-
[show abstract]
[hide abstract]
ABSTRACT: Taste buds contain two types of taste receptor cells, inositol 1,4,5-triphosphate receptor type 3-immunoreactive cells (type II cells) and synaptosomal-associating protein-25-immunoreactive cells (type III cells). We investigated their postnatal development in mouse fungiform taste buds immunohistochemically and electrophysiologically. The cell density, i.e. the number of cells per taste bud divided by the maximal area of the horizontal cross-section of the taste bud, of type II cells increased by postnatal day (PD)49, where as that of type III cells was unchanged throughout the postnatal observation period and was equal to that of the adult cells at PD1. The immunoreactivity of taste bud cell subtypes was the same as that of their respective subtypes in adult mice throughout the postnatal observation period. Almost all type II cells were immunoreactive to gustducin at PD1, and then the ratio of gustducin-immunoreactive type II cells to all type II cells decreased to a saturation level, ∼60% of all type II cells, by PD15. Type II and III cells generated voltage-gated currents similar to their respective adult cells even at PD3. These results show that infant taste receptor cells are as excitable as those of adults and propagate in a subtype-dependent manner. The relationship between the ratio of each taste receptor cell subtype to all cells and taste nerve responses are discussed.
European Journal of Neuroscience 03/2012; 35(11):1661-71. · 3.63 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The tonicity of taste stimulating solutions has been usually ignored, though taste substances themselves yielded the tonicity. We investigated the effect of hypertonicity on bullfrog taste nerve responses to inorganic salts by adding nonelectrolytes such as urea and sucrose that elicited no taste nerve responses. Here, we show that hypertonicity alters bullfrog taste nerve-response magnitude and firing pattern. The addition of urea or sucrose enhances the taste nerve-response magnitude to NaCl and shifts the concentration-response curve to the left. The effect of hypertonicity on responses to CaCl(2) is bimodal; hypertonicity suppresses CaCl(2) responses at concentrations less than ~30 mM and enhances them at concentrations greater than ~30 mM. The hypertonicity also enhances response magnitude to other monovalent salts. The extent of the enhancing effects depends on the difference between the mobility of the cation and anion in the salt. We quantitatively suggest that both the enhancing and suppressing effects result from the magnitude and direction of local circuit currents generated by diffusion potentials across tight junctions surrounding taste receptor cells.
Pflügers Archiv - European Journal of Physiology 03/2012; 463(6):845-51. · 4.46 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Taste buds endure extreme changes in temperature, pH, osmolarity, so on. Even though taste bud cells are replaced in a short span, they contribute to consistent taste reception. Each taste bud consists of about 50 cells whose networks are assumed to process taste information, at least preliminarily. In this article, we describe a neural network model inspired by the taste bud cells of mice. It consists of two layers. In the first layer, the chemical stimulus is transduced into an irregular spike train. The synchronization of the output impulses is induced by the irregular spike train at the second layer. These results show that the intensity of the chemical stimulus is encoded as the degree of the synchronization of output impulses. The present algorithms for signal processing result in a robust chemical-sensing system.
Biological Cybernetics 07/2011; 105(1):21-7. · 1.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We show here the expression, permeability and pharmacology of a voltage-gated channel in certain taste bud cells (TBCs) which is known to be permeable to Lucifer Yellow CH (LY) and known to release ATP as a neurotransmitter in response to taste substances. LY dissolved in a 200 mM K(+)-containing solution label TBCs immunoreactive to PLCβ2, a phospholipase subtype, but not the TBC subtype immunoreactive to SNAP-25, a SNARE protein. In addition to these subtypes, LY also labelled a few of the non-immunoreactive TBCs. Monovalent and divalent anion probes with molar mass less than 1200 also label PLCβ2-immunoreactive TBCs and a few non-immunoreactive TBCs, whereas a cation probe, rhodamine B, labels the cell membrane of TBCs nonselectively and K(+) independently. The number of LY-labelled TBCs is decreased by 5 μM DIDS (4,4'-diisothiocyanostilbene-2-2'disulfonate), 1mM octanol and 10(-5)M H(+), but not by 10 μM carbenoxolone, 2mM probenecid, 10mM TEA, or 30 μM flufenamic acid. PLCβ2-immunoreactive TBCs and a few non-immunoreactive TBCs generate a TEA-insensitive outwardly rectifying current. DIDS decreases this current in magnitude with IC(50) of ~0.4 μM in a voltage-independent manner. Also 10(-5)M H(+) and 1mM octanol decreases the current magnitude, but 10 μM carbenoxolone and 2mM probenecid do not. These results show that the LY-permeable channel preferably permeates anions and occurs not only on PLCβ2-immunoreactive TBCs but also on certain non-immunoreactive TBCs. Also the results show that the pharmacology of the LY-permeable channel is different from hemichannels reported. The discussion focuses on the pharmacology and the role of the LY-permeable channel.
