Presentation Details
| Sour suppresses sweet, salty, and bitter: does this begin in the taste bud? Isabella R Fleites, Elizabeth Pereira, Kevin Morales, Stephen D Roper, . University of Miami Miller School of Medicine, Miami, FL, USA |
Abstract
Citric acid is known to suppress sweet, salty, and bitter taste. This likely underlies the culinary wisdom of adding a twist of lemon to balance flavors. One proposed mechanism is that acid-sensing Type III taste bud cells release inhibitory transmitters, including serotonin (5HT), that dampen neighboring taste cell responses. We tested this notion by recording activity of gustatory neurons in the mouse geniculate ganglion. These neurons carry the output from taste buds of the anterior tongue and palate into the hindbrain. Using in vivo Ca²⁺ imaging in mice that express GCaMP6 in sensory neurons, we measured ganglion neuron responses (ΔF/F) to single tastants and to mixtures containing acid. Adding 10 mM citric acid or HCl to sucrose, NaCl, or a bitter mixture significantly reduced ganglion neuron responses for each tastant from control levels (no acid) to 36% (71 neurons, p<0.0001), 63% (26 neurons, p<0.0001), and 26% (27 neurons, p=0.001), respectively. Next, we manipulated 5HT levels in taste buds. Increasing the 5HT content of taste buds by injecting mice with 5‑hydroxytryptophan (5HTP) doubled the 5HT‑immunopositive cells in taste buds (37%→76%, 502 cells, p=.002) and enhanced acid‑mediated inhibition of sucrose responses (36%→7% of control, 58 neurons, p=0.027). Conversely, reducing 5HT by treating mice with parachlorophenylalanine (PCPA) weakened acid inhibition of sucrose responses (36%→61%, 71 neurons, p=.0003). Inexplicably, PCPA did not alter the incidence of 5HT‑immunopositive taste bud cells. These data support the conclusion that acids suppress other taste qualities in part through 5HT‑mediated paracrine inhibition within taste buds. The findings emphasize that some degree of signal processing takes place in these peripheral sensory organs.
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No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author.
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