Odorant responsiveness of embryonic mouse olfactory sensory neurons expressing the odorant receptors S 1 or MOR 23

The mammalian olfactory system has developed some functionality by the time of birth. There is behavioral and limited electrophysiological evidence for prenatal olfaction in various mammalian species. However, there have been no reports, in any mammalian species, of recordings from prenatal olfactory sensory neurons ( OSN s) that express a given odorant receptor ( OR ) gene. Here we have performed patch‐clamp recordings from mouse OSN s that express the OR gene S1 or MOR23 , using the odorous ligands 2‐phenylethyl alcohol or lyral, respectively. We found that, out of a combined total of 20 OSN s from embryos of these two strains at embryonic day ( E )16.5 or later, all responded to a cognate odorous ligand. By contrast, none of six OSN s responded to the ligand at E 14.5 or E 15.5. The kinetics of the odorant‐evoked electrophysiological responses of prenatal OSN s are similar to those of postnatal OSN s. The S 1 and MOR 23 glomeruli in the olfactory bulb are formed postnatally, but the axon terminals of OSN s expressing these OR genes may be synaptically active in the olfactory bulb at embryonic stages. The upper limit of the acquisition of odorant responsiveness for S1 and MOR 23 OSN s at E 16.5 is consistent with the developmental expression patterns of components of the olfactory signaling pathway.