Identification of two types of synaptic activity in the earthworm nervous system during locomotion

Neuroscience. 2003;121(2):473-8. doi: 10.1016/s0306-4522(03)00492-5.


In the ventral nervous system of the earthworm, a central pattern generator and motor neurons are activated during locomotion. We have previously reported that bath application of octopamine (OA) induces fictive locomotion in the earthworm, and the burst frequency of electrical activity from the first lateral nerves increases with OA concentration. However, there are no reports concerning locomotor neural networks in the earthworm. To identify neural networks involved in fictive locomotion, we optically monitored activity-dependent fluorescent staining in the earthworm ventral nerve cord (VNC) with a styryl dye, N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl)pyridinium dibromide (FM1-43), and a confocal laser scanning microscope. OA induces FM1-43 fluorescence in a dose-dependent manner, with bright fluorescent spots of 3-10 microm in diameter observed to be localized around specified neurons in the segmental ganglion of the VNC. We compared OA dose-response curves for FM1-43 fluorescence with the bursting frequency for fictive locomotion, and found that two types of curves could be identified: one fluorescence response shows a similar dose-dependency to that of the burst frequency, while another response has a higher sensitivity to OA. From these results, we suggest that OA acts as one of the neuromodulators for the earthworm locomotion. This is the first attempt to record motor and inter-neuronal activities simultaneously in a locomotor network in the earthworm.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / drug effects
  • Adrenergic alpha-Agonists / pharmacology
  • Animals
  • Benzenesulfonates / metabolism
  • Dose-Response Relationship, Drug
  • Electrophysiology
  • Fluorescent Dyes
  • Locomotion / drug effects
  • Locomotion / physiology*
  • Microscopy, Confocal
  • Nervous System / drug effects
  • Nervous System Physiological Phenomena*
  • Neurons / drug effects
  • Neurons / physiology
  • Octopamine / pharmacology
  • Oligochaeta
  • Pyridinium Compounds / metabolism
  • Quaternary Ammonium Compounds / metabolism
  • Synapses / classification
  • Synapses / drug effects
  • Synapses / physiology*


  • Adrenergic alpha-Agonists
  • Benzenesulfonates
  • FM1 43
  • Fluorescent Dyes
  • Pyridinium Compounds
  • Quaternary Ammonium Compounds
  • Octopamine
  • WW-781