Fig. 1.

CO₂ activates GC-D⁺ neurons. (A) Targeted recording of GC-D⁺ neurons. GC-D⁺ cells were identified by green fluorescence in both somata and knobs in an olfactory epithelial preparation from GCD-ITG mice (Left). An electrode was guided toward a GC-D⁺ cell (arrows) by using DIC microscopy (Right) for cell-attached extracellular recording. (B) The mean firing rate of a GC-D⁺ cell was dramatically enhanced after CO₂ application in the perfusion solution (arrow). (C) Sample physiological traces showing the firing of the neurons shown in B before (pre), during (CO₂), and after CO₂ application (post). (Scale bar, 2 s.)