2009 Abstracts - Association for Chemoreception Sciences

#P227 Poster session V: Chemosensory memory/Central synaptic physiology/NeurogenesisChloride imaging in trigeminal sensory neurons of miceDebbie Radtke 1,2 , Nicole Schoebel 1,2,3,4 , Hanns Hatt 1,2,4 ,Jennifer Spehr 11Department of Cellular Physiology, Ruhr-University Bochum,Germany, 2 Ruhr-University Research School Bochum,Germany, 3 Graduiertenkolleg “Development and Plasticityof the Nervous System”, Ruhr-University Bochum, Germany,4International Graduate School of Neuroscience,Ruhr-University Bochum, GermanyThe trigeminal system has a warning function that protects thebody from potential noxious stimuli. Receptors located on freetrigeminal nerve endings detect different environmental stimulilike temperature, touch and chemicals. Recent work showed theinvolvement of ligand-gated cation channels in the detection ofchemical stimuli. Until now, a potential role of ligand-gatedchloride channels in trigeminal chemodetection has not beeninvestigated. In contrast to central neurons, in which theexpression of chloride transporters is changed postnatally,trigeminal ganglion (TG) neurons keep high levels of theNa + K + 2Cl - cotransporter NKCC1 and thereby probablyaccumulate chloride intracellularly. Thus, opening of a chlorideconductance would lead to a chloride efflux and therebydepolarizing the neuron. Indeed, current work in our lab showsCa 2+ transients upon stimulation with g-aminobutyric acid(GABA) in TG neurons of mice in Ca 2+ imaging experiments.Here, we use the chloride imaging technique to investigatechanges of intracellular chloride concentration upon GABAapplication on dissociated TG neurons. We show that GABAstimulation leads to a chloride efflux in soma and neurites.Creation of a higher Cl - gradient across the cell membrane byremoval of extracellular Cl - enhances the GABA-induced Cl -efflux. In further experiments we will characterize this Cl - effluxusing pharmacological tools. Our data show that opening of achloride conductance by GABA leads to an efflux of Cl - and thusto a depolarization of trigeminal sensory neurons. Neuronalexcitation by activation of GABA receptors makes them potentialtargets for the trigeminal perception of toxic chemicals.#P228 Poster session V: Chemosensory memory/Central synaptic physiology/NeurogenesisOdor discrimination by mice with long-term unilateral narisocclusion and contralateral bulbectomyCathy Angely, David M. CoppolaRandolph-Macon College Ashland, VA, USAUnilateral naris occlusion (UNO) has been the most commonmethod of effecting stimulus deprivation in studies of olfactoryplasticity. However, despite the large corpus on this manipulation,dating back to the 19 th century, there is almost nothing knownabout the behavioral capabilities of animals raised with UNO.Here we report the results of olfactory habituation studies on twogroups (n = 38) of control and perinatally UNO adult mice beforeand after unilateral bulbectomy (bulb-x). Control and UNOmice formed two groups termed young (1-3 months) and old(>6 months). For UNO mice, the bulb-x was opposite the side ofocclusion. Olfactory discrimination was tested using a two-odorhabituation paradigm in which investigation times to sixconsecutive presentation of one odor were compared to that for anovel odor presented in a seventh trial. The odors were 0.1% v/vethyl butyrate or isoamyl acetate in mineral oil or mixtures ofthese two solutions. If mice showed habituation-dishabituation tothe pure odors they were tested with decreasing dilutions of testodor mixed in the habituation odor (1:10, 1:50, 1:250). Foruntreated mice neither age nor bulb-x significantly influenced theability to discriminate between the habituating odor and the testodor down to a dilution mixture of 1:50. Also, discrimination wasunaffected by UNO prior to bulb-x. Surprisingly, after bulb-x,young and old UNO mice were still able to discriminate thehabituation and test odor down to a mixture of 1:50. Youngbulb-x mice in the control and UNO group failed to discriminatethe habituation and test odor at a dilution of 1:250. Thesecounterintuitive results suggest that UNO is neither an absolutemethod of deprivation nor does its diminish odor discrimination.#P229 Poster session V: Chemosensory memory/Central synaptic physiology/NeurogenesisCharacterization of GABA-Induced Responses ofTrigeminal Sensory NeuronsNicole Schoebel 1,2,3,4 , Annika Cichy 1 , Debbie Radtke 1,4 ,Hanns Hatt 1,3,4 , Jennifer Spehr 11Department of Cellular Physiology, Ruhr-University Bochum,Germany, 2 Graduiertenkolleg Bochum, Germany, 3 InternationalGraduate School of Neuroscience, Ruhr-University Bochum,Germany, 4 Ruhr-University Research School Bochum, GermanyIn the adult central nervous system opening of chlorideconductances leads to neuronal inhibition. Different from centralneurons, some populations of peripheral neurons namelyolfactory receptor neurons (OSNs) and neurons of the dorsal rootganglia (DRG) maintain high levels of the Na + K + 2Cl - -cotransporter (NKCC1) at adulthood. NKCC1 accumulateschloride in OSNs and DRG neurons which results in cellulardepolarization upon opening of chloride channels. As aconsequence, DRG neurons are excited by the inhibitoryneurotransmitter g-aminobutyric acid (GABA). Althoughproposed, there is no experimental evidence showing that thesame logic applies to neurons of the trigeminal ganglia (TG) todate. Here, we examine the effect of GABA on primary sensoryneurons isolated from murine trigeminal ganglia. In whole-cellpatch-clamp experiments GABA elicited responses in all TGNs ina dose dependent manner. Furthermore, GABA stimulation leadto a quick and robust increase of intracellular calcium in TGneurons observable in calcium-imaging measurements. GABAinducedexcitation could be seen in neurons of differentdevelopmental stages and was independent of culturingconditions. Preincubation with the NKCC1 blocker bumetanideinhibited the calcium rise in TG neurons from early postnatal aswell as adult animals suggesting that a high intracellular Cl -concentration is essential for the response. Pharmacologicalcharacterizations showed that the responses are mediated byGABA A receptors and involve an influx of extracellular calciumvia voltage gated calcium channels (VGCCs). In summary, wesuggest intracellular Cl - accumulation in TG neurons produced byNKCC1 leading to a depolarizing efflux of chloride uponGABA A receptor opening which in turn is followed by an influxof extracellular Ca 2+ through VGCCs.98 | AChemS Abstracts 2009