Figure 5. Dendrograms of taste-evoked responses from geniculate ganglion neurons show clustering into sweet, umami, salty, sour and bitter.

Five prototypic taste solutions were sequentially perfused over the tongue and palate and responses recorded (see Fig. 2d). Two ranges of stimulus concentrations were compared, (a) low (<EC₅₀) and (b) mid-range (∼1.5 to 2 × EC₅₀) as described in the text. Five main clusters are evident: sweet (Su, sucrose); umami (MSG, monosodium glutamate plus IMP); salty (Na, NaCl); sour (CA, citric acid); and bitter (Cyx, cycloheximide; Q, quinine·HCl). Data represent 101 neurons from 12 mice (a), and 155 neurons from 9 mice (b). Taste stimuli, low concentrations (a): 100 mM sucrose; 60 mM NaCl; 3 mM citric acid; mixture of 0.6 μM cycloheximide with 0 or 0.1 mM quinine; 60 mM monosodium glutamate with 1 mM IMP. Taste stimuli, mid-range concentrations (b): 300 mM sucrose; 250 mM NaCl; 10 mM citric acid; mixture of 1 μM cycloheximide with 0.3 mM quinine; 100 mM monosodium glutamate with 1 mM IMP.