ON THE GUSTATORY EFFECTS OF MIRACULIN AND GYMNEMIC ACID IN THE MONKEY

The summated response from the chorda tympani proper nerve of9 monkeys was recorded during stimulation with solutions ofacetic and citric acids, sodium chloride, quinine sulfate, sucrose,glucose and fructose before and after application of extractsof Synsepalum dulcificum-miraculin- and Gymnema sylvestre-gymnemicacid-on the tongue. It was observed that (a) miraculin enhancedthe response to all acids used (b) miraculin had no significanteffect on the response of the other taste stimuli (c) its effectlasts for more than h and was not removed by rubbing of thetongue (d) gymnemic acid had no significant effect on the responseto any of the stimuli used if miraculin had not been appliedbeforehand (e) gymnemic acid applied after miraculin diminishedthe response to acid, then miraculin enhanced the response toacid again. It was concluded that these electrophysiologicalfindings in monkey parallel the psychophysical observationsin man with regard to the effect of miraculin and gymnemic acidon the response to acids, but that they differ with regard tothe effect of gymnemic acid on the response to sugars. ^* On leave from Dept. of Psychology, University of New Hampshire,U.S.A. ^** On leave from Dept. of Oral Physiology, Osaka University,Japan.     

Interstrain differences in bitter taste responses in mice

Interstrain differences in bitter taste responses were examinedusing inbred strains of mice. Taste responses were recordedfrom the glossopharyngeal and chorda tympani nerves of SWR/J,LP/J, BDP/J and DBA/2J mice. There were large differences inthe magnitude of responses to sucrose octaacetate (SOA) in boththe glossopharyngeal and chorda tympaninerves of SWR/J miceas compared with the other strains of mice. SOA thresholds ofSWR/J mice were 10^–7–^–6 M, whereas they were– 10^–4 M in LP/J mice. On the other hand, no appreciabledifferences were observed in the responses to quinine hydrochlorideand pnenyl-thio-carbamide. The results obtained in the presentexperiments fully explain the findings in behavioral studiesshowing that only SWR/J mice avoid SOA solutions whereas otherstrains do not. ^*Present address: Department of Physiology, Niigata UniversitySchool of Dentistry, Niigata 951, Japan     

Activity in salt taste fibers: peripheral mechanism for mediating changes in salt intake

In order to study the role of peripheral taste sensitivity inmediating increases in salt intake of the rat, the effects ofsodium deprivation and adrenalectomy on chorda tympani nerveresponses to taste stimulation were determined. Sodium deprivationresulted in a reduction in whole nerve responsivity to suprathresholdNaCl concentrations requiring a 10-fold increase in concentrationto elicit the same neural signal of control preparations. Saltintake of sodium deprived rats was predicted by adjusting datain a 10-min intake test from control rats for the reduced neuralsignal and lower salivary sodium levels of sodium deprived rats.The whole nerve responses to LiCl and KCl, as well as to NaCl,were reduced after sodium deprivation and adrenalectomy. Themultifiber response of the chorda tympani is comprised of theindividual responses of NaCl sensitive N-best fibers and HCl/NaClsensitive H-best fibers. After sodium deprivation N-best fibers'responses to suprathreshold concentrations of NaCl were reduced;H-best fibers' responses were not affected by sodium deprivation.Future studies will determine the effect of KCl and other saltson responses of N-best and H-best fibers. Applying Beidler'sbiophysical model to the single fiber data suggests that sodiumdeprivation influences receptor mechanisms for NaCl of N-bestfibers and not H-best fibers. Because repeated NaCl stimulationresulted in increased chorda tympani responsivity to NaCl, wesuggest that sodium deprivation may alter the salt receptorsimply by disuse. Altered receptor sensitivity may be an adaptivemechanism to influence salt consumption by a shift in suprathresholdNaCl intensity.     

