AN AUTORADIOGRAPHIC STUDY OF DEVELOPMENT OF ANTERIOR THALAMIC GROUP AND LIMBIC CORTEX IN RABBIT

Using autoradiographic technique the migratory movements of cells destined to form the anterior thalamic nuclear group and the limbic cortex were studied in 54 embryos or newborn rabbits the mothers of which were injected with a single dose of tritiated thymidine on the fifteenth to twenty‐fifth day of gestation. Neurons which form the anterior thalamic group originate between the fifteenth and eighteenth day of gestation. An orderly relation exists between the time of origin of the anterior thalamic neurons and their definitive position within the dorsal thalamus. The cells which originate earliest lie most laterally in the dorsal thalamus; those which originate later lie successively more medially. No nucleus in the anterior group is isochronic in regard to the origin of its cells and in each a latero‐medial gradient corresponding to early‐late origin is apparently present. Neurons forming the limbic cortex (upon which the anterior thalamic group projects) originate between the fifteenth and twenty‐fifth day of gestation. The anterior and the posterior limbic regions seem to develop synchronously. In agreement with other workers it is concluded that neurons which originate earliest form the VIth layer of the differentiated cortex while those which originate later form successively the more superficial cortical layers. No retrograde movements of the migrating cells were observed. It is suggested that during cortical development each migratory wave of cells, after passing the thickness of the already existing cortical plate, constitutes at some stage the most superficial cell layer of the then existing cortex. Copyright © 1969 The Wistar Institute of Anatomy and Biology