1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

269 Poster Central Olfaction and Chemical EcologyIN VIVO TWO-PHOTON IMAGING OF MITRAL CELL ODORRESPONSIVENESSNagayama S. 1 , Zeng S. 1 , Fletcher M.L. 1 , Xiong W. 1 , Chen W.R. 11 Department of Neurobiology, Yale University, New Haven, CTRecent advances in molecular biology and functional imaging haveestablished that odor information is represented as spatial patterns ofactivated glomeruli on the olfactory bulb surface. How these glomerularcoding patterns are subsequently transformed into the mitral-cellensemble output has emerged as a next critical question forunderstanding odor discrimination and recognition. To date, no directcomparison has been made between odor-evoked glomerular activityand its corresponding mitral cell output. In an effort to address thisissue, we have carried out in vivo imaging of odor responses both fromolfactory glomeruli and individual mitral cells. The odorants tested inthis study were a homologous series of aliphatic aldehydes. Thealdehyde-evoked glomerular activity pattern was imaged with the OMPsynapto-pHluorinmice originally developed in Peter Mombaerts´laboratory. Mitral cells in these GFP mice were labeled with a calciumsensitiveindicator. By taking advantage of deep-tissue imaging of twophotonmicroscopy, we were able to trace the glomerular projection ofindividual mitral cells, and then characterized odor responses of theseneurons with known glomerular identity. This approach revealedoptically the excitatory molecular receptive range of individual mitralcells in the dorsal olfactory bulb. The odorant receptive range of amitral cell was found to be similar to that of the correspondingglomerulus. These results suggest a tight functional coupling between aglomerulus and its associated mitral cells. We are currently exploringthe conditions under which a mitral cell could have a different odorresponseprofile from its glomerulus. Supported by an NIH grant(DC003918).270 Poster Central Olfaction and Chemical EcologyNEUROANATOMICAL AND FUNCTIONALCHARACTERIZATION OF MOR-EG GENE-TARGETED MICE: AXON CONVERGENCE AND ODORANT RESPONSESKatada S. 1 , Oka Y. 1 , Omura M. 1 , Yoshihara Y. 2 , Touhara K. 11 Department of Integrated Biosciences, The University of Tokyo, Chiba,Japan; 2 RIKEN Brain Science Institute, Saitama, JapanWe recently identified the odorant-binding site of a mouse eugenolreceptor, mOR-EG, providing the structural basis for olfactory receptors(ORs) that recognize broad but selective ligand spectrum [1]. Wecreated three transgenic mouse lines in which olfactory sensory neuronsexpressing mOR-EG co-expressed gap-EGFP. The zonal distribution ofthe fluorescent neurons was conserved in all these transgenic lines,whereas aberrant axonal projections to the olfactory bulb were detectedin two lines. A gene-targeting approach was also applied to visualizethe glomerular convergence of endogenous mOR-EG neurons by X-galstaining, and we compared axon convergence of mOR-EG neurons ingene-targeted mice with that in transgenic lines. To examine odorantresponses in these genetically modified mice, we utilized c-Fos as aneuronal activity marker. Eugenol induced c-Fos expression inperiglomerular cells and granule cells around the endogenous mOR-EGglomeruli as well as minor mOR-EG glomeruli observed in thetransgenic mice. The eugenol-response pattern in the olfactory bulbdetermined by c-Fos induction correlated well with that obtained by acalcium imaging method. [1] Katada et al. (2005) J. Neurosci. 25,1806-1815. Supported by PROBRAIN, Japan.271 Poster Central Olfaction and Chemical EcologyRESPONSE SPECIFICITY OF OLFACTORY FOREBRAINUNITS IN THE CHANNEL CATFISH TO AMINO ACIDSNikonov A.A. 1 , Caprio J. 1 1 Biological Sciences, Louisiana StateUniversity, Baton Rouge, LAWe previously described the odotopic maps of both the olfactory bulb(OB) (J. Neurophysiol. 86:1869-1876, 2001) and forebrain (FB) (PNAS102:18688-18693, 2005) in the channel catfish to amino acids (AA),nucleotides and bile salts. We now report on the specificity of FB unitsto AA and how it compares to that determined for OB units (J.Neurophysiol. 92:123-134, 2004). All recordings were performed invivo within the AA zone of the FB, and only excitatory responses arereported. As in the OB, FB units of both high (Group I) and lower(Group II) specificities were obtained. Both Group I FB and Group IOB units were excited by only one of three major types of AA: (1)neutral L-amino acids with short side-chains (e.g. Ala or Ser), (2)neutral amino acids with long side-chains (e.g. Met) and (3) basicamino acids (e.g. Arg); responses to acidic AA (e.g. Glu) were scarce atboth OB and FB levels. FB units were excited by a lower (~1 log unit)concentration than were OB units, but dose-response functions weresimilar. The more broadly-tuned Type II FB units showed a broaderspecificity than the Type II OB units. In addition, complex units wereidentified in the FB, but not the OB, that were excited by differentclasses of AA and by nucleotides (feeding stimuli). Supported by NSFIBN-0314970 and NIH DC-03792.272 Poster Central Olfaction and Chemical EcologySELECTIVITY OF BILE SALT RESPONSIVE NEURONS INTHE OLFACTORY BULB OF THE CHANNEL CATFISHRolen S. 1 , Caprio J. 1 1 Biological Sciences, Louisiana State University,Baton Rouge, LAAn odotopic map of biologically relevant odorants (bile salts, aminoacids and nucleotides) exists in the olfactory bulb (OB) of channelcatfish, Ictalurus punctatus (Nikonov and Caprio, J. Neurophysiol.86:1869-1876, 2001). We previously reported that OB neurons of thisregion were (1) selectively excited by bile salts that were nonconjugatedat carbon 24, (2) selectively excited by bile salts thattaurine-conjugated at C24, or (3) generalists that were excited by (1),(2), and glycine-conjugated (C24) bile salts. Previous behavioral studiessuggest that bile salts are socially relevant odorants in fishes. Thepresent report indicates that OB neurons are selective for particularcombinations of molecular features located at three additional carbonpositions (C3, C7, C12) along the perhydrocyclopentanophenanthrenering. OB neurons previously categorized as (1) and (2) show additionalselectivity for hydroxylation (or lack thereof) at C7 and C12 andhydroxylation at C3; other category (2) units require sulfonation at C3.Further, the data suggest that the majority of category (3) neuronsrespond excitedly to hydroxylation at C7 in combination withhydroxylation at C3 (irrespective of the molecular feature of C24).Olfactory thresholds of OB neurons to conjugated bile salts were lower(0.01-1 µM) than those to non-conjugated bile salts (1-10 µM).Supported by NSF IBN-0314970 and NIH DC-03792.68