1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

369 Poster Chemosensory Molecular Genetics andVNO/PheromoneREPLICATION OF LINKAGE AND ASSOCIATION OF PROPPERCEPTION TO CHROMOSOME 7 AND SUGGESTION OFNOVEL LOCI ON CHROMOSOME 6Hansen J.L. 1 , Reed D.R. 2 , Wright M.J. 1 , Martin N.G. 1 , Breslin P.A. 21 Queensland Institute of Medical Research, Brisbane, Queensland,Australia; 2 Monell Chemical Senses Center, Philadelphia, PAThis study was conducted to replicate linkage to chromosome 7,association with known TAS2R38 haplotypes and to search for otherchromosomal regions that may influence PROP perception. Theperceived bitterness of a 6.0 x 10-4 M propylthiouracil (PROP) solutionand a dry PROP strip (from a saturated solution) was examined in agenetically informative sample of 62 MZ and 131 DZ twin pairs and237 sib pairs. Multipoint linkage analysis (761 microsatellites) andassociation analyses (rs713598, rs1726866) were performed using thesoftware packages MERLIN and Mx respectively. Linkage analysisgenerated a LOD score of 4.9 on chromosome 7 (D7S684) for thePROP solution with no evidence of linkage to this region for the PROPstrip. The highest peak for the PROP strip was on chromosome 6(D6S1017) with a LOD score of 2.0 with the PROP solution having aLOD score of 1.7 at the previous marker (D6S2427). Association withthe three TAS2R38 haplotypes (PAV, AAV and AVI) indicated thatTAS2R38 accounts for 66% and 24% of the variation in the perceivedintensity of the PROP solution and strip respectively. Given that theheritability of both the solution and strip measures is 0.75, there areadditional genes responsible for variation in perceived intensity ofPROP, especially the strip, and we suggest that these may reside onchromosome 6. Supported by Australian National Health and MedicalResearch Council and National Institutes of Health (DC02995 andDC004698).370 Symposium Olfactory Bulb ComputationsMECHANISMS THAT GENERATE PRECISE SYNCHRONY INOLFACTORY BULB NEURONSSchoppa N. 1 1 Physiology and Biophysics, University of ColoradoHealth Sciences Center, Aurora, COSynchronized oscillatory activity at the gamma frequency (30-70 Hz)is thought to be important for information processing in many sensorysystems, including olfaction. Here, I used patch-clamp recordings inneuron-pairs to assess mechanisms underlying such “gamma” activity inrat olfactory bulb slices. During recordings from pairs of excitatorymitral cells, patterned electrical stimulation of afferents that mimicked anatural odor stimulus elicited rapidly synchronized spikes (lag ≤ 5 ms),along with ~50 Hz gamma frequency activity. Analysis of couplingpotentials, combined with dendritic sectioning, indicated that mitral cellsynchrony was driven by precisely timed inhibitory post-synapticpotentials (IPSPs) imposed by GABAergic granule cells atdendrodendritic synapses. Recordings in granule cell pairs, done todetermine the mechanisms underlying the synchronized IPSPs, revealedthat granule cells were themselves synchronized following afferentstimulation. Granule cell synchrony, which would enhance mitral cellsynchrony by coordinating GABA release, was due to divergentexcitatory inputs imposed by mitral cells, in combination with rapidspike response-times. Significantly, both mitral/mitral andgranule/granule cell synchrony occurred in the absence of electricalcoupling. Taken together, these results indicate that rapid gammafrequency activity in the olfactory bulb is a consequence of the preciseback-and-forth synaptic interplay between populations of mitral cellsand granule cells, rather than direct cell-to-cell coupling. Supported byNIH DC006640371 Symposium Olfactory Bulb ComputationsOPTICAL STUDIES OF ACTIVE PROPERTIES IN DENDRITESOF OLFACTORY BULB NEURONSDelaney K. 1 , Zelles T. 2 , Davison I. 3 , Hardy A. 1 1 Biology, University ofVictoria, Victoria, British Columbia, Canada; 2 Institute forExperimental Medicine, Hungarian Academy of Science, Budapest,Hungary; 3 Neuroscience, Duke University, Durham, NCThe majority of neurons in the olfactory bulb release neurotransmitterfrom dendrites so the modulation of dendritic Ca 2+ influx directlycontrols synaptic transmission within the bulb. We use a combination ofelectrophysiological recording and imaging of fluorescent Ca 2+indicators to examine activity dependent Ca 2+ influx into dendrites withparticular attention to conditions that alter the spatial distribution ofinflux along or between different branches. In mitral cells the extent ofaction potential (AP) propagation into secondary dendrites, and thus theamount of voltage-dependent Ca influx that results along the length ofthese processes, is under the control of fast inactivating K + (Ia)channels. Activation of D2 receptors reduces Ca 2+ influx primarilythrough hyperpolarization induced removal of inactivation of Ia with adistinct proximal to distal gradient of effectiveness. Ca 2+ influx isreduced in distal denrite more than proximal due to progressive loss ofAP amplitude. Granule cell dendrites readily support antidromic andorthodromically propagating Na + dependent APs. However, APsinitiated in a distal dendrite may or may not fully invade thesoma/proximal dendritic segment. If distally generated APs do notinitate APs in the soma/proximal dendrite then subsequent propagationout into other dendrites does not occur with the result that Ca 2+ influx,and thus transmitter release, can be restricted to a subset of presynapticrelease sites on specific branches. Supported by Canadian Institute forHealth Research.372 Symposium Olfactory Bulb ComputationsPERSISTENT ACTIVITY IN INHIBITORY LOCAL CIRCUITSIN THE OLFACTORY BULBStrowbridge B. 1 , Pressler T. 1 1 Department of Neurosciences, CaseWestern Reserve University, Cleveland, OHInhibitory local circuits in the olfactory bulb play a critical role indetermining the firing patterns of output neurons following sensorystimulation. Recent studies have identified several local circuitinteractions that affect the sensory input stage of olfactory processing.By contrast, relatively little is known about the synaptic circuitry in themajor plexiform layers of the olfactory bulb except for the reciprocaldendrodendritic synapse formed between mitral and axonless granulecells. We have recently identified Blanes cells, large stellate-shapedinterneurons located in the granule cell layer, as a local circuit circuitsource of inhibitory input to granule cells. We found that Blanes cellsare GABAergic and, unlike granule cells, generate large ICANmediatedafterdepolarizations following bursts of action potentialsunder normal pharmacological conditions. Using paired 2-photonguided intracellular recordings, we found that Blanes cells have apresumptive axon and monosynaptically inhibit granule cells. Blanescells receive excitatory input following sensory neuron stimulation thatcan trigger long epochs of persistent spiking that can be reset byhyperpolarizing membrane potential steps. Persistent firing in Blanescells may represent a novel mechanism for representing short-termolfactory information though by modulation of the tonic inhibitorysynaptic input to bulbar neurons. Supported by NIH (DC04285).93