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A central pattern generator producing alternative outputs: pattern, strength, and dynamics of premotor synaptic input

Brian J Norris1, Adam L Weaver, Angela Wenning

  • 1Department of Biology, Emory University, Atlanta, GA 30322, USA.

Journal of Neurophysiology
|September 7, 2007
PubMed

Insights

The central pattern generator in leeches coordinates heartbeat using inhibitory connections from premotor interneurons to motor neurons. This network

Area of Science:

  • Neuroscience
  • Computational Biology
  • Physiology

Background:

  • The heartbeat central pattern generator (CPG) in medicinal leeches involves identified and unidentified pairs of segmental heart interneurons.
  • These interneurons form inhibitory synaptic connections with segmental heart motor neurons, influencing motor output.
  • The CPG generates asymmetric coordination patterns, leading to asymmetric heart constriction.

Purpose of the Study:

  • To assess the strength and dynamics of premotor inhibitory synaptic output onto heart motor neurons.
  • To investigate conduction delays within the CPG's coordination modes.
  • To understand how premotor interneurons coordinate segmental motor neurons for functional heartbeat activity.

Main Methods:

  • Extracellular recordings from premotor interneurons in 69 isolated leech nerve cords.
  • Voltage-clamp recordings of ipsilateral segmental motor neurons.
  • Assessment of synaptic connectivity, strengths, and dynamics across coordination modes.

Main Results:

  • Premotor interneurons establish a stereotypical pattern of intersegmental synaptic connectivity, strengths, and dynamics.
  • This pattern remains invariant across different heartbeat coordination modes.
  • Variations in connectivity and dynamics were observed among different leech preparations.

Conclusions:

  • The premotor interneuron network provides a consistent framework for heartbeat coordination.
  • The invariant synaptic properties suggest a robust mechanism for generating rhythmic motor patterns.
  • Temporal activity patterns and spatial synaptic organization of premotor interneurons are crucial for coordinating motor neurons.

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