TOPOGRAPHIC PATTERNS OF RESPONSIVENESS TO ODORANTS IN THE RAT OLFACTORY EPITHELIUM

1. Regional differences in odorant-induced responsiveness of the rat o lfactory epithelium were measured via electrophysiological recordings [negative componenent of electro-olfactogram (V (eog(-))) made from th e surface of the olfactory epithelium on the nasal septum]. The nasal septum provided a flat surface from which multiple recordings could be made. 2. V (eog(-))s were recorded from a standardized grid of 16 sit es. This grid of recording sites extended over most of the surface of the olfactory epithelium on the nasal septum. 3. Twenty-one animals we re tested for their responses to seven odorants. The animals were divi ded into three groups, each of which was tested with two different odo rants plus amyl acetate, which provided a comparison between the group s. 4. For each odorant in each animal, topographic maps of relative re sponsiveness were derived to test whether odorants elicited different patterns of responses in the same individual. Topographic maps of resp onsiveness were derived also for the animal groups to test for the gen erality of the form of the maps for different odorants. Response laten cies were also measured for each odorant at each recording site. 5. Al l individuals showed different topographic patterns of responses to th e three test odorants. For most odorants, the location of the most res ponsive site was similar in all animals. In different animals the topo graphic maps for the same odorant were remarkably similar. Topographic maps for the odorants were all different from one another. 6. These r esults are consistent with the hypothesis that odorant quality is enco ded in the differential spatial distribution of receptor cells whose d ifferences in responsiveness appear to be distributed as a continuum a cross the epithelium. The results establish for a mammalian species wh at was previously reported in amphibians. These differences are presum ed to be due to differential expression of odorant receptor proteins. 7. The mean response latency was 32 ms. This period was similar for al l odorants, all animals, and all recording sites and was independent o f V (eog(-)) amplitude. It is concluded that diffusion through the muc us contributed similar to 6 ms to the latency of onset of the response s to these odorants.