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The Journal of Experimental Biology 204, 3483-3495 (2001)
© 2001 The Company of Biologists Limited

Dual ecdysteroid action on the epitracheal glands and central nervous system preceding ecdysis of Manduca sexta

Inka Zitnanová1,2, Michael E. Adams2 and Dusan Zitnan2,3,*

1 Institute of Medical Chemistry and Biochemistry, School of Medicine, University of Komensky, Sasinkova 1, 81108 Bratislava, Slovakia,
2 Departments of Entomology and Neuroscience, 5419 Boyce Hall, University of California, Riverside, CA 92521, USA and
3 Institute of Zoology, Slovak Academy of Sciences, Dúbravská Cesta 9, 84206 Bratislava, Slovakia

*Author for correspondence (e-mail: uzaedus{at}savba.sk)

Accepted July 13, 2001

Initiation of the ecdysis behavioural sequence in insects requires activation of the central nervous system (CNS) by pre-ecdysis-triggering hormone (PETH) and ecdysis-triggering hormone (ETH), which are released from the Inka cells of the epitracheal glands. Here, we show that the developmental events preceding larval and pupal ecdysis of Manduca sexta involve a dual action of ecdysteroids on the epitracheal glands and CNS. The low steroid levels in freshly ecdysed and feeding larvae are associated with small-sized epitracheal glands, reduced peptide production in Inka cells and insensitivity of the CNS to ETH. The elevated ecdysteroid levels before each ecdysis lead to a dramatic enlargement of Inka cells and increased production of peptide hormones and their precursors. As blood ecdysteroids reach peak levels, the CNS becomes responsive to Inka cell peptides. These effects of natural ecdysteroid pulses can be experimentally induced by injection of 20-hydroxyecdysone or the ecdysteroid agonist tebufenozide (RH-5992) into ecdysed larvae, thus stimulating peptide production in Inka cells and inducing CNS sensitivity to ETH. A direct steroid action on the CNS is demonstrated by subsequent treatment of isolated nerve cords from ecdysed larvae with 20-hydroxyecdysone and ETH, which results in pre-ecdysis or ecdysis bursts. Our data show that ecdysteroid-induced transcriptional activity in both the epitracheal glands and the CNS are necessary events for the initiation of the ecdysis behavioural sequence.

Key words: Inka cell, pre-ecdysis-triggering hormone, ecdysis-triggering hormone, ecdysteroid, hydrazine, behaviour, Manduca sexta.




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© The Company of Biologists Ltd 2001