The rubrospinal tract. I. Effects on alpha-motoneurones innervating hindlimb muscles in cats.

Abstract

1. The effect of stimulation of the red nucleus on lumbosacral motoneurones was investigated in cats with conditioning of monosynaptic test reflexes and intracellular recording. 2. Experimental procedures were adopted to assure that the effect of stimulation was mediated by the rubrospinal tract. 3. Excitation of flexor and inhibition of extensor motoneurones is common but a mixture of EPSPs and IPSPs is found in many motoneurones. In some extensor (particularly toe extensor) motor nuclei there is dominating excitation. 4. Differential effects are found in motor nuclei innervating fast and slow muscles, excitation being more prevalent in the former and inhibition in the latter. 5. For both EPSPs and IPSPs the minimal synaptic linkage is disynaptic but in one exceptional case a monosynaptic EPSP was observed. 6. The results are discussed in relation to other findings regarding the interneuronal organization in the spinal cord.