ABSTRACT
Fifteen male albino rats were utilized in this research aiming to study the histological alterations in the memory system [hippocampal formations] during aging, They were divided into three age groups [5 animals each]. The first group was the young one [2weeks] and the second one was the adult group [5 months]. Whereas, the third one was the aged group [15 months]. All the animals were anaesthetized with ether inhalation and their brains were dissected out carefully. Specimens from the hippocampal formations were obtained and processed for light and electron microscope examinations. Light microscope examination of the different age groups revealed that the hippocampus in coronal sections had three areas, CA1, CA2 and CA3.Each area was formed of three layers. The first and third ones contained few cells. Whereas, the second layer was formed of numerous pyramidal cells. Pyramidal cells in area CA1 in the young age group were impacted and their nerve processes were not defined. Whereas, pyramidal cells in the same area in the adult group were slightly dispersed and their nerve processes were apparent. Few glial cells were observeved. However, pyramidal cells in the aged group showed an observable decrease in their number with many glial cells in between. Also, their nerve processes were not prominent. Electron microscope examination of the same groups revealed that pyramidal cells in the young group appeared with large rounded euchromatic nuclei and their cytoplasm contained many free ribosomes. The surrounding neuropil showed astrocytes with small rounded euchromatic nuclei and electron lucent cytoplasm. Also, pyramidal cells in the adult group had large euchromatic nuclei and the cytoplasm contained many free ribosomes and rough endoplasmic reticulum. The surrounding neuropil was packed with nerve processes and glial cells. Astrocytes appeared as that demonstrated in the young group.Whereas, oligodendrocytes showed electron dense cytoplasm with few processes. In the aged group, some pyramidal neurons showed apoptosis. These affected neurons were in close contact with large oligodendrocytes with their characteristic electron dense cytoplasm and euchromatic indented nuclei with prominent nucleoli. The surrounding neuropil showed astrocytes with an increase in their nuclear heterochromatin contents and many electron lucent spaces. In conclusion, the hippocapmus showed an observable loss in its pyramidal cells during aging especially that in area CA1 with glial cell alterations which may contribute to this neuronal loss. These histological changes may clarify why amnesia is a wide spread age- related memory disorder