1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

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301 Slide Central OlfactionOLFACTORY BULB GLOMERULAR ACTIVITY PATTERNSAS A BASIS FOR ODORANT QUALITY CODING:PREDICTING PERCEPTUAL BEHAVIOR FROM 2-DGFUNCTIONAL MAPSYoungentob S.L. 1 , Johnson B.A. 2 , Leon M. 2 , Kent P.F. 1 1 Neuroscienceand Physiology, SUNY Upstate Medical University, Syracuse, NY;2 Neurobiology and Behavior, University of California, Irvine, Irvine,CAWe tested whether odorant-evoked spatial activity patterns at thelevel of the olfactory bulb could be the neural code underlying odorantquality perception. Using operant techniques, rats were trained todifferentially identify the odorants santalol, n-propanol, -pinene,acetone, and pentadecane. The animals were tested using a 5 x 5odorant confusion matrix task, and the results of the psychophysicaltests were used to measure the degree of perceptual dissimilaritybetween odorant pairs. By way of multidimensional scaling analysis(MDS), the dissimilarity measures yielded a two-dimensionalperceptual odorant space for each test animal. Likewise, using 2-DGactivity maps of the rat olfactory bulb in response to the same odorants,an MDS analysis of the similarity measures between all possible pairsof glomerular patterns yielded a two-dimensional odorant space basedon functional activity. Formal statistical analysis demonstrated a highlysignificant predictive relationship between the similarity of an odorant´sglomerular activity pattern and the perceptual relationship among theodorants (R 2 = 0.434; F 1,18 = 16.54; P = nil) that was homogeneousacross animals (F 5,18 = 0.899; P > 0.5). The successful prediction of theperceptual relationship between odorants based on the similarity in theirrespective glomerular activity patterns gives strong support to thehypothesis that odorant identity is based on a spatial code at the level ofthe olfactory bulb.302 Slide Central OlfactionDEVELOPMENT OF FUNCTIONAL ODOR MAPS IN THERODENT OLFACTORY BULBAlbeanu D. 1 , Soucy E. 1 , Sato T. 1 , Meister M. 1 , Murthy V.N. 11 Molecular & Cellular Biology, Harvard University, Cambridge, MAOlfactory sensory axons expressing a particular odorant receptorproject to about two glomeruli in each olfactory bulb in adult mice. Atbirth, the projections are more promiscuous and converge to the adultpattern with a time course that can be affected by sensory experience.To examine whether functional odor maps reflect these anatomicalchanges during development, we imaged odor-evoked responses ingene-targeted mice expressing the presynaptic reporter synaptopHluorinin olfactory sensory neurons (Neuron 42:9). Using a panel of ~100odors, we could reliably identify individual glomeruli across differentanimals based on their functional signatures. Most of the nearly 80responsive glomeruli per hemisphere were functionally unique. Onaverage, each functionally unique glomerulus was represented 1.28 ±0.09 times on each dorsal surface. This matches the number ofglomeruli per odorant receptor estimated from gene-targeted mice,supporting the assumption that each functionally unique glomeruluscorresponds to an individual receptor. Functional odor maps werepresent even in 1-week old animals. At two weeks, glomerular mapswere very similar to those in adults – individual glomeruli did not havemore promiscuous responses to odors and individual odors did notevoke responses in more glomeruli. Similar results were obtained in ratsusing intrinsic optical signals. Our results indicate that precisefunctional maps develop early in mice and rats. Preliminaryexperiments have indicated that functional odor maps are relativelyunaltered if sensory experience is altered by unilateral naris occlusion.Support: NIH, EJLB and Pew.303 Slide Central OlfactionRELATIONSHIP BETWEEN SNIFFING AND ODORREPRESENTATIONS IMAGED FROM THE OLFACTORYBULB OF AWAKE RATS.Verhagen J.V. 1 , Wesson D.W. 1 , Wachowiak M. 1 1 Biology, BostonUniversity, Boston, MARodents actively explore their olfactory environment by sniffing,which modulates the flow of odorants across the nasal epithelium. Weare investigating the relationship between sniffing and odorrepresentations in the olfactory bulb using optical imaging ofpresynaptic calcium influx in awake, head-fixed rats. Rats learned atwo-odor, go-no-go discrimination task. Olfactory receptor neuronswere loaded with calcium-sensitive dye and a chronic imaging windowinstalled over the dorsal olfactory bulb. Odorant-evoked calcium signalswere imaged