1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

421 Poster Central Taste and Chemosensory BehaviorINHIBITION OF MUSCARINIC ACETYLCHOLINERECEPTORS ALTERS PERFORMANCE OF MICE IN ANODOR DISCRIMINATION TASKSchutzman J. 1 , Clevenger A.C. 1 , Doucette W. 1 , Caldwell S. 2 , SalcedoE. 2 , Restrepo D. 2 1 Neuroscience Program, University of ColoradoHealth Sciences Center, Aurora, CO; 2 Cell and Developmental Biology,University of Colorado Health Sciences Center, Aurora, COThe olfactory bulb (OB) is heavily innervated by cholinergic fibersoriginating in the horizontal limb of the diagonal band of Broca, andacetylcholine (ACh) has been postulated to modulate OB processingthereby affecting the ability to distinguish structurally similar odorants(Linster,C. and Cleland,T.A., Neural Netw. 15, 709-717, 2002). In thispreliminary study we have altered the function of nicotinic andmuscarinic ACh receptors either through drug infusion into the OB, orby using a mouse defective for the α7 ACh receptor. Mice wereimplanted with bilateral cannulae allowing direct drug injection intoeach OB. Immediately following drug injection, mice were tested on ago-no go odor discrimination task in which one odor was rewarded.Mice treated with scopolamine, an inhibitor of muscarinic receptors,displayed a delay in attaining criterion compared to controls. Incontrast, mice treated with mecamylamine, a nicotinic receptorinhibitor, did not display differences from controls in the go-no go task.In order to determine whether mice defective for the α7 ACh receptorhave a deficiency in discrimination threshold, we used a MaximumLikelihood Parameter Estimation by Sequential Testing (MLPEST)procedure (Clevenger and Restrepo, Chem. Senses. 31:9-26, 2006). Wedid not find any differences between α7 knockouts and controls. Furtherstudies are being performed to determine whether the thresholdmeasured using MLPEST is different in α7 knockouts and controlswhen the mice are subjected to extensive training. Supported by NIHgrant MH068582 (DR), F30 DC 5740 (AC) and a NARSAD EsselInvestigator award (DR)422 Poster Central Taste and Chemosensory BehaviorSPEED-ACCURACY TRADEOFF IN OLFACTIONRinberg D. 1 , Koulakov A. 2 , Gelperin A. 1 1 Monell Chemical SensesCenter, Philadelphia, PA; 2 Freeman Building, Cold Spring HarborLaboratory, Cold Spring Harbor, NYThe basic psychophysical principle of speed accuracy tradeoff (SAT)has been used to understand key aspects of neuronal informationprocessing in vision and audition, but has not yet been reported inolfaction. We present the first direct observation of SAT in olfactionand resolve a seeming controversy between results obtained inreaction-time experiments by Uchida and Mainen (Nat. Neurosci., 6,1224, 2003) and Abraham, Spors, et al. (Neuron, 44, 865, 2004). Wedeveloped a behavioral paradigm for mice in which both the time ofodor exposure and the difficulty of the odor discrimination task werecontrolled by the experimenter. The mouse was trained to keep its nosein the odor sampling port during odor delivery until an auditory signalindicated the availability of water reward in one of two water ports. Theodor stimulus indicated whether reward was available in the left or rightwater port. The difficulty of the task was varied by presenting more orless similar pairs of mixtures.. We found that longer enforced odorexposure (from 200–1200 msec) led to more accurate odordiscrimination (from 60 to 95%), even beyond the level at which miceperformed voluntarily, in the reaction-time paradigm developed for ratsby Uchida and Mainen (2003). The presence of SAT in olfactionprovides strong evidence for temporal integration in olfaction andconstrains the applicability of different models of olfactory informationprocessing. Supported by the Army Research Office and the WhitehallFoundation.423 Poster Central Taste and Chemosensory BehaviorROLE OF CHOLINERGIC MODULATION IN THE MAINOLFACTORY BULB IN RATS FOR OLFACTORY ACUITYAND DISCRIMINATION LEARNINGFerreti C. 1 , Mandairon N. 1 , McNamara A. 2 , Stack C. 1 , Linster C. 11 Cornell University, Ithaca, NY; 2 Neurobiology and Behavior, CornellUniversity, Ithaca, NYThe objective of this study was to investigate the specific role ofcholinergic modulation in olfactory bulb processing. We tested the roleof cholinergic modulation in the olfactory bulb of cannulated rats bybilateral injections of vehicle (6 µL saline), the cholinergic antagonistsscopolamine (20 µg and 100 µg), the nicotinic antagonist MLA (20 µgand 100 µg), a combination of both drugs, or the cholinesteraseinhibitor neostigmine (dosage) 20 minutes before the behavioral tasks.We tested the role of cholinergic modulation on spontaneous odordiscrimination in the absence of reward conditioning using a habituationtask. A second test involved a olfactory discrimination task in which aodor-reward association has to be formed. We found that spontaneousdiscrimination between chemically related odorants was impaired whennicotinic, but not muscarinic receptors were blocked in the olfactorybulb. Additionally, the spontaneous discrimination between very similarodorants was enhanced when cholinergic modulation was increased.Interestingly, no effect of modulating the action of acetylcholine in theolfactory bulb was seen when rats were trained on a forced choice, twoodor discrimination task. Supported by the Marie Curie Foundation(NM) and NIDCD grant DC005130 (CL).424 Poster Central Taste and Chemosensory BehaviorBROAD ACTIVATION OF THE OLFACTORY BULBPRODUCES LONG-LASTING CHANGES IN ODORPERCEPTION IN RATSMandairon N. 1 , Kiselycznyk C.L. 2 , Stack C. 1 , Ferreti C. 1 , Linster C. 11 Cornell University, Ithaca, NY; 2 Neurobiology and Behavior, CornellUniversity, Ithaca, NYA number of electrophysiological experiments have shown that odorexposure alone, unaccompanied by behavioral training, changes theresponse patterns of neurons in the olfactory bulb (Buonviso & Chaput,2000; Buonviso, Gervais, Chalansonnet, & Chaput, 1998; Montag-Sallaz & Buonviso, 2002; Wilson et al., 1985). As a consequence ofthese changes, across mitral cells in the olfactory bulb, individual odorsshould be better discriminated due to previous exposure. We havepreviously shown that a daily 60 minute exposures to odorants duringtwo weeks enhance rats´ ability to discriminate between chemicallysimilar odorants in a relative odor-unspecific manner (Mandairon et al.,1996). Here we first show that the perception of test odorants is onlymodulated by enrichment with odorants that activate at least partiallyoverlapping regions of the olfactory bulb. Second, we show that a broadactivation of olfactory bulb neurons by daily local infusion of NMDAinto both olfactory bulbs enhances the discrimination betweenchemically related odorants in a manner similar to the effect of dailyexposure to odorants. The results strongly suggest that (1) changes inolfactory processing are responsible for the observed modulation ofodor perception and (2) increased activity in the olfactory bulb networkis sufficient to produce these changes. Funded by the Curie Foundation,France (ML).106