Human Salty And Bitter Taste Mechanisms


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I gave this presentation to the Summer Research Committee as a Research Fellow at the UCONN Health Center

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  • Hi, my name is Diana Frank and the study I am currently working on is Human Salty and Bitter Taste Mechanisms. Principle Investigator: Dr. Marion Frank Study Coordinator: Dr. Larry Savoy According to the Grover article, perceived intensity of 1M NaCl was reduced more at CN VII sites (fungiform and palate) than CN IX sites after CHX rinse. Also, post-CHX CN IX sites were rated for quinine as more intense than post-water. Also, the mean intensity ratings after both rinses were higher at CN IX sites. This suggests that CN IX sites (circumvallate and foliate) are more sensitive to taste stimuli. Therefore, in the current study we reduced the concentrations for the CN IX sites to see if we could get more solid data (NaCl and quinine reducing intensity equally for both nerve sites).
  • There are 50-150 taste cells in each taste bud. The only parts of the taste cell exposed to taste stimuli are the microvilli. Taste stimuli that are detected by the microvilli fibers induce action potentials that cause the release of neurotransmitters at synapses at the basal pole of the taste cell with gustatory nerves that send the sensory information to the brain.
  • The regions that are stimulated in my study are located on the fungiform, foliate, circumvallate, and palate, but they can also be found on the pharynx, epiglottis, and upper third of the esophagus.
  • This is a diagram of the tongue and palate (here are the teeth, and here is the throat). This is also the diagram used in the study. On this tip of the tongue are the fungiform papillae (represented by large blue ovals), the foliate papillae (circles, filled), circumvallate papillae (ovals, horizontal stripe), and the palatal area between soft and hard palate (circles, vertical stripe).
  • Will CHX produce a taste for water? WChlorhexidine is a prescription mouthwash used to kill bacteria. According to Grover, et al., Chlorhexidine reduces the intensity of salty and bitter substances, more so for the areas of the mouth innervated by the Facial Nerve (7 th ). We are interested in how exactly CHX exerts its inhibitory effects on salty and bitter tastes (mechanisms) and if it effects only certain taste bud areas innervated by different nerves.
  • In the Grover study, subjects rated taste stimuli on a fixed interval scale. They found that the differences in control and chlorhexidine rinse ratings were larger for sodium chloride at the fungiform and palatal area stimulation sites (facial nerve, CN VII) than at the vallate and foliate areas (GL, CN IX). However, these results might not be conclusive. Control intensity ratings for all taste stimuli were significantly higher for GL sites than facial sites. In view of this fact, it is safe to conclude that the vallate and foliate areas are more sensitive to regional taste stimuli. The authors even noted that the percent of control intensity ratings for both sodium chloride and quinine influenced post-chlorhexidine ratings at GL innervated sites, but did not comment on the issue. It is possible that the vallate and foliate areas remained more sensitive to stimuli even after the chlorhexidine rinse, which could have impacted the differential intensity reductions across the areas associated with the 2 cranial nerves. To strengthen Grover et al’s conclusion that sodium chloride does reduce intensity ratings more at the facial areas after chlorhexidine rinse, I tried to control for such increased sensitivity at the GL areas while replicating the methods and materials used in that experiment as much as possible. Thus, I reduced the concentrations applied to the GL areas to get similar intensity ratings during the control session for both nerve areas so as to have a solid baseline with which to compare the ratings after the Chlorhexidine rinse. I also added water as one of the tastants, both as a control and to see how Chlorhexidine affects a “taste stimulus” that is inherently tasteless.
  • 9 th nerve ratings were higher for each substance.
  • The larger decrement for nacl in 7 region could mean there are different receptors in the 2 nerve regions. Figure 5
  • Jonathan Ryder and I are conducting the same study, 6 subjects each. Subjects were recruited from the staff and students of the University of Connecticut Health Center via broadcast message and flyers asking for volunteers for taste and/or smell studies conducted by myself, Jonathan, and Kelly. Volunteers were screened by the UCHC call center, and then distributed between the three of us. So far, Jonathan and I have tested three subjects each. I have compiled both of our data to show preliminary results. During the first training session, the solutions were identified by taste quality. For the second session, the subject was given the same solutions in a randomized order and asked to identify taste quality and then rate the intensity using a fixed interval scale. Intensity data taken from training session was used to identify substantial differences in taste sensitivity between subjects so as to remove outliers, if necessary.
  • During the first training session, the solutions were identified by taste quality. For the second session, the subject was given the same solutions in a randomized order and asked to identify taste quality and then rate the intensity using ____ scale.
  • Subjects rate how strong the solutions applied to their mouth taste to them and give the taste quality (either by pointing or saying)
  • This is the form used to collect subject intensity ratings.
