At the end of each molt, insects shed the old cuticle upon release of ecdysis triggering hormones (ETHs) into the hemolymph. ETH-induced motor patterns corresponding to each step of the ecdysis behavioral sequence can be recorded from the isolated CNS, indicating they are centrally patterned. We found that ETH receptors are expressed in diverse ensembles of central peptidergic neurons. In Manduca sexta, ETHRs occur in neurosecretory L3-4 cells of the abdominal ganglia, which co-express kinins and diuretic hormones. Exposure of the isolated CNS to these peptides results in fictive pre-ecdysis behavior. ETHRs also occur in interneurons IN704 of the abdominal ganglia, which co-express CCAP and MIPs. Bath application of a CCAP/MIP cocktail elicits fictive ecdysis behavior. These results suggest ETH activates peptidergic ensembles, which in turn recruit central pattern generators underlying each successive step of the ecdysis sequence. Do these peptidergic ensembles become active at appropriate times during the ecdysis behavioral sequence? In Drosophila, we used real time imaging of calcium dynamics to monitor activities of ETHR ensembles during fictive behaviors. FMRFamide neurons are activated during pre-ecdysis, EH, CCAP and CCAP/MIP neurons are active prior to and during ecdysis, and activity of CCAP/MIP/bursicon neurons coincides with post-ecdysis. Mechanism(s) through which ETH recruits peptidergic ensembles with appropriate delays is currently under investigation. These findings provide new insights into how innate, centrally patterned behaviors are programmed via peptidergic signaling in the CNS.

Supported by NIH Grant GM 67310 to M.E.A.