1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

437 Symposium Neural Dynamics and ChemosensoryBehaviorNORADRENALINE MODULATION OF MAIN OLFACTORYBULB NETWORK ACTIVITY: BEHAVIORALCONSEQUENCESDoucette W. 1 , Restrepo D. 1 1 Neuroscience, University of ColoradoHealth Sciences Center, Aurora, COThe role of Noradrenaline (NE) in the main olfactory bulb (MOB)has been characterized for early preference learning (EPL), whereneonatal rats learn to prefer an odor associated with stroking. EPL isblocked by adrenergic antagonists. Adult rodents utilize a morecomplex neural system allowing for increased behavioral flexibility.Thus, NE modulation in the MOB would be expected to take on asubtler context-dependent role in the adult. Our goal is to linkbehavioral deficits caused by blockade of NE signaling withperturbations in mitral cell ensemble activity observed during thebehavioral task. We have studied the consequences of localizedblockade of NE signaling in the MOBs of adult mice performing go-nogo odor discrimination tasks. Mice received bilateral 2 µl injections ofsaline, phentolamine, alprenolol, or a combination of the two drugsimmediately preceding the task. The odor pairs were of varyingmolecular similarity. Animal groups receiving saline, alprenolol, orphentolamine did not differ in the number of trials to discrimination.The injection of both drugs resulted in an odor pair-dependent effect,ranging from complete blockade for similar odors to no disturbance. Weconclude that blockade of NE signaling in the MOB does not impairodor discrimination behavior per-se, but does impair the ability todiscriminate similar odors. We have begun to characterize normallearning-related plasticity of mitral cell ensemble activity in miceperforming the go-no go task. Once characterized, we will utilize NEsignaling blockade to understand the network underpinnings ofbehavioral deficits caused by blockade of NE signaling in the MOB.Supported by: DC00566, DC04657, MH068582 (DR) and DC008066(WD).438 Symposium Neural Dynamics and ChemosensoryBehaviorTOWARDS REALISTIC MODELS OF CONCENTRATION-INVARIANT, BACKGROUND-RESISTANT ODORRECOGNITION IN THE MAMMALIAN OLFACTORY BULBBrody C. 1 1 Cold Spring Harbor Laboratory, Cold Spring Harbor, NYSpike synchronization across neurons can be selective for thesituation where neurons are driven at similar firing rates, a “many areequal” computation. This can be achieved in the absence of synapticinteractions between neurons, through phase locking to a commonunderlying oscillatory potential. Based on this principle, we instantiatean algorithm for robust odor recognition into a model network ofspiking neurons whose main features are taken from known propertiesof biological olfactory systems. Recognition of odors is signaled byspike synchronization of specific subsets of “mitral cells.” Thissynchronization is highly odor selective and invariant to a wide range ofodor concentrations. It is also robust to the presence of strong distractorodors, thus allowing odor segmentation within complex olfactoryscenes. Funded by NIH R01-DC06104439 Symposium Neural Dynamics and ChemosensoryBehaviorSTATE-DEPENDENT CHANGES IN TASTE PROCESSINGFontanini A. 1 , Katz D.B. 1 1 Volen Center for Complex Systems andDepartment of Psychology, Brandeis University, Waltham, MASensory processing is a function of network states. In awake animalsbackground activity and the overall state of cortical networks varydepending on the behavioral state of the subject. We will discuss resultsshowing that rats engaged in a fluid self-administration task display asudden shift between two very different behavioral states characterizedby distinct patterns of oscillatory activity in the gustatory cortex. Wewill further show that gustatory processing differs in the two conditionsand provide evidence that changes in such states specifically modifypalatability-related information in neural taste responses, and that thismodification is temporally specific. While recording multiple singleunits in the gustatory cortex, we delivered stimuli to rats before andafter they went through the spontaneous state change (“disengagement”)that is associated with sudden reduction in interest in the experimentaltask and the simultaneous emergence of 7-12 Hz rhythms in cortex. Thepercentage of cortical neurons that responded to tastes remained stablewith disengagement, but the particulars of these responses changeddrastically. When analyzed at the population level the changes werepalatability-related—the similarity among aversive tastes increasedwhile the similarity between a highly aversive taste and the palatabletastes decreased. Furthermore, most of these changes were found nearthe time when palatability-specific information emerges in corticalresponses. These data demonstrate that an animal´s state determines themeaning attached to sensory input, and that disengagement broadenspalatability-related generalizations by modulating the time-course ofresponses. Supported by R01 DC006666 to DBK and Sloan-Swartz toAF440 Symposium Neural Dynamics and ChemosensoryBehaviorTEMPORAL CODING OF TASTE IN THE BRAIN STEM:INFORMATION AND FUNCTIONDi Lorenzo P.M. 1 , Victor J.D. 2 1 Psychology, SUNY, Binghamton,Binghamton, NY; 2 Neurology and Neuroscience, Weill Medical Collegeof Cornell University, New York, NYMost theories of taste coding in the central nervous system havefocused on the spatial aspects of neural responses, utilizing the sum ofresponse-related spikes over time as the relevant response measure.However, recent data have shown that the temporal arrangement ofspikes may also convey information about taste. In a series of relatedexperiments, temporal coding in the mammalian gustatory system wasinvestigated in two ways. First, electrophysiological responses to tastestimuli were recorded in the nucleus of the solitary tract (NTS) inanesthetized rats. Information-theoretic analyses (Victor and Purpura,1996) revealed that about half of the taste-responsive cells in the NTSconveyed a significant amount of information about taste qualitythrough spike timing, especially in the initial response interval. Second,the function of temporal coding in taste-guided behavior was studied inawake, behaving rats with electrodes implanted in the taste-responsivearea of the NTS. Lick-contingent electrical pulse trains, designed tomimic the temporal arrangement of spikes in a sucrose or quinineresponse of single NTS cells, were delivered to the NTS in waterdeprivedrats drinking only water. Rats avoided licking when thesepulse trains mimicked quinine responses but licked avidly whenrandomized control patterns were presented. In addition, rats thatlearned an aversion to the sucrose-simulation pattern of electrical pulsesgeneralized that aversion to natural sucrose, but not to NaCl, HCl orquinine. Collectively, these data strongly suggest that temporal codingis one of the methods used for communication about taste in the NTS.110