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At least 19 recordsLinked to original sources
PubMed2006

Differential taste coding of salt and acid by correlative activities between taste-sensitive neuron types in rat gustatory cortex.

Using a multi-electrode recording technique, the present study aimed to elucidate the role of broadly-tuned taste-sensitive neurons in the rat gustatory cortex in discriminating between salt and acid. A majority of taste-sensitive neurons (94/119 neurons; 78%) were classified as NaCl (N)-, HCl (H)- or NaCl and HCl (NH)-best neurons. Of 63 neuron pairs (94 neurons), 31 showed significant peaks and/or troughs in their cross-correlograms (CCs) during taste stimulation periods. During NaCl stimulation, the incidence of significant correlation and the mean frequency of correlated discharges (FC) in the N/N and NH/NH pairs were higher than those in the other best-taste pairs. In contrast, during HCl stimulation both indices in the N/N or H/H pairs were very low, while those in the NH/NH pairs were high. These results suggest that (1) correlated activities between N-best neurons and those between NH-best neurons play a significant role in taste quality coding of salt, and that (2) correlated activities between NH-best neurons may be important for sour taste coding as well. Peak formation in CCs tended to be more frequent in the homo-types (N/N, H/H and NH/NH pairs) than in the hetero-types (N/NH, N/H and H/NH pairs). In contrast, troughs were observed mostly in the hetero-types. Inhibitory interaction in hetero-type pairs together with coactivation in homo-type pairs may enhance taste discrimination by taste-sensitive neuron populations.

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PubMed1996

Amiloride disrupts NaCl versus KCl discrimination performance: implications for salt taste coding in rats.

Amiloride, an epithelial sodium channel blocker, suppresses the responsiveness of narrowly tuned sodium-responsive taste afferents when orally applied in the rat. Broadly tuned salt-responsive taste afferents, which respond to sodium and nonsodium salts and acids, are relatively unaffected by the drug. We used amiloride treatment to examine the consequences of the specific removal of input from narrowly tuned sodium-responsive afferents on taste discrimination. Five water-restricted rats were trained in a gustometer to press one lever after licking NaCl and another lever after licking KCl across a range of concentrations (0.05, 0.1, and 0.2 M). Correct responses were rewarded with brief water access, and incorrect responses were punished with a time-out. After training, animals averaged about 90% correct responses and maintained competent performance during subsequent control sessions. Amiloride was then placed in all solutions at a given concentration (1-100 microM) for single test sessions. Control sessions were interposed between amiloride sessions. At high amiloride concentrations, overall responding was reduced to 50% correct and progressively improved as the drug concentration was lowered. The sigmoidal dose-response functions corresponded quantitatively with electrophysiological findings. Performance deficits occurred primarily with NaCl and were concentration dependent; performance during KCl trials was relatively undisturbed by amiloride adulteration. At high amiloride concentrations, rats treated NaCl as if it were KCl. Given that amiloride is tasteless to the rat, these results provide convincing evidence of the importance of narrowly tuned afferents in the discrimination between sodium and nonsodium salts and suggest that this is a general coding principle in the gustatory system.

Amiloride↗
PubMedDate not supplied

Artificial neural networks estimate the contribution of taste neurons to coding.

Taste qualities are believed to be coded in the activity of populations of taste neurons. However, it is not clear whether all neurons are equally responsible for coding. To clarify the point the relative contribution of each taste neuron to coding was assessed by constructing simple three-layer neural networks with input neurons that represent cortical taste neurons of the rat. The networks were trained by the back-propagation learning algorithm to classify the neural response patterns to the basic taste stimuli (sucrose, HCl, quinine-hydrochloride, and NaCl). The networks had four output neurons representing the basic taste qualities, the values of which provide a measure for similarity of test stimuli to the basic taste stimuli. We estimated relative contributions of input neurons to the taste discrimination of the network by examining their significance S(j), which is defined as the sum of the absolute values of the connection weights from the jth input neuron to the hidden layer. When the input neurons with a smaller S(j) (e.g., 15 out of 39 input units) were "pruned" from the trained network, the ability of the network to discriminate the basic taste qualities was not greatly affected. On the other hand, the taste discrimination of the network progressively deteriorated much more rapidly with pruning of input neurons with a larger S(j). These results suggest that cortical taste neurons differentially contribute to the coding of taste qualities. Input neurons with a larger S(j) tended to be with a larger variation of neural discharge rates to the basic taste stimuli. The variation of neural discharges may be important in the coding of taste qualities.

