Gustatory sensitivities of the hamster's soft palate

The response properties of taste receptors distributed on thesoft palate of the hamster were studied by recording integratedresponses from the greater superficial petrosal (GSP) nerveStimuli were concentration series of sucrose, NaCl, HCl andquinine hydrochloride (QHCl), and several other 0.1 M saltsand 0.5 M sugars. For comparison, integrated responses wererecorded from the chorda tympani (CT) nerve in many of the sameanimals from which recordings were made from the GSP. Responsesin each preparation were scaled relative to the phasic responseto 0.1 M NaCl and were then expressed for each nerve as a proportionof the total response magnitude (TRM)—the sum of all theresponses to the four concentration series. In this way, therelative response of each nerve to all of the stimuli couldbe evaluated. There were significant differences between theGSP and CT nerves in the responses to NaCl, QHCl and sucrose.Both the phasic and tonic responses to sucrose were larger inthe GSP than in the CT, whereas the tonic responses to NaCland QHCl were smaller. The slopes of the concentration-responsefunctions for NaCl, HCl and sucrose were significantly differentbetween the two nerves. The responses to 0.1 M sodium and lithiumsalts were significantly greater in the CT than in the GSP;whereas the 0.5 M sugars elicited responses in the GSP thatwere 2–3 times greater than in the CT nerve. A comparisonof the relative responsiveness to 0.3M sucrose, 0 3 M NaCl,0.01 M QHCl, 0.01 M HCl and distilled water among the GSP, CT,glossopharyngeal (IXth) nerve and superior laryngeal nerve (SLN)indicated that the vast majority of information about sucroseand NaCl is transmitted to the brainstem by the VIIth nerve. ¹Present address: Department of Oral Physiology, Kagoshima UniversityDental School, Kagoshima 890, Japan     

The neural activities of the greater superficial petrosal nerve of the rat in response to chemical stimulation of the palate

A comparison of the integrated responses of the rat's greatersuperficial petrosal (GSP) and chorda tympani (CT) nerves toa number of taste stimuli was studied. The GSP nerve of therat was very responsive to the chemical stimulation of the oralcavity. Among the selected stimuli related to the four basictaste qualities, 0.5 M sucrose produced the greatest neuralresponse in the GSP nerve, whereas, 0.1 M NaCl produced thegreatest in the CT nerve. The GSP nerve integrated responseto 0.5 M sucrose solution was approximately three times as greatin magnitude as that to a 0.1 M NaCl solution. The neural responsemagnitude of the GSP and CT nerves were as follows: GSP nerve;0.5 M sucrose >0.02 M Na-saccharin >0.05 M citric acid>0.1 M NaCl > 0.01 M quinine-HCl. CT nerve; 0.1 M NaCl> 0.05 M citric acid > 0.02 M Na-saccharin > 0.01 Mquinine-HCl >0.5 M sucrose. The response magnitudes of theGSP nerve to 0.3 M chloride salt solutions were: LiCl > CaCl₂> NaCl > NH₄Cl > KCl, whereas the response magnitudesof the CT nerve to the above salts were: LiCl > NaCl >NH₄Cl > CaCl₂ > KCl. All 0.5 M solutions of the selectedsugars (sucrose, rhamnose, galactose, lactose, fructose, -methyl-D-glucoside,xylose, mannose, arabinose, maltose, sorbose and glucose) evokedneural responses in both GSP and CT nerves. The order of theresponse magnitudes of the GSP nerve to the selected sugarswas similar to that of the CT nerve but the absolute magnitudesof the GSP nerve were greater.     