  • Rinses labeled as ‘special rinses’ TABLE
  • Preliminary Results Show that during the water rinse session, subjects rated the taste stimuli as being similar in intensity across nerve sites. No taste confusion for fungiform for water solution before and after CHX rinse. No taste confusion for sucrose. % correct identification on y-axis Difference between intensity ratings for each stimulus
  • In this figure, the decrement in sodium chloride ratings are larger for 7 th nerve sites after CHX rinse, but the decrement in quinine ratings were similar. Subjects were almost taste blind to quinine for 7 th nerve sites, and by reducing the beginning concentration, assuming a similar decrement, I would like to see if 9 th nerve sites also become taste blind to quinine. In this figure, the larger intensity given for quinine for the water rinse shows no evidence of taste blindness in the 9 th nerve.
  • Both Capsaisin and Menthol are known to be sensory irritants. Capsaisin is traditionally used as an experimental probe to desensitize a class of trigeminal nerves that transmits information about heat and acidity, producing a burning sensation. Menthol, another sensory irritant, was included in the experiment as another possible gustatory stimulus. There is minor evidence that capsaicin and methnol may have gustatory properties. There is minor evidence that both sensory irritants may stimulate the gustatory system. Green and Schullery investigated the possibility that capsaicin and menthol could evoke weak sensations of taste on different parts of the tongue.
  • For experiment one, the authors hypothesized that both menthol and capsaicin would stimulate taste via different gustatory nerves.
  • Figure 1 shows the log-means of the intensity ratings for the four taste qualities, burning and cold that were given in the first rating interval (20 s after application). Individual subject means were converted to logarithms to normalize the data before statistical analysis (Green et al., 1993). For both stimuli there was a clear trend for bitterness to be strongest in the circumvallate region, where it was rated at least ‘ moderate’ in intensity. No other taste qualities were rated significantly stronger than ‘barely detectable’. Cold sensations, which were reported only with menthol, also tended to be higher on the circumvallate papillae, whereas burning was rated stronger for both chemicals in the fungiform region.
  • Figure 4 displays the ratings for the four prototype taste stimuli. Taste responsiveness did not vary appreciably among the three sites. A three-factor (stimulus × site × quality) repeated measures ANOVA indicated that there was a significant main effect of stimulus [ F(3,42) = 5.9, P < 0.0001] as well as interactions between stimulus and quality [ F(9,126) = 45.3, P < 0.0001], and among stimulus, site and quality [ F(18,252) = 2.0, P < 0.05]. Post hoc tests showed that the three-way interaction resulted from differences in the intensities of weak ‘side tastes’ at different sites rather than to differences in the principal taste evoked by each stimulus. Thus unlike the much stronger bitterness of capsaicin and menthol in the circumvallate region, a slight tendency for the bitterness of QHCl to be higher in the same region was not significant.
  • Capsaicin and menthol produced moderate bitterness in the circumvallate region
  • Human Salty And Bitter Taste Mechanisms

    1. 1. Diana Frank 2008 Summer Research Fellowship Principal Investigator: Dr. Marion Frank Study Coordinator: Dr. Larry Savoy
    2. 2. Introduction <ul><li>Taste Cells </li></ul><ul><ul><li>Taste Pore </li></ul></ul><ul><ul><li>Microvilli </li></ul></ul><ul><ul><li>Gustatory afferent nerve </li></ul></ul><ul><li>Taste Mechanisms </li></ul><ul><ul><li>Salty: Na+ passage through Na+ channels </li></ul></ul><ul><ul><li>Sour: H+ passage through Na+ channels or blockage of K+ channels </li></ul></ul><ul><ul><li>Sweet: G protein-coupled processes </li></ul></ul><ul><ul><li>Bitter: G protein-coupled processes or blockage of K+ channels </li></ul></ul>
    3. 3. Taste Bud Regions <ul><li>CN VII-Facial Nerve </li></ul><ul><ul><li>Fungiform: innervated by the Chorda Tympani (CT) branch </li></ul></ul><ul><ul><li>Palate: innervated by the Greater Superficial Petrosal (GSP) branch </li></ul></ul><ul><li>CN IX- Glossopharyngeal (GL) Nerve </li></ul><ul><ul><li>Foliate: innervated by the lingual branch </li></ul></ul><ul><ul><li>Circumvallate Papillae: innervated by the lingual branch </li></ul></ul>
    4. 4. Diagram of tongue and palate showing regions stimulated in the Spatial Taste Test. (Figure modified from Bartoshuk [1989]). Circumvallate Palate Foliate Fungiform