across the bulb during odor discriminations while sniffingwas measured. Rats typically discriminated after a single sniff. Sniffingvaried in amplitude, waveform, and frequency. Response amplitude wasnot correlated with sniff amplitude but was highly correlated with sniffinterval. Most sniffing occured at 1–2 Hz, but increased to > 4 Hz whenrats were presented with a novel odorant. During slow sniffing,glomerular input was tightly synchronized to inhalation, with a latencyof ~200 ms and risetime of ~ 100ms.During fast sniffing, phasic inputfollowing each sniff was attenuated and instead appeared dominated bytonic input. Glomerular response maps were temporally dynamic,changing over the course of a single sniff as well as across sniffs.Surprisingly, one cause of this variation was the failure of someglomeruli to respond to certain sniffs during an odor presentation. Thesedata suggest that the parameters of odor sampling can shape both spatialand temporal representations of odor information in the olfactory bulb.Supported by NIDCD DC06441.304 Slide Central OlfactionADRENERGIC ENHANCEMENT OF GABA INHIBITORYTRANSMISSION IN THE OLFACTORY BULBAraneda R.C. 1 , Firestein S. 1 1 Biological Sciences, Columbia University,New York, NYNoradrenergic modulation of dendrodendritic synapses between themitral and granule cells in the olfactory bulb is postulated to play a keyrole in the formation of memory in olfactory mediated behaviors.Current models propose that noradrenaline (NA) increases excitation ofmitral/tufted cells (M/TCs) by decreasing the release of GABA fromgranule cells. Here, in recordings from AOB slices, we show that NAdecreases the firing frequency of M/TCs in cell-attached patch and incurrent-clamp recordings. This effect is due to an increase in the GABAinhibitory input to M/TCs. Application of NA (10 µM) produced a ~20-fold increase in the frequency of GABA induced miniature inhibitorypostsynaptic currents (mIPSCs) without changing their amplitude. Apharmacological analysis indicated that the increase in mIPSCsfrequency results from activation of α1-adrenergic receptors. We havefound a similar increase mIPSC frequency in the main olfactory bulb.Taken together, our results suggest that NA increases the release ofGABA from granule cells by acting on presynaptic receptors. Thus, therole of the noradrenergic activity in the olfactory bulb may be morecomplex than previously suggested. Supported contributed by NIDCD.76
305 Symposium Approaching Taste and Olfaction at theSystems LevelTHE INTEGRATION OF MULTIPLE SENSORY MODALITIESAND THE CREATION OF FLAVORBreslin P.A. 1 1 Monell Chemical Senses Center, Philadelphia, PAThe central neural creation of flavor from stimulation originatingwithin the upper airways represents what is arguably the single mostprofoundly multi-modal sensory integration of which the brain iscapable. Inputs from the upper airways reflect taste (salt, sweet, bitter,sour and savory), olfaction (and it myriad qualities), static tactilesensations (touch, pressure, stretch), dynamic tactile sensations(vibration, astringency, creaminess, viscocity, coating), thermalsensations (warm, cool, hot, cold), nociception (stinging, burning,prickling, itching), proprioception (bolus texture, resistance, chewiness,brittleness, crunchiness), and auditory input (via the sounds arising inthe oral cavity and bone conduction when foods are manipulated andchewed). Flavor may be conceived of or defined as the congruentintegration of all these inputs into a single perceptual gestalt that isprojected to originate within the mouth. Some of these differentphysical inputs may interact at the receptor cell or primary afferent levelsuch as thermal-taste or tactile-taste interactions. Higher in the CNSthere are brain areas that appear to process and relay inputs from all ofthese modalities such as the insula/operculum, orbitofrontal cortex, andamygdala. How these diverse systems are integrated, under whatconditions, and the role of attention and learning in these pathways arethe focus of an ever-growing and fascinating body of research.306 Symposium Approaching Taste and Olfaction at theSystems LevelLEARNING TO SMELL: CORTICAL PLASTICITY AND ODORPERCEPTIONWilson D.A. 1 1 Zoology, University of Oklahoma, Norman, OKOlfactory perception involves at least two distinct processes. First,most odors are composed of several to hundreds of volatile molecules.However, under most conditions odor perception is synthetic, withlimited access to the underlying features of complex