The effects of amiloride on the labellar taste receptor cells of the fleshfly Boettcherisca peregrina

Amiloride is known to inhibit the taste response of vertebrates to salt by blocking the amiloride-sensitive sodium channel. In this study, we investigated electrophysiologically the effect of amiloride on the taste response of the fleshfly Boettcherisca peregrina. When 0.5 mM amiloride was included in taste solutions, the response of the salt receptor cell (salt response) to sodium chloride (NaCl) was not depressed but those of the sugar receptor cell (sugar responses) to sucrose, glucose, fructose, l-valine (l-Val) and l-phenylalanine (l-Phe) were strongly depressed. An inhibitory effect of amiloride on the concentration-response relationship for both sucrose and l-Phe was clearly revealed, but not at high concentrations of sucrose. After pretreatment of a chemosensory seta with 0.15 mM amiloride for 10 min, the salt response to NaCl was not affected. On the other hand, the sugar responses to sucrose, fructose, l-Val and l-Phe were depressed just after amiloride pretreatment. The sugar response to adenosine 5’-diphosphate (ADP) mixed with 0.5 mM amiloride was not depressed, but the response to ADP alone was depressed after amiloride pretreatment. It was therefore observed that amiloride depressed the responses to all stimulants that react with each of the receptor sites of the sugar receptor cell.     

Behavioral and electrophysiological taste responses change after brief or prolonged dietary sodium deprivation

Dietary Na+ deprivation elicits a hormonal response to promote sodium conservation and a behavioral response to increase sodium ingestion. It has generally been accepted that the former occurs within 24 h after sodium deprivation, while the latter is delayed and may not appear until as much as 10 days later. Na+ deprivation of similar duration also decreases the sensitivity of the chorda tympani nerve (CT) to NaCl, suggesting that changes in CT responses are necessary for increased NaCl intake. However, previous work from our laboratory showed that licking responses to NaCl solutions increase after only 2 days of Na+ deprivation, suggesting rapidly occurring changes in response to NaCl taste. The present experiments examined the effects of 2 days of dietary Na+ deprivation on CT responses to NaCl and patterns of NaCl consumption and found that Na+-deficient rats licked significantly more during the first NaCl intake bout compared with control rats. CT responses to NaCl were reduced at all concentrations after brief Na+ deprivation compared with Na+-replete control rats and did not decrease further with prolonged (10 days) dietary Na+ deficiency. Moreover, amiloride, which suppressed CT responses to NaCl by approximately 30% in control rats, had virtually no effect on CT responses in Na+-deprived rats. Thus, 2 days of Na+ deprivation is sufficient to alter patterns of ingestion of concentrated NaCl and to reduce gustatory responses to NaCl. Furthermore, changes in gustatory responses to NaCl during dietary Na+ deprivation may involve the amiloride-sensitive component of the CT.     

Amiloride inhibition on NaCl responses of the chorda tympani nerve in two 129 substrains of mice, 129P3/J and 129X1/SvJ

Amiloride, a sodium channel blocker, is known to suppress NaCl responses of the chorda tympani (CT) nerve in various mammalian species. In mice, the NaCl suppressing effect of amiloride is reported to differ among strains. In C57BL mice, amiloride inhibits NaCl responses to about 50% of control, whereas no such clear suppression was evident in prior studies with 129 mice. However, evidence from behavioral studies is not entirely consistent with this. Recently, it has been found that genetic backgrounds of 129 mice differ within substrains. 129X1/SvJ (formerly 129/SvJ) mice differ from the 129P3/J (formerly 129/J) strain by 25% of sequence length polymorphisms. Therefore, we examined possible substrain difference between 129P3/J and 129X1/SvJ mice in the amiloride sensitivity of electrophysiologically recorded NaCl responses. Amiloride significantly suppressed CT responses to NaCl without affecting responses to KCl both in 129P3/J and 129X1/SvJ mice. However, the magnitude of the amiloride inhibition was significantly larger (approximately 50% of control in response to 0.01-1.0 M NaCl by 100 microM amiloride) in 129X1/SvJ than in 129P3/J mice (approximately 20% of control in response to 0.03-0.3 M NaCl by 100 microM amiloride). Threshold amiloride concentration for suppression of responses to 0.3 M NaCl was 30 microM in 129P3/J mice, which was higher than that in 129X1/SvJ mice (10 microM). In 129X1/SvJ mice, the threshold amiloride concentration eliciting inhibition of NaCl responses and the magnitude of the inhibition were comparable with those in C57BL/6 mice. These results suggest that amiloride sensitivity of NaCl responses differs even among the 129 substrains, 129P3/J and 129 X1/SvJ, and the substrain difference of 129 mice in amiloride sensitivity is as large as that between two inbred strains (129P3/J and C57BL/6).     