Taste responses of the gerbil IXth nerve

Summated taste responses to 12 taste solutions were recordedfrom the IXth (glossopharyngeal) nerve of 38 Mongolian gerbils(Meriones unguiculatus). 0.3 M NH₄Cl was the most effectivestimulant. The relative magnitude of the peak summated responsewas a positively accelerated function of log molar concentration.Absolute thresholds were determined for three chemicals: 0.002M NaCl, 0.0003 M HCl, and 0.002 M sucrose. The relative magnitudesof the responses to quinine, NH₄Cl, and KCl were greater forthe IXth nerve than for the chorda tympani nerve, whereas NaClwas more effective for the chorda tympani. A similar patternis seen in the rat. Acetic and citric acid may bind to commonreceptor sites. NH₄Cl, KCl, and HCl may also have receptor sitesin common.     

On the sense of taste in two Malagasy Primates (Microcebus murinus and Eulemur mongoz)

The relationship between phylogeny and taste is of growing interest.In this study we present recordings from the chorda tympaniproper (CT) nerve of two lemuriforme primates, the lesser mouselemur (Microcebus murinus) and the mongoose lemur (Eulemur mongoz),to an array of taste stimuli which included the sweeteners acesulfame-K,alitame, aspartame, D-glucose, dulcin, monellin, neohesperidindihydrochalcone (NHDHC), saccharin, sodium superaspartame, stevioside,sucralose (TGS), sucrose, suosan, thaumatin and xylitol, aswell as the non–sweet stimuli NaC1, citric acid, tanninand quinine hydrochloride. In M.murinus the effects of the tastemodifiers gymnemic acid and miraculin on the CT response wererecorded. Conditioned taste aversion (CTA) experiments in M.murinusand two-bottle preference (TBP) tests in E.mongoz were alsoconducted. We found that all of the above tastants except thaumatinelicited a CT response in both species. The CTA technique showedthat M.murinus generalized from sucrose to monellin but notto thaumatin. The intake of aspartame, ranging in concentrationfrom 0.1 to 30 mM was measured in E.mongoz with TBP tests. Atno concentration did we see a preference, but there was a significantrejection of 10 and 30 mM aspartame (P     

Inhibition of hamster chorda tympani neural response by copper chloride

Copper chloride was evaluated as a specific inhibitor of neuralresponses to sweet taste stimuli in the goldern hamster (Mesocricetusauratus). The chorda tympani whole-nerve response to taste stimuliwas recorded before and after the tongue was treated for 30s with 0.01, 0.1 and 1 mM CuCl₂. Sweet stimuli [sucrose, fructose,saccharin (calcium salt), D-phenylalanine], which primarilystimulate chorda tympani S fibers, and non-sweet stimuli (NaCl,NH₄Cl) were used. At 0.01 mM, copper chloride had little effect.At 0.10 mM it partially inhibited responses to sucrose and saccharin,but had little effect on responses to D-Phe, fructose, NaCl,NH₄Cl, or a mixture of sucrose plus L-Phe. L-Phe, which hasthe same chelating properties as D-Phe, is not an S-fiber stimulusand likely reduced sucrose inhibiton by chelating the cupricion.Analysis of concentration–response functions revealedthat 0.1 mM copper chloride inhibited the neural response tolow concentrations of sucrose by about 25%, but did not significantlyinhibit high concentrations of surcrose, suggesting competitiveinhibition. In contrast, 0.1 mM CuCl₂ reduced saccharin responsesby 25% throughtout the effective range, suggesting non-competitiveinhibition. Occupation of a saccharide receptor site by coppermay interfere with dimer but not monomer reception and distortthe saccharin receptor site. At 1 mM, CuCl₂ non-competitivelyinhibited responses to sucrose, fructose, saccharin and thenon-sweet NaCl (an N-fiber stimulus), but not NH₄Cl (an H-fiberstimulus). The mechanisms of copper chloride inhibition aredifficult to establish because its effects are weak at concentrationswhere they are specific.     

