[Reflex reactions of the spinal motor center of rats in the early periods following birth].

Reactions of the spinal motor center to tetanic stimulation of afferent nerve fibers in the peripheral nerve or dorsal roots L4--L6, have been investigated in rat pups ageing from 1 to 30 days. EMG was recorded in m. gastrocnemius. Within the first 12 days, in response to a constant stimulation periodic motor activity was observed which in its pattern was similar to the spontaneous cycles in newborn animals. On further development of rats, periodic form of the reaction is abolished, although it may be elicited after decerebration or during fatigue caused by a prolondged tetanization. Within the first week, tetanization of the afferents by the increasing stimuli either does not affect the periodic pattern of the activity, or results in a stepwise increase of the amplitude and duration of separate periods. On further development, gradual dependence of the intensity of the response from the stimulus strength is established, which is associated with functional differentiation of various motor units. The data obtained are discussed in relation to the role of afferent systems in evolution of functions of the central nervous system.