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The sweet taste quality is linked to a cluster of taste fibers in primates: lactisole diminishes preference and responses to sweet in S fibers (sweet best) chorda tympani fibers of M. fascicularis monkey.

Wang Y, Danilova V, Cragin T, Roberts TW, Koposov A, Hellekant G - BMC Physiol. (2009)

Bottom Line: The addition of lactisole significantly diminished the preference for all sweeteners but had no effect on the intake of non-sweet compounds or the intake of water.It had no effect on the responses to any other stimuli in all other taste fibers.The absence of the effect of lactisole on the faint responses in some S fibers to other stimuli as well as the responses to sweet and non-sweet stimuli in non-S fibers suggest that these responses originate from other taste receptors.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physiology and Pharmacology, Medical School, University of Minnesota-Duluth, 1035 University Dr, Duluth, MN 55812, USA. yiwenwang@gmail.com

ABSTRACT

Background: Psychophysically, sweet and bitter have long been considered separate taste qualities, evident already to the newborn human. The identification of different receptors for sweet and bitter located on separate cells of the taste buds substantiated this separation. However, this finding leads to the next question: is bitter and sweet also kept separated in the next link from the taste buds, the fibers of the taste nerves? Previous studies in non-human primates, P. troglodytes, C. aethiops, M. mulatta, M. fascicularis and C. jacchus, suggest that the sweet and bitter taste qualities are linked to specific groups of fibers called S and Q fibers. In this study we apply a new sweet taste modifier, lactisole, commercially available as a suppressor of the sweetness of sugars on the human tongue, to test our hypothesis that sweet taste is conveyed in S fibers.

Results: We first ascertained that lactisole exerted similar suppression of sweetness in M. fascicularis, as reported in humans, by recording their preference of sweeteners and non- sweeteners with and without lactisole in two-bottle tests. The addition of lactisole significantly diminished the preference for all sweeteners but had no effect on the intake of non-sweet compounds or the intake of water. We then recorded the response to the same taste stimuli in 40 single chorda tympani nerve fibers. Comparison between single fiber nerve responses to stimuli with and without lactisole showed that lactisole only suppressed the responses to sweeteners in S fibers. It had no effect on the responses to any other stimuli in all other taste fibers.

Conclusion: In M. fascicularis, lactisole diminishes the attractiveness of compounds, which taste sweet to humans. This behavior is linked to activity of fibers in the S-cluster. Assuming that lactisole blocks the T1R3 monomer of the sweet taste receptor T1R2/R3, these results present further support for the hypothesis that S fibers convey taste from T1R2/R3 receptors, while the impulse activity in non-S fibers originates from other kinds of receptors. The absence of the effect of lactisole on the faint responses in some S fibers to other stimuli as well as the responses to sweet and non-sweet stimuli in non-S fibers suggest that these responses originate from other taste receptors.

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An overview of the response profiles of 40 single CT taste fibers with the use of a topographical method. The area of the dots represents impulse activity per sec over 5 sec of stimulation. Absence of mark shows that data are missing. The stimuli were arranged along the x-axis in order of salty, sour, bitter and sweet and along the y-axis in groups: NaCl (N fibers), acids (H fibers), bitter (Q fibers) and sucrose best fibers (S fibers). Every second column showed the response to the sweetener with lactisole added.
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Figure 2: An overview of the response profiles of 40 single CT taste fibers with the use of a topographical method. The area of the dots represents impulse activity per sec over 5 sec of stimulation. Absence of mark shows that data are missing. The stimuli were arranged along the x-axis in order of salty, sour, bitter and sweet and along the y-axis in groups: NaCl (N fibers), acids (H fibers), bitter (Q fibers) and sucrose best fibers (S fibers). Every second column showed the response to the sweetener with lactisole added.

Mentions: Figure 2 presents an overview of the response in each individual fiber with its identity along the vertical axis and stimulus listed along the horizontal. The stimuli were arranged along the X axis in order of salty, umami (MSG and MSG with GMP), sour, bitter and sweet, and the fibers along the Y axis in groups of NaCl- (N cluster), MSG-, citric acid- (H cluster), QHCl- (Q cluster) and sucrose-best (S cluster) as shown in Figure 3. The area of each dot in Figure 2 represents the impulse activity over the first 5 sec of stimulation minus spontaneous activity before each stimulation. Absence of a dot shows that data are missing. Every second column shows the response to the tastant mixed with 1.25 mM lactisole.


