| Objective:Schizophrenia(SCZ)is one of the common severe mental disorders,usually with onset in late adolescence and early adulthood,and the clinical symptoms include negative and positive symptoms as well as cognitive impairment,the pathogenesis of which still remains unclear,so it is important to establish a suitable animal model to study the disease.At present,animal models induced by noncompetitive N-methyl-D-aspartate receptor(NMDAR)antagonists have been widely used to study the exploration of the pathological mechanism of schizophrenia and the study of related therapeutic drugs.Animal models constructed with different dosing regimens and dosing regimens result in variable experimental outcomes.Meanwhile,most of the current dosing time for animal modeling of schizophrenia is focused on adulthood,whereas little is known about the effects of early pubertal dosing on early adult schizophrenic model rats.Therefore,in this study,we selected early adolescence rats and repeated administrations of dizocilpine maleate(MK-801),a noncompetitive NMDAR antagonist at different doses,were used to construct a rat model of schizophrenia,which was evaluated at multiple levels and searched for the optimal model by animal behavior,magnetic resonance imaging,and analysis of immune related gene expression,It is hoped to provide a scientific basis for future optimization of the construction protocol of animal models of schizophrenia induced by NMDAR antagonists.Methods:(1)First,Sprague Dawley(SD)male rats at postnatal day(PND)28 were randomly divided into three groups,0.5 mg/kg of MK-801,0.25 mg/kg of MK-801(dissolved in saline)and an equal volume of saline(5 ml/kg),and MK-801 dissolved in saline was administered intraperitoneally for 14 consecutive days.Then,three kinds of behavioral tests,open field,novel object recognition and Y-maze,were sequentially performed in early adulthood(PND60).(2)After completion of the behavioral experiments,all experimental animals underwent structural magnetic resonance imaging(MRI)experiments in early adulthood(PND67)to objectively detect and evaluate brain structure in the model rats.Structural magnetic resonance imaging data acquisition was done by a dedicated 7T small animal magnetic resonance imager(Bio Spec70/20 USR,Bruker,Germany)coupled with a dedicated small animal coil.(3)Hippocampal tissues from all experimental animals were removed at early adulthood(PND70)for expression detection of candidate immune related genes using q RT-PCR.Candidate immune related genes were accessed as follows: microarray gene chip expression profiles of postmortem hippocampal tissues from patients with schizophrenia were obtained from the Gene Expression Omnibus(GEO)database:GSE53987,which contains postmortem hippocampal tissues from 15 schizophrenia and18 healthy controls,and immune-related genes were obtained from the immport shared data database.Differentially expressed immune-related genes in postmortem hippocampal tissues of schizophrenia were selected out by R software,the differentially expressed immune-related genes were subjected to correlation analysis,protein-protein interaction(PPI)analysis,and finally candidate immune-related genes were identified by using the cyto Hubba plug-in of Cytoscape.Results:(1)Behavioral test results: in the open field test,the total locomotion distance significantly increased in the 0.25 mg/kg MK-801(P < 0.05)and 0.5 mg/kg MK-801 groups(P < 0.001)compared with the saline group(control),and these findings indicate that repeated MK-801 administration in early adolescence leads to rats exhibiting increased locomotor activity in early adulthood.The time spent in center zone activity was significantly lower in the 0.25 mg/kg MK-801 group(P < 0.01)and 0.5 mg/kg MK-801 group(P < 0.001)compared with the saline group.These findings indicate that repeated injections of MK-801 in early adolescence produce a reduction in the exploratory capacity of rats in early adulthood as well as an increase in the level of anxiety.In the novel object recognition experiment,compared with the normal saline group,the novel object recognition index of the 0.25 mg/kg MK-801 group(P <0.01)and the 0.5 mg/kg MK-801 group(P <0.001)were significantly decreased,This result indicates that repeated MK-801 administration in early adolescence impairs the short-term recognition and memory ability of early adult rats.In the Y-maze test,the rate of spontaneous correct alternation was reduced in the 0.25 mg/kg MK-801 group(P <0.01)and the 0.5 mg/kg MK-801 group(P < 0.001),as compared with the saline group.These findings indicate that repeated MK-801 administration in early adolescence leads to impaired spatial working memory in rats in early adulthood.Results of the structural magnetic resonance imaging(MRI)experiments: compared with the saline group,the gray matter volume(GMV)of the hippocampus was decreased in the 0.25 mg/kg MK-801(P < 0.05)and 0.5 mg/kg MK-801 groups(P < 0.001),but the reduction was more significant in the 0.5 mg/kg MK-801 group than in the 0.25 mg/kg MK-801 group.(3)Experimental results of immune-related genes: Eighty differentially expressed genes(DEGs)were identified in postmortem hippocampal tissue of patients with schizophrenia,among which 20 differentially expressed immune-related genes(7up-regulated genes and 13 down-regulated genes),correlation analysis and PPI results indicated the relationship of these immune related genes correlation and interaction,We next identified four candidate immune-related genes(NPY,SST,CCK and TAC1)by using the cyto Hubba plugin in Cytoscape,and finally used q RT-PCR to detect the expression of candidate immune related genes in the hippocampus of rats in early adulthood,and found that only NPY m RNA expression levels were significantly decreased in the hippocampus of the 0.25mg/kg MK-801 group(P < 0.01)compared with the saline group,The m RNA expression levels of NPY(P < 0.01),SST(P < 0.01)),CCK(P < 0.05)in the hippocampus were significantly decreased in the 0.5 mg/kg MK-801 group.Meanwhile,compared with the saline group,TAC1 m RNA expression levels showed no obvious differences in the hippocampus between the 0.25 mg/kg MK-801 group(P > 0.05)and the 0.5 mg/kg MK-801 group(P > 0.05).Conclusion:The present study suggests that repeated MK-801 administration in early adolescence may have effects on behavior,brain structure,and the expression of immune related genes in rats in early adulthood,in which high-dose(0.5 mg/kg)administration is preferable.(1)The results of behavioral experiments show that repeated MK-801 administration in early adolescence produces behavioral phenotypes associated with schizophrenia in rats in early adulthood;(2)Structural magnetic resonance imaging results showed that repeated MK-801 administration in early adolescence resulted in reduced hippocampal gray matter volume in rats in early adulthood;(3)Immune related gene expression experimental results showed that repeated high-dose MK-801 administration in the hippocampus of rats in early adolescence had a greater effect on the expression of immune related genes in the hippocampus than in early adulthood.In conclusion,this study may provide support for establishing an animal model of schizophrenia based on repeated high-dose MK-801 administration in early adolescence,and also provide a suitable animal model for exploring the pathogenesis of schizophrenia.Meanwhile,it is also speculated that the changes in behavior and brain structure may not depend on the changes in the expression of immune related genes. |
PDF Full Text Request