[The interaction of symmetrical cortical descending influences on lumbar motoneurons]

Postsynaptic potentials (PSPs) of the cat motoneurons elicited by stimulation of contralateral and ipsilateral motor cortex, and their changes during combination of both kinds of stimulation were studied with use of the intracellular recording technique. For elicitation of ipsilateral PSPs, the cortex stimulation of greater intensity was needed as compared with contralateral activation. The ipsilateral synaptic reactions had a longer latency and time of segmental delay than the contralateral ones. Conditioning stimulation of the ipsilateral cortex exerted an inhibitory effect upon contralateral cortically evoked EPSP and IPSP of motoneurons and upon potential recorded at the spinal cord surface. Suppression of conditioned PSPs occurred without changes of their sign or pattern in most cases. The data obtained suggest that inhibitory interaction of cortically evoked descending activities involves segmentary inhibitory interneurons and is realized at an interneuronal level and/or at the membrane of the motoneurons.