Time of origin of Purkinje cells and neurons of the deep cerebellar nuclei of the chick embryo examined by 3H-thymidine autoradiography.

The time of origin of Purkinje cells and deep cerebellar neurons was studied by 3H-thymidine autoradiography in chick embryos which received isotope at stages 17 to 29 and which were sacrificed at stage 36. These neurons originated throughout stages 17 to 27. Neurons of each cerebellar nucleus originated throughout these stages, so that histogenetically the cerebellar nuclei could be regarded as a single cell mass. Large neurons originated at stage 17, medium sized ones at stages 19 to 21, and small ones after stage 23. Purkinje cells aggregated at stage 36 to form a row of cell clusters under the external granular layer. These cell clusters were more or less labeled in the embryos which received isotope at stages 17 to 21, while unlabeled cell clusters were observed in the embryos which received isotope after stage 23. These unlabeled cell clusters showed 4 longitudinal bands in the lateral cerebellar cortex. In the embryo which received isotope at stage 27, Purkinje cells in the pars intermedius and lateralis were almost unlabeled, whereas in the vermis and the lobus flocconodularis, a fairly large number of labeled Purkinje cells were still observed. Purkinje cells were all medium sized regardless of their time of origin.