Distal forelimb cross-innervation effectively induces formation of corticorubral synapses

We investigated whether cross-innervation of the distal forelimb extensor and flexor muscles effectively induced formation of corticorubral synapses in cats. The average time-to-peak of the corticorubral EPSPs in the red nucleus (RN) neurons innervating cervicothoracic segments (C-cells) of animals with distal forelimb cross-innervation was significantly less than that of animals with elbow cross-innervation. These fast-rising corticorubral EPSPs were shown to be induced by newly formed synapses located on the proximal soma-dendritic membrane of RN neurons, indicating that distal forelimb cross-innervation is more effective for inducing synapse formation in C-cells than elbow cross-innervation. Thus corticorubral synapse formation after forelimb cross-innervation appears to be related to direct rubrospinal connections to distal forelimb motoneurons and of functional importance to RN neurons for performing voluntary distal forelimb movement.