2009 Abstracts - Association for Chemoreception Sciences

naïve T cells were uncommon. This may reflect the activation ofnaïve T cells at the site of exposure to repeated antigen stimulationTh1 cells were more predominant in FP than Th2 T cells. Thissuggests that the local immune response in the gustatory system isTh1-type biased. Few gamma/delta TCR T cells were in FP. Thisstudy provides background for understanding inflammatoryresponses in gustatory tissue and clinical interactions between theimmune and gustatory systems.#P144 Poster session III: Cortical chemosensory processing/Receptor genomics and molecular biologyNeutrophil infiltration impairs peripheral taste functionLiqiao Shi, Lynnette McCluskeyMedical College of Georgia Augusta, GA, USAUnilateral chorda tympani (CT) nerve sectioning induces rapidfunctional changes in the neighboring, intact population of tastereceptor cells. Within one day after contralateral sectioning,neural responses to sodium are specifically decreased. We proposethat these injury-induced changes in taste function are mediatedby leukocytes. Neutrophils invade the taste system within hoursof injury, in parallel with decreased responses to sodium in theintact CT nerve. Dietary treatments that amplify the neutrophilresponse extend the functional impairments. Importantly,depletion of neutrophils restores normal taste responses. In thecurrent study, we tested the hypothesis that neutrophil infiltrationin the absence of nerve sectioning also impairs sodium tastefunction. Specified pathogen-free (SPF) Sprague-Dawley ratsreceived injections of the endotoxin, lipopolysaccharide (LPS; 10µg in 10 µl sterile PBS), to the ventral tongue. This treatmentsignificantly increased the number of neutrophils in the anteriorfungiform field. Neurophysiological recordings from the CTnerve were performed at 24 hr post-injection. CT responses toNaCl and sodium acetate were suppressed in LPS-injected vs.PBS-injected rats. In contrast, neural responses to non-sodiumstimuli did not differ between groups. These findings indicate thatneutrophils have a negative impact on sodium taste function,whether they are elicited by nerve injury or endotoxin. Wesuggest that neutrophils responding to tissue damage, nerveinjury, or bacterial infection release molecules that selectivelydownregulate sodium channel expression and/or function in tastereceptor cells.#P145 Poster session III: Cortical chemosensory processing/Receptor genomics and molecular biologyMouse taste buds express vesicular glutamate transportertype 2Leslie Stone 1,2 , Catherine Anderson 1,2 , Daniel Goldberg 1,2 ,Sue Kinnamon 1,21Dept. Biomedical Sciences, Colorado State University, FortCollins Colorado , 2 Rocky Mountain Taste & Smell Center,University of Colorado, Aurora, ColoradoVarious potential neurotransmitters are reported in taste buds, buttheir precise roles are mostly unknown. Previously, we presentedevidence that ATP is necessary for communication between tastebuds and taste nerves. In this study, we investigated the potentialrole of glutamate as a neurotransmitter by analyzing vescicularglutamate transporter (VGLUT ) expression in peripheral tastetissue. VGLUTs are a family of 3 proteins that load glutamateinto synaptic vesicles; the presence of VGLUTs in a cell ispresumptive evidence that it is glutamatergic. Previous studiessupport the idea that glutamate may be a transmitter in taste buds.Various metabotropic glutamate receptors (mGluRs) areexpressed in type II taste cells and in nerve fibers associated withtaste buds. Some taste cells exhibit robust immunoreactivity forglutamate. To further explore whether glutamate might be atransmitter in taste buds, we used immunocytochemistry andRT-PCR for VGLUTs on tissues obtained from mousecircumvallate papillae. Surprisingly, we found VGLUTexpression in nerves innervating the taste buds, but not in tastecells themselves. Immunocytochemical analysis shows that theVGLUT2+ nerve fibers are closely associated with gustducinexpressingtype II cells. To test whether taste cells might expresslow levels of VGLUTs, we performed RT-PCR of pooled mousecircumvallate taste buds. No VGLUT PCR products weredetected in RNA collected from taste buds, although there wasrobust expression of all VGLUT isoforms in the brain. Together,our results suggest that nerve fibers associated with taste buds arecapable of releasing glutamate. This may indicate that glutamateserves as an intragemmal modulator of taste bud function ratherthan as a means of transmission of information from taste cells tonerve fibers.#P146 Poster session III: Cortical chemosensory processing/Receptor genomics and molecular biologySerotonin Inhibits ATP Secretion in Mouse Taste BudsYijen A. Huang 1 , Stephen D. Roper 1,21Department of Physiology & Biophysics, Miller School ofMedicine, University of Miami Miami, FL, USA, 2 Program inNeuroscience, University of Miami Miami, FL, USADuring taste stimulation, Receptor (Type II) cells secrete ATP.ATP, in turn, activates adjacent Presynaptic (Type III) cells torelease serotonin (5-HT) and norepinephrine (NE) (Huang et al, JNeurosci, 2008). These interactions indicate feed-forward, cell-tocellcommunication within taste buds. Here, we tested whether 5-HT and NE exert feedback onto Receptor cells. We measuredATP secretion from isolated taste buds and from Receptor cellsusing biosensors (CHO cells stably transfected with P2X2/P2X3receptors and loaded with the calcium-sensitive dye, Fura-2;Huang et al, PNAS, 2007). As previously shown, taste budsisolated from mouse vallate papillae secreted ATP in response tostimulation with tastants (mixture of cycloheximide, 10 µM;saccharin, 2 mM; denatonium, 1 mM; SC45647, 0.1 mM). Bathapplied5-HT (10 nM) abolished taste-evoked ATP secretion fromisolated taste buds. 5-HT1A receptor agonists, 8-OH-DPAT (10nM) or BP554 (10 nM), similarly inhibited taste-evoked ATPsecretion. Finally, paroxetine (100 nM), a 5-HT reuptake inhibitor,reduced ATP secretion. In contrast, taste-evoked ATP secretionwas elevated ~2X by methysergide (10 nM), a 5-HT1,2 receptorantagonist, and by WAY100635 (10 nM), a 5-HT1A receptorantagonist. We did not detect any actions of NE on Receptor cells,either positive or negative (Huang et al, J Neurosci, 2008). In sum,these findings indicate that during taste stimulation, 5-HTreleased from Presynaptic (Type III) cells exerts negative feedbackonto Receptor cells by activating 5HT1A receptors and reducingATP secretion. This suggests that 5-HT plays an important role inmodulating peripheral taste responses.72 | AChemS Abstracts 2009