title: Homomeric RDL and heteromeric RDL/LCCH3 GABA receptors in the honeybee antennal lobes: two candidates for inhibitory transmission in olfactory processing.
abstract: gamma-Aminobutyric acid (GABA)-gated chloride channel receptors are abundant in the CNS, where their physiological role is to mediate fast inhibitory neurotransmission. In insects, this inhibitory transmission plays a crucial role in olfactory information processing. In an effort to understand the nature and properties of the ionotropic receptors involved in these processes in the honeybee Apis mellifera, we performed a pharmacological and molecular characterization of GABA-gated channels in the primary olfactory neuropile of the honeybee brain-the antennal lobe (AL)-using whole cell patch-clamp recordings coupled with single-cell RT-PCR. Application of GABA onto AL cells at -110 mV elicited fast inward currents, demonstrating the existence of ionotropic GABA-gated chloride channels. Molecular analysis of the GABA-responding cells revealed that both subunits RDL and LCCH3 were expressed out of the three orthologs of Drosophila melanogaster GABA-receptor subunits encoded within the honeybee genome (RDL, resistant to dieldrin; GRD, GABA/glycine-like receptor of Drosophila; LCCH3, ligand-gated chloride channel homologue 3), opening the door to possible homo- and/or heteromeric associations. The resulting receptors were activated by insect GABA-receptor agonists muscimol and CACA and blocked by antagonists fipronil, dieldrin, and picrotoxin, but not bicuculline, displaying a typical RDL-like pharmacology. Interestingly, increasing the intracellular calcium concentration potentiated GABA-elicited currents, suggesting a modulating effect of calcium on GABA receptors possibly through phosphorylation processes that remain to be determined. These results indicate that adult honeybee AL cells express typical RDL-like GABA receptors whose properties support a major role in synaptic inhibitory transmission during olfactory information processing.
authors.affiliation: Centre de Recherches sur la Cognition Animale, Université Paul Sabatier (Toulouse III), CNRS UMR 5169, 118 route de Narbonne, Toulouse Cedex 9, France.
authors.forename: Julien Pierre
authors.initials: JP
authors.lastname: Dupuis
authors.forename: Michaël
authors.initials: M
authors.lastname: Bazelot
authors.forename: Guillaume Stéphane
authors.initials: GS
authors.lastname: Barbara
authors.forename: Sandrine
authors.initials: S
authors.lastname: Paute
authors.forename: Monique
authors.initials: M
authors.lastname: Gauthier
authors.forename: Valérie
authors.initials: V
authors.lastname: Raymond-Delpech
mesh_terms: D000818:Animals; D001516:Bees; D001921:Brain / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D065101:Chloride Channel Agonists; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D018755:GABA Agonists / Q000008:administration & dosage / Q000494:pharmacology; D018756:GABA Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D019476:Insect Proteins / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D055696:Olfactory Perception; D018408:Patch-Clamp Techniques; D018079:Receptors, GABA / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D065101:Chloride Channel Agonists; D018118:Chloride Channels; D018755:GABA Agonists; D018756:GABA Antagonists; D019476:Insect Proteins; D018079:Receptors, GABA; D005680:gamma-Aminobutyric Acid; D002118:Calcium