The sweet taste quality is linked to a cluster of taste fibers in primates: lactisole diminishes preference and responses to sweet in S fibers (sweet best) chorda tympani fibers of M. fascicularis monkey.

Wang Y, Danilova V, Cragin T, Roberts TW, Koposov A, Hellekant G - BMC Physiol. (2009)

An overview of the response profiles of 40 single CT taste fibers with the use of a topographical method. The area of the dots represents impulse activity per sec over 5 sec of stimulation. Absence of mark shows that data are missing. The stimuli were arranged along the x-axis in order of salty, sour, bitter and sweet and along the y-axis in groups: NaCl (N fibers), acids (H fibers), bitter (Q fibers) and sucrose best fibers (S fibers). Every second column showed the response to the sweetener with lactisole added.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2662785&req=5

Figure 2: An overview of the response profiles of 40 single CT taste fibers with the use of a topographical method. The area of the dots represents impulse activity per sec over 5 sec of stimulation. Absence of mark shows that data are missing. The stimuli were arranged along the x-axis in order of salty, sour, bitter and sweet and along the y-axis in groups: NaCl (N fibers), acids (H fibers), bitter (Q fibers) and sucrose best fibers (S fibers). Every second column showed the response to the sweetener with lactisole added.
Mentions: Figure 2 presents an overview of the response in each individual fiber with its identity along the vertical axis and stimulus listed along the horizontal. The stimuli were arranged along the X axis in order of salty, umami (MSG and MSG with GMP), sour, bitter and sweet, and the fibers along the Y axis in groups of NaCl- (N cluster), MSG-, citric acid- (H cluster), QHCl- (Q cluster) and sucrose-best (S cluster) as shown in Figure 3. The area of each dot in Figure 2 represents the impulse activity over the first 5 sec of stimulation minus spontaneous activity before each stimulation. Absence of a dot shows that data are missing. Every second column shows the response to the tastant mixed with 1.25 mM lactisole.

Bottom Line: The addition of lactisole significantly diminished the preference for all sweeteners but had no effect on the intake of non-sweet compounds or the intake of water.It had no effect on the responses to any other stimuli in all other taste fibers.The absence of the effect of lactisole on the faint responses in some S fibers to other stimuli as well as the responses to sweet and non-sweet stimuli in non-S fibers suggest that these responses originate from other taste receptors.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physiology and Pharmacology, Medical School, University of Minnesota-Duluth, 1035 University Dr, Duluth, MN 55812, USA. yiwenwang@gmail.com

ABSTRACT

Background: Psychophysically, sweet and bitter have long been considered separate taste qualities, evident already to the newborn human. The identification of different receptors for sweet and bitter located on separate cells of the taste buds substantiated this separation. However, this finding leads to the next question: is bitter and sweet also kept separated in the next link from the taste buds, the fibers of the taste nerves? Previous studies in non-human primates, P. troglodytes, C. aethiops, M. mulatta, M. fascicularis and C. jacchus, suggest that the sweet and bitter taste qualities are linked to specific groups of fibers called S and Q fibers. In this study we apply a new sweet taste modifier, lactisole, commercially available as a suppressor of the sweetness of sugars on the human tongue, to test our hypothesis that sweet taste is conveyed in S fibers.

Results: We first ascertained that lactisole exerted similar suppression of sweetness in M. fascicularis, as reported in humans, by recording their preference of sweeteners and non- sweeteners with and without lactisole in two-bottle tests. The addition of lactisole significantly diminished the preference for all sweeteners but had no effect on the intake of non-sweet compounds or the intake of water. We then recorded the response to the same taste stimuli in 40 single chorda tympani nerve fibers. Comparison between single fiber nerve responses to stimuli with and without lactisole showed that lactisole only suppressed the responses to sweeteners in S fibers. It had no effect on the responses to any other stimuli in all other taste fibers.

Conclusion: In M. fascicularis, lactisole diminishes the attractiveness of compounds, which taste sweet to humans. This behavior is linked to activity of fibers in the S-cluster. Assuming that lactisole blocks the T1R3 monomer of the sweet taste receptor T1R2/R3, these results present further support for the hypothesis that S fibers convey taste from T1R2/R3 receptors, while the impulse activity in non-S fibers originates from other kinds of receptors. The absence of the effect of lactisole on the faint responses in some S fibers to other stimuli as well as the responses to sweet and non-sweet stimuli in non-S fibers suggest that these responses originate from other taste receptors.

Show MeSH
Related in: MedlinePlus