Convergence of reticulo-, vestibulo-, and rubrospinal influences on cervical spinal motoneurons in cats

Abstract

Intracellular recordings were made of synaptic responses of 93 motoneurons in the cervical region of the cat spinal cord to stimulation of the medial longitudinal bundle, the brain-stem reticular formation, the lateral vestibular nucleus of Deiters, and the red nucleus. In response to stimulation of the medial longitudinal bundle and the vestibular nucleus responses in the motoneurons of the distal groups of muscles of the forelimb were predominantly excitatory, whereas in motoneurons of the proximal extensor muscles they were predominantly inhibitory. During stimulation of the red nucleus, excitatory and inhibitory responses were recorded in almost equal numbers of cells regardless of their functional class. Monosynaptic EPSPs appeared in one-fifth of motoneurons in response to stimulation of the medial longitudinal bundle and, in a few cases, to stimulation of the vestibular and red nuclei. Otherwise, during stimulation of these structures polysynaptic responses were recorded in the motoneurons. In 62% of cases postsynaptic potentials arising in response to stimulation of the various suprasegmental structures tested were identical in direction in the same motoneurons. A mutually facilitatory effect was observed during stimulation of different suprasegmental inputs. The results are evidence that interaction between influences of the structures tested takes place largely at the level of spinal interneurons.