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Feedback Signal from Motoneurons Influences a Rhythmic Pattern Generator.

Horacio G Rotstein1, Elisa Schneider2,3, Lidia Szczupak4,3

  • 1Department of Mathematical Sciences, New Jersey Institute of Technology, University Heights, Newark, New Jersey 07102.

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
|August 20, 2017
PubMed
Summary

Motoneurons in leeches actively modulate crawling patterns, not just execute commands. Feedback from elongation motoneurons (CV) to the central pattern generator influences rhythmic activity and duty cycles during locomotion.

Keywords:
Morris–Lecar modelduty cycledye couplingleech crawlingleft-right symmetryphase relationship

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Area of Science:

  • Neuroscience
  • Animal Behavior
  • Computational Biology

Background:

  • Neuronal circuits generate rhythmic movements, traditionally viewed hierarchically with motoneurons as simple outputs.
  • Leech crawling involves rhythmic body elongation and contraction, controlled by specific motoneurons like CV and DE-3.
  • Dopamine can induce rhythmic, antiphasic activity in these motoneurons in isolated ganglia.

Purpose of the Study:

  • To investigate the role of motoneurons in rhythmic motor pattern generation.
  • To determine if motoneurons, specifically CV motoneurons, provide feedback to the central pattern generator (CPG) controlling leech crawling.
  • To explore the modulatory effects of CV motoneuron activity on the crawling rhythm.

Main Methods:

  • Electrophysiological recordings in isolated leech segmental ganglia during fictive crawling.
  • Manipulation of CV motoneuron membrane potential (excitation and hyperpolarization).
  • Monitoring crawling rhythm via DE-3 motoneuron activity.
  • Development of a computational model to simulate feedback mechanisms.

Main Results:

  • CV motoneuron activity dominates the leech crawling cycle, with elongation phases being prominent.
  • Excitation of CV motoneurons resets the DE-3 motoneuron rhythm, indicating feedback to the pattern generator.
  • Hyperpolarization of CV motoneurons accelerated the crawling rhythm, suggesting positive feedback to the elongation CPG.
  • Computational models showed that CV duty cycle depends on feedback strength to the CPG.

Conclusions:

  • Motoneurons are not just output units but actively participate in and modulate rhythmic motor pattern generation.
  • CV motoneurons provide crucial feedback to the leech crawling pattern generator, influencing rhythm and phase relationships.
  • These findings challenge hierarchical models, highlighting the dynamic interaction between motoneurons and central pattern generators in motor control.