Inhibitory effect of gurmarin on palatal taste responses to amino acids in the rat

Gurmarin (10 microg/ml), a protein extracted from Gymnema sylvestre, depressed significantly (40-50%) the phasic taste responses to sugars (sucrose, fructose, lactose, and maltose) and saccharin sodium recorded from the greater superficial petrosal nerve (GSP) innervating palatal taste buds in the rat. However, no significant effect of gurmarin was observed for taste responses to NaCl, HCl, and quinine hydrochloride. Phasic responses to D-amino acids that taste sweet to humans (His, Asn, Phe, Gln) were also depressed, but gurmarin treatment was without significant effect on taste responses to D-Trp and D-Ala, six L-amino acids (His, Asn, Phe, Gln, Trp, and Ala), and two basic amino acid HCl salts (Arg and Lys). With the exception of D-Trp, these inhibitory effects of gurmarin on GSP taste responses were related to the rat's preference for these substances.     

The active ion transport properties of canine lingual epithelia in vitro. Implications for gustatory transduction

The electrophysiological properties of the dorsal and ventral canine lingual epithelium are studied in vitro. The dorsal epithelium contains a special ion transport system activated by mucosal solutions hyperosmotic in NaCl or LiCl. Hyperosmotic KCl is significantly less effective as an activator of this system. The lingual frenulum does not contain the transport system. In the dorsal surface it is characterized by a rapid increase in inward current and can be quantitated as a second component in the time course of either the open-circuit potential or short-circuit current when the mucosal solution is hyperosmotic in NaCl or LiCl. The increased inward current (hyperosmotic response) can be eliminated by amiloride (10(-4) M). The specific location of this transport system in the dorsal surface and the fact that it operates over the concentration range characteristic of mammalian salt taste suggests a possible link to gustatory transduction. This possibility is tested by recording neural responses in the rat to NaCl and KCl over a concentration range including the hyperosmotic. We demonstrate that amiloride specifically blocks the response to NaCl over the hyperosmotic range while affecting the KCl response significantly less. The results suggest that gustatory transduction for NaCl is mediated by Na entry into the taste cells via the same amiloride-sensitive pathway responsible for the hyperosmotic response in vitro. Further studies of the in vitro system give evidence for paracellular as well as transcellular current paths. The transmural current-voltage relations are linear under both symmetrical and asymmetrical conditions. After ouabain treatment under symmetrical conditions, the short-circuit current decays to zero. The increase in resistance, though significant, is small, which suggests a sizeable shunt pathway for current. Flux measurements show that sodium is absorbed under symmetrical conditions. Mucosal solutions hyperosmotic in various sugars also induce an amiloride-sensitive inward current. In summary, this work provides evidence that the sodium taste receptor is most probably a sodium transport system, specifically adapted to the dorsal surface of the tongue. The transport paradigm of gustation also suggests a simple model for electric taste and possible mechanisms for sweet taste.     

Developmental changes in sugar responses of the chorda tympani nerve in preweanling rats

To clarify developmental changes in the gustatory system of the rat, integrated taste responses from the chorda tympani (CT) nerve were recorded and analyzed at different postnatal ages. The response magnitude was calculated relative to the response to the standard, 0.1 M NH4Cl. Even at 1 week of age, the CT responded well to all tested 0.1 M chloride salts (NH4Cl, NaCl, LiCl, KCl, RbCl and CsCl). The responses to 0.1 M NaCl and LiCl increased with increasing age of the rat while response magnitudes to KCl, RbCl and CsCl did not change up to 8 weeks. At 1 week, the integrated response pattern was quite similar to that in adult rats for NaCl, HCl and quinine hydrochloride (QHCl). The concentration-response functions for NaCl, HCl, QHCl and sucrose at 2 weeks were essentially the same as those at 8 weeks. These results suggest that taste buds in the 2-week-old rat are functionally mature for the detection of the four basic taste stimuli. The relative magnitude of the responses to the various sugars was smaller at 1 week compared to the adult rat and reached a maximum at weeks 3-4, then decreased gradually with age. Among the six sugars, sucrose was the most effective followed by lactose. From weeks 1-4, the magnitude of the integrated taste response to fructose was smaller than that to lactose except at 3 weeks of age. Maltose, galactose and glucose were less potent stimuli than the other sugars tested. The response magnitude to lactose at 4 weeks had decreased compared to that for the other sugars. Taste responses to the sugars in preweanling and adult rats were not cross-adapted by the individual sugars. These results suggest that after 1 week of age during postnatal development in the rat, taste information from the CT rapidly increases in its importance for feeding behavior.     

