Alpha and gamma fiber responses to peripheral nerve and reticular formation stimulation.

Abstract

Recordings were made from single alpha and gamma fibers of the ventral rootlets of anesthetized cats. Most of the gamma fibers were spontaneously active but alpha fibers were not. Both types of fiber were activated by skin and muscle nerve stimulation. In a few cases monosynaptic gamma fiber reflexes were seen but for the most part latencies indicated polysynaptic gamma reflex circuits. Silent gamma as well as alpha fibers were reflexly activated but a single reticular formation stimulation was not found to excite silent gamma fibers nor to have a facilitatory action other than on alpha motoneurons. Repetitive reticular formation stimulation temporarily augmented repetitive firing of some gamma fibers but eventually produced a long-lasting silent period. Single pulse stimuli of the reticular formation and afferent nerves likewise produced a silent period regardless of whether or not an initial excitatory action had occurred. Silent periods persisted for a longer time than did the excitation responses although those created by reticular formation stimulation did not invariably inhibit reflex excitation of gamma neurons. Gamma fibers appeared to be more readily affected than were alpha units; stronger afferent nerve or reticular formation stimuli were required to excite or inhibit alpha motoneurons. The gamma motoneurons possessed a functional similarity to interneurons.