Cerebellar and cerebral inputs to physiologically identified efferent cell groups in the red nucleus of the cat

Cells of the red nucleus of the cat have been classified into 4 projection sets, consisting of cells which could be fired antidromically from (1) only the contralateral spinal cord, (2) only the ipsilateral medulla, (3) both the contralateral spinal cord and the ipsilateral medulla, and (4) both the contralateral spinal cord and brachium conjunctivum. Each of these projection sets receives excitatory synaptic input from axons leaving the cerebellum in the superior cerebellar peduncle, crossing to the red nucleus of the opposite side, and sending axon collaterals — in at least some cases — to the thalamus. Most cells in each projection set are also excited following stimulation of the ipsilateral precruciate cerebral cortex. Rubral cells with medullary, cerebellar, and spinal-projecting axons are found dispersed throughout the rostrocaudal extent of the nucleus, although caudal cells are primarily rubrospinal and rubral cells sending axons to the ipsilateral medulla are predominantly located in the rostral portions of the red nucleus.