咸味觉厌恶模型大鼠鼓索神经对味觉刺激的电生理反应特性

目的:探索大鼠咸味觉厌恶建立后外周鼓索神经(CT)对咸味觉及其他味觉刺激的电生理反应特性的改变。方法:将14只SD成年雄性大鼠分为咸味觉厌恶模型组(CTA)和对照组(n=7/group)。实验第1日给予大鼠30min的0.1mol/LNaCl饮食,随后CTA组和对照组大鼠分别腹腔注射2ml0.15mol/LLiCl和同等量生理盐水。在第2、3和4日,测量两组大鼠每天30min内对NaCl和蒸馏水饮用量。于第4日行为学测试后,分别记录CTA组大鼠和对照组大鼠CT对口内给予系列浓度NaCl溶液、0.3mol/LNaCl与0.1mmol/L阿米洛利(一种舌上皮钠通道阻断剂)混合液和其他四种基本味觉刺激溶液的电生理反应。结果:与对照组相比,CTA组大鼠CT对系列浓度NaCl和其他4种基本味觉刺激的电生理反应特性没有发生明显变化(P>0.05);舌上皮钠通道阻断剂阿米洛利强烈抑制CTA大鼠对NaCl的反应(P<0.01)。结论:条件性咸味觉厌恶模型大鼠CT对各种味觉刺激的电生理反应特性没有发生明显改变。     

Transecting the gustatory branches of the facial nerve impairs NH(4)Cl vs. KCl discrimination in rats

Ammonium and potassium chloride share a common taste quality and an amiloride-insensitive route of transduction. An amiloride-sensitive pathway might also be partially activated by these salts, although very few studies have reported effects of amiloride on nonsodium salt perception. This experiment was designed to determine 1) whether rats could discriminate KCl from NH(4)Cl and, if discrimination was evident, whether performance was impaired with 2) amiloride or 3) gustatory nerve transection. Rats were trained to discriminate KCl from NH(4)Cl (n = 8) and NaCl from NH(4)Cl (n = 8). Amiloride (100 microM) impaired NaCl vs. NH(4)Cl but not KCl vs. NH(4)Cl performance, whereas both groups showed significant impairments after transection of the chorda tympani (CT) and greater superficial petrosal (GSP) branches of the facial nerve. This suggests that rats can discriminate between KCl and NH(4)Cl and that this discrimination does not rely on an amiloride-sensitive mechanism but does depend on the CT and/or GSP nerves. This experiment supports the hypothesis that the facial nerve is important for salt taste recognition and discrimination.     

Amiloride alters lick rate responses to NaCl and KCl in rats

The role-of cation channels on taste cell membranes to salttaste sensation was assessed in rats. We measured the numberof licks during multiple 10-s presentations of NaCl and KClconcentrations (0.05, 0.09, 0.16, 0.28, 0.5 M) dissolved ineither water or in 100 µM amiloride, a sodium-channelblocker. The number of licks to water and 0.3 M sucrose wasalso measured. The number of licks to NaCl was significantlylower and the number of licks to KCl was significantly higherwhen these test solutions were dissolved in amiloride than inwater. There were no differences in lick responses to waterand sucrose. These results suggest that amiloride may have alteredthe taste of NaCl and KCl. The results are discussed in relationshipto prior electrophysiological studies characterizing the effectof amiloride in blocking salt responses of the chorda tympaninerve.     

