A functional map in rat olfactory epithelium

Multiple (four or eight) electrode arrays were placed for simultaneous electro-olfactogram (EOG) recordings of responses to a series of odors applied directly to the olfactory epithelium. Three different surfaces of the epithelium were exposed in rats immediately after death by anesthetic overdose. We tested three terpene compounds (carvone, limonene and 1,8-cineole) across the epithelium along the medial surface of the endoturbinate bones. Carvone, a ketone, evoked larger responses dorsally on the epithelium. The largest responses to 1,8-cineole (an ether) were seen in an intermediate-ventral region. The responses to limonene (a hydrocarbon) did not vary greatly across the regions, although they were often larger ventrally. The response distributions deviated from this simple pattern on the caudal part of endoturbinate IV, where the carvone responses were small and the limonene responses were larger. These differences were evident across a substantial concentration range. Similar distributions were seen for these three odors in tests along the dorsal-to-ventral direction across the nasal septum and in the medial-to-lateral direction across the dorsal aspect of one of the endoturbinate bones reaching out into the lateral recess. We argue that the spatial distributions of responses are correlated with the olfactory receptor gene expression zones.