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Fig. 9. The shape of both action potential (AP) classes was influenced by the injection of 8-bromo cyclic GMP (8bcGMP). (A) The waveform of large APs was averaged for intervals of 10 min and plotted versus the time of the recording. After the injection of 8bcGMP at t=182 min (transparent wall) both positive and negative phases of the APs increased, indicating an increase in the resistance of the ORN. (B) The voltage levels were color-coded and projected into a plane (C). Before the injection amplitude and time course of the APs remained relatively constant, but 8bcGMP increased the peak-to-peak amplitude and prolonged the negative phase of the APs. (D) Average AP waveforms at the times indicated in C, normalized to the same positive peak amplitude to visualize changes in the time course. When compared to the waveform before the injection (t₀, dotted line), the negative phase was prolonged and slightly reduced in amplitude (arrow) 140 min after the injection (t₁, solid line). Later, the negative phase was shortened again, and 300 min after the injection the time course of the averaged and normalized waveform (t₂, solid line) was identical to the pre-injection waveform (t₀, dotted line). (E) Changes in the waveform of the small APs also showed increases of the peak-to-peak amplitude and a prolongation of the negative phase, but over a different time course. The prolongation of the negative phase reversed after 50 min, while with the large APs the reversal occurred after 150 min. The peak-to-peak amplitude of the small APs was transiently reduced back to the pre-injection level between 70 and 120 min after the injection, while the large APs reached their highest peak-to-peak amplitude at the same time. During the gap in the data (gray areas in C and E), small and large APs could not be distinguished.

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