Histomorphology and histomorphometry changes in the hippocampal regions of kaolin-induced hydrocephalic adult rats

Abstract

Background: The pathological state known as hydrocephalus arises when cerebrospinal fluid builds up abnormally, causing the ventricles to expand and triggering a steady decline in neuronal health. To replicate this neurological anomaly in laboratory settings, researchers frequently administer kaolin—a type of aluminum silicate—directly into the cisterna magna. Despite its widespread application, there remains a noticeable gap in understanding how this experimental model specifically alters the microscopic anatomy and cellular metrics of the hippocampus, especially concerning the dentate gyrus. Consequently, the current investigation aimed to meticulously evaluate the morphological and morphometric shifts occurring within the adult rat hippocampus following sterile kaolin exposure. Methods: The experiment utilized mature male rats, initiating hydrocephalus via an intracisternal injection containing 0.04 mL of a 250 mg/mL kaolin mixture for the experimental cohort (n=6), whereas the control rats (n=6) underwent a sham operation. Throughout the four-week observation window, the animals' body masses were recorded on a weekly basis. At the conclusion of this period, intracardiac perfusion was performed to euthanize the rats and safely extract their brain tissue. To accurately evaluate the extent of neuronal degradation, the harvested specimens were subjected to Cresyl violet staining protocols. Subsequent data evaluation was executed utilizing ImageJ alongside GraphPad Prism version 8. Results: Statistical evaluations revealed a pronounced decrease in the overall body mass of the kaolin injected rats when juxtaposed with the sham-operated group (p<0.0001). Microscopic evaluation of the Cresyl violet-dyed hippocampal sections highlighted a severe disruption in the layered cellular architecture within the hydrocephalic specimens, standing in stark contrast to the preserved structure found in healthy controls. Furthermore, quantitative analysis demonstrated that the pyknotic indices (PI) specific to the CA3 and dentate gyrus zones were remarkably elevated in the 250 mg/mL kaolin group. Conclusion: The induction of hydrocephalus via kaolin leads to substantial deterioration of the hippocampus. This neurodegeneration manifests physically through the breakdown of cytoarchitecture, a noticeable drop in healthy neurons, and a surge in pyknotic (dying) cells. Ultimately, these morphological outcomes highlight the destructive impact of ventricular enlargement on hippocampal health, validating this specific animal model for observing structural brain damage.