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PubMed2003

Dynamic coding of taste stimuli in the brainstem: effects of brief pulses of taste stimuli on subsequent taste responses.

Recent studies have suggested that the response profiles of taste-responsive cells in the brainstem may be modulated by inhibitory interactions, potentially originating from activity in peripheral taste nerves. This idea was explored by testing the hypothesis that brief (100 msec) pulses of taste stimuli would alter the responses to subsequently presented tastants in the nucleus of the solitary tract (NTS) of urethane-anesthetized rats. Pulses of taste stimuli, called prepulses, were followed by a 3 sec presentation of the same or different taste stimulus. The prepulse-stimulus interval was either 1 or 5 sec, during which the tongue was rinsed with distilled water. Taste stimuli consisted of 0.1 m NaCl, 0.5 m sucrose, 0.01 m quinine HCl, and 0.01 m HCl. Taste prepulses suppressed (or enhanced) subsequent taste responses in 30 of 49 (61%) units when the prepulse-stimulus interval was 1 sec but were ineffective when this interval was 5 sec. Most commonly, NaCl or HCl prepulses attenuated the response to quinine. Control experiments showed that these effects were not attributable to adaptation, mixture effects, or response variability. In 19 (39%) of the units tested, effects of prepulses were large enough to change the order of effectiveness of the taste stimuli. Taste responses in these cells were "dynamically tuned" in that the magnitude of response was a function of the taste stimulus that immediately preceded it. Dynamic tuning may be the result of inhibitory interactions within the NTS; cells that show dynamic tuning may have a unique function in taste coding.

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PubMed1992

Difference in taste quality coding between two cortical taste areas, granular and dysgranular insular areas, in rats.

The responses of 84 taste neurons to stimulation of the oral cavity in rats were examined; most taste neurons were found in either a granular insular area (area GI; n = 55) or dysgranular insular area (DI; n = 25), and the others (n = 4) were in an agranular insular area (area AI). The fraction of neurons responding to only one of the four basic stimuli was significantly larger in area GI than in area DI. When neurons were classified by the stimulus which most excited the neuron among the four basic stimuli, every "best-stimulus category" of neurons was found in both GI and DI areas. Quinine-best and "multistimulus-type" neurons, whose responses to some non-best stimulus exceeded 90% of the maximum, were more numerous in the cortex than in the thalamocortical relay neurons. When responses were plotted against taste stimuli arranged in the order of sucrose, NaCl, HCl, and quinine along the abscissa (taste coordinate), response profiles of taste neurons often showed two peaks. The double-peaked type of response profiles were found in every best-stimulus category of neurons in both areas; though, a significantly large fraction of quinine-best neurons in area GI were of the double-peaked type. Some taste neurons in area GI (n = 21) and in area DI (n = 7) were inhibited by one to two taste stimuli, particularly by the stimuli present next to the best one along the taste coordinate. In correlation profiles--correlation coefficients between sucrose and NaCl and between HCl and quinine--pairs of stimuli which were located next to each other on the taste coordinate were significantly smaller in area GI than in area DI. It is thus highly probable that area GI plays an important role in fine taste discrimination and area DI in integration of taste information.

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PubMedDate not supplied

Neuronal cell types and taste quality coding.

Over the past 25 years, there have been two opposing views of how taste information is represented in the activity of gustatory neurons. One view, the across-fiber pattern (AFP) theory, postulates that taste quality is represented by the pattern of activity across the afferent population. Stimuli with similar tastes produce similar patterns of activity. The other view is that activity in a few distinct neuron types codes taste quality in a "labeled-line" fashion. Neurons responding best to sucrose, for example, would represent "sweetness," and those responding best to NaCl would code "saltiness." Some of these neuron types appear to have a biological significance, such as the NaCl-best cells, which receive input about sodium stimuli exclusively from an amiloride-sensitive epithelial ion channel. However, the relatively broad tuning of these neurons makes it unlikely that they are capable of unambiguously coding information about taste quality. Rather, these neuron types play a critical role in establishing unique AFPs that distinguish among taste stimuli. The relative activity across these cell types represent taste quality, much like the patterns of activity across broadly tuned photoreceptors code information about stimulus wavelength.