mixtures. Thus,multi-component odorant mixtures can be perceived as unique odorobjects through experience-dependent mechanisms hypothesized to besimilar to object perception in vision. Second, odors are almostinvariably experienced against odorous backgrounds from which theforeground odor must be extracted from the background through ananalytical (as opposed to synthetic) process (figure-ground separation).Work in our lab has been examining piriform cortical contributions toboth of these processes. Here I will focus on the process of olfactoryfigure-ground separation. Neurons within the piriform cortex showrapid, odor-specific adaptation, despite relatively maintained input fromolfactory bulb mitral/tufted cells. This cortical adaptation is mediated bypre-synaptic metabotropic glutamate receptors that induce an activitydependentdepression of afferent synapses. Pharmacologicalmanipulations show that cortical adaptation contributes to backgroundodor adaptation and short-term behavioral odor habituation.Behaviorally, rats are able to filter background odors and identify atarget odor presented against that background. Similarly, piriformcortical neurons adapt to background odors, and respond to novel targetodors presented against that background as if the target odors werepresented alone. These findings present a specific cortical mechanism toallow perception of odors in odorous backgrounds. Supported by NIH& NSF.307 Symposium Approaching Taste and Olfaction at theSystems LevelNEURAL POPULATION CODING OF SATIETY STATESDe Araujo I. 1 1 Neurobiology, Duke University, Durham, NCVoluntary feeding involves behavioral states associated with mealinitiation (hunger) and termination (satiety). In this activity multiplebrain regions act in concert to regulate the onset of these behaviors.Previous electrophysiological investigations revealed that singleneurons located in primate brain areas such as lateral hypothalamus(LH) and orbital frontal cortex (OFC) decrease their firing rate levels asanimals transition from hunger to satiety. Similar responses wereobserved in human functional neuroimaging studies. We will presentrecent data obtained from hungry rats that have bundles ofmicroelctrodes implanted in their LH, OFC , insular cortex (IC) andamygdala (AM) that freely lick to satiety. These data show that singleunits mostly encode for specific hunger states within a feeding cycle(hunger–satiety-hunger), while neuronal population activity reflects theoverall motivational (hunger/satiety) state across several cycles bycombining information from its constituent units. This population codeseems to be distributed across LH-IC-OFC-AM circuits of both lean andobese/diabetic rats. We suggest that this distributed code underlies thecontrol of voluntary feeding behavior under different metabolic states.This work was supported by grants DC-01065 and Philip Morris USAand Philip Morris International.308 Symposium Approaching Taste and Olfaction at theSystems LevelHEDONIC ASPECTS OF CHEMICAL STIMULI:CORTICOLIMBIC CIRCUITS THAT MEDIATE REWARDAND CHOICE.Balleine B. 1 1 Psychology, University of California, Los Angeles, LosAngeles, CAThat chemical stimuli can exert powerful effects on behavior is dueboth to evolutionary pressures and to learning; i.e. the formation ofassociations with biologically potent events such as nutrients, fluids,illness and so on. Associations of this kind modify the affective valenceand, hence, the preference for specific flavors and tastes but they arealso the basis for changes in the hedonic response to these stimuli.Current evidence suggests that this latter aspect is a product ofcontiguous emotion feedback elicited by the stimulus through a systemof sensory-motivational and affective connections, and that itdetermines the assignment of reward value to a particular stimulus.Thus, for example, shifts in motivational state do not reduce the rewardvalue that animals´ assign to taste stimuli until the effect of the shift instate is experienced through direct consummatory contact with the taste.Sensory-specific satiety is a particularly potent means of producingselective changes in the reward value of stimulus events as indexed bychanges in the performance of actions that gain access to those events.Evidence from rodents will be presented suggested that these changesare mediated by a corticolimbic circuits involving particularlyconnections between gustatory insular cortex, basolateral amygdala andthe nucleus accumbens.77
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