    5. 5. Taste Study <ul><li>Chlorhexidine </li></ul><ul><ul><li>The active ingredient in the prescription mouthwash, Peridex*, to treat Gingivitus </li></ul></ul><ul><ul><li>Affects salty and bitter taste qualities and intensities </li></ul></ul><ul><ul><li>Has a bitter taste </li></ul></ul><ul><li>Why is Chlorhexidine’s effect on taste so interesting? </li></ul>
    6. 6. Regional Specificity of Chlorhexidine Effects on Taste Perception Grover and Frank, 2008 <ul><li>Chlorhexidine reduced the intensity of NaCl at fungiform and palatal area stimulation sites (CN VII) </li></ul><ul><li>Control intensity ratings were significantly higher at foliate and circumvallate sites (CN IX) </li></ul><ul><li>The increased sensitivity of 9 th nerve sites could have affected the results </li></ul>
    7. 8. Hypothesis <ul><li>The decrement in NaCl intensity ratings with CHX rinses would remain larger for CN VII than CN IX regions </li></ul><ul><li>The decrement in quinine intensity ratings with CHX rinses would remain equal for CN VII than CN IX regions </li></ul><ul><li>Lowering the concentrations for CN IX areas would not produce results different from the Grover et al study </li></ul>
    8. 9. Materials and Methods <ul><li>Subjects: 6 subjects (anticipated), aged 18-28 </li></ul><ul><li>Exclusion Criteria: non-smokers, no history of taste and smell disorders, and in general good health </li></ul><ul><li>Consists of a single, 1 hour session </li></ul><ul><li>Subjects are compensated $8 </li></ul>
    9. 10. Materials and Methods <ul><li>2 training trials to familiarize subjects with taste stimuli and experience rating intensities using the 0-9 point, fixed interval scale </li></ul><ul><ul><li>Training solutions: </li></ul></ul><ul><ul><ul><li>0.1M NaCl (Salty), 0.1M Sucrose (Sweet), 3mM Citric Acid (Sour), Water (Tasteless), and 0.1mM Quinine (Bitter) </li></ul></ul></ul><ul><ul><li>1 st trial: solution identity given </li></ul></ul><ul><ul><li>2 nd trial: subject identifies and rates solution intensity </li></ul></ul>
    10. 11. Fixed Interval Scale Taste Qualities
    11. 12. Data Collection
    12. 13. Materials and Methods <ul><li>Subject rinses with a rinse and then given a 5 minute break </li></ul><ul><li>Subject is given a diagram of the areas of the mouth to be tested (show diagram again) </li></ul>
    13. 14. Materials and Methods <ul><li>Two testing sessions </li></ul><ul><ul><li>Test solutions: </li></ul></ul><ul><ul><li>1 st session: 3 - 5mL water rinses </li></ul></ul><ul><ul><li>2 nd session: 3 - 5mL 1.34 mM CHX rinses </li></ul></ul>CN VII CN IX NaCl 1 M 0.32 M Quinine 1 mM 0.32 mM Sucrose 1 M 0.32 M
    14. 15. Materials and Methods <ul><li>Each taste stimulus was sequentially applied to the same areas: fungiform, foliate, circumvallate, and palate </li></ul><ul><li>Before each solution was applied, subject was given directions on how to present mouth (by experimenter demonstration) </li></ul>
    15. 16. Preliminary Results
    16. 18. Preliminary Results NaCl Quinine Sucrose
    17. 19. Related Article <ul><li>Green, B.G. and Schullery, M.T. (2003) Stimulation of Bitterness by Capsaicin and Menthol: Differences Between Lingual Areas Innervated by the Clossopharyngeal and Chorda Tympani Nerves. Chem. Senses 28: 45-55. </li></ul>
    18. 20. Introduction <ul><li>Capsaicin is traditionally used to desensitize a class of trigeminal nerves </li></ul><ul><ul><li>Evokes sensations of heat and acidity-producing a burning sensation </li></ul></ul><ul><li>Menthol is used as an artificial cooling agent </li></ul><ul><li>There is minor evidence that capsaicin and methnol may have gustatory properties </li></ul>
    19. 21. Hypothesis <ul><li>Capsaisin and Menthol would both stimulate taste via different gustatory nerves </li></ul>
    20. 22. Methods and Materials
    21. 23. Results
    22. 24. Results
    23. 25. Conclusions <ul><li>Capsaicin and menthol produced moderate bitterness in the circumvallate region and weak bitterness in the folliate and fungiform regions </li></ul><ul><li>Sensory irritation from Capsaicin was rated significantly higher at the fungiform region </li></ul><ul><li>Menthol coolness was rated higher in the circumvallate region </li></ul>
    24. 26. Acknowledgements <ul><li>Marion Frank </li></ul><ul><li>Thomas Hettinger </li></ul><ul><li>Larry Savoy </li></ul><ul><li>Jonathan Ryder </li></ul><ul><li>Kelly O’Neil </li></ul><ul><li>Lesley Mancini </li></ul><ul><li>Tom Kiely </li></ul><ul><li>Kathy Salomone </li></ul><ul><li>Lisa Burgio </li></ul>