Fig. 3. Physiological sensillum types were identified by the response spectra of their olfactory receptor neurones (ORNs) when challenged with volatiles collected from different fruits. (A) An S3A ORN (number 52) stimulated with a volatile collection from passion fruit. A strong response is elicited by ethyl hexanoate [peak 4 in the gas chromatogram (GC)], while smaller responses are elicited by ethyl butyrate (1), ethyl 3-hydroxybutyrate (2), ethyl 3-hydroxyhexanoate (5) and an unidentified compound (3). The physiological response is represented in the histogram displaying the single cell (SC) response over time (spikes s^-1; vertical bar, 25 spikes s^-1; horizontal bar, 1 min). (B) The same neurone challenged with a volatile collection from banana reveals three smaller responses to isoamyl acetate (6), methyl hexanoate (7) and butyl butyrate (8). (C) Two S3A ORNs (numbers 19 and 31) show the repeatability of the responses of a certain ORN type to a particular extract, here a pineapple volatile collection, where ethyl hexanoate (4) is again the major stimulus, while methyl hexanoate (7) elicits a weaker response.

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