Brain research 02/2011; 1373:17-24. · 2.46 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Mammalian taste bud cells (TBCs) consist of several cell types equipped with different taste receptor molecules, and hence the ratio of cell types in a taste bud constitutes the taste responses of the taste bud. Here we show that the population of immunohistochemically identified cell types per taste bud is proportional to the number of total TBCs in the taste bud or the area of the taste bud in fungiform papillae, and that the proportions differ among cell types. This result is applicable to soft palate taste buds. However, the density of almost all cell types, the population of cell types divided by the area of the respective taste buds, is significantly higher in soft palates. These results suggest that the turnover of TBCs is regulated to keep the ratio of each cell type constant, and that taste responsiveness is different between fungiform and soft palate taste buds.
Brain research 10/2010; 1367:13-21. · 2.46 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The purpose of our project is to develop brain-inspired chemical sensor arrays from physiological, theoretical, and engineering
points of view. In the previous work, a computational model for chemical sensor arrays has been proposed based on physiological
properties of mouse taste bud cells (TBCs). The model consists of three functional parts: the chemical sensor, the random
pulse generator, and the stochastic synchronizer. The chemical sensor array based on the computational model detects the concentration
of chemical substances as the degree of stochastic synchronization. For practical implementation, we compare the probabilistic
firing properties of an array of resonate-and-fire neuron (RFN) models and those of an array of leaky integrate-and-fire neuron
models in order to consider their feasibility as the second part of a chemical sensor array. We further investigate stochastic
synchronization in uncoupled integrated circuits implementing the RFN model in order to confirm if they act as the third part
of a chemical sensor array on a practical hardware platform.
11/2009: pages 129-133;
-
[show abstract]
[hide abstract]
ABSTRACT: Lucifer Yellow CH (LY), a fluorescent membrane-impermeable cell-marker dye, has been routinely loaded into cells through recording electrodes to visualize these cells after electrophysiological investigation. Recently we showed that LY produced superoxide when LY was exposed to light at ordinary intensities for microscopy, and that the resultant superoxide retarded the inactivation of voltage-gated Na+ channels even in the dark. Here, we show that superoxide produced by exposure to light prolongs the duration of action potentials, and increases the magnitude of outward rectifier K+ currents and inward rectifier K+ currents in cultured mouse hippocampal neurons. Superoxide also increases the current response of AMPA receptors, but has no effect on that of kainate and NMDA receptors, GABA(A) receptors, high-voltage activated Ca2+ channels of the hippocampal neurons, nor on 5HT3 receptors of N1E-115 cells. These superoxide effects are irreversible. The addition of superoxide dismutase, an enzyme that selectively decomposes superoxide, to LY-loaded recording electrodes reverses the superoxide effects, but addition of heat-inactivated superoxide dismutase fails to reverse the effects. The application of dithiothreitol, a free radical scavenger, to a bathing solution also reverses the superoxide effects. This shows that superoxide rather selectively modifies ion channels. The effects of exogenous and endogenous superoxide on the superoxide-susceptible channels are discussed.