Inhibition of taste nerve responses to sugars and amino acids by cupric and zinc ions in mice

Inhibition of chorda tympani nerve responses to sugars and aminoacids by CuCl₂ and ZnCl₂ was studied in ddy mice. Responsesto sugars (sucrose, fructose, glucose and maltose) and Na saccharinwere markedly depressed after adaptation of the tongue to 0.1mM CuCl₂ or ZnCl₂. No significant difference in the amount ofinhibition by either salt was found among sugars. The concentration-responsecurve for sucrose was shifted towards the right along the abscissaby treating the tongue with CuCl₂ or ZnCl₂ at 0.1 mM. Reciprocalplots of the concentration-response relationship yielded straightlines, which intersected at a point along the ordinate. Theresults indicate that binding of surcrose as well as other sugarsto sweet receptor molecules is competitively inhibited by Cu²⁺or Zn²⁺. Responses to amino acids (Gly, L-Ala, L-Ser, L-Pro,L-Val and D-Trp) were either slightly or scarcely inhibitedby 0.1 mM CuCl₂ or ZnCl₂. Reciprocal plots of the concentration-responserelationship for Gly before and after adaptation of the tongueto either metal salt failed to yield straight lines. It is proposedthat amino acids would bind to a small proportion of sweet receptormolecules and, in addition, stimulate other receptor mechanismsresponsible for initiating impulses in fibers responsive totaste stimuli other than sucrose.     

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.     

Chorda tympani proper nerve responses to intra-arterial and surface stimulation of the tongue in rhesus monkey and rat

The effect of intra-arterial injection of the proteins monellin,thaumatin and miraculin on the activity of the chorda tympaniproper nerve were recorded in the rhesus monkey (Macaca mulatto)and the rat (Sprague–Dawley). The substances were injectedinto the blood stream to the lingual artery. It was found thatmonellin and thaumatin elicited a response only in the monkeyand not in the rat. Acetylated thaumatin, a tasteless substance,gave no increase of the nerve activity. Miraculin had no effectin either species. NaCl, sucrose and citric acid injected intra-arteriallygave a response in both species. It is concluded that the responsesto intra-arterial injections were caused by stimulation of thetaste buds and not nerve fibers. The results suggest there aretaste receptors also on the parts of the taste cells not facingthe oral cavity. The finding that there was no cross-adaptationbetween intra-arterial and oral application supports this conclusion.     

ON THE GUSTATORY EFFECTS OF GYMNEMIC ACID AND MIRACULIN IN DOG, PIG AND RABBIT

The effects of gymnemic acid, 1 mg/ml, and miraculin, 1 mg/mlor in a tablet (Miralin^TM) on the taste response to sucrose,citric acid, NaCl and quinine have been studied in dog, pigand rabbit. In the dog gymnemic acid suppressed the responseto sucrose for about 5 min in two out of three animals. It alsoaffected the response to NaCl. Miraculin caused a slight short-lastingincrease in the response to acid. No effects of the taste modifierswere observed in the pig. In the rabbit gymnemic acid did notsuppress the response to sucrose while miraculin enhanced theresponse to citric acid in one out of three animals for a fewminutes.     

Chemosensitive responses from the cat epiglottis

Responses were recorded from single and few-fiber preparationsof the cat superior laryngeal nerve during stimulation of theepiglottis with 0.5 M KCl, NH⁴Cl, NaCl, and LiCl; distilledwater, 0.005 M citric acid, 0.01 N HCl; and light touch. Epiglottalreceptive fields were mapped. The order of effective stimuliis KCl > HCl > NH⁴Cl > distilled water > citricacid; NaCl and LiCl are generally not effective. Since (a) similarstimuli elicit responses from the cat chorda tympani nerve duringstimulation of tongue taste buds, and (b) receptive fields ofsuperior laryngeal nerve fibers compare well with a map of epiglottaltaste buds, we conclude that the chemosensitive responses fromthe epiglottis are probably mediated by taste buds.     

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.     

