An initial phasic depolarization exists in the receptor potential of taste cells.

When frog taste cells were stimulated by varying salts after adaptation to water, quinine or acetic acid, a phasic depolarization appeared initially in the receptor potential of taste cells. The initial transient depolarization may be related to the enhancement of an initial phasic response in the taste nerve.     

Molecular neurophysiology of taste in <Emphasis Type="Italic">Drosophila</Emphasis>

The recent identification of candidate receptor genes for sweet, umami and bitter taste in mammals has opened a door to elucidate the molecular and neuronal mechanisms of taste. Drosophila provides a suitable system to study the molecular, physiological and behavioral aspects of taste, as sophisticated molecular genetic techniques can be applied. A gene family for putative gustatory receptors has been found in the Drosophila genome. We discuss here current knowledge of the gustatory physiology of Drosophila. Taste cells in insects are primary sensory neurons whereupon each receptor neuron responds to either sugar, salt or water. We found that particular tarsal gustatory sensilla respond to bitter compounds. Electrophysiological studies indicate that gustatory sensilla on the labellum and tarsi are heterogeneous in terms of their taste sensitivity. Determination of the molecular bases for this heterogeneity could lead to an understanding of how the sensory information is processed in the brain and how this in turn is linked to behavior.Received 12 May 2003; received after revision 9 June 2003; accepted 13 June 2003     

Peptide interactions with taste receptors: overlap in taste receptor specificity

Two hitherto unrelated areas of taste appear to provide an important insight into a class of taste receptor sites. A region of the sweet protein monellin is similar to a savory tasting beef octapeptide, and this peptide region could represent an overlap in the specificity of binding to a common peptide taste receptor site. Such an overlap in binding specificity explains the low but significant level of sweetness observed with savory tasting stimuli.     

Peptide interactions with taste receptors: Overlap in taste receptor specificity

Summary Two hitherto unrelated areas of taste appear to provide an important insight into a class of taste receptor sites. A region of the sweet protein monellin is similar to a savory tasting beef octapeptide, and this peptide region could represent an overlap in the specificity of binding to a common peptide taste receptor site. Such an overlap in binding specificity explains the low but significant level of sweetness observed with savory tasting stimuli.The work from this laboratory was supported by NIH Research Grant No. NS-15740 from NINCDS and by the Veterans Administration.     

Electrical responses to taste chemicals across the dorsal epithelium of bullfrog tongue

Summary Stimulation of the bullfrog tongue with taste chemicals produced a slow change in transepithelial potential difference across the dorsal epithelium. The potential profile was in many respects similar to that of the intracellularly recorded potential changes in taste cells and to the activity of taste fibers in frogs.     

Electrical responses to taste chemicals across the dorsal epithelium of bullfrog tongue

Stimulation of the bullfrog tongue with taste chemicals produced a slow change in transepithelial potential difference across the dorsal epithelium. The potential profile was in many respects similar to that of the intracellularly recorded potential changes in taste cells and to the activity of taste fibers in frogs.     

Receptor potential of rat taste cell to potassium benzoate

Summary Rat taste cells responded to relatively low concentrations of K-benzoate with a hyperpolarization and to the high concentrations with a depolarization. During both responses the membrane resistance of a taste cell decreased. Depolarization elicited by application of a combination of 0.25 M NaCl and 0.05 M K-benzoate was smaller than that by the NaCl alone, indicating a depressant action of K-benzoate.     

Receptor potential of rat taste cell to potassium benzoate.

Rat taste cells responded to relatively low concentrations of K-benzoate with a hyperpolarization and to the high concentrations with a depolarization. During both responses the membrane resistance of a taste cell decreased. Depolarization elicited by application of a combination of 0.25 M NaCl and 0.05 M K-benzoate was smaller than that by the NaCl alone, indicating a depressant action of K-benzoate.     

Influence of temperature on taste perception

Daily experience tells us that temperature has a strong influence on how we taste. Despite the longstanding interest of many specialists in this aspect of taste, we are only starting to understand the molecular mechanisms underlying the temperature dependence of different taste modalities. Recent research has led to the identification of some strong thermosensitive molecules in the taste transduction pathway. The cold activation of the epithelial Na⁺ channel and the heat activation of the taste variant of the vanilloid receptor (TRPV1t) may underlie the temperature dependence of salt responses. Heat activation of the transient receptor potential channel TRPM5 explains the enhancement of sweet taste perception by warm temperatures. Current development of methods to study taste cell physiology will help to determine the contribution of other temperature-sensitive events in the taste transduction pathways. Vice versa, the analysis of the thermodynamic properties of these events may assist to unveil the nature of several taste processes. Received 29 August 2006; received after revision 5 October 2006; accepted 20 November 2006     

Substance P-like immunoreactive fibers in the frog taste organs

In the frog tongue, substance P(SP)-like immunoreactive fibers were consistently present in each fungiform papilla, which contained the gustatory apparatus. Numerous SP-like immunoreactive fibers were usually distributed in the periphery of the gustatory disc and formed a varicose meshwork among the ciliated cells encircling the gustatory disc. SP-like immunoreactive fibers were rarely evident inside the gustatory disc. The role of SP-containing fibers in the frog taste organ was discussed.     

