Fig. 2.
Confirmation of ephaptic inhibition of sustained ORN responses to constant odorant stimuli. (a) Fruit fly preparation for single sensillum recordings (SSR). We recorded from the ab3 sensillum which contains 2 olfactory receptor neurons: The larger ab3A neuron and the smaller ab3B neuron. Both neurons were simultaneously recorded with 1 tungsten electrode. VTEP, transepithelial potential (scheme of sensillum adapted from (Su et al. 2012)). (b) Top: Time course of the 2 odorant stimuli, methyl hexanoate (MHXE), and 2-heptanone (HEPN), measured with a photoionization detector (PID). MHXE is the cognate odorant for ab3A, and HEPN is the cognate odorant for ab3B. A pulse of MHXE was introduced into a constant background of HEPN, both at high concentrations. The moment the valve opened for the MHXE pulse is marked as Time = 0. The right panels provide a detailed view of the left. Middle: Recorded voltage traces of 3 individual trials from an ab3 sensillum during stimulation with high-concentration odorants. Spikes were automatically detected, with spikes from ab3A marked in blue and those from ab3B marked in orange. Bottom: Instantaneous spike rates of three ab3A (thin blue lines) and ab3B (thin orange lines) along with their means (bold lines). Note that color indicates odorant in the top traces, and their cognate neurons in the lower 2. (c) same as (b) but the 2 odorants were interchanged. (d) Spike rates, recorded during 0.1 to 0.35 s after opening of the valve for the cognate odorant, are shown without (green) and with the incognate odorant (purple). Data from 8 flies for low and 6 flies for high odorant concentrations, each stimulus was repeated 3 times. Bars show mean, and error bars show 95% confidence intervals. Stars show the significance level of paired t-tests (*P < 0.05; **P < 0.005). A color version of this figure appears in the online version of this article.