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First published online July 20, 2006
Journal of Experimental Biology 209, 2911-2919 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02339

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Neuromodulation of the locust frontal ganglion during the moult: a novel role for insect ecdysis peptides

Y. Zilberstein¹, J. Ewer² and A. Ayali^1,*

¹ Department of Zoology, Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel
² Entomology Department, Cornell University, Ithaca, NY 14853, USA

^* Author for correspondence (e-mail: ayali{at}post.tau.ac.il)

Accepted 8 May 2006

In insects, continuous growth requires the periodic replacement of the exoskeleton during the moult. A moulting insect displays a stereotypical set of behaviours that culminate in the shedding of the old cuticle at ecdysis. Moulting is an intricate process requiring tightly regulated physiological changes and behaviours to allow integration of environmental cues and to ensure the proper timing and sequence of its components. This is under complex hormonal regulation, and is an important point of interaction between endocrine and neural control.

Here, we focus on the locust frontal ganglion (FG), an important player in moulting behaviour, as a previously unexplored target for ecdysis peptides. We show that application of 10^-7 mol l^-1 ecdysis-triggering hormone (ETH) or 10^-7 mol l^-1 and 10^-6 mol l^-1 Pre-ecdysis-triggering hormone (PETH) to an isolated FG preparation caused an increase in bursting frequency in the FG, whereas application of 10^-6 mol l^-1 eclosion hormone (EH) caused an instantaneous, though temporary, total inhibition of all FG rhythmic activity. Crustacean cardioactive peptide (CCAP), an important peptide believed to turn on ecdysis behaviour, caused a dose-dependent increase of FG burst frequency. Our results imply a novel role for this peptide in generating air-swallowing behaviour during the early stages of ecdysis. Furthermore, we show that the modulatory effects of CCAP on the FG motor circuits are dependent on behavioural state and physiological context. Thus, we report that pre-treatment with ETH caused CCAP-induced effects similar to those induced by CCAP alone during pre-ecdysis. Thus, the action of CCAP seems to depend on pre-exposure to ETH, which is thought to be released before CCAP in vivo.

Key words: ecdysis, neuropeptides, neuromodulation, crustacean cardioactive peptide, frontal ganglion, Schistocerca gregaria