Generation of motoneurons in the rabbit brainstem.

Autoradiography of 3H-thymidine incorporation was used to determine the time of origin of motoneurons in the rabbit brainstem. With the exception of the facial nucleus, neurons of the branchial motor column originated earlier (days 9 and 10) than somatic motor column neurons (day 11). Labeling was obtained as early as embryonic day 8 for many motor nuclei and the mesencephalic trigeminal nucleus. The significance of temporal patterns of neurogenesis is discussed.