Time of Origin of the Neurons in the Caudal Brain Stem of Rat

This study was designed to determine the time of origin of neurons in the caudal brain stem of rat. A single injection of [3H]-thymidine was given to a pregnant animal for each of the days of gestation from 11 to 20. By analyzing the location of the heavily labeled neurons in the offspring of these animals, it was determined that the neurons in this part of the brain of rat originated on days 11–16 of gestation. The motor neurons were heavily labeled on days 11–13 of gestation, with the majority labeled on day 12 in all motor nuclei except in the facial nucleus where they peaked on day 13. The somatic and visceral sensory neurons were heavily labeled on days 12–15 of gestation with the peak on days 13 and 14. The neurons derived from the rhombic lip were heavily labeled on days 12–16.