Abstract
Drosophila olfactory receptor neurons are found within specialized sensory hairs on antenna and maxillary palps. The linking of odorant-induced responses to olfactory neuron activities is often accomplished via Single Sensillum Recordings (SSR), in which an electrode inserted into a single sensory hair records the neuronal activities of all the neurons housed in that sensillum. The identification of the recorded sensillum requires matching the neuronal responses with known odor-response profiles. To record from specific sensilla, or to systematically screen all sensillar types, requires repetitive and semi-random SSR experiments. Here, we validate an approach in which the GAL4/UAS binary expression system is used for targeting specific sensilla for recordings. We take advantage of available OrX-Gal4 lines, in combination with recently generated strong membrane targeted GFP reporters, to guide electrophysiological recordings to GFP-labeled sensilla. We validate a full set of reagents that can be used to rapidly screen the odor-response profiles of all basiconic, intermediate, and trichoid sensilla. Fluorescence-guided SSR further revealed that two antennal trichoid sensilla types should be re-classified as intermediate sensilla. This approach provides a simple and practical addition to a proven method for investigating olfactory neurons, and can be extended by the addition of UAS-geneX effectors for gain-of-function or loss-of-function studies.
Highlights
Drosophila olfactory receptor neurons on the third antennal segments and maxillary palps are housed in specialized porous sensory hairs called sensilla
During our validation of Fluorescence-guided Single Sensillum Recording (FgSSR), we found that some olfactory receptor neurons (ORNs) previously classified as “trichoid” [3] were not housed in what appeared to be trichoid sensilla
With Differential Interference Contrast (DIC) combined with confocal images as the measurement of sensillar lengths (Fig 4A–4E), we found that these other sensilla were significantly shorter than trichoid sensilla, ranging from 10.38 ± 0.17μm for at2 and 8.49 ± 0.17 μm for at3 (Fig 4F and 4G)
Summary
Drosophila olfactory receptor neurons on the third antennal segments and maxillary palps are housed in specialized porous sensory hairs called sensilla. There are ~1200 ORNs in each antenna, housed in the four sensillar categories: basiconic (ab1-ab10), trichoid (at1-at4), intermediate (ai1), and coeloconic (ac1-ac4) sensilla [3]. The maxillary palps contain an order of magnitude fewer ORNs (~120) and all of the ORNs are housed in basiconic sensilla (pb1-pb). In the single sensillum recordings (SSR) technique, a recording electrode is inserted into the base of the sensillum [4]. This allows for extracellular-field potential measurements of action potentials generated by all the ORNs within a single sensillum, and provides a quantitative method to investigate olfactory responses to stimuli
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