title: Molecular and pharmacological evidence for a facilitatory functional role of pre-synaptic GLUK2/3 kainate receptors on GABA release in rat trigeminal caudal nucleus.
abstract: BACKGROUND
  Gamma-aminobutyric acid (GABA) and glutamate (GLU) are involved in nociceptive signals processing in the trigeminal system. In this study, we investigated the influence of excitatory transmission on GABA release in nerve terminals isolated from the rat trigeminal caudal nucleus (TCN).
  
  
  METHODS
  We utilize biochemical (superfused synaptosomes loaded with [(3) H]GABA) and morphological (immunofluorescence experiments with specific antibody) techniques.
  
  
  RESULTS
  Our results show that GLU potentiates the release of [(3) H]GABA evoked by 9, 15 and 30 mM [K(+)](e); 15 mM [K(+)](e)-evoked [(3) H]GABA release was also reinforced by domoate and kainate (KA), two naturally occurring GLU-receptor agonists. The enhancement of 15 mM [K(+)](e)-evoked [(3) H]GABA release produced by 100 μM KA was abolished by NBQX, a mixed AMPA/KA receptor antagonist, but was not affected by GYKI52466, a selective AMPA receptor antagonist. ATPA, a selective agonist for KA receptors containing the GLUK1 subunit, had no effect on depolarization-induced [(3) H]GABA release, and UBP310, which selectively antagonizes these same receptors, failed to reverse the KA-induced potentiation of 15 mM [K(+)](e)-evoked [(3) H]GABA release. The KA-induced potentiation was also unaffected by concanavalin A (10 μM), a positive allosteric modulator of GLUK1- and GLUK2-containing KA receptors. Immunofluorescence experiments revealed that GABAergic nerve terminals in the TCN differentially expressed GLUK subunits, with GLUK2/3-positive terminals being twice more abundant than GLUK1-containing synaptosomes.
  
  
  CONCLUSIONS
  These findings indicate that pre-synaptic KA receptors facilitating GABA release from TCN nerve terminals mainly express GLUK2/GLUK3 subunits, supporting the notion that different types of KA receptors are involved in the various stages of pain transmission.
authors.affiliation: Institute of Pharmacology, Catholic University of Sacred Heart, Rome, Italy.
authors.forename: I
authors.initials: I
authors.lastname: Samengo
authors.forename: D
authors.initials: D
authors.lastname: Currò
authors.forename: P
authors.initials: P
authors.lastname: Navarra
authors.forename: V
authors.initials: V
authors.lastname: Barrese
authors.forename: M
authors.initials: M
authors.lastname: Taglialatela
authors.forename: M
authors.initials: M
authors.lastname: Martire
mesh_terms: D000818:Animals; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D007608:Kainic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018092:Kainic Acid Receptors / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D014275:Trigeminal Caudal Nucleus / Q000187:drug effects / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*; D000097806:GluK2 Kainate Receptor; D000097808:GluK3 Kainate Receptor
chemical_list: D018690:Excitatory Amino Acid Agonists; D007608:Kainic Acid; D018092:Kainic Acid Receptors; D005680:gamma-Aminobutyric Acid; D000097806:GluK2 Kainate Receptor; D000097808:GluK3 Kainate Receptor; C012301:domoic acid