Homomeric RDL and heteromeric RDL/LCCH3 GABA receptors in the honeybee antennal lobes: two candidates for inhibitory transmission in olfactory processing.
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.
Dupuis
Julien Pierre
JP
Centre de Recherches sur la Cognition Animale, Université Paul Sabatier (Toulouse III), CNRS UMR 5169, 118 route de Narbonne, Toulouse Cedex 9, France.
Bazelot
Michaël
M
Barbara
Guillaume Stéphane
GS
Paute
Sandrine
S
Gauthier
Monique
M
Raymond-Delpech
Valérie
V
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
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