Stereological quantification of olfactory receptor neurons in mice

•No data are available on the total number of olfactory receptor neurons (ORNs).•Stereological analyses were applied for the total quantification of ORNs in mice.•We concluded that the total number of ORNs was approximately 10,000,000.

The total number of olfactory receptor neurons (ORNs) in the mouse main olfactory epithelium (MOE) was estimated using stereological sampling. Noses and skulls of male and female 8-week-old C57BL/6J mice were de-calcified, embedded in paraffin, cut into 10-μm-thick sections serially at 100-μm intervals, and processed for immunohistochemistry for the olfactory marker protein (OMP), a specific marker for ORNs. The number of OMP (+) receptor neurons was measured using an optical fractionator with the Stereo-Investigator software. The mean values of the total number of OMP (+) receptor neurons in the unilateral MOE were 5,140,000 ± 380,000 in males and 5,210,000 ± 380,000 in females, with no significant differences between the sexes. We concluded that the total number of ORNs in the unilateral MOE is approximately 5 × 106 in mice.