Gurmarin inhibition of sweet taste responses in mice

The inhibitory effects of gurmarin (a peptide isolated from the leaves of Gymnema sylvestre) on sweet taste responses were studied by examining the chorda tympani nerve responses to various taste substances before and after lingual treatment with gurmarin in C57BL and BALB mice. Treatment with gurmarin at 3 micrograms/ml or more selectively suppressed responses to sucrose without affecting responses to NaCl, HCl, and quinine in C57BL mice, whereas gurmarin at 100 micrograms/ml did not significantly suppress sucrose responses in BALB mice. Responses to various sweet substances in C57BL mice decreased to approximately 45-75% of control after gurmarin, and the suppressive effect of gurmarin was reversible. The profile of the residual responses of C57BL mice to various sweeteners after gurmarin was almost identical to that of BALB mice, which was hardly affected by gurmarin. These results strongly suggest that there are at least two types of sweet taste receptors in mice, gurmarin-sensitive and -insensitive. Probably, C57BL and BALB mice share an identical gurmarin-insensitive receptor, and C57BL mice also have a gurmarin-sensitive receptor.

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Sweet Taste Responses of Mouse Chorda Tympani Neurons: Existence of Gurmarin-Sensitive and -Insensitive Receptor Components

Journal of Neurophysiology ◽

10.1152/jn.1999.81.6.3087 ◽

1999 ◽

Vol 81 (6) ◽

pp. 3087-3091 ◽

Cited By ~ 22

Author(s):

Yuzo Ninomiya ◽

Toshiaki Imoto ◽

Tadataka Sugimura

Keyword(s):

Sweet Taste ◽

The Other ◽

Chorda Tympani ◽

Chorda Tympani Nerve ◽

Inhibitory Effects ◽

Single Fibers ◽

Taste Cells ◽

C57bl Mice ◽

Mouse Taste

Sweet taste responses of mouse chorda tympani neurons: existence of gurmarin-sensitive and -insensitive receptor components. Inhibitory effects of gurmarin (gur) on responses to sucrose and other sweeteners of single fibers of the chorda tympani nerve in C57BL mice were examined. Of 30 single fibers that strongly responded to 0.5 M sucrose but were not or to lesser extent responsive to 0.1 M NaCl, 0.01 M HCl, and 0.02 M quinine HCl (sucrose-best fibers), 16 fibers showed large suppression of responses to sucrose and other sweeteners by lingual treatment with 4.8 μM (∼20 μg/ml) gur (suppressed to 4–52% of control: gur-sensitive fibers), whereas the remaining 14 fibers showed no such gur inhibition (77–106% of control: gur-insensitive fibers). In gur-sensitive fibers, responses to sucrose inhibited by gur recovered to ∼70% of control responses after rinsing the tongue with 15 mM β-cyclodextrin and were almost abolished by further treatment with 2% pronase. In gur-insensitive fibers, sucrose responses were not inhibited by gur, but were largely suppressed by pronase. These results suggest existence of two different receptor components for sweeteners with different susceptibilities to gur in mouse taste cells, one gur sensitive and the other gur insensitive. Taste cells possessing each component may be specifically innervated by a particular type of chorda tympani neurons.

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Lack of gurmarin sensitivity of sweet taste receptors innervated by the glossopharyngeal nerve in C57BL mice

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1997.272.3.r1002 ◽

1997 ◽

Vol 272 (3) ◽

pp. R1002-R1006 ◽

Cited By ~ 9

Author(s):

Y. Ninomiya ◽

M. Inoue ◽

T. Imoto ◽

K. Nakashima

Keyword(s):

Proteolytic Enzyme ◽

Sweet Taste ◽

Glossopharyngeal Nerve ◽

Differential Sensitivity ◽

Taste Receptors ◽

Chorda Tympani ◽

Sweet Taste Receptors ◽

C57bl Mice

Effects of a sweet response inhibitor, gurmarin, on responses of the chorda tympani and glossopharyngeal nerves were studied in the C57BL/KsJ strain of mice. The lingual application of gurmarin at 3.0 microg/ml (approxiamtely 0.7 microM) or more significantly suppressed chorda tympani responses to 0.5 M sucrose, as previously reported. The magnitude of gurmarin inhibition of the chorda tympani responses reached a plateau (approximately 45% of control) at 50 microg/ml (approximately 11.9 microM). In contrast, no such gurmarin inhibition of sucrose responses was observed in the glossopharyngeal nerve even at 100 microg/ml (approximately 23.8 microM). The lingual application of a proteolytic enzyme, pronase, suppressed sucrose responses to <20% of control in both chorda tympani and glossopharyngeal nerves. These results suggest differential sensitivity to gurmarin by sweet taste receptors innervated by the chorda tympani and the glossopharyngeal nerves. The former apparently possess gurmarin sensitivity, whereas most of the latter may be lacking sensitivity.

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Chemospecific deficits in taste detection after selective gustatory deafferentation in rats

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1990.258.3.r820 ◽

1990 ◽

Vol 258 (3) ◽

pp. R820-R826 ◽

Cited By ~ 15

Author(s):

A. C. Spector ◽

G. J. Schwartz ◽

H. J. Grill

Keyword(s):

Detection Threshold ◽

Conditioned Avoidance ◽

Taste Bud ◽

Taste Receptors ◽

Chorda Tympani ◽

Chorda Tympani Nerve ◽

Before And After ◽

The Mean ◽

Taste Detection ◽

Response To Water

Electrophysiological data support the existence of sodium-specific taste receptors that appear to be limited to the anterior tongue. However, previous behavioral findings suggest that bilateral transection of the chorda tympani nerve (CTn) has minimal consequences on NaCl intake and preference. This study employed a conditioned avoidance procedure to measure detection thresholds to NaCl and sucrose both before and after bilateral transection of the CTn. Rats were trained to maintain spout contact in response to water presentations (70 microliters) and to avoid spout contact when a taste solution (70 microliters) was presented. In experiment 1, all rats (n = 3) showed statistically significant impairments in the detectability of NaCl after bilateral section of the CTn. The mean increase in the NaCl detection threshold was 1.41 log units. In contrast, sucrose threshold in these same rats was marginally affected by CTn section (mean increase = 0.22 log units). Experiment 2 (n = 4) replicated the findings of the first experiment. The mean increase in the NaCl detection threshold was 2.23 log units. Sucrose threshold in these rats was, again, only marginally affected by CTn section (mean increase = 0.83 log units). Histological examination of the anterior tongue from the rats in experiment 2 indicated that the CTn transections were complete. These findings reveal that the anterior oral receptive field (innervated by the CTn) containing only 15% of the total taste bud population is critical for the normal detection of NaCl.

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