Oxytocin Signaling in Mouse Taste Buds

The neuropeptide, oxytocin (OXT), acts on brain circuits to inhibit food intake. Mutant mice lacking OXT (OXT knockout) overconsume salty and sweet (i.e. sucrose, saccharin) solutions. We asked if OXT might also act on taste buds via its receptor, OXTR.Using RT-PCR, we detected the expression of OXTR in taste buds throughout the oral cavity, but not in adjacent non-taste lingual epithelium. By immunostaining tissues from OXTR-YFP knock-in mice, we found that OXTR is expressed in a subset of Glial-like (Type I) taste cells, and also in cells on the periphery of taste buds. Single-cell RT-PCR confirmed this cell-type assignment. Using Ca2+ imaging, we observed that physiologically appropriate concentrations of OXT evoked [Ca2+]i mobilization in a subset of taste cells (EC50 approximately 33 nM). OXT-evoked responses were significantly inhibited by the OXTR antagonist, L-371,257. Isolated OXT-responsive taste cells were neither Receptor (Type II) nor Presynaptic (Type III) cells, consistent with our immunofluorescence observations. We also investigated the source of OXT peptide that may act on taste cells. Both RT-PCR and immunostaining suggest that the OXT peptide is not produced in taste buds or in their associated nerves. Finally, we also examined the morphology of taste buds from mice that lack OXTR. Taste buds and their constituent cell types appeared very similar in mice with two, one or no copies of the OXTR gene.We conclude that OXT elicits Ca2+ signals via OXTR in murine taste buds. OXT-responsive cells are most likely a subset of Glial-like (Type I) taste cells. OXT itself is not produced locally in taste tissue and is likely delivered through the circulation. Loss of OXTR does not grossly alter the morphology of any of the cell types contained in taste buds. Instead, we speculate that OXT-responsive Glial-like (Type I) taste bud cells modulate taste signaling and afferent sensory output. Such modulation would complement central pathways of appetite regulation that employ circulating homeostatic and satiety signals

Effects of dietary Na+ deprivation on epithelial Na+ channel (ENaC), BDNF, and TrkB mRNA expression in the rat tongue

<p>Abstract</p> <p>Background</p> <p>In rodents, dietary Na⁺deprivation reduces gustatory responses of primary taste fibers and central taste neurons to lingual Na⁺stimulation. However, in the rat taste bud cells Na⁺deprivation increases the number of amiloride sensitive epithelial Na⁺channels (ENaC), which are considered as the "receptor" of the Na⁺component of salt taste. To explore the mechanisms, the expression of the three ENaC subunits (α, β and γ) in taste buds were observed from rats fed with diets containing either 0.03% (Na⁺deprivation) or 1% (control) NaCl for 15 days, by using <it>in situ </it>hybridization and real-time quantitative RT-PCR (qRT-PCR). Since BDNF/TrkB signaling is involved in the neural innervation of taste buds, the effects of Na⁺deprivation on BDNF and its receptor TrkB expression in the rat taste buds were also examined.</p> <p>Results</p> <p><it>In situ </it>hybridization analysis showed that all three ENaC subunit mRNAs were found in the rat fungiform taste buds and lingual epithelia, but in the vallate and foliate taste buds, only α ENaC mRNA was easily detected, while β and γ ENaC mRNAs were much less than those in the fungiform taste buds. Between control and low Na⁺fed animals, the numbers of taste bud cells expressing α, β and γ ENaC subunits were not significantly different in the fungiform, vallate and foliate taste buds, respectively. Similarly, qRT-PCR also indicated that Na⁺deprivation had no effect on any ENaC subunit expression in the three types of taste buds. However, Na⁺deprivation reduced BDNF mRNA expression by 50% in the fungiform taste buds, but not in the vallate and foliate taste buds. The expression of TrkB was not different between control and Na⁺deprived rats, irrespective of the taste papillae type.</p> <p>Conclusion</p> <p>The findings demonstrate that dietary Na⁺deprivation does not change ENaC mRNA expression in rat taste buds, but reduces BDNF mRNA expression in the fungiform taste buds. Given the roles of BDNF in survival of cells and target innervation, our results suggest that dietary Na⁺deprivation might lead to a loss of gustatory innervation in the mouse fungiform taste buds.</p