Monosodium glutamate but not linoleic acid differentially activates gustatory neurons in the rat geniculate ganglion

To date, only one study has examined responses to monosodium glutamate (MSG) from gustatory neurons in the rat geniculate ganglion and none to free fatty acids. Accordingly, we recorded single-cell responses from geniculate ganglion gustatory neurons in anesthetized male rats to MSG and linoleic acid (LA), as well as to sucrose, NaCl, citric acid, and quinine hydrochloride. None of the 52 neurons responded to any LA concentration. In contrast, both narrowly tuned groups of gustatory neurons (sucrose specialists and NaCl specialists) responded to MSG, as did 2 of the broadly tuned groups (NaCl generalist(I) and acid generalists). NaCl-generalist(II) neurons responded only to the highest MSG concentration and only at low rates. No neuron type responded best to MSG; rather, responses to 0.1 M MSG were significantly less than those to NaCl for Na(+) -sensitive neurons and to sucrose for sucrose specialists. Interestingly, most Na(+) -sensitive neurons responded to 0.3 M MSG at levels comparable with those to 0.1 M NaCl, whereas sucrose specialists responded to 0.1 M MSG despite being unresponsive to NaCl. These results suggest that the stimulatory effect of MSG involves activation of sweet- or salt-sensitive receptors. We propose that glutamate underlies the MSG response of sucrose specialists, whereas Na(+) -sensitive neurons respond to the sodium cation. For the latter neuron groups, the large glutamate anion may reduce the driving force for sodium through epithelial channels on taste cell membranes. The observed concentration-dependent responses are consistent with this idea, as are cross-adaptation studies using 0.1 M concentrations of MSG and NaCl in subsets of these Na(+) -sensitive neurons.     

Effects of amiloride on gustatory neural responses to salts in the frog.

In frogs, the glossopharyngeal nerve (GL) innervates taste receptors on almost the entire tongue. The mandibular branch (MBF) and palatine branch (PN) of the facial nerve innervate taste receptors on a very small area at the base of the tongue and on the palate, respectively. In the present study, effects of amiloride, an epithelial sodium channel blocker, on the tonic responses of the GL, MBF and PN in frogs to NaCl, LiCl, KCl and CaCl(2) were investigated. In three nerves, amiloride at 0.5 mM, a relatively high concentration, did not affect the responses to 0.15 (concentration just above threshold)-0.5 M NaCl, 0.5 M LiCl and 0.3 M KCl, whereas it almost completely inhibited the response to 1.0 mM CaCl(2). Amiloride may exert an inhibitory action on the response to CaCl(2) by a competitive antagonism between Ca(2+) and a monovalent cation of amiloride, because the response to Ca(2+) is competitively inhibited by other cations such as Na(+) and Mg(2+). The lack of inhibitory effect of amiloride on the responses in the GL, MBF and PN to NaCl suggests that amiloride-sensitive sodium channels in the apical membrane of taste receptor cells are not involved in sodium taste transduction in frogs.     

Capsaicin Modifies Responses of Rat Chorda Tympani Nerve Fibers to NaCl

Single-fiber preparations of the rat chorda tympani (CT) nervewere used to study the mechanism of action of capsaicin on salt-tastetransduction. Capsaicin selectively suppressed the responsesto NaCl of the CT nerve fibers (N-fibers) that are sodium-specific(insensitive or poorly sensitive to potassium). Among the morebroadly responsive, cation-sensitive fibers (E-fibers) thereare two subtypes, both of which responded to capsaicin but indifferent ways (‘enhanced’ type and ‘suppressed’type). In both N- and E-fibers, 5% ethanol (the vehicle forcapsaicin) slightly reduced the response to 100 mM NaCl. Thesuppressive effect of capsaicin on the response of the N-typefibers to 100 mM NaCl was significantly stronger than the effectof 5% ethanol. The suppression lasted for at least 20 s afterthe simultaneous application of 100 p.p.m. capsaicin-100 mMNaCl. These results indicate that 100 p.p.m. capsaicin can modifythe response of CT fibers to NaCl. The observed effect of capsaicinon gustatory fibers could be the net result of opposite suppressiveand enhancing processes in the taste buds cells and excitedintra- or extragemmal trigeminal nerve endings. Chem. Senses22: 249–255, 1997. ^*These authors contributed equally to this study     

