Fig. 1

Direct electrical interaction drives lateral inhibition between ORNs. a The sustained response of ab1A and ab1B was cross-inhibited by the transient activation of ab1C. Top: ab1A/B responded (large spikes in trace) to a sustained stimulus of apple cider vinegar (3 × 10⁻³ dilution, v/v in water, long blue bar). A 500-ms pulse of carbon dioxide (CO₂, orange bar above trace) activated ab1C (small spikes). The responses of ab1A and ab1B were inhibited by the CO₂ stimulus (decreased frequency of large spikes). In the average spike responses on the right, the orange trace represents the response of ab1C to CO₂, and the blue trace represents the response of the large-spike neurons. ab1A and ab1B spikes could not be sorted reliably and were grouped. The sustained responses of the large-spike ORNs (blue traces) are indicated in the parentheses (spikes s⁻¹). Line width indicates s.e.m. Bottom: in the CO₂ receptor mutant flies, CO₂ did not activate ab1C or inhibit the sustained response of ab1A/B to vinegar. b Cross-inhibition between electrically coupled ORNs. Top: a tungsten electrode was used to electrically couple two adjacent sensilla: ab3 (distal) and ab1 (proximal). Activation of ab1A/B by a sustained stimulus of vinegar (3×10⁻³ dilution) was inhibited by the excitation of ab3B housed in the electrically coupled sensillum by a pulse of E2-hexenol (10⁻³). Middle: when the same two sensilla were no longer electrically coupled, E2-hexenol ceased to inhibit the sustained response of ab1A/B to vinegar. Bottom: when ab3 sensillum was recorded alone, no cross-inhibition was observed between ab3A and ab3B by the same odor stimuli. c A tungsten electrode was used to electrically couple two adjacent sensilla: ab1 (distal) and ab3 (proximal). The sustained ab3A activity in response to optogenetic activation was inhibited by a pulse of CO₂, which excited ab1C housed in the electrically coupled sensillum. Light stimulation: 470 nm, 2.66 μW mm⁻². Of note, in the bridged configuration, spike amplitudes of the ORNs housed in the distal sensillum are typically smaller than those in the proximal sensillum. n = 9 for all recordings. ORN olfactory receptor neuron