2009 Abstracts - Association for Chemoreception Sciences

#P157 Poster session III: Cortical chemosensory processing/Receptor genomics and molecular biologyThe effect of learning and attention on odor responses inpiriform cortexJennifer D Whitesell 1,2 , Wilder Doucette 1,2 , Diego Restrepo 1,21Neuroscience Program Denver, CO, USA, 2 Cell andDevelopmental Biology Denver, CO, USAThe piriform cortex (PC) is the primary target of afferent signalsfrom the olfactory bulb and is believed to be the site of odorperception. The anterior PC (aPC) receives more direct sensoryinput relative to the posterior PC, which has more intrinsicconnections. Recently it has become clear that the aPC is moreassociational in nature than was previously believed, with cellularodor responses that can change based on learning (Schoenbaum etal, 2007). We have found that cells in aPC display robust odorresponses, but only after an odor-reward association has beenlearned. We performed extracellular recordings from the aPC ofawake-behaving mice receiving a water reward paired with anodor stimulus. Animals initially received odor-water pairs onevery trial (all S+) and subsequently learned to discriminate oneunrewarded odor (S-) from a series of rewarded ones (multipleS+). Preliminary results indicate that aPC cells respond to odoronly when the animal has learned to identify an unrewarded odorin a series of rewarded ones. Passive sampling of odors or odordelivery paired with water reward did not elicit odor responses.Therefore, firing of cells in aPC may be modulated by attention,with cells only responding when the animal is attending to theodor stimulus. Comparing cellular responses when the animalmade a correct decision to responses during mistakes indicatesthat some cells respond primarily to odor, but the response ofmost cells depends on both odor and reward. Individual cells werevariable in the degree to which their response was modulated byreward or expectation of reward. In conclusion, cells in PC showcontext-dependent activity that is modulated by learning andattention.#P158 Poster session III: Cortical chemosensory processing/Receptor genomics and molecular biologyMapping Local Inhibitory Circuits in the Rat PiriformCortex using Photostimulation of Caged GlutamateVictor M. Luna, Diana L. PettitDept of Neuroscience, Albert Einstein College of Medicine Bronx,NY, USAThe piriform cortex (PC) is considered the major cortical centerfor integrating olfactory inputs from the olfactory bulb (OB). Keyto understanding PC computation is elucidating how principalexcitatory neurons are functionally connected to local inhibitorycircuits. To do this, we performed whole-cell recordings onsemilunar (SL) and pyramidal (Pyr) cells. We then focallystimulated interneurons (IN) in each of the anatomic layers of thePC (Ia, Ib, IIa, IIb, and III) using flash photolysis of cagedglutamate. Strength of inhibitory connections was assessed bymeasuring the peak amplitude, duration, and number ofinhibitory postsynaptic currents (IPSC) recorded from eachuncaging site. Our preliminary data indicate that PC-INconnections were stronger than SL-IN (mean IPSC numberacross all layers for Pyr vs SL, 3±0.5 vs 1±0.1; amplitude, 34.2±6.6vs 19.5±1.5 pA; duration, 79.8±12.3 vs 62.9±10.3 ms; n=6). Also,for either SL or Pyr, strength of connectivity depended on thelayer in which the uncaging beam was directed. SL and Pyrshowed the most robust IPSCs in response to uncaging at layerIIa, the weakest when uncaging at layer Ia. SL and Pyr showedmoderate responses to layer IIb uncaging. On the other hand, weobserved contrasting results between SL and Pyr when weuncaged at layer Ib and III. SL were strongly connected to layerIb cells, but weakly connected to layer 3 cells; the reverse was truefor Pyr. Thus, our results suggest that SL and Pyr may bedifferentially connected to distinct IN subsets. As such, SL andPyr would have unique input-output characteristics in response tothe same OB input. Understanding these marked computationalcapabilities may be important in deciphering the processesinvolved in encoding and representing olfactory information.#P159 Poster session III: Cortical chemosensory processing/Receptor genomics and molecular biologyThe olfactory bulb as cortical model systemThomas A. ClelandDept. Psychology, Cornell University Ithaca, NY, USAModel systems that reduce the scope and complexity of full-scalebiological systems while retaining the principal variables ofinterest have a distinguished history in neuroscience. Some of themost productive reduced model systems are those that enablemeaningful links between the cellular, circuit, and behaviorallevels of analysis, enabling study of their interplay. Olfactorylearning is a distributed phenomenon involving changes insynaptic weights and gene expression profiles throughout thecentral nervous system, thereby underlying a number of potentialchanges in animal behavior. My colleagues and I have sought toidentify an aspect of this broader odor learning that can belocalized within the olfactory bulb (OB). I here present the casefor olfactory generalization gradients, in both their nonassociative(cross-habituation) and associative (rewarded) forms, as plasticbehavioral measures dependent on learning and attention andmediated substantially by OB neural circuitry. Olfactorygeneralization gradients are regulated by multiple determinants oflearning including the amount of training, CS salience, US rewardvalue, and training-testing latency, as well as by neuromodulatoractivity within the OB. Aging and dementia model mice alsoexhibit shallower gradients after conditioning, indicative ofreduced learning rates. Computational circuit models are used toillustrate how known neuromodulatory effects can mediatecoordinated changes in OB odor responses and predict behavioraloutcomes. I suggest that these effects are microcosms of largerscalephenomena affecting cortical networks generally, and thatinsights gained from the reduced system of the OB therefore canbe applied to broader questions of cortical function anddysfunction.76 | AChemS Abstracts 2009