Organization of the larval pre-ecdysis motor pattern in the tobacco hornworm, Manduca sexta.
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 pre-ecdysis 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.
Novicki
A
A
Institute of Neuroscience, University of Oregon, Eugene 97403.
Weeks
J C
JC
D000818:Animals; D002413:Cations, Divalent / Q000494:pharmacology; D004594:Electrophysiology; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000502:physiology; D007301:Insect Hormones / Q000502:physiology; D007395:Interneurons / Q000502:physiology; D007814:Larva / Q000502:physiology; D008675:Metamorphosis, Biological / Q000502:physiology*; D008959:Models, Neurological; D009036:Moths / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology
D002413:Cations, Divalent; D007301:Insect Hormones