Comparison of the responses of the chorda tympani and glossopharyngeal nerves to taste stimuli in C57BL/6J mice

Abstract

Background: Recent progress in discernment of molecular pathways of taste transduction underscores the need for comprehensive phenotypic information for the understanding of the influence of genetic factors in taste. To obtain information that can be used as a base line for assessment of effects of genetic manipulations in mice taste, we have recorded the whole-nerve integrated responses to a wide array of taste stimuli in the chorda tympani (CT) and glossopharyngeal (NG) nerves, the two major taste nerves from the tongue.

Results: In C57BL/6J mice the responses in the two nerves were not the same. In general sweeteners gave larger responses in the CT than in the NG, while responses to bitter taste in the NG were larger. Thus the CT responses to cyanosuosan, fructose, NC00174, D-phenylalanline and sucrose at all concentrations were significantly larger than in the NG, whereas for acesulfame-K, L-proline, saccharin and SC45647 the differences were not significant. Among bitter compounds amiloride, atropine, cycloheximide, denatonium benzoate, L-phenylalanine, 6-n-propyl-2-thiouracil (PROP) and tetraethyl ammonium chloride (TEA) gave larger responses in the NG, while the responses to brucine, chloroquine, quinacrine, quinine hydrochloride (QHCl), sparteine and strychnine, known to be very bitter to humans, were not significantly larger in the NG than in the CT.

Conclusion: These data provide a comprehensive survey and comparison of the taste sensitivity of the normal C57BL/6J mouse against which the effects of manipulations of its gustatory system can be better assessed.

Figure 1

Summated responses from the chorda tympani and glossopharyngeal nerves during stimulation of the tongue in two C57BL/6J mice. Recordings of the whole CT and NG nerve activity in mice MO01D19 and MO01F22. In both animals the responses were obtained from both the CT and NG nerves. The glossopharyngeal nerve recordings were obtained after the chorda tympani. The horizontal axis shows the time in seconds. The thick bar at the bottom of each recording indicates the time of stimulation. Stimulation time was 20 seconds.

Figure 2

Chorda tympani and glossopharyngeal nerves responses to sweeteners. Comparison of the chorda tympani (open circles, dashed line) and glossopharyngeal nerves (black circles, solid line) integrated responses to sweeteners. Error bars are SE. Asterisks indicate significant (p < 0.05) difference between responses of the two nerves.

Figure 3

Chorda tympani and glossopharyngeal nerves responses to sweeteners. Comparison of the chorda tympani (open circles, dashed line) and glossopharyngeal nerves (black circles, solid line) responses to sweeteners. Maximum amplitude was used as a parameter. Error bars are SE. Asterisks indicate significant (p < 0.05) difference between responses of the two nerves.

Figure 4

Chorda tympani and glossopharyngeal nerves responses to bitter compounds. Comparison of the chorda tympani (open circles, dashed line) and glossopharyngeal nerves (black circles, solid line) integrated responses to bitter stimuli. Error bars are SE. Asterisks indicate significant (p < 0.05) difference between responses of the two nerves.

Figure 5

Chorda tympani and glossopharyngeal nerves responses to bitter compounds. Comparison of the chorda tympani (open circles, dashed line) and glossopharyngeal nerves (black circles, solid line) responses to bitter stimuli. Maximum amplitude was used as a parameter. Error bars are SE. Asterisks indicate significant (p < 0.05) difference between responses of the two nerves.

Figure 6

Chorda tympani and glossopharyngeal nerves responses to salts, acids and umami compounds. Comparison of the chorda tympani (open circles, dashed line) and glossopharyngeal nerves (black circles, solid line) integrated responses to salts and acids. Error bars are SE. Asterisks indicate significant (p < 0.05) difference between responses of the two nerves.

Figure 7

Chorda tympani and glossopharyngeal nerves responses to salts, acids and umami compounds. Comparison of the chorda tympani (open circles, dashed line) and glossopharyngeal nerves (black circles, solid line) responses to salts and acids. Maximum amplitude (B) was used as a parameter. Error bars are SE. Asterisks indicate significant (p < 0.05) difference between responses of the two nerves

Figure 8

Difference between chorda tympani and glossopharyngeal responses. Integrated response was used as a measure of responses. Different taste qualities of stimuli (for humans) are coded by different pattern in the columns and different font in the names. Open columns and italized names indicate salts, umami compounds and acids; cross-hatched, bitter compounds; and black columns and bold font, sweeteners. In cases when several concentrations of a compound were tested the responses were averaged and then subjected to the comparison. Generally, responses to sweeteners were larger in the CT and responses to bitter compounds were larger in the NG.