2009 Abstracts - Association for Chemoreception Sciences

educed granule cell spiking. These results indicate that a1 anda2 receptor activation exert opposing effects on granule cellexcitability. a1 and a2 receptor subtypes have differing affinitiesfor NE. Consequently, granule cell-mediated inhibition may bebi-directionally modulated as a function of extracellular NElevels, which in turn, is dependent on behavioral state-dependentvariations in locus coeruleus neuronal firing rates.#P224 Poster session V: Chemosensory memory/Central synaptic physiology/NeurogenesisTaurine deficiency causes loss of mitral cells in theolfactory bulb of miceMartin Witt 1 , Maria Kammerer 2 , Ulrich Warskulat 3 ,Dieter Häussinger 3 , Thomas Hummel 41University of Rostock, Dept. of Anatomy Rostock, Germany,2TU Dresden, Dept. of Anatomy Dresden, Germany, 3 Universityof Düsseldorf, Experimental Hepatology Düsseldorf, Germany,4TU Dresden, Dept. of Otorhinolaryngology Dresden, GermanyAim: Taurine is, after glutamate, the most abundant free aminoacid in the cerebral cortex and in the olfactory bulb (OB). Taurinewas found to play an important role in regulating thedepolarization-evoked GABA release via GABA receptors.Furthermore, taurine is involved in cell volume homeostasis,antioxidant defense and protein stabilization. Previous studies ontaurine transporter knockout mice (taut -/-) showed degenerationof retina, skeletal muscle and olfactory epithelium. The aim of thisstudy was to investigate cellular reactions due to taurinedeficiency of more central olfactory components, such as mitralcells, which constitute the major output neurons of the OB.Methods: The present study assesses quantitative differencesbetween taut -/- mice and controls (on postnatal day 21, 42, 70)concerning the size of the OB as well as numbers andcircumference of glomeruli and mitral cells. For histochemicalidentification of mitral cells in tissue sections we used an antibodyagainst PGP 9.5. Results and Conclusions: Taut -/- mice hadsignificantly smaller OBs than controls. Furthermore, the averagecell circumference of mitral cells is higher in control mice of everyage. After 21d, taut-/- animals showed more mitral cells, but laterthey presented significantly less mitral cells than controls. Also,the OB size of taut -/- mice were significantly smaller in taut -/-mice. The results suggest that taurine plays an important role indevelopment and maintenance of neurons in the olfactorypathway, especially during embryogenesis. Further, loss ofolfactory receptor neurons may lead to a subsequent loss of thesecondary relay neurons, namely mitral cells.#P225 Poster session V: Chemosensory memory/Central synaptic physiology/NeurogenesisAdult and developmental expression of a GABA transporter bya subset of centrally derived glial cells in the antennal lobe ofthe mothLynne A Oland, Nicholas J Gibson, Leslie P TolbertUniversity of Arizona Tucson, AZ, USAA subset of glial cells in the olfactory (antennal) lobe (AL) of themoth expresses a high-affinity membrane GABA transporter(MsGAT) throughout their extent. Early in development of theAL, GABAergic dendrites extend into the shell of glial cells thatsurrounds the neuropil and that includes the MsGAT-positivecells. In the adult, GABAergic dendrites form a dense meshworkof processes within the glia-surrounded glomerular neuropil. Thejuxtaposition of GABAergic dendrites and transporter-expressingglia suggests that the transporter may be important in modulatingthe GABA levels to which neurons and glia cells are exposed inboth developing and adult systems. Using immunocytochemistry,we have shown that the transporter is expressed from thebeginning of metamorphic development in certain glia but not indeveloping neurons. We also have shown that (1) MsGATcontinues to be expressed in the adult, in a subset of glia that havethe morphological appearance of a cell type we have called“complex” glia, (2) MsGAT is not found in adult AL neurons, and(3) GABA is not detectable in MsGAT-positive glial cells underresting conditions. GABA is, however, detectable in most glialcells after brief incubation in 10-50 uM GABA; the intensity ofGABA labeling in the dendrites of GABAergic neurons is greatlyenhanced under the same conditions. These data suggest that thekinetics of transporter-mediated GABA uptake into glial cellsmay be relatively slow or that the transporter has a nontransporterfunction in vivo despite its similarity to rat and humanGAT-1 in sequence and in biochemical and pharmacologicalprofile when expressed in Xenopus oocytes (Mbungu et al.,1995). The data also suggest that a second, as yet unidentified,form of GABA transporter may be present on Manduca neurons.#P226 Poster session V: Chemosensory memory/Central synaptic physiology/NeurogenesisHeterogeneous Expression of Pannexin 1 and Pannexin 2in the Olfactory Epithelium and Olfactory BulbHonghong Zhang, Chunbo ZhangDepartment of Biological, Chemical and Physical Sciences,Illinois Institute of Technology Chicago, IL, USAGap junctions regulate a variety of functions by directlyconnecting two cells through intercellular channels. Gap junctionsare formed by connexins or pannexin gene families. Connexinsand Pannexins may form independent gap junction channels inthe same tissues. Here, we report expression patterns of pannexin1 (Px1) and pannexin 2 (Px2) in the olfactory system of adultmice. In situ hybridization revealed that mRNAs for Px1 and Px2were expressed in the olfactory epithelium and olfactory bulb.Cells expressing Px1 and Px2 were distributed in themain olfactory bulb and the accessory olfactory bulb. Althoughexpressed in spatial patterns, many mitral cells, tufted cells,periglomerular cells and granule cells were Px1 and Px2 positive.Expression of Px1 was weak in portions of the dorsal-lateralolfactory bulb, while the medial regions had relatively highexpression. In contrast, expression of Px2 was stronger in thedorsal and lateral regions than medial regions of the olfactorybulb. There were more Px2 mRNA positive mitral cells andgranule cells compared to those of Px1. Expression of Px1 andPx2 was mainly found in cell bodies below the supporting celllayer in the olfactory epithelium although there might be Px2positive supporting cells in few areas. A majority of the olfactoryepithelium expressed Px1 and Px2 while degrees of expressionvaried among neighboring cells. In summary, Px1 and Px2 arespatially expressed in neurons in the olfactory epithelium andolfactory bulb. Our findings of expression of pannexins in theolfactory system of adult mice raise the novel possibility thatpannexins play a role in information processing in the olfactorysensation. Demonstration of expression patterns of Px1 and Px2in the olfactory system provides anatomical basis for futurefunctional studies.P O S T E R SAbstracts | 97