Fig. 4. Flight initiated by stimulating the tritocerebral commissure giant interneurone (TCG) and its reversible blockade by atropine. (A) Pictogram of the TCG interneurone [after Bacon and Tyrer (Bacon and Tyrer, 1978)] showing the site of electrical stimulation (tcc, posterior tritocerebral commissure) and recording (con, connective; Sog, Pro, Meso, Meta, suboesophageal and the three thoracic ganglia, respectively). (Bi) TCG stimulation (stim; 20, 0.1 ms, 5 V pulses, 200 Hz) evokes bouts of flight muscle activity as shown by electromyograms of right (D_h-r) and left (D_h-l) hindwing depressor muscles. (Ci) Expanded record of the sequence marked in Ai (arrow). Note the cross talk of an elevator muscle (e) revealing rhythmic alternation with depressor muscle activity (d). Asterisks mark stimulus artefacts. (Bii,Cii) Same recordings and animal showing that flight initiation by TCG stimulation is fully blocked during atropine (10 mmol l^–1) superfusion and completely restored after washing with saline (Biii,Ciii). Scale bars, A, 1 mm; B, 10 s; C, 100 ms.