1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

261 Poster Central Olfaction and Chemical EcologyTHE ANTIBODY OR-I7 SELECTIVELY AFFECTS THEDETECTION OF N-OCTANAL AND THE ODOR INDUCED C-FOS EXPRESSION PATTERN IN THE RAT OLFACTORYBULBDeutsch S. 1 , Apfelbach R. 1 1 Animal Physiology, University ofTübingen, Tübingen, GermanySeveral pharmacological studies have shown that the rat I7 olfactoryreceptor (OR-I7) responds preferentially to the n-aliphatic aldehyde n-octanal. However, there are n-octanal related odor compounds—e.g.citral—which also interact with OR-I7. To understand how these twoaldehyds interact with the olfactory receptor OR-I7 we performedbehavioral experiments and subsequently immunhistochemical (c-fos)studies in which the polyclonal antibody OR-I7: I7-MAP-PEPTIDE (AbOR-I7) was applied to the rat olfactory epithelium. Rats were trained inan olfactometer by operant conditioning to detect and discriminate lowconcentrations of n-octanal (n = 10) or citral (n = 5) from clean air. AbOR-I7 application reduced the animals' detection performance for n-octanal but not for citral. In the immunhistochemical part of this studywe compared the number of c-fos positive periglomerular cells in theolfactory bulb (OB) before (n = 6) and after (n = 6) antibodyapplication. Ab OR-I7 application resulted in a strong reduction of Fosimmunoreactivity in the OB of n-octanal stimulated animals. However,Ab OR-I7 application had no effect on the Fos staining patterns in citralstimulated animals (n = 6). Our data are in agreement with recent resultsand give strong evidence that n-aliphatic aldehydes evoke overlappingbut also significantly different patterns of neuronal activity in the ratOB. We thank RAM Research Ltd., London, for financial support andKrishna Persaud for the polyclonal antibody OR-I7.262 Poster Central Olfaction and Chemical EcologyCOLUMNAR ORGANIZATION IN THE OLFACTORY BULBWillhite D.C. 1 , Nguyen K.T. 1 , Masurkar A.V. 1 , Chen W.R. 1 , GreerC.A. 1 , Shepherd G.M. 1 1 Neurobiology, Yale University, New Haven, CTModular organization of glomerular units in the olfactory bulb hasbeen well established. While the olfactory module has been comparedto columns previously, more information on the synaptic connectivity isneeded to define the nature and extent of column-like architecture. Toprobe the synaptic organization of the olfactory bulb, we injected aretrograde specific strain (Bartha) of the pseudorabies virus into theolfactory bulb. The viral staining patterns reveal striking columnarorganization not only in the known column-like region from theglomerulus to the mitral cell layer, but throughout the whole depth ofthe granule cell layer as well. This pattern may arise from virus-specificeffects, but we hypothesize that the columns represent functionalglomerular units. Further, specific patterning is observed suggestingconnectivity that is specific to selected glomeruli, rather than strictlydistance dependent. These patterns are restricted to either the medial orlateral half of the bulb when the injection is made in the respective area,with the exception of a population on the opposite side assumed to arisefrom the mirror glomerulus projection. The results provide a new basisfor interpreting the synaptic connections between mitral and granulecells within the context of the columnar organization in the olfactorybulb, and have implications for olfactory coding and networkorganization. This work was supported by the NIDCD.263 Poster Central Olfaction and Chemical EcologyPATTERNED PROJECTIONS IN THE OLFACTORY BULBFROM OLFACTORY CORTEX REVEALED BYTRANSSYNAPTIC LABELINGNguyen K.T. 1 , Willhite D.C. 1 , Chen W.R. 1 , Shepherd G.M. 11 Neurobiology, Yale University, New Haven, CTOlfactory information from the olfactory bulb is sent to the olfactorycortex. Genetic labeling has shown that input from a single receptor cellpopulation targets specific clusters of cortical pyramidal cells, and thatthese clusters overlap to some degree with input from other receptors.The extent of receptor representation and differences in bulb projectionpattern from different regions of olfactory cortex is currently unknown.To address this question, we injected retrograde specific pseudorabiesvirus into five primary areas of olfactory cortex, the posterior piriformcortex, the dorsal anterior piriform cortex, the ventral anterior piriformcortex, the dorsal anterior olfactory nucleus, and the lateral anteriorolfactory nucleus. The pseudorabies virus is an alphaherpes virus whichis neuron specific, and infects neurons in a transsynaptic manner. Threedays after infection, staining patterns in the olfactory bulb show specificpatterning of glomerular unit labeling, including columns extendingthroughout the granule cell layer discussed in another abstract (seeWillhite, et al., accompanying abstract). The staining from all areas isbilaterally specific within the ipsilateral bulb, with only the anteriorolfactory nucleus showing contralateral bulb staining. The degree ofbulb staining directly correlates with injection radius (i.e. volume). Avariety of patterns from the various areas is revealed using thisapproach. This work was supported by the NIDCD.264 Poster Central Olfaction and Chemical EcologyESTIMATING THE NUMBER OF MODULES IN RATOLFACTORY BULB BY PREDICTION OF ODORANTDESCRIPTORSYamanaka T. 1 , Gutierrez-Osuna R. 1 1 Computer Science, Texas A&MUniversity, College Station, TXThe intrinsic dimensions of odor space are of great interest for thestudy of olfactory coding mechanisms. Recent genome studies haveestimated the repertoire of olfactory receptors to be around 1,000 in themouse and 500-750 in humans, which serves as an upper bound of theintrinsic dimensions. An alternative estimate of intrinsic dimensionalitymay be obtained by considering that glomeruli with similar affinitiescluster in close proximity, forming functional modules. The objective ofthis paper is to extract such intrinsic modules using machine learningtechniques. Images of glomerular activity were obtained from thearchive by Leon & Johnson at the University of California, Irvine. Onehundred and seventy two images were used to extract modules using adimensionality-reduction technique known as non-negative matrixfactorization. The optimum number of modules was estimated bymaximizing the prediction of odorant percepts (ten Flavornetdescriptors) from module activity using a support vector machine. Theresults of the prediction were two-folds. First, the predictiveperformance (geometric mean of true-positive and true-negative rates:85%) was much higher than chance level (geometric mean: 50%),supporting a hypothesis that odorant information is represented byspatial activity in the glomerular layer. Second, the highest predictiveperformance was achieved with 80-100 modules, which serves as anestimate of the intrinsic dimensions of odor space. T. Yamanaka issupported by a postdoctoral fellowship (2004) from Japan Society forthe Promotion of Science. R. Gutierrez-Osuna is supported by NSFCareer award 0229598.66