Effects of spinal recurrent inhibition on motoneuron short-term synchronization

Biol Cybern. 2007 Jun;96(6):561-75. doi: 10.1007/s00422-007-0151-7. Epub 2007 Apr 13.

Abstract

Spinal recurrent inhibition linking skeleto- motoneurons (alpha-MNs) via Renshaw cells (RCs) has been variously proposed to increase or decrease tendencies toward synchronous discharges between alpha-MNs. This controversy is not easy to settle experimentally in animal or human paradigms because RCs receive, in addition to excitatory input from alpha-MNs, many other modulating influences which may change their mode of operation. Computer simulations help to artificially isolate the recurrent inhibitory circuit and thus to study its effects on alpha-MN synchronization under conditions not achievable in natural experiments. We present here such a study which was designed to specifically test the following hypothesis. Since many alpha-MNs excite any particular Renshaw cell, which in turn inhibits many alpha-MNs, this convergence-divergence pattern establishes a random network whose random discharge patterns inject uncorrelated noise into alpha-MNs, and this noise counteracts any synchronization potentially arising from other sources, e.g., common inputs (Adam et al. in Biol Cybern 29:229-235, 1978). We investigated the short-term synchronization of alpha-MNs with two types of excitatory input signals to alpha-MNs (random and sinusoidally modulated random patterns). The main results showed that, while recurrent inhibitory inputs to different alpha-MNs were indeed different, recurrent inhibition (1) exerted rather small effects on the modulation of alpha-MN discharge, (2) tended to increase the short-term synchronization of alpha-MN discharge, and (3) did not generate secondary peaks in alpha-MN-alpha-MN cross-correlograms associated with alpha-MN rhythmicity.

MeSH terms

  • Action Potentials / physiology
  • Animals
  • Cell Communication / physiology
  • Computer Simulation
  • Humans
  • Interneurons / physiology*
  • Models, Neurological*
  • Motor Neurons / classification
  • Motor Neurons / physiology*
  • Nerve Net / physiology
  • Neural Inhibition / physiology*
  • Periodicity*
  • Spinal Cord / cytology*