Taste Responses in the Nucleus of the Solitary Tract in Saccharin-preferring and Saccharin-averse Rats

A minority of rats consistently reject the taste of sodium saccharinat concentrations that the majority find palatable. We choserats that selected either water (WP), or 0.03 M NaSaccharin(SP) in two-bottle preference tests and monitored single unitresponses to a range of taste qualities in the nucleus of thesolitary tract. WP rats gave significantly greater responsesto Na/Li salts and QHCI. Their responses to sugars were equalto those from SP rats. Total activity to NaSaccharin did notdiffer between the two groups, but its distribution across thethree identified neuron types did. The response was skewed fromone in which sugar (S) and sodium salt (N) participated nearlyequally (SP) to one dominated by the activity of N cells andnearly devoid of an S cell contribution (WP rats). Accordingly,the response profile for NaSaccharin was correlated nearly aswell with those of the sugars (+ 0.60) as with the Na/Li salts(+ 0.73) in SP rats, but was reshaped in WP rats to be nearlyidentical with those of the salts (+ 0.85) and unlike sugars(+ 0.30). In their heightened sensitivity to stimuli that humanscall salty and bitter, and in their rejection of the complextaste of NaSaccharin, WP rats showed many of the characteristicsof human tasters of PTC/PROP. Chem. Senses 21: 147–157,1996.     

Amiloride does not block taste transduction in the mudpuppy, Necturus maculosus

Activity of the glossopharyngeal nerve was recorded with bipolarsilver wire electrodes while taste stimuli were applied to thelingual surface in anesthetized mudpuppies. Taste stimuli wereinjected into a continuous stream of distilled water which wasrunning over the tongue, KCl, CaCl₂ and LiCl₂ at 0.4 M elicitedbrisk responses, as did HCl at 0.2 M and quinine at 6 x 10^–4M. Sucrose, glucose and saccharin did not elicit responses.Twenty amino acids were surveyed for their ability to evokea response at 0.04 M: 1-arginine, 1-valine, 1-phenylalanine,1-tryptophan, 1-tyrosine, 1-glutamic acid, 1-lysine and histidinealways evoked responses, whereas other amino acids either didnot evoke responses or only occasionally evoked responses. Thesupernatants from solutions of minced worms and minnows andPurina Trout Chow were effective taste stimuli. Pre-adaptingthe tongue to Ringer's solution by running a continuous streamof Ringer's solution over it eliminated responses to quinineand decreased responses to NaCl. Pre-adapting the tongue to10^–4 to 10^–3 M amiloride, a potent sodium channelblocker, did not alter the responses to NaCl, LiCl, or othertaste stimuli.     

A psychophysical and electrophysiological analysis of salt taste in Trpv1 null mice

Current evidence suggests salt taste transduction involves at least two mechanisms, one that is amiloride sensitive and appears to use apically located epithelial sodium channels relatively selective for Na(+) and a second that is amiloride insensitive and uses a variant of the transient receptor potential vanilloid receptor 1 (TRPV1) that serves as a nonspecific cation channel. To provide a functional context for these findings, we trained Trpv1 knockout (KO) and wild-type (WT) C57BL/6J mice (n = 9 or 10/group) in a two-response operant discrimination procedure and measured detection thresholds to NaCl and KCl with and without amiloride. The KO and WT mice had similar detection thresholds for NaCl and KCl. Amiloride shifted the NaCl sensitivity curve to the same degree in both groups and had virtually no effect on KCl thresholds. In addition, a more detailed analysis of chorda tympani nerve (CT) responses to NaCl, with and without benzamil (Bz, an amiloride analog) treatment revealed that the tonic portion of the CT response of KO mice to NaCl + Bz was absent, but both KO and WT mice displayed some degree of a phasic response to NaCl with and without Bz. Because these transients constitute the entire CT response to NaCl + Bz in Trpv1 KO mice, it is possible that these signals are sufficient to maintain normal NaCl detectabilty in the behavioral task used here. Additionally, there may be other amiloride-insensitive salt transduction mechanisms in taste receptor fields other than the anterior tongue that maintain normal salt detection performance in the KO mice.     

