The temporal pattern of neural activity underlying ecdysis behavior is regulated by neuropeptides downstream of Ecdysis Triggering Hormone. John Ewer, Wilson Mena. Centro Interdisciplinario de Neurociencias, Universidad de Valparaiso, Valparaiso, Valparaiso, Chile.

   The insect molt culminates with ecdysis, an innate and vital behavior that is used to shed the remains of the old cuticle. Ecdysis includes several behavioral subroutines that are expressed sequentially to loosen and then shed the old cuticle, then expand and harden the new one. Ecdysis is triggered by the neuropeptide, Ecdysis-Triggering Hormone (ETH), which activates sequentially a number of peptidergic neurons, all of which express the A isoform of the ETH receptor (ETHR). Current models propose that each class of peptidergic neurons then activates or modulates the different phases of the ecdysis motor programs. We examined ecdysis behavior and used the calcium sensitive GFP, GCaMP, to monitor the activation of direct ETH targets, as well as that of motoneurons, which provided an in vitro readout of the resulting behavior. We determined the pattern of GCaMP activation in wild-type animals and also in animals in which ETHR was disabled using RNAi or were mutant for specific neuropeptides. All these manipulations affected ecdysis behavior. However, whereas decreasing ETHR expression using RNAi caused a quantitative reduction in the neural response to ETH, eliminating neuropeptides downstream of ETH caused qualitative changes to the pattern of neural activity induced by this triggering hormone. Thus, unlike the model in which neuropeptides downstream of ETH are the outputs that are sequentially activated to then turn on specific ecdysial subroutines, our results suggest that these neuropeptides configure the networks response to ETH, which then controls the ensuing behaviors. In addition to contributing to the further understanding of how this critical insect behavior is regulated, our results provide insights for understanding how multiple peptides regulate complex physiological and behavioral responses.