1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

245 Poster Central Olfaction and Chemical EcologyTHE PHYLOGENY OF A PUTATIVE CIRCADIANMODULATOR OF OLFACTORY SENSITIVITYDacks A. 1 , Christensen T. 1 , Hildebrand J.G. 2 1 Neurobiology, Universityof Arizona, Tucson, AZ; 2 University of Arizona, Tucson, AZInsects are among the most widely used olfactory models and theirodor-driven behaviors and olfactory systems are quite variable. Thisdiversity highlights the importance of comparative studies to determinethe ubiquity of anatomical and functional traits across taxa. In thesphinx moth Manduca sexta, a single serotonergic neuron innervateseach antennal lobe and serves as a circadian modulator of olfactorysensitivity. The cell body resides in one antennal lobe, while the axoncrosses the posterior midline to innervate the contralateral antennallobe. To determine the phylogenetic breadth of this neuron´scharacteristic bilateral morphology, brains of 40 insect species (38families, 9 orders) were labeled using serotonin immunocytochemistry.Structurally homologous neurons were found in the Lepidoptera,Trichoptera, Diptera, Coleoptera and Neuroptera, but not in theHymenoptera nor in the hemimetabolous orders examined. Within thehemimetabola, serotonergic antennal lobe neurons are strictly unilateral,projecting only to the ipsilateral antennal lobe and protocerebrum. Ourdata suggest that the phenotype common to the Lepidoptera most likelyoriginated near the divergence of the holometabola from thehemimetabola some 300 million years ago. This study provides a list ofcandidates within the insects for which serotonin may act as a circadianmodulator of olfactory sensitivity. Supported by grants from NSERCCanada to AD (PGS B 244345) and from NIH to TC (DC05652).246 Poster Central Olfaction and Chemical EcologyAPPLICATION OF MAGNETIC RESONANCESPECTROMETRY IN THE OLFACTORY SYSTEMXu F. 1 , Jiang L. 1 , Patel A.B. 1 , Rothman D.L. 1 , Hyder F. 1 , Behar K. 1 ,Shepherd G.M. 2 1 Diagnostic Radiology, Yale University, New Haven,CT; 2 Neurobiology, Yale University, New Haven, CTMagnetic resonance spectrometry (MRS) is a non-invasivetechnology that measures in vivo concentrations of individualmetabolites. We have developed MRS methods for determining cerebralmetabolic fluxes associated with glutamate and GABAneurotransmitters in olfactory bulb (OB). In present study we testedwhether, in terms of neurotransmitter releasing rates, the OB is "quiet"or "noisy". Overnight fasted urethane anesthetized animals wereinfused with [1,6- 13 C 2 ]glucose for different time. Amino acids 13 Clabeling was measured using 1 H-{ 13 C} NMR in vivo as well as ex vivo.GABA and taurine level in the OB were the highest in the measuredbrain region. Under resting conditions, the neurotransmitter cyclingrates in OB were slightly lower for glutamate and higher for GABAcompared with the cerebral cortex, indicating that overall the OB is`quieter´. The cycling rates for glutamate and GABA increasedsignificantly with odor stimulation and the increase correlated withstimulation strength. Since the cycling rates for neurotransmitters reflectsynaptic activity, the data can be used to correlate/calibrate the resultsfrom other studies, such as the BOLD signal in fMRI, the optical signalin intrinsic imaging, and the radioactive signal in 2-deoxyglucosemapping. The methods can be readily used to study synaptic propertiesat different developmental stages, and the effects of transgenicmanipulations in various types of diseases and physiological conditions.The research was supported by NIH grants: DC-03710, DC-00086 &DK27121.247 Poster Central Olfaction and Chemical EcologyOSCILLATIONS, GABA AND SPIKE TIMING IN THE MOTHMANDUCA SEXTAPeters O. 1 , Daly K.C. 1 1 Biology, West Virginia University,Morgantown, WVOdor stimulation drives spatial responses, slow patterns of spikebursting, and local field potential oscillations (LFPOs). Thesephenomena are observed in vertebrate and invertebrate models and havebeen correlated to odor discrimination. However, oscillatory-basedtemporal models in remain highly controversial. To further explore thismodel, whole M. sexta moths were restrained and a window was openedin the head capsule. Physiological saline was bath applied and 16channel electrodes implanted into one AL. Multiunit and multi-LFPsrecordings were made in response to 9 closely related odorants, eachpresented at high concentrations in 20 100-ms stimulations. This panelof stimuli was repeated before, during, and after bicuculline (BMI; 200µM in saline) application. Spikes were sorted and LFP data filteredusing standard techniques. We observed odor-driven high frequencyLFPOs with a spectral peak at ~80 Hz. These LFPOs were: multiphasic,BMI sensitive, coherent across stimulations, initiated at ~50 msand were highly coherent across recording sites, suggesting a distributedphenomenon. Furthermore, we observed unit-specific crosscorrelationsbetween LFPOs and spiking with spikes from units typically precedingthe peak of the LFPO. Interestingly, application of BMI abolished earlyphase LFPOs. In contrast to the temporal model, BMI also appeared toamplify and enhance the coherence of later phase LFPOs and enhancethe coherence between LFPOs and spikes. These results indicate afundamentally different relationship between GABA LFPO control andspike timing.This work was supported by NIH-DC05535 to KCD &NIH-RR015574 to GS & KCD248 Poster Central Olfaction and Chemical EcologyCELL TYPE SPECIFIC ACTIVITY-DEPENDENTREGULATION OF GAD ISOFORMS IN THE GLOMERULARLAYER OF THE MOUSE MAIN OLFACTORY BULBAungst S. 1 , Puche A.C. 1 , Shipley M.T. 1 1 Department of Anatomy andNeurobiology, University of Maryland at Baltimore, Baltimore, MDThe inhibitory neurotransmitter -aminobutyric acid (GABA) isexpressed by subpopulations of interneurons in the mouse mainolfactory bulb (MOB). The majority of these GABAergic interneuronsare periglomerular (PG) cells located in the glomerular layer andgranule cells located in the granule cell layer. GABA is synthesizedfrom L-glutamic acid by the enzyme glutamic acid decarboxylase(GAD). In adult, there are two major isoforms of GAD protein, 65kDa(GAD65) and 67kDa (GAD67). There is heterogeneity in the expressionof the 65kDa or 67kDa isoforms among PG cells. Of the approximately1.2 million cells in the glomerular layer, 24% express only GAD65,19% express only GAD67 and 5% express both isoforms. Preferentialuse of GAD65 or 67 by PG cells correlates with expression of otherneurochemicals. For example, ~60% of dopaminergic PG cells,identified by expression of tyrosine hydroxylase (TH) express onlyGAD67, ~6% express only GAD65, and ~12% express both GAD65and GAD67. Lesion of the olfactory receptor neurons (ORNs) decreasesexpression of TH in PG cells. Expression of GAD65 is generallyreported to be activity independent in most brain regions while the67kDa isoform can be modulated by activity, e.g. in the hippocampus.We find that ORN lesion has no effect on the number of cellsexpressing GAD65, but reduces the number of cells expressing GAD67by 70%. These data show different populations of PG cells preferentialuse the 65kDa or 67kDa isoform of GAD and that the presence of ORNaxons modulates only expression of the 67kDa isoform. This work wassupported by NIH grants DC36940 & DC0217362