An Easier Method to Analyze Stereologically the Pig’s Hippocampus

Abstract

Most neuro-pathophysiological research involving the hippocampus uses rodents as a nonhuman model, due to the extensive experimental descriptive literature and favorable cost. The findings from the rodent hippocampus may not be generalizable to humans, though, as ontogenetically they have different hippocampal components. While the rodent model has these limitations, the use of nonhuman primates is often not feasible due to economic and ethical considerations. Pigs are a translational alternative due to the anatomic similarity of the hippocampus in humans and pigs. Materials and Methods: Eight pigs’ brains were harvested and then analyzed according to our previously established technique. Five brains were frozen and three were stored in formalin. All eight brains were then sent to an independent histology service, where they were sectioned according to the methodology established by Holm 1994. The slabs were 10 µm with 2.5 cm2 of hippocampus cross-sectional area. Results: The mean total hippocampus volume was 892.84 mm3 ± 198.91 mm3 using Holm’s methodology. The mean number of cells per sample (20X magnification settings) was 9996.75, using automated ImageJ cell counting. Discussion: In this study, the counts of hippocampus cells were divided into two regions of interest: CA1 and CA3. Our results show that the mean number of hippocampus cells observed was 5.75 million and 2.25 million, in the CA1 and CA3 regions respectively. Holm reported 4.12 million cells in the CA1 region and 1.51 million cells in the CA3 region. The results presented here indicate the CA1 and CA3 cell percentages being 23% and 9% respectively, which are similar to the percentages reported by Holm (21% and 12%). Conclusion: These results corroborate previous findings and demonstrate a novel and cost-effective way to study the hippocampus of pigs in translational neurological research.