1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

85 Poster Peripheral Olfaction and Peripheral TasteTIME COURSE OF ALTERED CHORDA TYMPANI NERVERESPONSE AFTER CONTRALATERAL NERVE SECTION INSODIUM-RESTRICTED RATSWall P.L. 1 , McCluskey L. 1 1 Institute of Molecular Medicine andGenetics, Medical College of Georgia, Augusta, GAUnilateral section combined with dietary sodium restriction results indecreased sodium responses from the intact chorda tympani (CT) nerveby day 4 post-section; no other taste modalities are affected. Werecorded CT responses from sodium-restricted rats during the earlyperiod following contralateral nerve section to provide insight into themechanisms underlying this functional plasticity. SPF Sprague-Dawleyrats received unilateral CT section and a low sodium diet (0.03% vs.1.0%) on day 0. Recordings from the intact CT were performed at days2, 3, and 4 post-section. From day 2 to 4, there was a gradual decreasein the CT response to NaCl. Other taste modalities were unaffected.Therefore, the mechanism by which this alteration occurs is not sudden,but progresses over several days. In the presence of the epithelialsodium channel (ENaC) blocker, amiloride, sodium responses werereduced to equal levels in control and experimental rats. We proposethat there is a concomitant, gradual decrease in ENaC expression and/orfunction. The gradual decrease in sodium sensitivity suggests that thebiosynthesis of ENaCs within intact taste receptor cells, rather thanENaC stability in the membrane, may be affected by contralateral CTsection and sodium restriction. Within this period, sodium-restricted ratsalso exhibit a deficient immune response to CT sectioning. Perhaps adecrease in the presence of beneficial cytokines ultimately results indecreased ENaC expression. Supported by NIH DC005811.86 Poster Peripheral Olfaction and Peripheral TasteEXPRESSION AND REGULATION OF LINGUAL VASCULARADHESION MOLECULES FOLLOWING UNILATERALCHORDA TYMPANI NERVE SECTIONCavallin M. 1 , McCluskey L. 2 1 Physiology, Medical College of Georgia,Augusta, GA; 2 IMMAG, Medical College of Georgia, Augusta, GAActivated macrophages increase in number on both sides of thetongue following unilateral chorda tympani nerve (CT) sectioning. Themechanisms responsible for recruiting these macrophages to the tongueare unknown. We hypothesize that adhesion molecules, specificallyintracellular adhesion molecule (ICAM)-1 and vascular cell adhesionmolecule (VCAM)-1, are upregulated following CT sectioning andallow macrophage entry. SPF Sprague-Dawley rats received unilateralCT or sham section. Rats were euthanized at several time points rangingfrom 6 hours to 7 days post-sectioning, and frozen sections wereprocessed for immunohistochemical staining for ICAM-1 and VCAM-1. In separate groups of rats, ELISAs (R & D Systems) and Westernblot analyses were used to quantify relative changes in adhesionmolecule expression in tongue homogenates. The endothelial layer ofblood vessels robustly expresses ICAM-1 (1:1000; Accurate Chemicaland Scientific Corporation) on both sides of the tongue following CTsection. The peak increase in ICAM-1 expression occurs on thesectioned side of the tongue at 24 hours post-sectioning compared tosham animals (p < 0.001). However, VCAM-1 (1:250; Covance)expression remains minimal after CT section. We propose that ICAM-1is important for macrophage recruitment following CT section.Ultimately, we propose that leukocytes modulate taste function afterneural injury by secreting growth factors and cytokines that act on tastereceptor cells. Supported by NIH DC005811-01A1 (L.M.) andDC008263-01 (M.C.).87 Poster Peripheral Olfaction and Peripheral TasteMACROPHAGE ACTIVATION PATTERNS FOLLOWINGCHORDA TYMPANI NERVE SECTIONPhillips M. 1 , McCluskey L.P. 1 1 Institute of Molecular Medicine andGenetics, Medical College of Georgia, Augusta, GAWithin days following unilateral chorda tympani (CT) nerve section,there is a bilateral increase in activated lingual macrophages. Thismacrophage response to injury does not occur in sodium-restricted rats,which also have deficits in sodium taste function in the intact CT.Therefore, activated macrophages are associated with normal tastefunction after injury, and may communicate with taste receptor cells viacytokines. We investigated the effects of CT section on cytokines thatare stereotypical of classical (IL-1b) or innate (TGF-b) macrophageactivation. Macrophage activation markers were also examined. SPFfemale adult Sprague Dawley rats received unilateral CT or shamsectioning and a control or low-sodium diet (1.0% vs. 0.03%). At 6 hrto 4 days post-section, rats were sacrificed, tongues dissected, andprotein lysates collected for ELISAs. Cryosections were obtained fromseparate groups, and immunohistochemistry was performed. At day 2post-section, levels of the proinflammatory cytokine, IL-1b, wereelevated in control-fed but not sodium-restricted rats as measured byELISA. IL-1b was expressed by activated macrophages. A subset oftaste receptor cells, epithelial cells, neurons, and endothelial cells werealso IL-1b+ regardless of surgical or dietary treatment. Levels of TGFb,a hallmark of the innate activation pathway, were low in all treatmentgroups. Likewise, macrophages did not express arginase or mannosereceptors, which are typical of alternative activation. These data suggestthat macrophages that respond to neural and taste receptor cell injuryare classically activated, and may modulate taste function either directlyor indirectly through IL-1 and other proinflammatory cytokines.Supported by NIH DC005811.88 Poster Peripheral Olfaction and Peripheral TasteBRIEF AND PROLONGED DIETARY SODIUM DEPRIVATIONREDUCE CHORDA TYMPANI NERVE RESPONSES TO NACLVaughn J.M. 1 , Curtis K.S. 1 , Contreras R.J. 1 1 Program in Neuroscience,Florida State University, Tallahassee, FLEight to ten days of dietary Na + deprivation are necessary to increase24 h intake of a concentrated NaCl solution. Na + deprivation of similarduration also decreases the sensitivity of the chorda tympani nerve (CT)to NaCl, suggesting that changes in CT responses are necessary forincreased NaCl intake. However, our studies indicate that behavioraltaste responses change following as little as two days of dietary Na +deprivation. Specifically, short-term lickometer tests andmicrostructural analysis showed that after two days of Na + deprivation,rats increased licking to concentrated NaCl solutions. Accordingly, thegoal of the current study was to determine whether brief dietary Na +deprivation decreases CT responses to NaCl, and to assess CTamiloride-sensitivity after brief (2 days) or prolonged (10 days) dietaryNa + deprivation. We recorded whole nerve electrophysiological activityfrom the CT in response to lingual application of NaCl (75, 150, 300,450, 600 mM) and to NaCl mixed with 100 µM amiloride, an epithelialNa + transport blocker. CT responses to NaCl were reduced at allconcentrations after both brief and prolonged Na + deprivation comparedto Na + -replete controls. Moreover, amiloride, which suppressed CTresponses to NaCl by 35% in controls, had virtually no effect on CTresponses in Na + -deprived rats. These results suggest that both brief andprolonged Na + deprivation lead to changes in CT responses to NaCl thatmay selectively involve the amiloride-sensitive component of NaCltaste. Supported by NIH Grants DC 04785 (RJC), T32 NS07437 (JMV).22