Monosynaptic excitory postsynaptic potentials in thoracic motoneurons under reticulospinal influences

We studied synaptic processes in motoneurons of thoracic segments (T_IX-T_XI) evoked by stimulation of the medial area of the giant-cell reticular nucleus in decerebrated cats. Monosynaptic EPSP were recorded in the majority of investigated motoneurons upon activation of the most rapidly conducting reticulospinal fibers. In some cells, such monosynaptic EPSP were accompanied by late EPSP or IPSP. Amplitude of monosynaptic EPSP attained 5 mV, but this value usually was insufficient for development of an action potential. Upon summation of single monosynaptic EPSP, the membrane potential reached the critical level and an action potential arose in the motoneuron. The efficiency of summary processes evoked by stimulation of the reticular formation exceeded the intensity of synaptic processes that arise in thoracic motoneurons on stimulating the nucleus of Deiters. Functional characteristics of reticular and vestibular monosynaptic EPSP are discussed in the work.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 243–252, November–December, 1969.