Estimation of the projection frequencies of single inhibitory interneurones to motoneurones in the cat spinal cord.

An estimate has been deduced for the percentage of motoneurones in the lumbosacral spinal cord inhibited by single interneurones mediating group I non-reciprocal inhibition. The estimate is derived from data for the percentage of interneurones discharged, and percentage of motoneurones inhibited, by the same group I afferents. These experimental data are compared with theoretical curves for the percentage of motoneurones in which inhibition would be expected following discharges in various numbers of interneurones, for different values of projection frequency. It is estimated that each interneurone projects to less than 5% of target motoneurones.