Odorant response of individual sensilla on the Drosophila antenna.

We have documented odor responses of all morphological classes of sensilla on the surface of the Drosophila antenna: sensilla basiconica, sensilla trichodea, and sensilla coeloconica. Both subtypes of s. basiconica, large and small, respond to odors. S. trichodea fall into different functional types. Type 1 appears narrowly tuned, as it responded only to cis-vaccenyl acetate, believed to be a pheromone. Type 2 responded to trans-2-hexenal and 4-methyl cyclohexanol. These two types of s. trichodea are differentially distributed on the antennal surface, and have dramatically different frequencies of spontaneous action potentials. Likewise, there are multiple types of s. coeloconica. One type if broadly tuned, responding most strongly to a test stimulus of butyric acid, but also to a variety of other odors; it is restricted to the dorso-medial portion of the third antennal segment. A second type gave detectable responses only to trans-2-hexenal. These results demonstrate that all classes of sensilla are olfactory, and they reveal the organizational complexity of the Drosophila olfactory system.