Animals↗
PubMed2005

The receptors and coding logic for bitter taste.

The sense of taste provides animals with valuable information about the nature and quality of food. Bitter taste detection functions as an important sensory input to warn against the ingestion of toxic and noxious substances. T2Rs are a family of approximately 30 highly divergent G-protein-coupled receptors (GPCRs) that are selectively expressed in the tongue and palate epithelium and are implicated in bitter taste sensing. Here we demonstrate, using a combination of genetic, behavioural and physiological studies, that T2R receptors are necessary and sufficient for the detection and perception of bitter compounds, and show that differences in T2Rs between species (human and mouse) can determine the selectivity of bitter taste responses. In addition, we show that mice engineered to express a bitter taste receptor in 'sweet cells' become strongly attracted to its cognate bitter tastants, whereas expression of the same receptor (or even a novel GPCR) in T2R-expressing cells resulted in mice that are averse to the respective compounds. Together these results illustrate the fundamental principle of bitter taste coding at the periphery: dedicated cells act as broadly tuned bitter sensors that are wired to mediate behavioural aversion.

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PubMed1997

Parabrachial neural coding of taste stimuli in awake rats.

Parabrachial neural coding of taste stimuli in awake rats. J. Neurophysiol. 78: 2254-2268, 1997. In awake, behaving rats, the activity of 74 single neurons in the pontine parabrachial nucleus (PBN) was recorded in response to sapid stimulation by 15 chemicals. Of these, 44 taste cells were tested with all 15 stimuli. Based on their responsiveness to 4 standard stimuli, these neurons were categorized as follows: 23 NaCl-best, 15 sucrose-best, 5 citric acid-best, and 1 quinine HCl-best. Several forms of multivariate analyses indicated that the taste responses matched both the behavioral responses to and, less well, the chemical structure of, the sapid stimuli. A hierarchical cluster analysis of the neurons substantially confirmed the best-stimulus categorization, but separated the NaCl-best cells into those that responded more to Na+-containing salts and those that responded more to Cl--containing salts. The cells that responded best to the Na+ moiety actually were somewhat more correlated with the sucrose-best cells than with those that responded to the Cl--containing stimuli. Citric acid-best neurons and the lone quinine-best unit formed a single cluster of neurons that responded well to acids, as well as to NH4Cl and, to a lesser extent, NaNO3. A factor analysis of the neuronal response profiles revealed that three factors accounted for 78.8% of the variance in the sample. Similar analyses of the stimuli suggested that PBN neurons respond to four or five sets of stimuli related by their chemical makeup or by human psychophysical reports. The capacity of rats to make these discriminations has been documented by other behavioral studies in which rodents generalize across sapid chemicals within each of 5 stimulus categories. Furthermore, a simulation analysis of the neural data replicated behavioral results that used amiloride, a Na+ channel blocker, in which rats generalized NaCl to non-Na+, Cl- salts. Thus, using a variety of analyses, in awake rats, the activity of PBN taste neurons tracks their behavioral responses to a variety of chemical stimuli.

Amiloride↗
PubMedDate not supplied

The neural code for taste in the brain stem: response profiles.

