ABSTRACT
The postnatal development of the ectoplasmic specialization (ES) of Sertoli cells was investigated in the rats from 1st to 8th week after birth and the adult by electron microscopy. At the end of the 1st week. ES is in the beginning of its formation. Some high electron dense materials accumulate in the submembranous regions and short cisternae of endoplasmic reticulum align in these zones. At the end of the 2nd week the short cisternae are fused each other and straight microfilaments bundles appear and are sandwiched between the flattened cisternae and cell membrane. The density of microfilaments is increased in the 3th week and numerous tight junctions appear between adjacent Sertoli cells. The ES is gradually completed in its structure until the 5th week and fully extend and circumscribed around the base of Sertoli cells. Thereafter, there is no more morphological changes. We conclude that the first 5 weeks after birth is the important period for the development of ES of Sertoli cell as well as the blood-testis barrier in rats.