Effect Of Estrogen Replacement Therapy On The Myelinated Fibers In CA1of Hippocampus In Middle-aged Ovariectomized Rat

As the new biological functions of estrogen discovered, estrogenreplacement therapy (ERT) preventing age-related degeneration in centralnervous system has raised concern. Many researches oncognition-protective ERT influenced the volume of hippocampus werealmost neuroimaging studies while their conclusion were still different.Previous studies have provided that ERT improved cognitive function andspatial memory which regulated by hippocampus through impact thecomponents of neural circuit despite the myelinated fibers. we used Morriswater maze and stereological method to measure spatial memory, the totalvolume of hippocampus and its subfields, and several parameters about themyelinated fibers of hippocampal CA1in middle-aged ovariectomy rats inorder to determine if ERT has an impact on myelinated fibers in CA1subregion of hippocampus of middle-aged ovariectomy rats and to realizethe relationship between the cognition and CA1myelinated fibers. Methods1.110-month-age female rats were bilaterally ovariectomized andrandomly divided into OVX＋Veh group (9rats) and OVX＋E2group (10rats).1.2Four weeks after the operation, in OVX＋Veh rats and OVX＋E2rats, placebo and17β-estradiol were subcutaneously injected respectivelyfor4weeks.1.3Morris water maze was applied for testing the spatial referencememory.1.4The frozen section technique and stereological methods wereapplied to quantitatively investigate the total volumes of the hippocampusand the CA1of the hippocampus.1.5The electron microscope technique and stereological methodswere applied to quantitatively investigate the total volume of themyelinated fibers、the myelin sheaths and the axons; total length and meandiameter of the myelinated fibers in the hippocampal CA1.Results2.1The mean escape latency in spatial navigation of Morris watermaze test in OVX＋E2group from day1to5was significantly shortenedwhen compared to OVX＋Veh group (P＜0.05).2.2There was no significant difference in the hippocampal volume between two groups (P=0.100).2.3There was no significant difference in the volume of CA1ofhippocampus between two groups(P=0.366).2.4When compared to OVX＋Veh group, the total volume of themyelinated fibers in OVX＋E2group were significantly increased by31.4%(P=0.016).2.5When compared to OVX＋Veh group, the total volume of themyelin sheaths in OVX＋E2group were significantly increased by37.8%(P=0.009).2.6The total volume of axon of myelinated fibers in the CA1ofOVX+E2rats were not significant change (P=0.087) when compared tothat of OVX+Veh rats.2.7The total length of myelinated fibers in OVX+E2rats were notsignificant change (P=0.105) when compared to that of OVX+Veh rats.2.8The mean diameter of myelinated fibers in the CA1of OVX+E2rats were not significant change (P=0.828) when compared to that ofOVX+Veh rats.Conclusion1.Continuous four week ERT improved the spatial memory ofmiddle-aged ovariectomized rat.2.Continuous four week ERT had protective effects on the myelinated fibers and myelin sheaths in the hippocampal CA1of middle-agedovariectomized rat.