Taste modifiers: parotid reflexes can differ from taste judgements

Sweetness-depressing gymnemic acid (G) and sweetness-inducingmiraculin (M) helped determine the extent to which parotid salivaryresponses match behavioral and neural gustatory responses. Parotidflow rates and tastes intensities were obtained from four subjectsfor four sweeteners (before and after G) and for citric acid(CA) before and after M and G. A mixture of 20 mM CA and 10%sucrose was also tested. Although G depressed sweetness forglucose, sucrose, fructose and aspartame, G generally failedto alter parotid responses or depress post-G ratings for bitterintensity. In fact, G markedly elevated parotid responses forthe acid–sucrose mixture. Residual sweetness after G,detected mainly from the posterior tongue, probably contributedonly partially to sustaining post–G parotid responses.We speculate that side tastes from the sweeteners and oral irritationfrom CA in the mixture contributed to elevated flow rates afterG. Sucrose- and M-induced sweetness generally elevated parotidresponses for 20 mM CA. This result agrees with human chordatympani responses after M but differs for sucrose–acidmixtures in that parotid responses approached the calculatedsum of the components. We speculate that non-gustatory inputsmay also affect sweet–sour responses and advise cautionin relating parotid reflexes only to taste judgements. ¹Present address: Department of Biological Sciences, San JoseState University, San Jose, CA 95192, USA     

Taste Responses to Binary Mixtures of Amino Acids in the sea catfish, Arius felis

In vivo electrophysiological recordings in the sea catfish,Arius felis, showed that the magnitude of the integrated facialtaste responses to binary mixtures of amino acids was predictablewith knowledge obtained from previous cross-adaptation studiesof the relative independence of the respective binding sitesof the component stimuli. Each component from which equal aliquotswere drawn to form the mixtures was adjusted in concentrationto provide for approximately equal reponse magnitudes. The magnitudeof the taste responses to binary mixtures whose component aminoacids showed minimal cross-adaptation was significantly greaterthan that to binary mixtures whose components exhibited considerablecross-reactivity. There was no evidence for mixture suppression.The relative magnitude of the taste responses in the sea catfishto stimulus mixtures is similar to that previously reportedfor olfactory receptor responses in the freshwater channel catfishand chorda tympani taste responses in the hamster. Chem. Senses21: 45–53, 1996.     

Effects of chorda tympani nerve anesthesia on taste responses in the NST

Human clinical and psychophysical observations suggest that the taste system is able to compensate for losses in peripheral nerve input, since patients do not commonly report decrements in whole mouth taste following chorda tympani nerve damage or anesthesia. Indeed, neurophysiological data from the rat nucleus of the solitary tract (NST) suggests that a release of inhibition (disinhibition) may occur centrally following chorda tympani nerve anesthesia. Our purpose was to study this possibility further. We recorded from 59 multi- and single- unit taste-responsive sites in the rat NST before, during and after recovery from chorda tympani nerve anesthesia. During anesthesia, average anterior tongue responses were eliminated but no compensatory increases in palatal or posterior tongue responses were observed. However, six individual sites displayed increased taste responsiveness during anesthesia. The average increase was 32.9%. Therefore, disinhibition of taste responses was observed, but infrequently and to a small degree in the NST At a subset of sites, chorda tympani-mediated responses decreased while greater superficial petrosal-mediated responses remained the same during anesthesia. Since this effect was accompanied by a decrease in spontaneous activity, we propose that taste compensation may result in part by a change in signal-to-noise ratio at a subset of sites.      

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     

Reduction of the suppressive effects of gurmarin on sweet taste responses by addition of beta-cyclodextrin

Cyclodextrins (CDs) have the remarkable ability to form inclusion complexes with a wide variety of guest molecules. In the present study, possible influences of CDs on gurmarin inhibition of the chorda tympani responses to sucrose were examined in C57BL mice. Responses to sucrose were suppressed to approximately 50% of control by treatment of the tongue with 30 micrograms/ml (approximately 7.1 microM) gurmarin. Rinsing the tongue with 15 mM beta-CD after gurmarin gave rapid recovery of the suppressed sucrose responses to approximately 85% of control, whereas 15 mM alpha- or gamma-CD did not. When gurmarin was mixed with beta-CD, the suppressive effects of gurmarin on sucrose responses were largely reduced. No such reduction was observed for mixtures with alpha- and gamma-CD. Gurmarin includes tyrosine and tryptophan residues whose aromatic rings are directed outward and can probably form inclusion complexes with beta-CD. Therefore, the observed reduction of the effects of gurmarin may be due to steric hindrances in inclusion complexes of gurmarin with beta-CD that may interfere with gurmarin binding to sweet taste receptors.      

