Sites and mode of termination of reticulo‐spinal fibers in the cat. An experimental study with silver impregnation methods

Abstract

Following lesions in the brain stem reticular formation in 20 cats the ensuing degeneration within the spinal cord has been studied with silver impregnation methods with special reference to the laminar organization of the gray matter described by Rexed ('52, '54). Reticule‐spinal fibers do not arise in the mesencephalon. Pontine reticulo‐spinal fibers descend in the ventral funiculus, almost exclusively homolaterally. Some cross to the contralateral side in the anterior commissure. Medullary reticulo‐spinal fibers descend bilaterally in the ventral part of the lateral funiculus, mostly homolaterally. Both contingents of fibers descend the whole cord throughout. Pontine reticulo‐spinal fibers are more numerous than medullary ones. Pontine fibers terminate bilaterally in lamina VIII and adjacent parts of lamina VII. Contralateral terminations are established mainly by way of fibers crossing in the anterior commissure. Medullary fibers terminate chiefly in lamina VII. A few terminations are found in lamina IX, possibly on large α‐motoneurons and on small neurons. Reticulo‐spinal fibers of both contingents terminate on cells of all sizes, on somata as well as on dendrites.