The molecular receptive range of an olfactory receptor in vivo (Drosophila melanogaster Or22a).
Understanding how odors are coded within an olfactory system requires knowledge about its input. This is constituted by the molecular receptive ranges (MRR) of olfactory sensory neurons that converge in the glomeruli of the olfactory bulb (vertebrates) or the antennal lobe (AL, insects). Aiming at a comprehensive characterization of MRRs in Drosophila melanogaster we measured odor-evoked calcium responses in olfactory sensory neurons that express the olfactory receptor Or22a. We used an automated stimulus application system to screen [Ca(2+)] responses to 104 odors both in the antenna (sensory transduction) and in the AL (neuronal transmission). At 10(-2) (vol/vol) dilution, 39 odors elicited at least a half-maximal response. For these odorants we established dose-response relationships over their entire dynamic range. We tested 15 additional chemicals that are structurally related to the most efficient odors. Ethyl hexanoate and methyl hexanoate were the best stimuli, eliciting consistent responses at dilutions as low as 10(-9). Two substances led to calcium decrease, suggesting that Or22a might be constitutively active, and that these substances might act as inverse agonists, reminiscent of G-protein coupled receptors. There was no difference between the antennal and the AL MRR. Furthermore we show that Or22a has a broad yet selective MRR, and must be functionally described both as a specialist and a generalist. Both these descriptions are ecologically relevant. Given that adult Drosophila use approximately 43 ORs, a complete description of all MRRs appears now in reach.
Pelz
Daniela
D
Institut für Neurobiologie, Freie Universität Berlin, D-14195 Berlin, Germany.
Roeske
Tina
T
Syed
Zainulabeuddin
Z
de Bruyne
Marien
M
Galizia
C Giovanni
CG
D000818:Animals; D002118:Calcium / Q000378:metabolism; D003952:Diagnostic Imaging; D004305:Dose-Response Relationship, Drug; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster; D005260:Female; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009812:Odorants; D009833:Olfactory Pathways / Q000378:metabolism*; D018034:Olfactory Receptor Neurons / Q000378:metabolism*; D018408:Patch-Clamp Techniques / Q000379:methods; D011401:Promoter Regions, Genetic / Q000502:physiology; D018035:Receptors, Odorant / Q000235:genetics / Q000378:metabolism*; D012679:Sense Organs / Q000166:cytology
D029721:Drosophila Proteins; C496847:OR22a protein, Drosophila; D018035:Receptors, Odorant; D049452:Green Fluorescent Proteins; D002118:Calcium