Selective procaine inhibition of rat chorda tympani responses to electric taste stimulation

1. The lingual treatment of 1% procaine for 10 min selectively suppressed responses of the rat chorda tympani nerve to anodal current applied to the tongue with NaCl in the bathing medium to about 50% of control but the drug produced no significant suppression in responses to chemical taste stimuli. 2. The magnitude of suppression of response to anodal current varied with concentration of procaine and kind of bathing medium for the current stimulation (larger in the order of NaCl greater than KCl greater than CaCl2 greater than HCl). 3. Such ion specificity in procaine suppression suggests that responses of the chorda tympani nerve to anodal current are provoked through the taste cell (not direct action on the taste nerve), and that the receptor mechanisms for anodal current are at least partly different from that for chemical taste stimuli.     

Strain differences among mice in taste psychophysics of sucrose octaacetate

SWR/J inbred mice consistently avoided a 10^–4 M sucroseoctaacetate (SOA) solution in unconditioned two-bottle preferencetests whereas mice of all other inbred strains tested did not(confirming a previous report that used SWR mice of a differentsubline). In a conditioned taste aversion procedure SWR/J miceavoided SOA at concentrations from 10^–3 M to 10^–7M but not at 10^–8 M. Various other inbred strains firstfailed to avoid SOA at concentrations from 10^–3 M to 10^–5M. The major strain difference between SWR and other inbredmice was robust across rearing regimes and when tested withother psychophysical procedures. In single-bottle, free-lickingtests SWR/J mice differed from C57L/J mice in response to SOAfollowing extremely brief exposure to the SOA.The SOA detectionthreshold differences indicated by these psychophysical proceduresare also consistent with differences reported from electrophysiologicalrecordings from glossopharyngeal and chorda tympani nerves inmice of several of the same strains.     

Stimulation of the gerbil's gustatory receptors by methyl glycopyranosides

The gustatory responses from the chorda tympani nerve of theMongolian gerbil Meriones unguiculatus were tested with somemethyl glycopyranosides and inhibitors. Except for one compound,methyl 4,6 dichloro-4,6-dideoxy -D-galactopyranoside, all sugarsstimulated the taste nerve. In our previous research, we foundone of the most effective methyl glycosides was methyl -D-glycopyranoside(MAD-Glu). We also found that methyl glycosides, which differedfrom MAD-Glu by the orientation of a substituent group at C-1,C-2 and C-4, were always less effective taste stimuli. In ourpresent study, we have extended this finding to include theC-3 epimer which was also found to be less effective than MAD-Glu.In a second set of experiments, we looked at deoxy sugars. Incontrast to orientation effects found in the epimers, substitutionof the hydroxyl groups of MAD-Glu by hydrogen atoms (deoxy-sugars)had variable effects. The 3-deoxy and 6-deoxy derivatives werefound to be as effective as MAD-Glu, while the 4-deoxy derivativewas less effective. In addition, substituting chlorine atomsfor the hydroxyl groups appears to have a deleterious effect.For example, the 6-chloro derivative was less effective thanMAD-Glu while the 4,6-dichloro derivative of methyl -D-galactopyranosidedid not stimulate the nerve at all. Finally, in addition tostructure-activity experiments mentioned above, we examinedthe possibility that the sugar taste response may involve otherphysiological factors. In this vein, we found that the sugartransport inhibitors phloretin and phlorhizin and the sodiumchannel blocker, amilonde had no effect on the gerbil's sucroseor glucose taste responses