Changes in myelinated fibers in the hippocampus of streptozotocin-induced diabetic rats: a stereological investigation.

Diabetes causes cognitive impairment, and the hippocampus is important for long-term and permanent memory function. However, the mechanism of their interaction is still unclear. In this study, rat models of diabetes mellitus were generated by a single injection of streptozotocin (STZ). This study aims to explore the changes in myelinated fibers in the hippocampus of type 1 diabetic rats. The unbiased stereological methods and transmission electron microscopy were used to obtain the total volume of the hippocampus, the total volume of the myelin sheath, the total length of the myelinated nerve fibers, the distribution of the length with different diameters of the myelinated fibers, and the distribution of the length with different thickness of the myelin sheath. Stereological analysis revealed that, compared to that of the control group, the total myelinated fibers volumes and the total myelinated fibers length were decreased slightly, while the total volume and the thickness of myelin sheaths were significantly decreased in the diabetic group. Finally, when compared with the control group, the total length of myelinated fibers in the diabetes group was significantly reduced, with diameters ranging from 0.7 to 1.1 μm and thicknesses of myelin sheaths from 0.15 to 0.17 μm. This study provides the first experimental evidence by stereological means to demonstrate that myelinated nerve fibers may be the key factor in cognitive dysfunction in diabetes.