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PubMed2000

Serotonergic agonists inhibit calcium-activated potassium and voltage-dependent sodium currents in rat taste receptor cells.

Recently we reported that rat taste receptor cells respond to the neurotransmitter serotonin with an inhibition of a calcium-activated potassium current [17]. In the present study, this observation is confirmed and extended by studying the effects of an array of serotonergic agonists on membrane properties, calcium-activated potassium current, and voltage-dependent sodium current in taste receptor cells using the patch-clamp recording technique in the whole-cell configuration. Serotonergic inhibition of calcium-activated potassium current was mimicked by the agonists N-(3-trifluoromethylphenyl)piperazine and by (+/-)-2-dipropylamino-8-hydroxy-1,2,3,4-tetrahydronaphthalene. Both produced reversible inhibition of K(Ca) as well as significantly increasing the input resistance of the cell. The agonists 1-(1-naphthyl)piperazine and buspirone (both serotonin receptor 1A agonists) were similarly effective in reducing K(Ca). Outward current was unaffected by application of phenylbiguanide, a serotonin receptor 3 agonist, though current was affected by subsequent application of (+/-)-2-dipropylamino-8-hydroxy-1,2,3, 4-tetrahydronaphthalene. Two agonists-N-(3-trifluoromethylphenyl)piperazine and (+/-)-2-dipropylamino-8-hydroxy-1,2,3,4-tetrahydronaphthalene-were also tested on voltage-dependent sodium currents; both were effective and reversible in reducing its magnitude at a variety of applied potentials. These data are consistent with the notion that serotonin effects in rat taste receptor cells are mediated by serotonin 1A receptors, though other receptor subtypes may be additionally expressed. Serotonin may affect the taste cell electrical properties during active stimulation in a paracrine fashion.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1998

A basolateral chloride conductance in rat lingual epithelium.

We used Ussing chamber measurements and whole-cell recordings to characterize a chloride conductance in rat lingual epithelium. Niflumic acid (NFA) and flufenamic acid (FFA), nonsteroidal anti-inflammatory aromatic compounds known to inhibit Cl- conductances in other tissues, reduced transepithelial short-circuit current (Isc) in the intact dorsal anterior rat tongue epithelium when added from the serosal side, and reduced whole-cell currents in rat fungiform taste cells. In both Ussing chamber and patch-clamp experiments, the effect of NFA was mimicked by replacement of bath Cl- with methanesulfonate or gluconate. In low Cl- bath solution, the effect of NFA on whole-cell current was reduced. Replacement of bath Ca2+ with Ba2+ reduced the whole-cell Cl- current. We conclude that a Ca2+-activated Cl- conductance is likely present in the basolateral membrane of the rat lingual epithelium, and is present in the taste receptor cells from fungiform papillae. Further experiments will be required to identify the role of this conductance in taste transduction.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2002

A highly sensitive taste receptor cell for pyrrolizidine alkaloids in the lateral galeal sensillum of a polyphagous caterpillar, Estigmene acraea.

Adult males of Estigmene acraea use pyrrolizidine alkaloids to produce pheromones and all stages probably use pyrrolizidine alkaloids for defense. The alkaloids are obtained from plants by the caterpillars. We demonstrate that a contact chemoreceptor neuron in the lateral galeal sensillum exhibits a dose-dependent response to seneciphylline N-oxide, a widely occurring pyrrolizidine alkaloid, down to concentrations of 10(-9) x mol l(-1), and even at 10(-12) x mol l(-1) the response is greater than to salt alone. At concentrations of 10(-6) mol x l(-1) and above the instantaneous firing rate is very high, and at 10(-4) mol x l(-1) initially exceeds 500 spikes s(-1). The firing rate declines in the 200 ms following stimulus onset but then is sustained with an instantaneous firing rate in excess of 100 spikes s(-1) for at least the next 800 ms. At lower concentrations a delay occurs before firing is initiated, and then the pattern of firing is irregular. The cell is equally sensitive to some but not all of several other pyrrolizidine alkaloids tested as free bases and their N-oxides. It also responds to ouabain, which may also serve as a defensive compound, and to asparagine and fructose but with much higher thresholds than to the pyrrolizidine alkaloids.

Action Potentials↗
PubMed2003

Experience influences gustatory responsiveness to pyrrolizidine alkaloids in the polyphagous caterpillar, Estigmene acrea.

Electrophysiological recordings from taste sensilla of the caterpillar Estigmene acrea with the pyrrolizidine alkaloid, seneciphylline N-oxide, demonstrated that prior feeding on plants with pyrrolizidine alkaloids caused an increase in responsiveness of the PA-sensitive cells in two sensilla, relative to feeding on plants without such chemicals. Rearing on synthetic diet without pyrrolizidine alkaloids for up to seven generations caused a continuous decline in responsiveness, that could be reversed by experience with powdered Crotalaria pumila in the diet or by pure pyrrolizidine alkaloid, monocrotaline, in the diet. Response to the cardiac glycoside, ouabain, that stimulates one of the two pyrrolizidine alkaloid-sensitive cells, showed a similar decline. Pyrrolizidine alkaloids had no measurable effect on growth and development. Responses in all other taste cells were unaffected. The data are discussed in relation to the possible adaptive significance and the possible mechanisms involved.

