1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

453 Poster Developmental, Neurogenesis, and ConsumerResearchHYPER-INNERVATION WITH PRESERVATION OF TASTEBUD-NEURON SPECIFICITY IN MICE OVER-EXPRESSINGNEUROTROPHIN IN THE TONGUE EPITHELIUMZaidi F. 1 , Krimm R.F. 2 , Whitehead M.C. 3 1 Howard Hughes MedicalInsitute, University of California, San Diego, La Jolla, CA; 2 AnatomicalSciences and Neurobiology, University of Louisville, Louisville, KY;3 Surgery/Anatomy, University of California, San Diego, La Jolla, CAA mouse fungiform taste bud is innervated by only 3-6 geniculateganglion cells that do not branch to other buds. Brain-derivedneurotrophic factor (BDNF) may influence the degree or specificity ofinnervation. We examined this by counting labeled ganglion cells afterinjecting single buds with different color markers in BDNF- lingual -overexpressing (OE) mice. Counts of taste buds and receptors wereobtained from progeny of: BDNF-OE mice X Gg (gustducin) GFPmice. Finally, palatal buds were assessed to establish whether thelingual receptoneural phenotype generalizes throughout the seventhnerve taste system. Fungiform bud numbers in BDNF-OE mice are65%, yet geniculate cell numbers are 195%, of normal. Neurons labeledby single fungiform bud injections in BDNF-OE animals wereincreased 5x vs. control mice (22 +/- 3.6 vs. 4 +/- 1.9). Injecting 3 budsrarely labeled cells multiply, identical with the "exclusive" pattern ofwild type mice. Thus, hyper-innervation of BDNF-OE buds involvesmore neurons innervating single buds, not increased fiber branching.Proportions of GgGFP/BDNF-OE buds with 0, 1-5 fluorescent cells wasidentical to those of GgGFP mice; i.e., hyper-innervation was notaccompanied by a change in receptor cell numbers. Numbers andpatterns of palatal buds of GgGFP/BDNF-OE mice were normal.Numbers and lack of branching of ganglion cells innervating palatalbuds were also normal. Thus, both wild type and BDNF-OE miceexhibit, in fungiform and palatal buds, the same, "exclusive"receptoneural pattern. Neurotrophin-related decreases in bud numbersand increases in innervation density apply to only fungiform buds.R01DC001901.454 Poster Developmental, Neurogenesis, and ConsumerResearchEXPRESSION OF TROPHIC FACTORS AND THEIRRECEPTORS IN A PRIMARY TASTE CELL CULTURESYSTEMOzdener H. 1 , Rawson N.E. 1 1 Monell Chemical Senses Center,Philadelphia, PAThe regenerative ability of the taste system is remarkably robust inthe face of ongoing exposure to a comparatively harsh environment.However, in patients where taste loss occurs—such as those undergoingoral radiation therapy—taste loss is a major concern due to malnutritionresulting from the lack of food intake. In spite of the importance of oursense of taste, the molecular mechanisms involved in the generation oftaste cells throughout life are not well understood. To study theseprocesses in a controlled environment, we developed a method thatmaintains taste cells obtained from rat tongue foliate and vallate papillain long-term culture and supports the de novo generation of new cellsexhibiting molecular and functional characteristics of mature taste cells(Ozdener et al., in press). To begin to study the trophic pathways thatmay be involved in taste cell generation, we examined the expression ofseveral molecules previously implicated in this process. BDNF, EGFreceptor or Trk-B immunoreactivity was detected on subsets of cells invitro. Labeling with bromodeoxyuridine (BrdU) demonstratedproliferation, and a subset of BrdU labeled cells also exhibited EGFR orTrk-B immunoreactivity. These findings indicate that further work withthis model system to investigate the processes of proliferation anddifferentiation of taste cells is warranted. Funded in part by NIH P50DC006760.455 Poster Developmental, Neurogenesis, and ConsumerResearchDIFFERENTIAL POSTNATAL DEVELOPMENT OFGUSTATORY NERVE TERMINAL FIELDS IN CONTROLRATS AND E3-E12 SODIUM-RESTRICTED RATS.Mangold J.E. 1 , Hill D.L. 1 1 Psychology, University of Virginia,Charlottesville, VARats given a low-sodium diet (0.03% NaCl) from embryonic day 3(E3) to E12 yielded enlarged chorda tympani (CT), greater superficialpetrosal (GSP) and glossopharyngeal (IX) nerve terminal fields in theNTS when compared to rats fed a sodium-replete diet (controls). Asthere is significant rearrangement of these three terminal fields duringnormal development, we sought to identify the developmental timecourse of terminal field development in E3-E12 sodium-restricted ratsto better understand how the dramatic diet-related differences atadulthood occur. An anterograde, triple fluorescent labeling techniquewas used to label the three nerves in rats aged postnatal day 15 (P15),P25, P35 and >P40 (adult). Nerve terminal fields were imaged usingconfocal microscopy, and then measured with computer software. Abiphasic development accounted for adult differences. First, control ratterminal fields decreased while field size remained similar in E3–E12restricted rats: control CT terminal field volumes decreased from P25–P35; control GSP and IX terminal field volumes decreased betweenP15–P25. Second, a later increase in field size occurred in E3–E12restricted rats while volumes remained constant in controls: all threenerve terminal field volumes increased from P35 to adulthood in E3–E12 restricted rats. The deviation from normal terminal fielddevelopment in E3–E12 sodium-restricted rats may lead tophysiological and behavioral consequences during development and inadulthood. Supported by NIH grant R01 DC00407.456 Poster Developmental, Neurogenesis, and ConsumerResearchMYCN IS REQUIRED FOR PROPER OLFACTORYEPITHELIUM DEVELOPMENTNickell M.D. 1 , Hardin D.H. 1 , McClintock T.S. 1 1 Physiology, Universityof Kentucky, Lexington, KYThe olfactory epithelium (OE) has the unique capacity for sustainedneurogenesis throughout adulthood. This process is responsible forensuring the continuing functionality of the system in the face of stress,damage and age. The production of new olfactory sensory neurons(OSNs) is dependent on a series of progenitor cells, which proliferateand differentiate to replace lost OSNs. Many factors influence the basalcell progenitor population. The bHLH transcription factor Mycn (v-mycmyelocytomatosis viral related oncogene, neuroblastoma derived) isexpressed in a subpopulation of globose basal cells and is known toincrease during repopulation of the damaged OE (Shetty et al., 2005.Mol. Cell. Neurosci. 30:90). We are using a conditional knockoutstrategy to test whether the absence of Mycn leads to deficits in OEdevelopment. Nestin-Cre dependent deletion of Mycn in the OE appearsto have a profound effect at early developmental stages. At postnatalday 0 (P0), the tissue is disorganized and exhibits disruption of thesustentacular cell layer. Additionally, an increase in OE thickness andin OSN number at this age (as marked by Gap43 and Omp expression)is observed. The tissue recovers over time, however, as adult (6 week)animals show qualitatively normal amounts of OSNs. We hypothesizethat Mycn is functioning in the OE to maintain the proliferative state ofOSN progenitors and that its loss leads to premature neuronaldifferentiation. Supported by NIH award R01 DC002736.114