Figure 4. Lateral inhibition does not require synapses.

a, ab3 sensilla in flies expressing TNT in ORNs via the Orco promoter . Neurons were exposed to a 500-ms pulse of the ab3B odorant, 2-heptanone (orange, 10⁻⁴), superimposed on the background ab3A odorant, methyl hexanoate (blue, 10⁻⁷). IN: representative interneuron. Right: ab3A activity during a 500-ms exposure to paraffin oil (PO) or 2-heptanone in the presence of methyl hexanoate. Error bars= S.E.M. *, p<0.05, one-way repeated measures ANOVA, multiple comparison versus control group (PO) with Dunnett’s method (n=12). b, T-maze choice between water and 25% ACV or between air and 0.67% CO₂. CO₂ neurons do not express Or genes. (n=9). c, Severed antennae (n=7). d, Cross-correlation analysis of spontaneous spikes from an ab3 sensillum, showing intervals between ab3A spikes and ab3B spikes, binned in 10 ms increments. Each ab3B spike is used as a reference. Another ab3 sensillum gave similar results. e, Recordings made 15 min after introduction of Cd²⁺ (n=12). f, VUAA1 (1 mM) or vehicle (1% DMSO) was delivered via the recording electrode³⁵. ab3A responses were recorded for 10 s. *** p<0.001, t-test (n=12).