Animals↗
PubMed2003

Changes in taste receptor cell sensitivity in a polyphagous caterpillar reflect carbohydrate but not protein imbalance.

Caterpillars of the polyphagous arctiid, Grammia geneura, have a single cell in the medial galeal sensillum that responds to some sugars and to some amino acids. After conditioning on artificial diet containing unbalanced amounts of carbohydrate and protein, the responses of this cell alter. After protein-biased food it increases slightly, but after carbohydrate-biased food it decreases. Responses to both sucrose and amino acids change in the same direction and the changes would not provide the information necessary to redress a shortage of protein. The lateral galeal sensillum contains one cell that responds to fructose and another responding to some amino acids. The responses of each of these cells in the lateral sensillum are not consistently affected by conditioning diets. After conditioning for 20 h on a protein- or carbohydrate-biased diet, the insects started to feed without delay if offered carbohydrate-biased diet, but only after a pause if given protein-biased diet. This occurred irrespective of the conditioning diet. The duration of the first feeding bout was also longer on carbohydrate-biased diet and the longest bouts followed protein-biased conditioning.

Action Potentials↗
PubMed2005

Position-dependent sensitivity and density of taste receptors on the locust leg underlies behavioural effectiveness of chemosensory stimulation.

Chemical stimulation of contact chemoreceptors located on the legs of locusts evokes withdrawal movements of the leg. The likelihood of withdrawal depends on the site of stimulation, in addition to the identity and concentration of the chemical stimulus. A significantly higher percentage of locusts exhibit leg avoidance movements in response to stimulation of distal parts of the leg with any given chemical stimulus compared to proximal sites. Moreover, the percentage of locusts exhibiting avoidance movements is correlated with the density and sensitivity of chemoreceptors on different sites of an individual leg. The effectiveness of chemical stimulation also differs between the fore and hind legs, with NaCl evoking a higher probability of leg withdrawal movements on the foreleg. Moreover, sucrose was less effective than NaCl at evoking withdrawal movements of the foreleg, particularly at low concentrations. The gradients in behavioural responses can be partially attributed to differences in the responsiveness and density of the contact chemoreceptors. These results may reflect the different specialization of individual legs, with the forelegs particularly involved in food selection.

Action Potentials↗
PubMed2003

Villin is a possible marker of receptor cells in frog taste organs.

We investigated lingual taste organs of four frog species mainly by means of fluorescence immunohistochemistry for villin, calbindin, and serotonin. Cells immunoreactive for villin appeared in the taste organs of all the species used. These villin-immunostained cells were basoapically elongated in shape and extended up to the apical surface. They were also immunoreactive for calbindin. On the other hand, serotonin-immunoreactive cells, identified as Merkel-like basal cells, were immunonegative for villin. Considering the present results combined with those of studies by other research groups, the villin-immunostained cells were postulated to function as taste receptors.

Animals↗
PubMed1997

Electrophysiological actions of quinine on voltage-dependent currents in dissociated rat taste cells.

How taste receptor cells participate in encoding disparate compounds into distinct taste qualities represents a fundamental problem in the study of gustatory transduction mechanisms. Quinine is the most common stimulus employed to represent bitterness yet its electrophysiological consequences on voltage-dependent ion channels in the taste receptor cell have not been elucidated in detail. This study examines such effects on taste receptor cells dissociated from the foliate and circumvallate papillae of the rat. Outward potassium currents, which include transient, sustained and calcium-activated components, were reversibly inhibited by bath application of quinine, with an IC50 of 5.1x10(-6)M. The time course of the current traces, along with voltage shifts in normalized conductance and inactivation curves, suggests that multiple mechanisms of inhibition may be occurring. Inwardly rectifying potassium currents were unaffected. Sodium currents, to somewhat higher concentrations of quinine (IC50 = 6.4x10(-5)M), were also reduced in magnitude without noticeable effects on activation or reversal potential but with a shift in inactivation. Calcium currents, visualized with barium as a charge carrier, were enhanced in magnitude by the presence of low concentrations of quinine (10(-5)M) but were suppressed by higher concentrations (10(-4)M). Quinine broadened the waveform of the gustatory action potential and increased the input resistance. These data serve as genesis to future investigations of the signal transduction mechanism of quinine on voltage-dependent currents.

Action Potentials↗
PubMed2003

Multi-photon microscopy of cell types in the viable taste disk of the frog.