Substance P-like immunoreactive fibers in the frog taste organs

Summary In the frog tongue, substance P(SP)-like immunoreactive fibers were consistently present in each fungiform papilla, which contained the gustatory apparatus. Numerous SP-like immunoreactive fibers were usually distributed in the periphery of the gustatory disc and formed a varicose meshwork among the ciliated cells encircling the gustatory disc. SP-like immunoreactive fibers were rarely evident inside the gustatory disc. The role of SP-containing fibers in the frog taste organ was discussed.     

Latency of taste nerve signals in frog (Rana catesbeiana).

The latency of frog gustatory neural impulses to 1.0 M NaCl was a mean of 86 msec. Electrical stimulation of taste cell membranes produced gustatory neural impulses with the mean 5 msec latency. It is concluded that most of the 86 msec latency of taste nerve responses to 1.0 N NaCl is due to the latency of taste receptor potential following the onset of gustatory stimulation.     

Bitter peptides and bitter taste receptors

Bitter peptides are a structurally diverse group of oligopeptides often generated in fermented, aged, and hydrolyzed food products that make them unfavorable for consumption. Humans perceive bitterness by a repertoire of 25 human bitter receptors, termed T2Rs. Knowledge of the structural features of bitter receptors and of the factors that stimulate bitter receptors will aid in understanding the mechanism responsible for bitter taste perception. This article reviews the current knowledge regarding structural features of bitter peptides and bitter taste receptors. Received 24 November 2008; received after revision 11 December 2008; accepted 16 December 2008     

Lipid characterization and 14C-acetate metabolism in catfish taste epithelium

The catfish, Ictalurus punctatus is an important model system for the study of the biochemical mechanisms of taste reception. A detailed lipid analysis of epithelial tissue from the taste organ (barbel) of the catfish has been performed. Polar lipids account for 62 +/- 1% of the total, neutrals for 38 +/- 1%. Phosphatidyl-cholines, serines and ethanolamines are the major constituents of the polar fraction. Plasmalogen concentration is high relative to that of non-neural tissues. [14C]-Acetate is incorporated into cell lipid fractions after incubation of barbel tissue at 37 degrees C for 60 min. Percentage amounts of most lipids change with time during this in vitro incubation. The phospholipids are the most metabolically active fractions. This work yields information for continuing reconstitution experiments and indicates that the taste epithelium of this important model system is a metabolically active tissue capable of supporting lipid turnover/synthesis.     

Lipid characterization and14C-acetate metabolism in catfish taste epithelium

Summary The catfish,Ictalurus punctatus is an important model system for the study of the biochemical mechanisms of taste reception. A detailed lipid analysis of epithelial tissue from the taste organ (barbel) of the catfish has been performed. Polar lipids account for 62±1% of the total, neutrals for 38±1%. Phosphatidyl-cholines, serines and ethanolamines are the major constitutents of the polar fraction. Plasmalogen concentration is high relative to that of non-neural tissues. [¹⁴C]-Acetate is incorporated into cell lipid fractions after incubation of barbel tissue at 37°C for 60 min. Percentage amounts of most lipids change with time during this in vitro incubation. The phospholipids are the most metabolically active fractions. This work yields information for continuing reconstitution experiments and indicates that the taste epithelium of this important model system is a metabolically active tissue capable of supporting lipid turnover/synthesis.This work was supported in part by NIH Research Grant No. NS-23622, NS-22620, and by the Veterans Administration.     

Do taste receptors respond to perturbation of water structure?

The pmr spin-spin pulse relaxation times (T2 values) of the L-amino acids are examined in relation to their taste threshold values. There is an inverse trend between T2 value and threshold value with a good correlation for amino acids whose natural pH is close to neutrality. These results may indicate that taste receptors respond to perturbation of water structure.     

Effects of selective removal of the salivary glands on taste bud cells in the vallate papilla of the rat

Summary The in-block removal of the main salivary glands produced a significant increase in the rate of development of the intermediate type of taste bud cells. Such effect was reproduced by removal of submaxillary-sublingual glands. Removal of parotid glands was not effective.Supported by a CAIT grant No. 1776.     

Do taste receptors respond to perturbation of water structure?

The pmr spin-spin pulse relaxation times (T₂ values) of the L-amino acids are examined in relation to their taste threshold values. There is an inverse trend between T₂ value and threshold value with a good correlation for amino acids whose natural pH is close to neutrality. These results may indicate that taste receptors respond to perturbation of water structure.     

Deletion mapping of a new gustatory mutant inDrosophila melanogaster

Summary A gustatory mutant ofDrosophila melanogaster insensitive to the taste of salt has been isolated. Genetic crosses and a deletion mapping analysis show that this mutation, designatedgust-M ₁ is located in the 93C_3–6-93D_6–7 region of the third chromosome.gust-M ₁ is also insensitive to the taste of quinine sulfate. The behavior of this mutant may be explained by assuming thatgust-M ₁ could be a mutation perturbing functions in the central nervous system affecting the responses to both compounds.     

Effects of deneravation and decentralization upon taste buds.

Denervation of vallate papillae results in failure of tactile and gustatory reception at a time when impulse conduction in the distal stump of the glossopharyngeal nerve is still unimpaired; delay of receptor deficit depends on axon length between receptor and axotomy sites; taste buds disappear by 10 days. Decentralization, through intracranial rhizotomy, does not modify lingual receptors structure or function.