Brain Research 09/2008; 1236:49-56. · 2.73 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Lucifer yellow CH (LY), a fluorescent membrane-impermeable cell marker dye, has been routinely loaded into cells through recording electrodes to visualize these cells after electrophysiological investigation, without considering its pharmacological effect. Recently, we showed that the exposure of cells loaded with LY to light for microscopy produced unidentified radical species that retarded the inactivation of voltage-gated Na+ currents irreversibly (Higure Y et al. 2003). Here, we show that superoxide dismutase, an enzyme that decomposes superoxide, reverses the retardation effect, which assures that superoxide is the unidentified radical species. The estimated mean lifetime of superoxide in recording electrodes (in the absence of cytoplasm) is approximately 6 min, and hence, the Na+ currents are retarded even in the dark, when LY is exposed to light before being loaded into the cell. Superoxide has no effect on voltage-gated Cl- currents. These results show that superoxide action on ion channels is rather selective. The breakdown of superoxide inside cells and the effect of endogenous superoxide on the superoxide-susceptible channels are discussed.
Chemical Senses 07/2008; 33(5):425-32. · 2.60 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Taste bud cells (TBCs) express various neurotransmitter receptors assumed to facilitate or modify taste information processing within taste buds. We investigated the functional expression of muscarinic acetylcholine receptor (mAChR) subtypes, M1-M5, in mouse fungiform TBCs. ACh applied to the basolateral membrane of TBCs elevates the intracellular Ca(2+) level in a concentration-dependent manner with the 50% effective concentration (EC(50)) of 0.6 microM. The Ca(2+) responses occur in the absence of extracellular Ca(2+) and are inhibited by atropine, a selective antagonist against mAChRs. The order of 50% inhibitory concentration (IC(50)) examined with a series of antagonists selective to mAChR subtypes shows the expression of M3 on TBCs. Perforated whole-cell voltage clamp studies show that 1 microM ACh blocks an outwardly rectifying current and that 100 nM atropine reverses the block. Reverse transcriptase-mediated polymerase chain reaction studies suggest the expression of M3 but not the other mAChR subtypes. Immunohistochemical studies show that phospholipase Cbeta-immunoreactive TBCs and synaptosome-associated protein of 25 kDa-immunoreactive nerve endings are immunoreactive to a transporter that packs ACh molecules into synaptic vesicles (vesicular acetylcholine transporter). These results show that M3 occurs on a few fungiform TBCs and suggest that a few nerve endings, and probably a few TBCs, release ACh by exocytosis. The role of ACh in taste responses is discussed.
Chemical Senses 02/2008; 33(1):47-55. · 2.60 Impact Factor
-
Proceedings IEEE CSE'08, 11th IEEE International Conference on Computational Science and Engineering, 16-18 July 2008, São Paulo, SP, Brazil; 01/2008
-
[show abstract]
[hide abstract]
ABSTRACT: Neurotransmitter receptors on taste bud cells (TBCs) and taste nerve fibres are likely to contribute to taste transduction by mediating the interaction among TBCs and that between TBCs and taste nerve fibres. We investigated the functional expression of P2 receptor subtypes on TBCs of mouse fungiform papillae. Electrophysiological studies showed that 100 microm ATP applied to their basolateral membranes either depolarized or hyperpolarized a few cells per taste bud. Ca(2+) imaging showed that similarly applied 1 mum ATP, 30 microm BzATP (a P2X(7) agonist), or 1 microm 2MeSATP (a P2Y(1) and P2Y(11) agonist) increased intracellular Ca(2+) concentration, but 100 microm UTP (a P2Y(2) and P2Y(4) agonist) and alpha,beta-meATP (a P2X agonist except for P2X(2), P2X(4) and P2X(7)) did not. RT-PCR suggested the expression of P2X(2), P2X(4), P2X(7), P2Y(1), P2Y(13) and P2Y(14) among the seven P2X subtypes and seven P2Y subtypes examined. Immunohistostaining confirmed the expression of P2X(2). The exposure of the basolateral membranes to 3 mm ATP for 30 min caused the uptake of Lucifer Yellow CH in a few TBCs per taste bud. This was antagonized by 100 microm PPADS (a non-selective P2 blocker) and 1 microm KN-62 (a P2X(7) blocker). These results showed for the first time the functional expression of P2X(2) and P2X(7) on TBCs. The roles of P2 receptor subtypes in the taste transduction, and the renewal of TBCs, are discussed.
