Dentate Gyrus in Aged Male Albino Rats (Histological and Tau-Immunohistochemical Study)

Introduction: Dentate gyrus is a subregion of the hippocampus that is crucial in learning and memory and it is vulnerable to the aging process. Tau is a microtubule associated protein in neurons which is implicated as a significant factor in the axonal growth and development of neuronal polarity. Aim of the Work: The present study aimed to investigate the histological and tau-immunohistochemical features of the dentate gyrus in aged male albino rats. Materials and Methods: Thirty male albino rats were divided equally into three groups: Group I (adult, 3-6 months), Group II (early senile, 18-20 months) and Group III (late senile, 30-31 months). Paraffin sections of hippocampus were prepared and stained with H E, Cresyl violet and immunohistochemically using anti- tau antibodies. Morphometric measurements were done and statistically analyzed. Results: The thickness of the granule cell layer of dentate gyrus showed significant reduction in group III as compared to group I and II. The granule cell layer of dentate gyrus of aged rats (Group II, III) showed significant reduction in the number of mature granule cells with detection of apoptotic cells. The number of immature cells showed significant increase in group II, while was significantly reduced in group III as compared with group I. The cells of the hilus appeared with disturbed arrangement and some appear with shortening of their processes with presence of apoptotic cells and microglia. The number of astrocytes showed significant age-dependent increase. Significant increase in the optical density of the tau immunoreaction within the dentate gyrus neuropil was observed with aged. Conclusion: Aging was associated with dentate gyrus neuronal loss which is accompanied with increase in abnormal tau accumulation in neuronal processes. Also, early stages of aging were accompanied with increase in immature cells. So, it is recommended to investigate the use of anti-tau drugs and stimulation of dentate gyrus neurogenesis by neurotrophic drugs as a protective approach for improvement of learning and memory during aging.