The development of the nucleus isthmi in Xenopus: an autoradiographic study.

The time of origin of the neurons of the nucleus isthmi (NI) in Xenopus has been investigated with [3H] thymidine autoradiography. The first cells of the NI were formed at stage 20 and they continued to be formed until stage 62. The majority of the neurons of the NI were generated between stages 45 and 55. The cells in the NI were distributed in a spatiotemporal manner. Cells generated earliest were located in the rostroventral pole of the NI followed in a dorsocaudal sequence by neurons formed later.