Excitability of spinal neurons and changes resulting from reticular formation stimulation

¹ Department of Physiology, State University of New York, Downstate Medical Center, Brooklyn, New York

The threshold of spinal motoneurons and interneurons to direct stimulation was tested by applying current pulses through an intracellular microelectrode. Membrane potentials and cellular responses were recorded from the same penetrating microelectrode. Reactions of these neurons to orthodromic (afferent nerve stimulation) and antidromic impulses (ventral root stimulation) were determined. Reflex responses were recorded from ventral roots. Reticular formation stimulation resulting in inhibition of reflex action caused an increase in the thresholds of spinal neurons. Facilitory reticular formation action had more of a mixed effect on these neurons but in a considerable percentage thresholds were lowered. The percentage of neurons thus affected varied as did the magnitude of reticular formation effect on reflex action in the spinal segment under study.