1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

249 Poster Central Olfaction and Chemical EcologyAGE-DEPENDENT MODULATION OF MEPSCS BYCARBACHOL IN RAT MOB GRANULE CELLSGhatpande A. 1 , Gelperin A. 1 1 Monell Chemical Senses Center,Philadelphia, PAThe main olfactory bulb (MOB) of rodents undergoes synapticdevelopment postnatally. Specifically, granule cells (GCs), the majorGABAergic neurons of the MOB, form dendrodendritic synapses withglutamatergic mitral cells (MCs) postnatally. During this period ofactive synaptogenesis, the MOB is thought to play a role in odor-guidedbehavior critical for survival. Does this behavior correlate withdendrodendritic synapse development? We used carbachol (CCh) toprobe the development of dendrodendritic synaptic signaling betweenMCs and GCs during the first few postnatal weeks. CCh has extensiveeffects on signaling in the MOB. We report an increased frequency ofpostsynaptic currents during bath application of CCh in 1 µM TTX and100 µM picrotoxin, recorded in whole-cell voltage clamp from GCs inMOB slices from 7-9 day old rats (n = 3, fold-change range: 3.2–20).These currents were sensitive to 10 µM DNQX and 50 µM APVindicating they were mEPSCs. By contrast, we found no change inmEPSC frequency recorded in GCs from slices of 11-17 day old rats (n= 3 out of 4 cells, range: 0.9-–1.3, one cell showed ~10-fold increase).Conversely, earlier experiments have shown an increased frequency ofmIPSCs, sensitive to GluR blockers, in recordings from MCs of OBslices of p7-9 rat pups and GluR blocker insensitive mIPSCs from theolder age group. These results suggest plasticity in presynapticmechanisms at dendrodendritic synapses during the first 10 days of life.Experiments exploring the mechanism/s underlying these agedependentsynaptic changes will be presented. Supported by the ArmyResearch Office and the Whitehall Foundation250 Poster Central Olfaction and Chemical EcologyNITRIC OXIDE IS NECESSARY FOR MAINTAININGMANDUCA SEXTA ANTENNAL LOBE NEURON ACTIVITYAND ODOR RESPONSIVENESSNighorn A. 1 , Christensen T. 1 , Wilson C. 1 1 ARL Division ofNeurobiology, University of Arizona, Tucson, AZDespite many studies in several species showing the presence of NOand its signaling components in the olfactory system, the function ofNO in the processing of olfactory information remains elusive. In orderto better understand the function of NO in the olfactory system, we areusing the moth Manduca sexta as a model. We have previously shownthat enzymes involved in NO signaling, including nitric oxide synthase(NOS) and soluble guanylyl cyclase (sGC), are expressed in subsets ofneurons within the M. sexta olfactory system and, moreover, that NO isproduced in olfactory glomeruli in response to odor stimulation. Thefunction of NO in the olfactory system was examined in individualolfactory neurons with intracellular recording techniques whilemanipulating levels of NO signaling with pharmacological agents.Blocking NOS with either L-NAME or 7-NI resulted in changes in thebehavior of both local interneurons (LNs) and projection neurons (PNs).Both PNs and LNs showed changes in baseline activity, including bothincreases and decreases in spike firing rate in LNs and the presence ofbursts in many PNs. The odor-evoked activity in both neuron types waseither missing or altered. The effects were mimicked in several neuronswhen sGC signaling was blocked using ODQ. However, some of theneurons that were affected by NO blockade did not contain detectablelevels of sGC as measured by immunohistochemistry of the recordedand dye-filled neurons. These results indicate that NO has a variety ofeffects on olfactory neurons and that these effects are mediated by bothsGC-dependent and sGC-independent mechanisms. This work is fundedby NIH–NIDCD DC04292 to A. Nighorn.251 Poster Central Olfaction and Chemical EcologyNITRIC OXIDE SIGNALING IN THE RODENT OLFACTORYBULB.Lowe G. 1 , Ma J. 1 , Buerk D.G. 2 , Ghatpande A. 1 , Alan G. 1 1 MonellChemical Senses Center, Philadelphia, PA; 2 Physiology,Bioengineering, University of Pennsylvania, Philadelphia, PAIn the brain, the gaseous messenger nitric oxide (NO) is synthesizedby the neuronal isoform of nitric oxide synthase (nNOS). In the mainolfactory bulb (MOB), both nNOS and soluble guanylyl cyclase, an NOtarget, are highly enriched. However, production of NO in the MOB hasnot been directly measured, and its actions on olfactory bulb neuronsare unknown. Here we report direct electrochemical and opticaldetection of NO production in the mouse MOB. Using an NO-selectivemicrosensor, we recorded transient extracellular signals from thegranule cell layer in vivo, in response to odor stimuli. In MOB slices,the microsensor detected steep endogenous NO gradients, and slowtransient signals evoked by electrical stimulation of glomeruli. Loadingslices with the fluorescent NO indicator DAF-FM revealed a stainingpattern consistent with known patterns of NOS immunoreactivity, i.e.strong labeling of periglomerular (PG) cells and granule cells. Stepincrements in PG cell fluorescence were evoked by stimulating theolfactory nerve layer, and spontaneous spiking of mitral cells wastransiently potentiated by L-nitroarginine, an inhibitor of nNOS. Ourdata show that NO signaling occurs both endogenously and in responseto exogenous stimuli, and NO can affect the activity of MOB neurons.We suggest that NO signaling plays a dynamic role in olfactoryinformation processing, perhaps by modulating synchronousoscillations of the mitral-granule network during odor recognition andodor memory formation. Support: NIH DC042808-04 (GL), NIHHL068164 (DB), ARO & Whitehall Foundation (AG).252 Poster Central Olfaction and Chemical EcologyINHIBITORY INTERACTIONS AMONG OLFACTORYGLOMERULI IN THE MOTH MANDUCA SEXTAReisenman C.E. 1 , Hildebrand J.G. 1 1 Neurobiology, University ofArizona, Tucson, AZInhibitory synaptic interactions are important in shaping the activityof output (projection) neurons (PNs) in primary olfactory centers. Suchinteractions promote coincidence among PNs and contrast enhancementof odor representations. We expect inhibitory interactions to occuramong glomeruli belonging to sets or clusters that are functionallyrelated. In initial tests of this idea, we recorded intracellularly theresponses of PNs arborizing in 3 neighboring glomeruli in the antennallobe (AL) of male M. sexta. Two of these glomeruli (the Toroid andCumulus) are part of the male-specific macroglomerular complex(MGC), respectively processing the 2 main components (E10, Z12-16-Al and E10, E12, Z14-16-Al, or A and B for simplicity) of theconspecific female's sex pheromone. The third glomerulus (G35) issexually isomorphic, processes information about a plant volatile (Z3-6-Acetate, Z3HA), and in males is adjacent to the MGC. All PNs gaveexcitatory responses to stimulation with their respective key odor input.As shown previously, Cumulus-PNs and Toroid-PNs respectively wereinhibited by stimulation with A and B—i.e. each by the input to theother glomerulus. However, these PNs were not significantly inhibitedby Z3HA. By contrast, preliminary results showed that stimulation withA and/or B inhibits G35-PNs, suggesting that inhibitory interactionsmay not always be reciprocal. These results indicate that inhibitoryinteractions are not necessarily dictated by spatial position but rather byresponse properties, chemical relatedness, or functional relationships.Supported by NIH grant R01-DC-02751 to JGH.63