, DOI modulation of 4AP-evoked glutamate release appeared to involve a phospholipase C/protein kinase C signaling cascade, insofar as pretreatment of synaptosomes with the phospholipase C inhibitor U73122 or protein kinase C inhibitors Ro320432 or GF109203X all effectively occluded the inhibitory effect of the agonist. Together, these results suggest that presynaptic 5-HT(2A) receptors present on glutamatergic terminals effect an unexpected depression of glutamate release by negatively modulating nerve terminal excitability and downstream VDCC activation through a signaling cascade involving phospholipase C/protein kinase C. These observations invoke presynaptic inhibitory 5-HT(2A) receptor function as a potential target for drugs to mitigate the effects of excessive glutamatergic transmission.
authors.affiliation: School of Medicine, Fu Jen Catholic University, Taipei Hsien, Taiwan.
authors.forename: Su-Jane
authors.initials: SJ
authors.lastname: Wang
authors.forename: Kai-Yun
authors.initials: KY
authors.lastname: Wang
authors.forename: Wei-Chieh
authors.initials: WC
authors.lastname: Wang
authors.forename: Talvinder S
authors.initials: TS
authors.lastname: Sihra
mesh_terms: D000662:Amphetamines / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002540:Cerebral Cortex / Q000166:cytology*; D003998:Dicarboxylic Acids / Q000494:pharmacology; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D007650:Ketanserin / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D014179:Neurotransmitter Uptake Inhibitors / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D011759:Pyrrolidines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044402:Receptor, Serotonin, 5-HT2A / Q000502:physiology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013141:Spiro Compounds / Q000494:pharmacology; D013449:Sulfonamides / Q000494:pharmacology; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors; D020867:omega-Agatoxin IVA / Q000494:pharmacology; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
chemical_list: C107821:8-(5-(5-amino-2,4-dimethoxyphenyl)-5-oxopentyl)-1,3,8-triazaspiro(4.5)decane-2,4-dione; D000662:Amphetamines; D002121:Calcium Channel Blockers; D003998:Dicarboxylic Acids; D004791:Enzyme Inhibitors; D014179:Neurotransmitter Uptake Inhibitors; D011759:Pyrrolidines; D044402:Receptor, Serotonin, 5-HT2A; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D013141:Spiro Compounds; D013449:Sulfonamides; D020867:omega-Agatoxin IVA; D018698:Glutamic Acid; D020866:omega-Conotoxin GVIA; D007650:Ketanserin; C083486:pyrrolidine-2,4-dicarboxylic acid; C015952:4-iodo-2,5-dimethoxyphenylisopropylamine; D002118:Calcium