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Background: Hippocampus is a neural structure in the temporal lobe that plays a crucial role in learning and memory. Cognitive impairment with learning disabilities is a common feature in hydrocephalus and is more prominent in adult-onset hydrocephalus. The aim of this study is to describethe morphological alterations in the pyramidal cells of the hippocampus of adult hydrocephalic mice.

Method: Hydrocephalus was induced in adult albino mice by intra-cisternal injection of kaolin suspension (250 mg/ml in sterile water). They were sacrificed 7, 14 and 21 days post-induction. Morphological analysis was carried out on hematoxylin and eosinstained coronal sections of the hippocampus: the pyramidal neurons (normal and pyknotic) in the CA1 and CA3 subregions were counted and the pyknotic index (PI) was calculated. The somatic and dendritic features of Golgistained pyramidal neurons were examined by light microscopy in both hydrocephalic and control mice.

Result: The PI was significantly greater in the CA1 region of the hippocampus in the hydrocephalic groups compared to the agematched controls. The dendritic processes of pyramidal neurons in the CA1 region were fewer with shorter terminal branches in the hydrocephalic mice than in controls; this was pronounced at 7 days post-induction. In the CA3 region, there was no difference in dendritic arborization between hydrocephalic and control mice.

Conclusion: Acute adult-onset hydrocephalus was associated with increased pyknosis and reduced dendritic arborization in hippocampal pyramidal cells in the CA1 but not CA3 region.