The Study Of The Relationship Between The Demyelination In The Hippocampus And Altered Behaviors Of The Schizophrenia Mice Induced By CPZ

Schizophrenia is one kind of devastating mental disorder and theetiology is unknown up to now. It affects approximately0.5%-1%ofgeneral population per year in the word. Recent studies showed that thedemyelination of the myelinated nerve fiber and pathological changes ofoligodendrocyte existed in the hippocampus of schizophrenia. Diffusiontensor imaging (DTI) studies revealed that the integrity of the nerve fiberwas correlated with the altered behaviors. However, there have been nostereological quantitative data of myelinated nerve fiber changes inschizophrenic hippocampus. Thus, it is difficult to objectively evaluate therelationship between demyelination of schizophrenic hippocampus andbehavioral alterations. Cuprizone (CPZ) model is a classic demyelination/remyelination animal model with schizophrenia-like behaviors. In thisstudy，we first established the CPZ-induced animal model of schizophrenia.Then, the stereological methods were used to investigate the microstructurechanges of the myelinated nerve fibers in the hippocampus of the CPZ-induced model. Finally, the correlation between the altered behaviorsand the microstructure changes of the myelinated nerve fibers in thehippocampus was estimated with a correlation analysis.PART Ⅰ1Materials and methods1.119male C57BL/6mice were randomly divided into the experimentalgroup and the control group. The experimental mice were given0.2%byweight CPZ mixed into a standard powdered rodent chow for6weeks toestablish a schizophrenia-like mouse model, while the control mice receivedthe standard chow without CPZ during this period.1.2To observe the change of weight during6weeks, the body weight of bothcontrol mice and experimental mice were measured every3days.1.3Open field test, elevated plus maze test, Morris water maze test, Rotarodtest and hole board test were used to investigate behavior changes.1.4Anti-MBP immunohistochemistry staining methods and transmissionelectron microscope technique were used to investigate the structurechanges of myelin sheaths.1.5The volume of the hippocampus and the volume of the myelinatednerve fibers in the hippocampus were investigated with the stereologicalmethods.1.6The correlation between the altered behaviors and the changedmyelinated nerve fibers in the hippocampus was estimated with a correlation analysis.2Results2.1The mean weight of the experimental mice was significantly less thanthat of the control mice (P <0.05).2.2The behavior test results indicated that anxiety and the spatial cognitiveability of the experimental mice were significantly different from those ofcontrol mice (P <0.05), while the action ability, exploration ability andworking memory of the experimental mouse were not significantly differentfrom the control mice (P>0.05).2.3The MBP positive nerve fibers in the experimental mouse hippocampuswere apparently less than those of the control mice. Demyelination of themyelinated nerve fibers in the hippocampus was observed undertransmission electron microscope.2.4The hippocampus volume of the experimental mice was not significantlychanged when compared to the control group (P>0.05), while the totalvolume of the mylinated nerve fibers in the hippocampus of the experimentalmice was significantly less than that of the control mice (P <0.01).2.5The correlation analysis results suggested that the close-arm distancerate was significantly and positively correlated with the volume of themyelinated nerve fibers in the hippocampus (r=0.83, P <0.01), while theopen-arm distance rate was negatively correlated with the volume of themyelinated nerve fibers in the hippocampus (r=-0.65, P <0.05). PartⅡ1Materials and methods1.1The respective stereological parameters of myelinated nerve fibers inmouse hippocampus, which included the total length of the myelinatednerve fibers, the diameters of the myelinated nerve fibers, the axon diameters,the ratio between axon diameters and the diameters of the myelinated nervefibers, and the differences between diameters of the myelinated nerve fibersand their axons, were obtained using stereological methods.1.2The relationships between the parameters of behavior tests and thestereological parameters were analysed.2Results2.1The total length, the diameters of the myelineted fibers, the axondiameters of the myelinated nerve fibers in hippocampus, and the ratiobetween the axon diameters and the diameters of the myelinated nerve fibersin hippocampus of the experimental mice were significantly decreasedcompared to those of the control group (P <0.01). The difference betweenthe diameters of the myelinated nerve fibers and their axon diameters inhippocampus of the experimental mice was not statistically significantcompared to that of control group (P>0.05).2.2The length of the myelinated nerve fibers in the CPZ-treated micehippocampus in the diameter range of0to0.2μm was significantlyincreased when compared to the control group (P <0.05), while those in the diameter range of0.4μm to0.6μm,0.6μm to0.8μm,0.8μm to1μm, and1.2μm to1.4μm in the CPZ-treated mice were significantly decreasedwhen compared to those of control mice (P <0.05), The length changes ofmyelinated nerve fibers in other diameter ranges were not statisticallysignificant when compared to those of control mice (P>0.05).2.3The axon diameters and the ratio between the axon diameters and thediameters of the myelinated nerve fibers in the experimental micehippocampus were both significantly decreased in the diameter range of0to0.2μm when compared to the control group (P <0.01); the thickness ofmyelin sheath, the differences between the diameters of the myelinatednerve fibers and their axon diametersin the experimental mice hippocampuswere not statistically significant in the diameter range of0to0.2μm whencompared to the control group (P>0.05).2.4The closed-arms distance ratio and the open-arms distance ratio werecorrelated with the stereological parameters of the myelinated nerve fibers inhippocampus (P <0.05).General Conclusion1This study proved that CPZ-treated mice could perform a series ofschizophrenia-like behaviors and the hippocampus of CPZ-treated miceundertook the pathological change of demyelination. The CPZ-treated micecan be a useful animal model to evaluate the role and mechanism of themyelin sheath change in schizophrenia. 2The data of the total length, diameters, the axon diameters and thickness ofmyelinated nerve fibers in mice hippocampus and hippocampus volumes ofthe control group of the3months old C57BL/6mice and the6weeksCPZ-treated mice, of which hippocampus undertook demyelination change,was obtained in this study, it can provide important stereological parametersfor further studies.3It was found that the total volume and the total length of the myelinatednerve fibers in hippocampus of the CPZ-treated mice were significantlydecreased when compared to the control group. The loss of myelinatednerve fibers in the diameter range of0.4μm to1μm might contribute to thevolume decrease of the myelinated nerve fibers in the CPZ-treated mice.4It was found that the thickness of the myelinated nerve fibers inCPZ-treated mice in the diameter range of0to0.4μm was constant, whilethat in the diameter range of0.6μm to1μm was increased. Thesedifferences inferred that the susceptibilities of the oligodendrocyteswrapping different diameters of the myelinated nerve fibers to the CPZtreatment were varying.5It was found that the open-arms distance ratio and the closed-arms distanceratio in the elevated plus maze were related with the stereologicalparameters of myelinated nerve fibers in hippocampus.