REGIONAL DISTRIBUTION OF RAT ELECTROOLFACTOGRAM

1. Electroolfactorgram (EGG) recordings were made from different regio ns of the rat olfactory epithelium to test for spatial distribution of odor responses.2. The EOG recordings showed spatial distribution of t he odor responses in the olfactory epithelium. While some odorants (am yl acetate, anisole, and ethyl butyrate) were more effective in evokin g responses in the dorsal recess near the septum, other odorants (incl uding limonene, cineole, cyclooctane, and hexane) were more effective in the lateral recesses among the turbinate bones. These differences w ere seen as statistically significant odorant-by-position interactions in analysis of variance. 3. Comparisons of recordings along the anter oposterior dimension of the epithelium produced smaller differences be tween the odor responses. These were not significant for 3-mm distance s, but were statistically significant for 5- to 6-mm distances along t he dorsomedial epithelium. 4. The latencies were significantly longer in the lateral recesses than in the medial region. This probably refle cts a more tortuous air path along the turbinate bones to the lateral recesses. 5. The olfactory receptor cells were activated by antidromic stimulation via the nerve layer of the olfactory bulb. The population spikes evoked from the olfactory receptor cells could be suppressed b y prior stimulation with odorants that evoked strong EOG responses. Th is collision of the antidromic action potentials with the odor-evoked action potentials indicates that the same population of receptor cells was activated in both cases. 6. The flow rate and duration of the art ificial sniff were varied systematically in some experiments. The diff erential distribution of response sizes was present at all flow rates and sniff durations. Some odors (e.g., amyl acetate and anisole) produ ced increased responses in the epithelium of the lateral recesses when flow rates or sniff durations were high. We suggest that these change s may reflect the sorptive properties of the nasal membranes on these odors. The responses to other odors (e.g., hexane or limonene) were no t greatly affected by how rate or sniff duration. 7. Taken with existi ng anatomic data, the results indicate that the primary olfactory neur ons that project axons to glomeruli in different parts of the olfactor y bulb are responsive to different odors. The latency differences betw een responses at medial and lateral sites are large enough to be physi ologically significant in the generation of the patterned responses of olfactory bulb neurons.