ABSTRACT
The hippocampal formation plays a demonstrated role in learning and memory, and it is selectively impaired in many developmental brain diseases. Developmental studies on this brain area are important for understanding the neurodevelopmental disorders. To study the postnatal development of the hippocampal formation. Five male albino rats from the following postnatal ages PO, P7, P14, and P90 were studied by histological, immunohistochemical, and morphometric methods. The general architecture of the hippocampus proper with its polymorphic, pyramidal, and molecular layers was present at PO, whereas the details of the adult structure appeared at P14. In the dentate gyrus, distinct lamination appeared at P7 and its maturation continued with the production of neurons at the interhilar zone that peaked at P14. Astrocytes increased in size and staining affinity for glial filaments, and acquired a stellate shape with age. Microtubule-associated protein 2 immunoreactivity was observed in the perikarya at PO and in the sprouting dendrites at P7 and P14. At P90, the dendrites occupied the whole thickness of the molecular layer. Number of light pyramidal neurons decreased, whereas that of dark neurons increased from PO to P90. Furthermore, the number of granule cell layers increased concomitantly with the increase in thickness of the molecular and polymorphic layers of both the hippocampus proper and the dentate gyrus. The important sequences of events in the growth and maturation of the hippocampal formation in male albino rat occurred in the first 2 postnatal weeks