The influence of the olfactory placode on the development of the telencephalon in Xenopus laevis.

Removal of the sensory plate in Xenopus laevis embryos was performed to study the influence of the olfactory anlage on the development of the forebrain. Embryos, which at stage 22-23 underwent removal of the olfactory anlagen, were killed from stage 47 to 60. In 79% of the animals, two olfactory organs reformed and gave origin to two olfactory nerves which contacted the forebrain. In this instance, the telencephalic hemispheres developed normally. In 14% of the animals, one olfactory organ reformed which contacted the brain by means of one olfactory nerve. This resulted in the development of a unique, reduced in size, cone-shaped telencephalic lobe. In the remaining animals, only a rudiment of the olfactory organ, unconnected with the brain, was present; in these cases, the telencephalon did not develop. Similar results were observed in embryos where olfactory anlagen removal was coupled with damage to, or partial removal of, the prosencephalic vesicle. In animals where lesion of the forebrain was performed without placodal removal, normal development of the forebrain was observed. The developmental relationship observed between the olfactory organ and the forebrain suggests an active role of the nose on the development of the brain.