1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

441 Symposium Neural Dynamics and ChemosensoryBehaviorTEMPORAL AND SPATIAL CODES MEDIATE THEDISCRIMINATION OF `BITTER´ TASTE STIMULI BY ANINSECTGlendinning J.I. 1 1 Barnard College, Columbia University, New York,NYA primary function of sensory systems is to discriminate functionallydistinct stimuli. In the taste system, most theories about discriminativeprocessing have focused on two spatial coding frameworks (labeled-linevs. across-fiber pattern), and largely ignored the potential contributionof temporal codes. I will discuss recent work on an herbivorous insect(the caterpillar of Manduca sexta), which displays unusually finediscriminating abilities for `bitter´ taste stimuli. I will present evidencethat the caterpillar uses a variety of coding mechanisms to accomplishthis discrimination: a labeled-line mechanism to discriminate salicin andGrindelia extract, an across-fiber mechanism to discriminate salicin andCanna extract, and a temporal coding mechanism to discriminate salicinand aristolochic acid. The only `bitter´ taste stimuli that cannot bediscriminated are those that elicit the same spatial and temporal code(e.g., salicin and caffeine). These findings show that this herbivorousinsect has evolved a complex set of gustatory mechanisms fordistinguishing among a diverse range of potentially toxic `bitter´compounds, which abound in its solanaceous foodplants. This projectwas supported by NIH DC02416.442 Poster Developmental, Neurogenesis, and ConsumerResearchEMBRYONIC ORIGIN DICTATES MATURE GUSTATORYNEURON FATEHarlow D.E. 1 , Barlow L.A. 1 1 Cell & Developmental Biology, Univ ofColorado Health Sciences Center, Aurora, COThe vertebrate tongue receives gustatory and somatosensoryinnervation from nerves whose cell bodies lie in cranial ganglia. Tasteand somatosensory neurons project centrally to specific hindbrainnuclei, and peripherally to taste buds and epithelium, respectively.These neurons arise from two distinct embryonic populations:epibranchial placodes and neural crest. We tested the hypothesis thattaste neurons arise from placodes, while somatosensory neurons derivefrom neural crest, via fate mapping in embryos of an aquaticsalamander, the axolotl. Embryos were globally labeled via injection ofGFP mRNA at the 2-cell stage. At mid-neurula stage, presumptiveplacodal ectoderm or premigratory neural crest/dorsal neural tube fromGFP-labeled donors was grafted isotopically into unlabeled hosts.Importantly, this method allowed visualization of both peripheral andcentral projections of neurons. Placodal neurons sent out peripheralfibers which contacted taste buds almost exclusively, while their centralprocesses projected to the nucleus of the solitary tract. Neural crestderived neurons, in contrast, did not innervate taste buds; rather theirperipheral fibers terminated as free nerve endings within oralepithelium. Central projections of crest derived neurons were obscuredby GFP label in the hindbrain, as the initial neural tube grafts comprisedboth premigratory neural crest and presumptive hindbrain. In sum, ourdata indicate that embryonic origin dictates a concise segregation ofmature neuron function; placodal neurons are gustatory, while neuralcrest neurons are somatosensory. Supported by NIDCD DC003947 toLAB443 Poster Developmental, Neurogenesis, and ConsumerResearchEMBRYONIC DEVELOPMENT OF NASAL SOLITARYCHEMORECEPTOR CELLS AND ASSOCIATED NERVEFIBERS IN MICEGulbransen B.D. 1 , Finger T. 2 1 Neuroscience, Univ of Colorado atDenver & Health Sciences Center, Aurora, CO; 2 Cell & DevelopmentalBiology, Univ of Colorado Health Sciences Center, Aurora, CONasal trigeminal chemosensitivity in mice and rats is mediated in partby solitary chemoreceptor cells (SCCs) in the nasal epithelium (Fingeret al. PNAS 2003). Mature SCCs express the G-protein gustducin aswell as other elements of the bitter taste signaling cascade such asPLCβ2 and T2R (bitter) taste receptors. Currently nothing is knownconcerning the development of nasal SCCs. The present experimentswere designed to answer two basic questions: (1) When do gustducinexpressing SCCs appear in the nasal epithelium during development?and (2) When do SCCs become innervated by the trigeminal nerve?Wild type C57/B6 embryos were taken at various stages from E14.5-E18.5, decapitated, and fixed in 4% PFA. Dual-labelimmunocytochemistry was used to identify SCCs (rabbit antigustducin)and nerve fibers (rabbit anti-PGP9.5). No gustducinimmunoreactive (ir) SCCs were present in E14.5 or E15 embryos.Although PGP9.5-ir growth cones were present in the mucosa at thesestages, no fibers penetrated into the nasal epithelium. Gustducin-irSCCs first appeared in the nasal epithelium at E15.5. At this stage,PGP9.5-ir nerve fibers innervated the nasal epithelium and occasionalSCCs. By E17.5, gustducin-ir SCCs were abundant and more frequentlycontacted by PGP9.5-ir nerve fibers. Further experiments are underwayto better delineate the timing and sequence of events leading up todevelopment and innervation of nasal SCCs. Supported by NIDCDGrants RO1 DC 006070 and P30 DC 04657444 Poster Developmental, Neurogenesis, and ConsumerResearchTASTE BUD DEVELOPMENT IN CHICKS AFTERTREATMENT WITH ß-BUNGAROTOXIN, OR OTOCYSTREMOVALGanchrow D. 1 , Witt M. 2 , Ganchrow J. 3 , Arki-Burstyn E. 3 1 Anatomy &Anthropology, Tel Aviv Univ, Tel Aviv, Israel; 2 Otorhinolaryngology,Univ of Technology Dresden, Med. Sch., Dresden, Germany; 3 Instituteof Dental Sciences, The Hebrew University-Hadassah School of DentalMedicine, Jerusalem, IsraelChick taste bud (gemmal) primordia normally appear on embryonicday (E)16 and incipient immature, spherical-shaped buds at E17. In ovoinjection of ß-bungarotoxin at E12 resulted in complete absence of tastebuds in lower beak and palatal epithelium at developmental ages E17and E21. However, putative gemmal primordia (solitary cells; small,cell groupings) remained, lying adjacent salivary gland duct openings asseen in normal chick gemmal development. Oral epithelium wasimmunonegative to neural cell adhesion molecule (NCAM) suggestinggemmal primordia are nerve-independent. Some NCAMimmunoreactivity was evident in autonomic ganglion-like cells andnerve fibers in connective tissue. After unilateral geniculateganglion/otocyst excision on E2.5, at developmental ages E18 andposthatching day 1, 10-15% of surviving ipsilateral geniculate ganglioncells sustained ~54% of the unoperated gemmal counts. After E18,proportional stages of differentiation in surviving developing budsprobably reflect their degree of innervation, as well as rate ofdifferentiation. Irrespective of degree of geniculate ganglion damage,the proportion of surviving buds can be sustained at the samedifferentiated bud stage as on the unoperated side, or differentiate to alater bud stage, consistent with the thesis that bud maintenance, survivaland maturation are nerve-dependent.111