Figure 6.

(A) Representative integrated chorda tympani nerve responses in Rgs21^Δ5/Δ5 mice. Indicated taste stimuli were applied for 30 s with 40-s intervening washes. (B) Amplitude of the integrated response for each tastant. Responses were normalized to the responses to 100 mM NH₄Cl, recorded both at the beginning and the end of each tastant series, to control for variability between mice. Responses show the mean ± SEM (n = 7–10 mice for each stimulus). No significant difference was observed between Rgs21^+/+ and Rgs21^Δ5/Δ5 mice for NH₄Cl or the sour tastants HCl and citric acid (unpaired Student’s t tests: P > 0.7 for NH₄Cl, P > 0.9 for sour tastants). Decreased responses of Rgs21^Δ5/Δ5 mice to the umami agonists MSG + IMP, the bitterant quinine, and the sweeteners sucrose and SC45647 were statistically significant (unpaired Student’s t tests: P < 0.03 for MSG + IMP, P < 0.022 for quinine, P < 0.0002 for sucrose, P < 0.002 for SC45647). A trend toward a decreased response to 100 mM NaCl was observed in Rgs21^Δ5/Δ5 mice, but the difference was not statistically significant (P < 0.16; Student’s t test). (C) Plotted are the ratios of the last 10 s to first 10 s of recorded CT nerve response (unpaired Student’s t tests: *P < 0.05; **P < 0.01; ***P < 0.001).