1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

381 Symposium Presidential: Why Have Neurogenesis inAdult Olfactory Systems?INTEGRATING NEW NEURONS INTO THE ADULTOLFACTORY SYSTEMLledo P. 1 1 Pasteur Institute, Paris, FranceIn the adult olfactory bulb, newly born neurons are constitutivelygenerated throughout life and form an integral part of normal functionalcircuitry. This process of late neurogenesis is subject, at various stages,to modulation and control by external influences, suggesting stronglythat it represents a plastic mechanism by which the brain´s performancecan be optimized according to the environment in which it finds itself.But optimized how? And why? This presentation will concentrate onsuch functional questions regarding neurogenic plasticity. Afteroutlining the processes of adult neurogenesis in the olfactory system,and after discussing their regulation by internal and environmentalinfluences, we shall ask how existing neuronal circuits can continue towork in the face of constant cell arrivals and departures, and explore thepossible functional roles that newborn neurons might subserve in theadult olfactory system. In particular, we shall report the degree ofsensitivity of the bulbar neurogenesis to the level of sensory inputs and,in turn, how the adult neurogenesis adjusts the neural networkfunctioning to optimize sensory information processing. We will bringtogether recently described properties and emerging principles of adultneurogenesis that support a much more complex role for the adultgeneratedcells than just providers of replaceable units. Throughout,and concentrating exclusively on mammalian systems, we shall stressthat adult neurogenesis constitutes another weapon in the brain´sarmory for dealing with a constantly changing world.382 Poster Central Taste and Chemosensory BehaviorCHORDA TYMPANI (CT), GREATER SUPERFICIALPETROSAL (GSP) AND IXTH NERVE TERMINAL FIELDS INHAMSTER SOLITARY NUCLEUS (NTS)Bradenham B.P. 1 , Harrison C.H. 1 , Stewart J.S. 2 , Stewart R. 2 1 Programin Neuroscience, Washington and Lee University, Lexington, VA;2 Psychology/Program in Neuroscience, Washington and Lee University,Lexington, VAIn mammals, GSP afferents innervate taste cells in palatal andnasoincisal mucosae, while CT and IXth nerves (IX) innervate tastecells of fungiform and circumvallate papillae, respectively. The nervesterminate centrally in the rostral pole of the NTS. In this study, wequantify anatomical overlap among terminal fields of these taste nervesin adult hamster NTS. We used triple fluorescent nerve labeling tovisualize CT, GSP, and LT-IX terminal fields in NTS. CT, GSP, and IXwere isolated, cut, and labeled with unique dextran amine conjugates.After 3-7 days survival, animals were sacrificed and perfused. Fixedbrains were sectioned horizontally and sections examined by confocalmicroscopy. Serial optical sections through physical sections ofcomplete terminal fields were analyzed offline. Data so far show that IXterminal field appears ~100 µm dorsal to GSP and CT, which enter therostral NTS nearly coincidently in the dorsal-ventral plane. GSPterminal field extends ~100 µm ventral to that of IX, while CT terminalfield extends ~ 50 µm ventral to that of GSP. IX and GSP terminal fieldvolumes are roughly similar and appear to be greater in volume than CTfield. This difference is attributable to the restricted caudal extent of CTterminal field. All three terminal fields overlap extensively throughoutthe dorsal-ventral plane. Nearly the entire volume of GSP field overlapswith IX or CT terminal fields, while IX and CT fields enjoy ~50 µm ofunique territory in dorsal and ventral NTS, respectively. These resultsprovide normative data for studies of development in the hamstercentral taste system. This work was supported by W&L R.E. LeeResearch Endowment (BPB, CHH)383 Poster Central Taste and Chemosensory BehaviorCA 2+ IMAGING OF PRIMARY GUSTATORY AFFERENTS INTHE VAGAL LOBE OF OF GOLDFISHHallock R. 1 , Ikenaga T. 2 , Finger T.E. 3 1 Psychology, State University ofNew York at Binghamton, Denver, CO; 2 Cell and DevelopmentalBiology, University of Colorado Health Sciences Center, Aurora, CO;3 Cellular and Structural Biology, University of Colorado HealthSciences Center, Aurora, COThe primary gustatory nucleus in goldfish has a characterizedanatomy whereby gustatory afferents terminate in distinct laminae. Weinjected Ca 2+ green dextran in the vagus nerve and allowed 3-daysrecovery to allow filling of the primary nerve terminals in the vagallobe. Vagal lobe slices were prepared for in vitro recording. Theprimary afferent fibers were electrically stimulated with pairs of 2.0 mspulses separated by 30 ms while optically recording Ca 2+ signals fromthe layers containing primary afferent terminals. Hence the Ca 2+ signalarose only from the primary afferent fibers. Results showed paired pulsefacilitation in that significantly more Ca 2+ was detected after the secondpulse than the first. This indicates more primary afferent terminals areactivated by the second pulse than the first. In addition, the area ofincrease in Ca 2+ signal after the second stimulating pulse was broaderthan that observed after the first pulse, suggesting that the first pulseactivates the internal circuitry of the sensory layer of the vagal lobe.Since the recorded signal arises entirely from primary afferents, thesefindings suggest that the primary afferent terminals may be under tonicinhibition which is released by the initial stimulus pulse. Supported byNIDCD Grant DC00147(T.E.F.).384 Poster Central Taste and Chemosensory BehaviorTEMPORAL PATTERNS OF NEURAL ACTIVITY IN THENUCLEUS OF THE SOLITARY TRACT OF C57BL/6BYJ MICEMcCaughey S. 1 1 Monell Chemical Senses Center, Philadelphia, PAThe spontaneous and evoked activity of taste-responsive neurons canbe characterized in terms of mean response rates over periods withspecific durations, but the temporal patterns of activity within thoseperiods may also contain important information. The goal of this workwas to examine temporal patterns of single-unit activity in the rostralnucleus of the solitary tract (NST) of C57BL/6ByJ mice. Theextracellular activity of 39 NST cells was measured in anesthetizedanimals. The spontaneous firing patterns of neurons were investigatedby plotting the distributions of interspike intervals (ISIs). ISIs less than10 ms were especially common in some neurons, which gave evidenceof a preferred firing interval. In general, the presence of a preferredinterval was a characteristic of a cell and was not changed byapplication of taste stimuli, and preferred intervals were more likely tobe found in neurons with salt- or acid-oriented response profiles than inthose with sugar-oriented profiles. Temporal patterns of taste-evokedresponses were also examined and were found to vary acrosscompounds that are thought to taste sweet to mice. This variation meantthat the sweeteners evoked similar across-neuron patterns of activityacross a 5-sec evoked period, but did not when evoked periods less than1 sec were used. Given that perceptions of sweetness are likely to occurin less than a second, these results suggest that factors besides acrossneuronpatterning make a substantial contribution to taste qualityperception. This work was supported by NIH grant R03 DC005929.96