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Organization of the larval pre-ecdysis motor pattern in the tobacco hornworm, Manduca sexta

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Abstract

The tobacco hornworm, Manduca sexta, undergoes several larval molts before transforming into a pupa and then an adult moth. Each molt culminates in ecdysis, when the old cuticle is shed. Prior to each larval ecdysis, the old cuticle is loosened by pre-ecdysis behavior, which consists of rhythmic compressions that are synchronous along the abdomen and on both body sides, and rhythmic retractions of the abdominal prolegs. Both pre-ecdysis and ecdysis behaviors are triggered by a peptide, eclosion hormone. The aim of the present study was to investigate the neural circuitry underlying larval preecdysis behavior. The pre-ecdysis motor pattern was recorded in isolated nerve cords from eclosion hormone-treated larvae, and the effects of connective transections and ionic manipulations were tested. Our results suggest that the larval pre-ecdysis compression motor pattern is coordinated and maintained by interneurons in the terminal abdominal ganglion that ascend the nerve cord without chemical synaptic relays; these interneurons make bilateral, probably monosynaptic, excitatory connections with identified pre-ecdysis motor neurons throughout the abdominal nerve cord. This model of the organization of the larval pre-ecdysis motor pattern should facilitate identification of the relevant interneurons, allowing future investigation of the neural basis of the developmental weakening of the pre-ecdysis motor pattern that accompanies the larval-pupal transformation.

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Abbreviations

A3, A4...:

abdominal ganglia 3, 4...

AT:

terminal abdominal ganglion

ALE:

anterior lateral external muscle

DN:

dorsal nerve

DNA :

anterior branch of the dorsal nerve

DNL :

lateral branch of the dorsal nerve

DNP :

posterior branch of the dorsal nerve

EH:

eclosion hormone

TP:

tergopleural muscle

VN:

ventral nerve

VNA :

anterior branch of the ventral nerve

VNL :

lateral branch of the ventral nerve

VNP :

posterior branch of the ventral nerve

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Authors and Affiliations

  1. Institute of Neuroscience, University of Oregon, 97403, Eugene, OR, USA

    A. Novicki & J. C. Weeks

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  1. A. Novicki
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  2. J. C. Weeks
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Novicki, A., Weeks, J.C. Organization of the larval pre-ecdysis motor pattern in the tobacco hornworm, Manduca sexta . J Comp Physiol A 173, 151–162 (1993). https://doi.org/10.1007/BF00192974

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