Fig. 1

Mouse Grueneberg ganglion neurons are activated by bitter tastants structurally related to the olfactory danger signals. a The Grueneberg ganglion (GG) ligands (blue panel) 2-sec-butylthiazoline (SBT), 2,4,5-trimethylthiazoline (TMT), 2,6-dimethylpyrazine (2,6-DMP), 2-propylthietane (2-PT), trimethylene sulphide (TS) and 1,3-dithiolane (1,3-DT) are structurally related to a category of bitter ligands (green panel) composed of, for example, 6-propyl-2-thiouracil (PTU), 6-methyl-2-thiouracil (MTU), 2-ethylpyrazine (2-EP), phenylthiocarbamide (PTC), methylthiocarbamide (MTC) and methimazole (MMI). In the external area are bitter ligands with a chemical structure unrelated to GG ligands: benzamide (BEN), cycloheximide (CYC), vitamin B1 (B1) and famotidine (FAM). b GG coronal slice under Hoffman phase contrast (hv) from an olfactory marker protein-green fluorescent protein (OMP-GFP) mouse where GG neurons can be visualized due to their intrinsic GFP fluorescence (upper panel). Uptake of Fura-2 AM into GG neurons measured at 380 nm in a colour-coded map (lower panel). c Percentage of responding GG neurons (GGn) following perfusion of bitter ligands. PTU (34/34), 2-EP (37/39), MTU (16/18), PTC (13/15), MTC (13/18), BEN (2/18), MMI (0/18), CYC (0/9), B1 (0/18), FAM (0/20). d Representative calcium imaging recordings from GG neurons under perfusion of bitter ligands (1 mM). Control KCl (10 mM) perfusion is systematically performed at the end of experiment. In b, scale bars are 20 μm. In c, n/x = number of cells responding/number of cells tested and viable; obtained in a minimum of three different animals and six tissue slices for each tested cue. In d, fluorescence intensity Fura-2 ratio = F340/F380 is indicated by arbitrary units (a.u.); time is indicated by a horizontal bar