1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

389 Poster Central Taste and Chemosensory BehaviorSOLITARY NUCLEUS–RETICULAR FORMATIONPROJECTIONS IN A NEONATAL SLICE PREPARATIONNasse J. 1 , Travers J.B. 1 1 Oral Biology, Ohio State University,Columbus, OHData obtained from in vivo studies suggest that projections from therostral nucleus of the solitary tract (rNST) to the subjacent reticularformation (RF) constitute a pathway through which taste stimuliinfluence oromotor responses of ingestion and rejection. To furtherinvestigate the underlying neural mechanisms, we conductedanatomical, behavioral and physiological studies to determine if thissubstrate could be studied in vitro. Injections of fluorescentmicrospheres into the hypoglossal nucleus of neonatal rats retrogradelylabeled pre-oromotor neurons in the intermediate zone of the RF (IRt)in a distribution identical to adult rats. Neurons in the RF becameopaque to iDIC microscopy after P14 however, thus limiting the abilityto record from identified neurons in a slice. Although RF neurons inyounger animals were visible under iDIC, it was unclear whether theseyounger animals also produce "adult-like" oromotor behavior. Onestudy suggested that neonatal rats gaped in response to QHCl(Ganchrow, 1986), however another study was more equivocal(Johanson & Shapiro, 1986). Thus, we re-evaluated the capacity of ratsfrom age P2 - P14 to gape in response to QHCl (0.01M). Although notall rats gaped, the likelihood of gaping as well as the magnitude of thegape response increased in a graded manner over time. Lastly, wedetermined from extracellular and patch clamp recordings, that neuronsin the IRt could be excited and suppressed by electrical stimulation ofthe rNST. Because electrical stimulation can elicit both licks and gapesin vivo, this may provide an approach to studying taste-oromotorpathways in a slice preparation. Supported by DC00417390 Poster Central Taste and Chemosensory BehaviorTHE ORGANIZATION OF THE GUSTATORY NEURALNETWORK IN THE HAMSTER BRAINSTEMCho Y.K. 1 , Li C. 2 1 Kangnung National University, Kangnung,Kangwondo, South Korea; 2 Anatomy, Southern Illinois University,Carbondale, ILTaste information elicited from the anterior tongue is first carried tothe nucleus of the solitary tract (NST) and then to the parabrachialnuclei (PbN), from which taste information is further transferred toforebrain gustatory nuclei. In the present study we examined thegustatory neural connectivity among gustatory nuclei in the brainstem.Three recording/stimulating electrode assemblies were used first torecord taste neurons and then electrically stimulate the nuclei in order:left PbN, right PbN and left NST. A fourth electrode, a micro glasscapillary was used to record taste cells in the right NST. A total of 45taste cells were isolated in the PbN and the responsiveness of each cellto electrical stimulation of the contralateral PbN was examined: 5neurons (11%) were antidromically invaded and 9 neurons (20%)responded orthodromically. In the NST, 123 taste cells were isolatedand responses of each NST cell to the stimulation of bilateral PbN weretested. Eighty-one percent of NST taste cells were ipsilateral PbNprojectioncells. The same proportion of NST taste neurons receiveddescending input from the ipsilateral PbN. In contrast, 3 cells sent axonsto the contralateral PbN and 47 NST neurons received descendinginfluence from the contralateral PbN. The influence of the NST tasteneurons to the contralateral NST stimulation was examined from 100NST taste neurons: 58 neurons were activated orthodromically and 11antidromically. These data demonstrate the intricate interconnectionamong the four gustatory nuclei in the brainstem. Supported byNIDCD006623391 Poster Central Taste and Chemosensory BehaviorVAGAL GUSTATORY REFLEX SYSTEMS IN GOLDFISHIkenaga T. 1 , Ogura T. 1 , Finger T.E. 1 1 Cell and Developmental Biology,University of Colorado Health Sciences Center, Aurora, COIn goldfish, the primary sensory nucleus for vagally mediated taste ispart of a complex laminated lobe. The sensory layers of this lobe areequivalent to the n. solitarius while the motor layers containmotoneurons equivalent to the n. ambiguus. The sensory layers arecoupled to the motor layers via a simple reflex arc homologous to thesolitario-ambigual reflex system of mammals. To detail the morphologyof neurons that form this reflex system in goldfish, the retrograde tracer,biocytin, was injected into the motor zone of in vitro slices. Diverseneurons were retrogradely labeled in the sensory zone, from the surface(layer II-III) to the deepest portion (XI). Most labeled neurons had amonopolar or bipolar soma with radially-directed dendrites branching inlayer IV, VI and IX—the layers of termination of primary vagalgustatory inputs. These projection neurons were organizedtopographically along the dorso-ventral axis, projecting only to theimmediately subjacent motoneurons. In functional imagingexperiments, motor neurons were retrogradely labeled by injections ofcalcium green dextran (Ca ++ indicator) into the vagus nerve. Increasesin Ca ++ followed electrical stimulation in the sensory zone of in vitroslices. These Ca ++ responses were enhanced by application of theGABA A receptor antagonist, bicuculin, suggesting tonic inhibition ofthe reflex pathways by GABAergic systems. Finally, reflex activationof the motoneurons was blocked by application of the glutamateantagonist DNQX suggesting that this gustatory reflex system utilizesglutamate acting on AMPA/kainate receptors as the principalneurotransmitter. Supported by NIH Grant DC 00147 (T.E.F.)392 Poster Central Taste and Chemosensory BehaviorTASTANT-INDUCED C-FOS EXPRESSION IN THE NST OFMICE THAT DON´T TASTEBarrows J.K. 1 , Finger T.E. 1 1 Cell and Developmental Biology,University of Colorado Health Sciences Center, Aurora, COATP is an essential neurotransmitter coupling taste buds to gustatorynerves. Genetic deletion of the ionotropic purinergic receptor subunitsP2X2 and P2X3 eliminates neural responses to all taste stimuli.However, these P2X2/P2X3 KO mice still avoid citric acid andcaffeine, as well as high concentrations of quinine hydrochloride(QHCL) (Finger et al 2005). We hypothesize that the P2X2/P2X3 KOmice detect some noxious substances via laryngeal and/orpharyngeal/esophogeal solitary chemoreceptor cells. We examinedcFos-like immunoreactivity (c-FLI) in the nucleus of the solitary tract(NST) of P2X2/P2X3 KO mice after stimulation with 1 mM QHCL,150 mM monosodium glutamate (MSG), or water. Water-induced c-FLIdid not differ between P2X2/P2X3 KO mice and wild-type controls.MSG-induced c-FLI was moderately reduced throughout the NST inP2X2/P2X3 KO mice compared to wild-type controls. QHCL-inducedc-FLI was elevated compared to water-induced c-FLI, within the caudalNST of P2X2/P2X3 KO mice, where afferents from the larynx andpharynx terminate. These preliminary results suggest that chemosensoryinput reaches the caudal NST in P2X2/P2X3 KO mice, probably arisingfrom the laryngeal or pharyngeal/esophageal nerves. This input may besufficient to allow the P2X2/P2X3 KO mice to avoid certain tastants.Future directions include intra-oral cannulation to control the volumewashed across the tongue and superior laryngeal nerve transactions inboth P2X2/P2X3 KO mice and controls. Funded by NIH GrantsDC006070, DC00244, P30 DC04657 and RO1 DC007495.98