Comparative histomorphologic and histomorphometric Study of the Hippocampus of African Giant Rats and Wistar Rats

Abstract

Introduction: The hippocampus plays critical roles in learning and memory, and there has been substantial progress in the understanding of the hippocampus in various species in the past 80 years.

Aim: This study aims to provide a comparative histomorphology and histomorphometry of the hippocampus of the African giant rats (AGR) and Wistar rats (WR).

Methods: Five (5) adult male African giant rats weighing 981 ± 54.1 g and five (5) adult male Wistar rats weighing 202 ± 4.6 g were used for this study. Hippocampal tissues were prepared for cresyl violet and Hematoxylin and eosin (H&E) staining after transcardial perfusion and fixation, first with normal saline to flush out blood cells, followed by 4% paraformaldehyde in 0.1 PBS. Across hippocampus subfields (CA1–CA4, dentate gyrus), sections were examined for cytoarchitecture, layer thickness, pyramidal cell stratification, and neuronal soma diameters.

Results: Results showed that the basic hippocampus structure, which includes the dentate gyrus, Cornu Ammonis (CA1–CA4), subiculum, and entorhinal cortex, were similar in both species. However, AGR showed unique characteristics, such as larger neuronal somata, considerably thicker pyramidal cell layers, especially in CA2–CA4 sub-regions (p<0.05), and more densely packed granular cells in the dentate gyrus. These structural variations imply that the AGR has a higher capacity for synaptic integration and cognitive processing than Wistar rats.

Conclusion: The results demonstrate the neuroanatomical benefits of the hippocampus of the AGR, bolstering its potential as a substitute rodent model for research on memory, learning, and associated neuropathology.