Fig. 10. Schematic diagram illustrating the interactions between inhibitors and activators of ecdysis behaviours and the role of cGMP levels in neurons regulating these behaviours. (A) Diagram of eclosion hormone (EH) neurons activating (+) both descending inhibitors (DI) from the suboesophageal ganglion or thoracic ganglia and crustacean cardioactive peptide (CCAP)-containing abdominal neurons (Ab). (B) Representational plots of cell excitability of the DI (Bi) and abdominal 27/704 neurons (Ab27/704) (Bii). The excitability of DI neurons declines below threshold (black dashed line) sooner than that of the abdominal 27/704 neurons. Thus, inhibition is lifted and CCAP is released from the abdominal 27/704 neurons. If a phosphodiesterase inhibitor (ZAP) is present (gray curve), cGMP levels are elevated and cell excitability stays high for longer (gray dashed line). Release of CCAP, and subsequently the onset of the ecdysis motor pattern, is therefore delayed.