This proposal is concerned with the organization and functional significance of spinal recurrent inhibition. The emphasis in this proposal is on the by hypothesis that spinal recurrent inhibition acts to desynchronize motoneuron discharge which occurs due to common synaptic drive. This hypothesis will be rested by comparing the incidence and magnitude of motoneuron synchronization during locomotor activity before and after blockage of recurrent inhibition by administration of cholinergic antagonists. Locomotor activity will be evoked by stimulation of the mesencephalic locomotor region, and motoneuron synchronization will be detected and quantified using averages of rectified neurograms. In addition. Patterns of synchronization between different muscle groups will be compared to the distribution of recurrent inhibition to their motor nuclei. Other projects will be performed to investigate the distribution of recurrent inhibition between pairs of motoneurons as a function of the distance separating them and to obtain estimates of the location, magnitude and time course of the conductance of recurrent inhibitory postsynaptic potentials. These projects will be performed to determine the extent of recurrent inhibition from individual motoneurons to other motoneurons in a motoneuron pool, and to determine the potential strength of recurrent inhibition. These studies will be performed using intracellular recording techniques. To determine the functional consequences of varying levels of motoneuron synchronization, the effects of synchronization will be examined on the development of force during isometric and load-moving contractions produced by activity of a small population of motor units. Finally, the effect of recurrent inhibition on the discharge, characteristics of a population of motoneurons will be examined in simulations. The intent of these simulations is to determine the sensitivity of the performance of a motoneuron pool to changes in the strength and distribution of recurrent inhibition and to different sources of central excitatory drive. The projects in this proposal will contribute to understanding of central nervous system and neuromuscular diseases producing tremor and associated motor disorders.
