Generation of the ocular motor nuclei and their cell types in the rabbit

Autoradiography of 3H‐thymidine incorporation was combined with horseradish peroxidase (HRP) transport to distinguish the birthdates of motoneurons and internuclear neurons of the abducens nucleus, and of specific motor pools within the oculomotor nucleus. Motoneurons were identified by their retrograde transport of HRP from the extraocular muscles. In other experiments, internucleur neuron types may be controlled by the local environment. The motor pools ofthe oculomotor nucleus are generated sequentially. This may reflect the mechanism whereby nuclei are constructed.