Establishment of a stereological method for myelinated fibers in hippocampal formation of rat brain

AIM: To establish a stereological method for the quantitative studies of hippocampal formation and myelinated fibers in the hippocampal formation.METHODS: Five 6-month female Long-Evans rats were used.The volume of hippocampal formation was estimated using the Cavalieri's principle.Five or six tissue blocks were obtained from the hippocampal formation in a uniform random fashion.Isotropic,uniform and random(IUR) sections were ensured by isector technique and one 60 nm-thicknesses section was cut from each block.From each section,15 fields of vision were randomly photographed using transmission electron microscope.The length density of the myelinated fibers in the hippocampal formation was estimated using an unbiased counting frame,the volume density of the myelinated fibers in the hippocampal formation was estimated using equidistant point counting grid and the total length and total volume of the myelinated fibers in the hippocampal formation were estimated by multiplying the length density and volume density by the total volume of hippocampal formation,respectively.The diameter of fibers sampled with the unbiased counting frame was estimated by measuring the profile diameter perpendicular to its longest axis.RESULTS: The average volume of rat hippocampal formation was(85.9±14.0)mm3 and the total length of the myelinated fibers in the hippocampal formation was(9.1±3.8) km.The total volume of the myelinated fibers in the hippocampal formation was(4.3±1.2) mm3 and the average diameter of the myelinated fibers in the hippocampal formation was(0.74±0.07)μm.CONCLUSION: The method established in this study provides a useful tool for the quantitative studies of the myelinated fiber changes of hippocampal formation in normal aging process and in various neurodegenerative diseases.