Dose-dependent responses of olfactory receptor neurons housed in antennal olfactory peg sensilla of Cimex lectularius. (A, B) Extracellular recordings of olfactory receptor neurons housed in (a) smooth- and (b) grooved-peg sensilla reveal dose-dependent responses to (E)-2-hexenal (black squares), (E)-2-octenal (grey squares), 4-oxo-(E)-2-hexenal (black triangles) and 4-oxo-(E)-2-octenal (grey triangles). The points represent an average over six to 26 replicates and error bars correspond to the standard error of mean. (c) Temporal response characteristics of olfactory receptor neurons housed in the grooved peg sensilla. Histogram bars represent firing rate changes due to injection of 4-oxo-(E)-2-hexenal (n = 15) and 4-oxo-(E)-2-octenal (n = 6) within a sampling period of 250 ms each. The 500 ms stimulation started 2 s after the beginning of the recording (9th and 10th bins). Asterisks indicate statistically significant responses compared to the control, calculated by Mann Whitney U-test with * P < 0.05, ** P < 0.01 and *** P < 0.001.