The Journal of Physiology 11/2007; 584(Pt 2):473-88. · 4.72 Impact Factor
-
Kiyonori Yoshii
Chemical Senses 02/2005; 30 Suppl 1:i35-6. · 2.60 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Taste bud cells (TBCs) on soft palates differ from those on tongues in innervation and chemosensitivity. We investigated voltage-gated channels involved in the taste responses of TBCs on mouse soft palates under in-situ tight-seal voltage/current-clamp conditions. Under the cell-attached mode, TBCs spontaneously fired action currents, which were blocked by application of 1 microM TTX to TBC basolateral membranes. Firing frequencies increased in response to taste substances applied to TBC receptor membranes. Under the whole-cell clamp mode, as expected, TBCs produced various voltage-gated currents such as TTX-sensitive Na+ currents (INa), outward currents (Iout) including TEA-sensitive and insensitive currents, inward rectifier K+ currents (Iir), and Ca2+ currents including T-type, P/Q-type, and L-type Ca2+ currents. We classified TBCs into three types based on the magnitude of their voltage-gated Na+ currents and membrane capacitance. HEX type (60% of TBCs examined) was significantly larger in Na+ current magnitude and smaller in membrane capacitance than LEX type (23%). NEX type (17%) had no Na+ currents. HEX type was equally distributed within single taste buds, while LEX type was centrally distributed, and NEX type was peripherally distributed. There were correlations between these electrophysiological cell types and morphological cell types determined by three-dimensional reconstruction. The present results show that soft palate taste buds contain TBCs with different electrophysiological properties, and suggest that their co-operation is required in taste transduction.
Brain Research 09/2003; 982(2):241-59. · 2.73 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Lucifer Yellow CH (LY), a membrane-impermeant fluorescent dye, has been used in electro-physiological studies to visualize cell morphology, with little concern about its pharmacological effects. We investigated its effects on TTX-sensitive voltage-gated Na+ channels in mouse taste bud cells and hippocampal neurons under voltage-damp conditions. LY applied inside cells irreversibly slowed the inactivation of Na+ currents upon exposure to light of usual intensities. The inactivation time constant of Na+ currents elicited by a depolarization to -15 mV was increased by fourfold after a 5 min exposure to halogen light of 3200 Ix at source (3200 Ix light), and sevenfold after a 1-min exposure to 12,000 Ix light. A fraction of the Na+ current became non-inactivating following the exposure. The non-inactivating current was approximately 20 % of the peak total Na+ current after a 5 min exposure to 3200 Ix light, and approximately 30 % after a 1 min exposure to 12,000 Ix light. Light-exposed LY shifted slightly the current-voltage relationship of the peak Na+ current and of the steady-state inactivation curve, in the depolarizing direction. A similar light-dependent decrease in kinetics occurred in whole-cell Na+ currents of cultured mouse hippocampal neurones. Single-channel recordings showed that exposure to 6500 Ix light for 3 min increased the mean open time of Na+channels from 1.4 ms to 2.4 ms without changing the elementary conductance. The pre-incubation of taste bud cells with 1 mM dithiothreitoL a scavenger of radical species, blocked these LY effects. These results suggest that light-exposed LY yields radical species that modify Na+ channels.
The Journal of Physiology 08/2003; 550(Pt 1):159-67. · 4.72 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Responses of endogenous transporters/receptors of Xenopus oocytes to l-alanine, l-arginine, l-leucine and l-serine were investigated under voltage clamp conditions, (a) Concentrationresponse relations for the amino acids followed Langmuir's adsorption isotherm, (b) The neutral amino acids required Na+ to elicit the responses, whereas l-arginine did not. (c) The responses to l-alanine decreased with decreasing pH and became undetectable at pH 5.5. The present experiments supply criteria to judge if the oocytes translate exogenous mRNA coding taste or olfactory receptor proteins for the amino acids, the best characterized stimuli, especially in fishes.
