Comparison of dose–response relationships for retronasal and orthonasal airflow. A: Odor maps from a single mouse, elicited with increasing concentrations of valeric acid (0.001% – 50% v/v). Retronasal stimuli were presented for 30 s at 300 ml/min (upper panels). Orthonasal stimuli were delivered for 10 s at 150 ml/min (lower panels). White arrow heads indicate glomeruli that exhibited responses at near-threshold concentrations for each airflow pathway. Scale bar = 200 μm. B: Spatial arrangement of activated glomeruli. Open circles show the positions of glomeruli whose responses were increased by 0.5% from resting fluorescence. Among open circles, numbered and colored circles indicate the numbered glomeruli that exhibited either or both retronasal and orthonasal responses at near-threshold concentrations in panel A (retronasal: green, #1 – #4; both: magenta, #5; orthonasal: red, #6 – #9). C: The dose–response relationship to retronasal (left) and orthonasal (right) odor. The response amplitudes were analyzed for glomeruli #1 – #9 that correspond to the number in panel B. Each value is the mean of 3 trials. Note: the apparent hotspot in upper right quadrant of 0.001% v/v retronasal map was a spurious signal from a blood vessel.