An attempt at determining the origin of the reticulo-spinal tract in the rat.

A search was made for retrograde changes in the cells of the reticular formation of the rhombencephalon and mesencephalon in 26 rats aged 7 to 32 days after lesions in different spinal cord segments with survival periods of 3 to 14 days. No retrograde changes were found in any of the animals. Negative results yieled by the method of retrograde degeneration appeared to show that the main mass of the axoplasm of the reticular cells in the rat aimed to other brain stem structures or in the ascending direction.