In the study of the neural code for taste, two theories have dominated the literature: the across neuron pattern (ANP), and the labeled line theories. Both of these theories are based on the observations that taste cells are multisensitive across a variety of different taste stimuli. Given a fixed array of taste stimuli, a cell's particular set of sensitivities defines its response profile. The characteristics of response profiles are the basis of both major theories of coding. In reviewing the literature, it is apparent that response profiles are an expression of a complex interplay of excitatory and inhibitory inputs that derive from cells with a wide variety of sensitivity patterns. These observations suggest that, in the absence of inhibition, taste cells might be potentially responsive to all taste stimuli. Several studies also suggest that response profiles can be influenced by the taste context, defined as the taste stimulus presented just before or simultaneously with another, under which they are recorded. A theory, called dynamic coding, was proposed to account for context dependency of taste response profiles. In this theory, those cells that are unaffected by taste context would provide the signal, i.e., the information-containing portion of the ANP, and those cells whose responses are context dependent would provide noise, i.e., less stimulus specific information. When singular taste stimuli are presented, noise cells would provide amplification of the signal, and when complex mixtures are presented, the responses of the noise cells would be suppressed (depending on the particular combination of tastants), and the ratio of signal to noise would be enhanced.

Animals↗
PubMed1998

Taste in chimpanzees. III: Labeled-line coding in sweet taste.

In peripheral taste the coding mechanism remains an enigma. Among coding theories the "across-fiber pattern" argues that activity across fibers codes for taste, whereas the "labeled line" claims that activity in a particular set of fibers underlies a taste quality. We showed previously that chimpanzee chorda tympani taste fibers grouped according to human taste qualities into an S-cluster, responding predominantly to sweet stimuli, a Q-cluster, sensitive to bitter tastants, and an N-cluster, stimulated by salts. The analysis showed that information in the S-line suffices to distinguish stimuli of one taste quality from the others. However, one condition for the labeled line remained: that blockage of activity in a particular line must cause blockage of one taste quality, but of no other, or its onset give rise to the sensation of a taste quality. Here we studied this requirement with gymnemic acids and miraculin. In humans and chimpanzees, gymnemic acids suppress the sweet taste of all sweeteners whereas miraculin adds a sweet taste quality to sour stimuli. Gymnemic acids also abolish miraculin-induced sweet taste. We found that gymnemic acids practically abolished the response to every sweetener in the chimpanzee S-cluster. Equally important, they had no effect on the responses of the Q- and N-clusters. After miraculin, the S-cluster fibers responded to acids as well as to sweeteners, although they had not responded to acids before miraculin. Gymnemic acids abolished this miraculin-induced response to acids and responses to sweeteners in the S-fibers. These results link the sweet taste quality to activity in fibers of the S-cluster. Thus the S-cluster fibers satisfy the definition of the labeled-line theory: "that activity in a particular fiber type represents a specific taste quality."

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PubMed2006

Taste perception and coding in the periphery.

Recent identification of taste receptors and their downstream signaling molecules, expressed in taste receptor cells, led to the understanding of taste coding in the periphery. Ion channels appear to mediate detection of salty and sour taste. The sensations of sweet, umami and bitter taste are initiated by the interaction of sapid molecules with the G-protein-coupled receptors T1Rs and T2Rs. Mice lacking either PLCbeta2 or TRPM5 diminish behavioral and nerve responses to sweet, umami and bitter taste stimuli, suggesting that both receptor families converge on a common signaling pathway in the taste receptor cells. Nevertheless, separate populations of taste cells appear to be uniquely tuned to sweet, umami and bitter taste. Since PLCbeta2-deficient mice still respond to sour and salty stimuli, sour and salty taste are perceived independent of bitter, umami and sweet taste. In this review, the recent characterization of the cellular mechanisms underlying taste reception and perception, and of taste coding in the periphery will be discussed.

Action Potentials↗
PubMedDate not supplied

Coding in taste receptor cells. The early years of intracellular recordings.

In the gustatory system, the mechanism of coding-the process of relaying the identity and intensity of the stimulus to the central nervous system-begins with the taste receptor cells. Ironically, although these are the first cells of the gustatory system to contact stimuli, they were the last from which neurophysiological recordings were obtained. How taste receptor cells decipher stimulus identity remains the subject of active research; its origins began with a series of intracellular studies. Prior to the first intracellular recording, it was unknown if taste receptor cells would be specialists, responding to only a single class of taste stimulus, or generalists, responding to multiple stimuli. The first reports established several major aspects of these cells' physiology. Taste receptor cells have varying response profiles to basic stimuli; they have obvious conductance changes during stimulation; they have low resting potentials. It became evident that multiple transduction schemes must underlie these responses, although the identity of these transduction schemes remained elusive. Additionally, these early recordings missed a major phenomenon-the presence of regenerative electrical events (i.e., the action potential) was not observed due to the low input resistance that accompanied this technique. Although intracellular recordings are essentially no longer used to study taste receptor cells, replaced by the superior method of patch-clamp recording, these early articles provided key insights into the then unknown electrical responses of taste receptor cells.

