Abstract
1. Effects of stimulating upper brain centers upon lumbar spinal alpha motoneurons, especially extensor ones, were analysed with intracellular potential recordings. Recordings from single spinal interneurons and descending tract fibers were also attempted in combination with upper brain stimulations.
2. Single stimulations of the bulbar reticular formation and the fastigial and the dentate nucleus elicited usually two group facilitations upon extensor motoneurons in population, the early and the late group facilitations. The early depolarizing PSP's, corresponding to the early group facilitation, were elicited by the stimulation markedly in phasic motoneurons but scarcely in tonic motoneurons. The late depolarizing PSP's, corresponding to the late group facilitation, were set up prominently in the tonic motoneurons but undistinguishably in the phasic motoneurons. Differences between PSP's of the phasic and the tonic motoneurons were observed also with the stimulation of the pyramidal decussation and the ventral-lateral nucleus of the thalamus. Such differences were rather quantitative and clear only in the extreme cases. Many extensor motoneurons responded to the stimulations in intermediate manner.
3. Response manners of spinal interneurons and descending tract fibers to the upper brain stimulations were, in approximation, classified into three, being the two specific types of PD and RF and the unspecific type. These interneurons and descending tract fibers may modulate and mediate supraspinal influences upon alpha motoneurons differentially and respectively.
