Effects of spinal recurrent inhibition on motoneuron short-term synchronization.
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.
Uchiyama
Takanori
T
Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology, Keio University, 3-14-1, Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan. uchiyama@appi.keio.ac.jp
Windhorst
Uwe
U
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002450:Cell Communication / Q000502:physiology; D003198:Computer Simulation; D006801:Humans; D007395:Interneurons / Q000502:physiology*; D008959:Models, Neurological; D009046:Motor Neurons / Q000145:classification / Q000502:physiology*; D009415:Nerve Net / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology*; D010507:Periodicity; D013116:Spinal Cord / Q000166:cytology*