Amiloride-sensitive NaCl taste responses are associated with genetic variation of ENaC alpha-subunit in mice

An epithelial Na(+) channel (ENaC) is expressed in taste cells and may be involved in the salt taste transduction. ENaC activity is blocked by amiloride, which in several mammalian species also inhibits taste responses to NaCl. In mice, lingual application of amiloride inhibits NaCl responses in the chorda tympani (CT) gustatory nerve much stronger in the C57BL/6 (B6) strain than in the 129P3/J (129) strain. We examined whether this strain difference is related to gene sequence variation or mRNA expression of three ENaC subunits (alpha, beta, gamma). Real-time RT-PCR and in situ hybridization detected no significant strain differences in expression of all three ENaC subunits in fungiform papillae. Sequences of the beta- and gammaENaC subunit genes were also similar in the B6 and 129 strains, but alphaENaC gene had three single nucleotide polymorphisms (SNPs). One of these SNPs resulted in a substitution of arginine in the B6 strain to tryptophan in the 129 strain (R616W) in the alphaENaC protein. To examine association of this SNP with amiloride sensitivity of CT responses to NaCl, we produced F(2) hybrids between B6 and 129 strains. Amiloride inhibited CT responses to NaCl in F(2) hybrids with B6/129 and B6/B6 alphaENaC R616W genotypes stronger than in F(2) hybrids with 129/129 genotype. This suggests that the R616W variation in the alphaENaC subunit affects amiloride sensitivity of the ENaC channel and provides evidence that ENaC is involved in amiloride-sensitive salt taste responses in mice.     

Amiloride-sensitive and amiloride-insensitive responses to NaCl + acid mixtures in hamster chorda tympani nerve

Component signaling in taste mixtures containing both beneficial and dangerous chemicals depends on peripheral processing. Unidirectional mixture suppression of chorda tympani (CT) nerve responses to sucrose by quinine and acid is documented for golden hamsters (Mesocricetus auratus). To investigate mixtures of NaCl and acids, we recorded multifiber responses to 50 mM NaCl, 1 and 3 mM citric acid and acetic acid, 250 μM citric acid, 20 mM acetic acid, and all binary combinations of each acid with NaCl (with and without 30 μM amiloride added). By blocking epithelial Na(+) channels, amiloride treatment separated amiloride-sensitive NaCl-specific responses from amiloride-insensitive electrolyte-generalist responses, which encompass all of the CT response to the acids as well as responses to NaCl. Like CT sucrose responses, the amiloride-sensitive NaCl responses were suppressed by as much as 50% by citric acid (P = 0.001). The amiloride-insensitive electrolyte-generalist responses to NaCl + acid mixtures approximated the sum of NaCl and acid component responses. Thus, although NaCl-specific responses to NaCl were weakened in NaCl-acid mixtures, electrolyte-generalist responses to acid and NaCl, which tastes KCl-like, were transmitted undiminished in intensity to the central nervous system. The 2 distinct CT pathways are consistent with known rodent behavioral discriminations.     

Vasopressin increases frog gustatory neural responses elicited by NaCl and HCl.

1. The effect of arginine vasopressin (AVP) on frog gustatory responses was investigated by recording integrated responses of the whole glossopharyngeal nerve by stimulation of the tongue with tastants. 2. After AVP (100 mUnits/ml) was perfused to the basolateral side of taste cells through the lingual artery, gustatory neural responses for NaCl and hydrochloric acid (HCl) stimuli were greatly enhanced, but the responses for CaCl2, quinine hydrochloride (Q-HCl) and galactose were not affected. 3. Three hours after the onset of AVP perfusion, the responses for NaCl and HCl increased to 260% and 270% of the respective controls. 4. The NaCl response which was insensitive to amiloride during normal saline perfusion became sensitive to amiloride during AVP perfusion. 5. When membrane-permeable 8-bromo-cyclic AMP (8-Br-cAMP, 0.1 mM) was perfused to the basolateral side of taste cells, the responses for NaCl and HCl decreased to 41 and 63% of the respective controls. 6. These results suggest that AVP may regulate the gustatory responses for monovalent salts and acids by a mechanism which is not necessary to activate adenylate cyclase.