Building sensory receptors on the tongue

Neurotrophins, neurotrophin receptors and sensory neurons are required for the development of lingual sense organs. For example, neurotrophin 3 sustains lingual somatosensory neurons. In the traditional view, sensory axons will terminate where neurotrophin expression is most pronounced. Yet, lingual somatosensory axons characteristically terminate in each filiform papilla and in each somatosensory prominence within a cluster of cells expressing the p75 neurotrophin receptor (p75NTR), rather than terminating among the adjacent cells that secrete neurotrophin 3. The p75NTR on special specialized clusters of epithelial cells may promote axonal arborization in vivo since its over-expression by fibroblasts enhances neurite outgrowth from overlying somatosensory neurons in vitro . Two classical observations have implicated gustatory neurons in the development and maintenance of mammalian taste buds—the early arrival times of embryonic innervation and the loss of taste buds after their denervation in adults. In the modern era more than a dozen experimental studies have used early denervation or neurotrophin gene mutations to evaluate mammalian gustatory organ development. Necessary for taste organ development, brain-derived neurotrophic factor sustains developing gustatory neurons. The cardinal conclusion is readily summarized: taste buds in the palate and tongue are induced by innervation. Taste buds are unstable: the death and birth of taste receptor cells relentlessly remodels synaptic connections. As receptor cells turn over, the sensory code for taste quality is probably stabilized by selective synapse formation between each type of gustatory axon and its matching taste receptor cell. We anticipate important new discoveries of molecular interactions among the epithelium, the underlying mesenchyme and gustatory innervation that build the gustatory papillae, their specialized epithelial cells, and the resulting taste buds.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47466/1/11068_2005_Article_3332.pd

Olfactory sensitivity to aminoacids in the juvenile stages of the European eel Anguilla anguilla (L.)

Scanning electron micrograph observations of the olfactory mucosa from both unpigmented glass eel(GE)andpigmentedelvers(EL)of the European eel, Anguilla anguilla(L.), revealed the presence of various cell types; amongst these, the ciliated and microvillous ones are likely to possess a chcmosensory function. Recording of underwater electro-olfactograms (EOGs) showed that various amino acids (glycine, L-alanine, L-valine, L-leucine, L-asparagine, L-glutamine and L-methionine) are effective stimulants for the olfactory mucosa. Dose response curves of stimulus concentrations v. EOG amplitudesfit regression linesat both GE and EL stages. Leucine was more stimulatory at the GE than at the EL stage. The stimulatory effect of the other six amino acids tested was similar at both developmental stages. The possible role of olfactory sensitivity in animal behaviour at different developmental stages is discussed

Morphology and EAG mapping of the antennal olfactory receptors in Dacus oleae

EAGs were recorded from various locations on the flagellar surface of the antennae of the olive fly Dacus oleae stimulated with compounds of behavioural significance to this species. This information was compared with data on the typology and distribution patterns of the olfactory sensilla. Results showed that: a) 3 types of olfactory sensilla are present on the antennae: long basiconica, short grooved basiconica and trichodea; b) 1\u2010hexanol, ethanol and volatiles belonging to the oily fraction of the olive pulp are the strongest stimuli, while those of the water fraction are little or not effective; c) EAG amplitude values vary as a function of the recording location on the flagellar surface; d) a significant correlation was found, for 2 stimuli of the oily fraction, between EAG amplitude and population density of long sensilla basiconica, thus suggesting this type as specifically responding to these substances. Morphologie des antennes de Dacus oleae et localisation de leurs r\ue9cepteurs olfactifs par \ue9lectroantennogramme Des EAG ont \ue9t\ue9 obtenus en diff\ue9rents points de la surface de flagelles d'antennes de la mouche de l'olive, stimul\ue9es par des substances ayant une signification pour le comportement de cette esp\ue8ce. Ces informations ont \ue9t\ue9 compar\ue9es avec les donn\ue9es tir\ue9es de la typologie et de la distribution des sensilles olfactives. Les r\ue9sultats mettent en \ue9vidence: a) 3 types de sensilles: longue basiconique, basiconique \ue0 petit sillon et trichodes; b) les stimuli les plus puissants de la pulpe sont l'1\u2010hexanol, l'\ue9thanol et les substances volatiles solubles dans l'huile, tandis que les substances hydrosolubles sont peu ou pas actives; c) une ampleur de l'EAG variant en fonction du lieu d'enregistrement sur la surface du flagelle; d) une corr\ue9lation significative pour 2 stimuli liposolubles entre l'amplitude de l'EAG et la densit\ue9 des longues sensilles basiconiques, ce qui sugg\ue8re une r\ue9action sp\ue9cifique de ce type de r\ue9cepteur \ue0 ces substances. 1989 The Netherlands Entomological Societ

Noise Properties of Single Open Ion Channels: an Atomistic Computational Approach

The paper presents the first results of a computational analysis of the noise associated with ion current in single open ion channels. The analysis is performed by means of a coupled Molecular Dynamics-Monte Carlo approach able to simulate the conduction process on the basis of all microscopic information today available from protein structural data and atomistic simulations. The case of potassium ions permeating the KcsA channel is considered in the numerical calculations. The obtained results show a noise spectrum different from what is theoretically predicted for uncorrelated ion-exit events (Poisson noise), confirming the existence of correlation in the ion motion within the channel