Animals↗
PubMed2006

Effects of acetylcholine on coding of taste information in the primary gustatory cortex in rats.

Acetylcholine (ACh) receptors are widely distributed throughout the cerebral cortex in rats. Recently, cholinergic innervation of the gustatory cortex (GC) was reported to be involved in certain taste learning in rats. Here, the effects of iontophoretic application of ACh on the response properties of GC neurons were studied in urethane-anesthetized rats. ACh affected spontaneous discharges in a small fraction of taste neurons (11 of 86 neurons tested), but influenced taste responses in 27 of 43 neurons tested. No correlations with ACh susceptibility were noted for spontaneous discharges and taste responses. Among the 27 neurons, ACh facilitated taste responses in 13, inhibited taste responses in 13 and either facilitated or inhibited taste responses depending on the stimuli in 1. Furthermore, ACh affected the responses to best stimuli that produced the largest responses among four basic tastants (best responses) in 7 of 27 taste neurons, to non-best responses in 9, and to both best and non-best responses in 11. ACh mostly inhibited the best responses (13 of 18 neurons). Thus, ACh often decreased the response selectivity to the four basic tastants and changed the response profile. Atropine, a general antagonist of muscarinic receptors, antagonized ACh actions on taste responses or displayed the opposite effects on taste responses to ACh actions in two-thirds of the neurons tested. These findings indicate that ACh mostly modulates taste responses through muscarinic receptors, and suggest that ACh shifts the state of the neuron network in the GC, in terms of the response selectivities and response profiles.

Acetylcholine↗
PubMed2005

Elucidating coding of taste qualities with the taste modifier miraculin in the common marmoset.

To investigate the relationships between the activity in different types of taste fibers and the gustatory behavior in marmosets, we used the taste modifier miraculin, which in humans adds a sweet taste quality to sour stimuli. In behavioral experiments, we measured marmosets' consumption of acids before and after tongue application of miraculin. In electrophysiological experiments responses of single taste fibers in chorda tympani and glossopharyngeal nerves were recorded before and after tongue application of miraculin. We found that after miraculin marmosets consumed acids more readily. Taste nerve recordings showed that after miraculin taste fibers which usually respond only to sweeteners, S fibers, became responsive to acids. These results further support our hypothesis that the activity in S fibers is translated into a hedonically positive behavioral response.

Animals↗
PubMed2000

The neural code for taste in the nucleus of the solitary tract of the rat: effects of adaptation.

Adaptation of the tongue to NaCl, HCl, quinine or sucrose was used as a tool to study the stability and organization of response profiles in the nucleus of the solitary tract (NTS). Taste responses in the NTS were recorded in anesthetized rats before and after adaptation of the tongue to NaCl, HCl, sucrose or quinine. Results showed that the magnitude of response to test stimuli following adaptation was a function of the context, i.e., adaptation condition, in which the stimuli were presented. Over half of all taste responses were either attenuated or enhanced following the adaptation procedure: NaCl adaptation produced the most widespread, non-stimulus-selective cross-adaptation and sucrose adaptation produced the least frequent cross-adaptation and the most frequent enhancement of taste responses. Adaptation to quinine cross-adapted to sucrose and adaptation to HCl cross-adapted to quinine in over half of the units tested. The adaptation procedure sometimes unmasked taste responses where none were present beforehand and sometimes altered taste responses to test stimuli even though the adapting stimulus did not itself produce a response. These effects demonstrated a form of context-dependency of taste responsiveness in the NTS and further suggest a broad potentiality in the sensitivity of NTS units across taste stimuli. Across unit patterns of response remained distinct from each other under all adaptation conditions. Discriminability of these patterns may provide a neurophysiological basis for residual psychophysical abilities following adaptation.

Action Potentials↗