Tricholine citrate solution

Extracellular single-unit recordings were performed using the tip-recording method [50 (link)]. 3 to 6-day-old flies, which are the appropriate age for taste physiological recording experiments, were briefly ice-anesthetized and their forelegs were removed. We used both male and female flies. A reference electrode containing Drosophila Ringer solution was inserted into the fly through the thorax to the tip of the labellum. To obtain neuronal signals, a labellar taste sensillum was contacted to a recording electrode (10–20 μm diameter) filled with tastant dissolved in 30 mM tricholine citrate solution (Sigma-Aldrich). The recording electrode was connected to TastePROBE (Syntech) with silver wire, and the neuronal signals from taste sensillum were collected by an acquisition controller (Syntech). Signals were amplified (10×), filtered (100–3000 Hz), and sampled at 12 kHz. LabChart 8 software (ADInstrument) was used to analyze neuronal firing rates. The neuronal firing rates were calculated by counting and doubling the number of spikes obtained in the first 500 ms after contact.