Fig. 4. Effect of pymetrozine on the resistance reflex response in the extensor tibiae motor nerve. (A,B) near-threshold concentration. (A) Sample recording from the middle leg's extensor nerve (i) before and (ii) after application of 10^–8 mol l^–1 pymetrozine, during ramp-and-hold stimulation of the fCO (bottom trace; stimulus amplitude 240 µm, or 40°). (B) Peristimulus time histograms (PSTHs) were constructed from the recording sample in A (i) before and (ii,iii) after pymetrozine application (bin width 20 ms; ordinates normalised to number of stimulus presentations, as in all following figures; stimulus, bottom trace). The histogram in Bii was constructed from experiments where a tonic spike discharge was observed after pymetrozine application (N=8), the histogram in Biii from experiments without such tonic discharge (N=2). (C,D) Effect of pymetrozine at higher concentrations (10^–5 mol l^–1); same presentation as in A and B. (C) Sample recording from the middle leg extensor nerve (i) before and (ii) after pymetrozine application (stimulus, bottom trace). (D) PST histograms constructed from the recordings (i) before and (ii) after pymetrozine application (bin width 20 ms; stimulus, bottom trace). (E) Increased stimulus amplitude [360 µm (60°); instead of 240 µm] or (F) increased stimulus velocity (455 deg. s^–1; instead of 45 deg. s^–1) did not restore the feedback response abolished by pymetrozine. Same recordings as in C and D, response before pymetrozine application in Ci and Di.