Comparative Biochemistry and Physiology Part A: Physiology. 11/1994;
-
[show abstract]
[hide abstract]
ABSTRACT: The purpose of our project is to establish how to design brain-inspired chemical sensor arrays from physiological, theoretical, and engineering points of view. In a previous work, a computational model for chemical sensor arrays has been proposed inspired from physiological properties of mouse taste bud cells. The computational model consists of three functional parts: the chemical sensor, the random pulse generator, and the stochastic synchronizer. The model converts the concentration of chemical substances into the degree of stochastic synchronization. We have implemented the chemical sensor array as a silicon devices. We discuss about functional significance of our device in view of noise-induced nonlinear phenomena: stochastic synchronization and array-enhanced coherence resonance.
2010 13th IEEE International Conference on Computational Science and Engineering.
-
[show abstract]
[hide abstract]
ABSTRACT: Each taste bud (a taste sensor) in mouse tongues consists of ∼50 taste bud cells (TBCs) that express various neurotransmitter receptors on their basolateral membranes. We investigated the expression of ATP receptor subtypes with neurophysiological, molecular biological, and immunohistochemical techniques. Here we show that TBCs expressed P2X2, P2X7 and P2Y1 subtypes. These results showed that ATP probably released from TBCs or taste nerves during taste responses could finely regulate the functions of neighbouring TBCs by stimulating their heterogeneous ATP receptor subtypes. Such interactions among TBCs may form cell networks within single taste buds and may process taste information on the tongue.
International Congress Series 1291:81-84.
-
[show abstract]
[hide abstract]
ABSTRACT: Taste buds, biological chemical sensors, consist of four types of taste bud cells (Types I to IV TBCs) classified morphologically or immunohistochemically. Since both morphological and immunohistochemical classification essentially require the fixation of TBCs, the physiological properties of classified cells are completely destroyed. We have developed a physiological classification, typically for Type II cells, taste receptor cells, as well as for Type III cells, the only one cell type that has synaptic contacts with taste nerve fibers, based on voltage-gated currents of TBCs. Here we show that the magnitude of outward rectifier currents was much larger in Type II and III cells than in Type I cells, and that the main component of the outward rectifier currents was TEA-insensitive Cl− channel currents in Type II cells but TEA-sensitive K+ channel currents in Type III cells. These results enable us to apply protocols appropriate to elucidate the physiological role of each cell type in taste reception.
International Congress Series 1301:254-257.
-
[show abstract]
[hide abstract]
ABSTRACT: This study shows a computational model of a taste-sensing system inspired by physiological properties of mammalian taste organs. The experimental results indicated that the taste bud cells (TBCs) form cell networks within single taste buds. The computational model includes those cell networks between taste-sensing cells (leaky integrate-and-fire (LIAF) model) and output cells (bursting cell model). Each LIAF model was heterogeneous. Outputs of a plurality of the LIAF models were integrated in the bursting cells. The dc bias current caused irregular interbeat intervals in the LIAF models. Noisy input from the LIAF models induced synchronization in the bursting cells. The degree of synchronization between the bursting cells was considered output of the network. The degree of synchronization increased with an increase in the mean dc current in the LIAF models. Although we do not know how the taste stimuli charge the LIAF models, the present network model potentially detects the taste stimuli as the degree of synchronization of TBCs.
International Congress Series 1301:52-55.
-
[show abstract]
[hide abstract]
ABSTRACT: Although tight junctions among taste bud cells (TBCs, animal chemical sensors) prevent the diffusion of food constituents to protect TBCs, these tight junctions are suggested to permeate some food constituents in order to elicit taste responses to them. In this study, we quantitatively investigated the ionic diffusion through these tight junctions. Here, we show that they are slightly permeable to small ions and that their permeability contributes to taste responses only when permeating ions have potent pharmacological effects. We discuss the role of tight junctions in taste reception and the contribution of tight junctions in engineering artificial chemical sensors.
International Congress Series 1291:73-76.
