The postnatal development of rat dentate gyrus and the effect of early thyroid hormone treatment.

The postnatal development of the dentate gyrus and the effect of 5 microgram/day triiodothyronine treatment was examined by means of tritiated thymidine autoradiography. The polymorph layer of the dentate gyrus is a secondary germinal layer and forms cells for the granular layer. The cell formation in the dentate gyrus was found to be nearly completed on the 21st day, but development ended only in adulthood. Thyroid-hormone treatment did not affect significantly the postnatal cell formation of the dentate gyrus, but resulted in the appearance of a great number of pycnotic cells in the granular layer.