The morphology of viable taste disks of the frog was explored with multi-photon microscopy. In order to identify single sensory or supporting cells within the tissue, we searched for fluorescent dyes that stained subsets of the cell population or possibly cell types. Some cell types indeed stained preferentially with certain fluorescent dyes. A subset of glia-like cells (type Ic) stained with BCECF, a H+-sensitive dye, and indo-1, a Ca2+-sensitive dye, both presented in the membrane-permeant ester form. BCECF-ester also stained the dendrites of type III receptor cells, but indo-1 ester did not. Receptor cells of type II stained with MQAE, a positively charged Cl- -sensitive dye. A subset of type II cells accumulated amiloride, a positively charged fluorescent diuretic. Certain supporting cells, i.e., wing cells (type Ib) and glia-like cells (type Ic), were labeled by negatively charged dyes, e.g., calcium green-1 dextran. Mucus cells (type Ia) were stained with only two of the 19 dyes examined, and Merkel-like basal cells (type IV) were stained only with a membrane-labeling voltage-sensitive dye, presumably by endocytosis. No dye was found which would stain all types of cells or all receptor cells. This finding reveals a potential problem for future functional imaging aiming at population responses, as the responses of unstained cells then would remain unobserved. Specificity of dyes with respect to cell types was sufficient to identify supporting cells and receptor cells. Cell shape could then be reconstructed, using optical slicing and rendering techniques. Thus populations of dye-loaded elongated cells, especially types Ic, II and III, could for the first time be visualized in three dimensions.

Acridines↗
PubMed2005

Distinct roles for Sema3A, Sema3F, and an unidentified trophic factor in controlling the advance of geniculate axons to gustatory lingual epithelium.

Geniculate ganglion axons arrive in the lingual mesenchyme on embryonic day 13 (E13), 3-4 days before penetrating fungiform papilla epithelium (E17). This latency may result from chemorepulsion by epithelial Sema3A (Dillon et al. (2004) Journal of Comparative Neurology 470, 13-24), or Sema3F, which we report is also expressed in this epithelium. Sema3A and Sema3F repelled or suppressed geniculate neurite outgrowth, respectively, and these effects were stage and neurotrophic factor dependent. BDNF-stimulated outgrowth is repelled by Sema3A until E17, but insensitive to Sema3F from E16. NT-4-stimulated neurite outgrowth is sensitive to Sema3A and Sema3F through E18, but NT-4 has not been detected in E15-18 tongue. E15-18 tongue explants did not exhibit net chemorepulsion of geniculate neurites, but the ability of tongue explants to support geniculate neurite outgrowth fluctuates: E12-13 (Rochlin et al. (2000), Journal of Comparative Neurology, 422, 579-593) and E17-18 explants promote and may attract geniculate neurites, but stages corresponding to intralingual arborization do not. The E18 trophic and tropic effects were evident even in the presence of BDNF or NT-4, suggesting that some other factor is responsible. Intrinsic neurite outgrowth capability (without exogenous neurotrophic factors) fluctuated similarly: ganglia deteriorated at E15, but exhibited moderate outgrowth at E18. The chemorepulsion studies are consistent with a role for Sema3A, not Sema3F, in restricting geniculate axons from the epithelium until E17, when axons penetrate the epithelium. The transient inability of tongue explants to promote geniculate neurite outgrowth may signify an alternative mechanism for restricting geniculate axons from the epithelium: limiting trophic factor access.

Animals↗
PubMed1993

Physicochemical properties accounting for cheese texture.

Perception of texture is a complex dynamic series of events which cannot be modelled easily by physicochemical measurements. Results using cheese analogues suggest that moisture and fat are key components in determining texture because they soften the protein matrix and provide weaknesses through which the cheeses fracture. These characteristics are sensed as firmness and work during chewing. Possible models are proposed for further investigation of the tactile determinants of cognitive mechanics involved in cheese texture description.

Cheese↗
PubMed1993

Touch and taste in the mouth: presence and character of sapid solutions.

Complex dynamic properties of a bolus in the mouth are specified by touch. Cooperation between touch and taste may help to specify the character of the bolus. The role of touch in specifying the presence of the oral bolus, in contrast to it's characteristics, remains a theoretical and experimental challenge.

Discrimination Learning↗
PubMed1995

A scanning electron-microscopic study of tongue development in the frog Rana pipiens.

Feeding behaviour changes drastically during metamorphosis as larval suction feeders become adult lingual feeders. In order to understand this transition, the general morphological development of the floor of the buccal cavity in embryonic and larval Rana pipiens was studied, up to the completion of metamorphosis, by scanning electron microscopy. Rana pipiens specimens were collected, anaesthetized with tricaine methanesulphonate, staged by the methods of Shumway and Taylor and Kollros, and fixed in 0.1 M phosphate-buffered 2.5% glutaraldehyde. The oropharyngeal floors were dissected and routinely prepared for scanning. The late embryonic period (Shumway stages 21-25) is marked by the appearance on the oropharyngeal floor of two midline premetamorphic lingual papillae (PMLP), located on the second branchial arch just caudal to the hyomandibular groove. The larval tongue anlage, which incorporates PMLP along its anterior border, does not appear until stage V of the premetamorphic developmental span (Taylor-Kollros stages I-XI). Prometamorphosis (stages XII-XIX) is marked by the incorporation of the larval tongue into the adult tongue, the disappearance of the PMLP, and the appearance of the true tongue papillae. The metamorphic span (stages XX-XXIV) marks further rapid growth and differentiation of the adult tongue.

Animals↗