Electrophysiological demonstration of a dentato-rubrospinal projection in cats

Electrophysiological experiments were performed in cats anesthetized with alpha-chloralose to demonstrate the existence of a dentato-rubrospinal projection. In one series of experiments lesions of the red nucleus were found to eliminate a response recorded at C-5 in the spinal cord following stimulation in the dentate nucleus. This response was unaffected by lesions placed in the interposed nuclei adjacent to the region of the dentate nucleus in which the stimulating electrode was located. Other experiments demonstrated that this response was evoked only when the stimulating electrode was located at the edge of or within the dentate nucleus. Together these studies show that stimuli applied in the dentate nucleus evoke a short latency response mediated by the red nucleus which does not result from current spread to the interposed nuclei. The effect of dentate stimulation on identified rubrospinal neurons was evaluated using extracellular and intracellular recordings. Rubrospinal neurons were identified by their antidromic activation from the spinal cord. In several of these neurons, stimulating in the dentate nucleus evoked short-latency synaptically mediated responses. Intracellular recording revealed that dentate stimulation evoked graded depolarizations in rubrospinal neurons with a mean latency of 1.4 ms. These findings indicate that the output of the dentate nucleus directly activates a component of the rubrospinal projection.