Fig. 2. (A-D) Recordings from four different animals showing the transepithelial potential (TEP) and flight activity during injections of octopamine. (A) After a delay of 1-2 min, the TEP oscillation was abolished by an injection of 1500 nmol of octopamine. Even after 15 h, the peak-to-peak amplitude had not recovered (after the axis break). During the gaps, current step protocols and resistance measurements (not shown) were performed. (B) While a control injection of haemolymph Ringer only slightly and transiently reduced the amplitude of the TEP oscillations, 150 nmol of octopamine almost completely suppressed it. At 113 min, the animal exhibited flight activity, marking the beginning of a non-oscillatory interval of approximately 2 h (not shown), after which the oscillation reappeared. (C) After an injection of 20 nmol of octopamine, the amplitude of the oscillation was reduced, but the time course of the TEP remained periodic. Over the course of several hours after the injection, the oscillation gradually regained its original amplitude and regularity. (D) The effect of an injection of 2 nmol of octopamine into an oscillation with a complex waveform could not reliably be distinguished from the effects of control injections. Note the two non-oscillatory intervals without TEP oscillations (12-30 min, 112-138 min) during which flight activity was recorded.