Figure 8: NaCl-evoked responses in geniculate ganglion neurons do not form distinct groups based on concentration-response relations or amiloride-sensitivity.

(a) NaCl concentration-response relations indicate a wide range of salt sensitivities (N=35 neurons from 6 mice). Plots shown in grey are best-fit sigmoidal curves as described in Fig. 5. Two curves (blue, green) are highlighted to show typical data spread for individual cells. (b) EC₅₀ (black symbols) and Hill slopes (red symbols) obtained from curves in a. There is no apparent grouping of NaCl sensitivities. (c) NaCl-evoked responses vary in their sensitivity to benzamil (a high-potency amiloride derivate). Bars above traces indicate oral stimulation with 250 mM NaCl. Responses from some neurons are blocked by benzamil (1 μM, top, AS, ‘amiloride-sensitive’), others are resistant (bottom, AI, ‘amiloride-insensitive’) and others are only partially blocked (middle). Replicate responses from one representative cell of each type are shown. Calibration, 10 s, 0.4 ΔF/F₀. (d) Concentration-response relations for neurons that were also tested for sensitivity to benzamil (1 μM). Thin black lines indicate responses that were blocked by benzamil (AS), thick grey lines show cells with intermediate sensitivity to benzamil, thick red line is a cell that was insensitive to benzamil (AI). Data are from 12 neurons, 3 mice. (e) Breadth of tuning for neurons that were also tested for benzamil sensitivity. Neurons are arranged in order of increasing sensitivity to benzamil (top 3 lines), that is, % inhibition of responses evoked by 250 mM NaCl without and with 1 μM benzamil added to stimulus solution. There is no apparent segregation of types of salt-sensitive geniculate ganglion neurons (for example, bitter- or sour-responding or breadth of tuning) based on their sensitivity to benzamil. (f) There is no correlation between benzamil sensitivity (x axis, % benzamil block of responses to oral stimulation with 250 mM NaCl) and the neuron’s sensitivity to NaCl stimulation (EC₅₀, black symbols; r=−0.154, Spearman correlation) or with Hill slopes (red symbols; r=0.175, Spearman correlation). N=13 neurons. (g) There is also no correlation between benzamil sensitivity and breadth of tuning (entropy, H) of a neuron (r=−0.330, Spearman correlation; n=24 neurons).