White Matter Injuries And Its Underlying Mechanism In A Mouse Model Of Schizophrenia Based On Nmda Antagonism

PARTⅠTHE PRELIMINARY STUDY ON WHITEMATTER INJURIES IN THE MOUSE MODEL OFSCHIZOPHRENIA INDUCED BY MK-801Objective: To explore the role of white matter injuries in the mousemodel of schizophrenia (SZ) induced by the NMDA receptor antagonist.Methods: Adult male C57BL/6J mice (n=96) were equally dividedinto four groups. One group was treated with saline, and the other threegroups were intraperitoneally treated with MK-801at dose of0.25mg/kg(M1),0.5mg/kg (M2) and1mg/kg (M3). The drug injection continued for14days. At the2ndand4thweek, Morris water maze, the hole-board test andthe accelerating Rota-rod test were done to test the behavioral changes inthese animals. The myelin basic protein (MBP) and the ultrastructure of themyelinated fibers in corpus callosum were investigated withimmunohistochemical method and transmission electron microscopetechnique.Results: At the2ndand the4thweek, any dose of MK-801treatment didnot induce impairment of spatial learning and memory abilities and themotor coordination. However, the MK-801treatments of0.25mg/kg and1mg/kg but not0.5mg/kg resulted in less exploration to a new environment atthe2ndweek. The myelin staining with anti-MBP antibody was less intense in all three schizophrenic groups when compared to saline control group (p <0.01) at the2ndweek. Furthermore, there were injured changes of the myelinsheaths in schizophrenia groups. The ratio of the injured myelinated nervefibers in the corpus callosum of MK-801treated mice [M3group,(22.42±4.24)%] was significantly higher when compared to the control mice [(3.84±1.35)%, p <0.01]. At the4thweek, schizophrenic-like behaviors of micein M1group and M3group disappeared. The pathological alterations ofmyelin sheaths including splitting lamellae and segmental demyelization inthe mouse model of SZ were rarely seen.Conclusions: The present study demonstrated that the white matterdamages, mainly low MBP expression and segmental demyelization incorpus callosum, existed in the mice sub-chronic treated with MK-801.These results provide further evidence of white matter deficits in SZ andindicate that the animal model of SZ induced by MK-801is a useful model toinvestigate mechanisms underlying white matter abnormalities in SZ. PARTⅡTHE FURTHER STUDY ON WHITE MATTERINJURIES AND THE STEREOLOGICAL STUDY ON THECHANGES OF THE MYELINATED FIBERS IN THECORPUS CALLOSUM OF THE MOUSE MODEL OFSCHIZOPHRENIA INDUCED BY MK-801Objective: To further understand the molecular and structural bases ofwhite matter injuries in the mouse model of schizophrenia (SZ) induced bythe NMDA receptor antagonist.Methods: Adult (8-10weeks old) male C57BL/6J mice (n=35) wererandomly divided into two groups. The control group (n=16) was treatedwith saline, and the SZ group (n=19) was treated intraperitoneally withMK-801(1mg/kg). The drug treatments lasted for14consecutive days. Allanimals were tested with Morris water maze, the open field test, the elevatedplus maze, the hole-board test and the accelerating Rota-rod test. The MBPand CNPase mRNA expressions were examined by RT-PCR. The total whitematter volume, corpus callosum volume, the total length of the myelinatedfiber in corpus callosum, as well as the total volume of the myelinated fiberand the total volume of myelin sheaths in corpus callosum were investigatedwith the modern stereological methods.Results: We found that the mice with repeated chronic MK-801administration showed increased locomotors activity in the open field test,less exploration of a novel environment in the hole-board test and increasedanxiety in the elevated plus maze, but no impairments were observed incoordination/motor function on accelerating Rota-rod or learning andmemory abilities on Morris water maze. The total white matter volume andcorpus callosum volume in the mice treated with MK-801were significantlydecreased compared to the control mice treated with saline. Myelin basic protein (MBP) and2’,3’-cyclic nucleotide3’-phosphodiesterase (CNPase)expression were also significantly decreased in the mouse model of SZ.Furthermore, we observed degenerative changes of the myelin sheaths in themouse model of SZ. The corpus callosum volume and the total length of themyelinated fibers in the corpus callosum of schizophrenia group weresignificantly decreased by9.4%and16.8%compared to the control group.Our results also revealed that the decreased total length of the myelinatedfibers was mainly due to the marked loss of the myelinated nerve fibers withthe diameter of0.4μm~0.5μm.Conclusions: These results indicated that in the mouse model ofschizophrenia induced by MK-801, the MBP expression and CNPaseexpression were low, and the myelinated fibers, especially the myelinatedfibers with small diameter, were lost in the corpus callosum whencompared to the control group. The structural changes and the molecularchanges in the present study suggested that the demyelination changes inthe white matter induced by MK-801might be one of the importantstructural bases for the schizophrenia-like behaviors. PART Ⅲ THE PRELIMINARY STUDY ON THEMECHANISM UNDERLYING WHITE MATTERINJURIES IN A MOUSE MODEL OF SCHIZOPHRENIAINDUCED BY MK-801Objective: To explore the effects of MK-801on the NMDA receptorsubunit in the mouse model of schizophrenia.Methods: The animals, drug treatment and behavioral tests were thesame as in the part two. After behavioral tests,5mice from the control groupand5mice from the schizophrenia group were selected for detecting NMDAreceptor subunit NR1, NR2C and NR3A with RT-PCR andimmunofluorescence technique.Results: The results of Morris water maze, the open field test, theelevated plus maze, the hole-board test and the accelerating Rota-rod testwere the same as in part two. The NR1subunits were mainly expressed onthe soma of neurons, the process of oligodendrocytes and the periphery ofaxons. The NR1subunit mRNA expression in cortex of the mice treated withMK-801was significantly decreased relative to the mice treated with saline(p=0.027<0.05), however, the NR1subunit mRNA expression in corpuscallosum and hippocampus were non-significantly different between twogroups. The NR2C subunit mRNA expression in cortex, corpus callosumand hippocampus were non-significantly different between two groups. TheNR3A subunit mRNA expression in corpus callosum of the mice treated withMK-801was significantly increased relative to the mice treated with saline(p=0.036<0.05), however, the NR3A subunit mRNA expression in cortexand hippocampus were non-significantly different between two groups.Conclusions: The decreased NR1subunit mRNA expression in cortexand the increased NR3A subunit mRNA expression in corpus callosum might provide one of mechanism underlying white matter injuries in themouse model of SZ induced by MK-801.