| Objective: Corticosteroid(CORT)is the end product of the hypothalamic-pituitaryadrenal axis(HPA)and is an important endocrine hormone in the body.Studies have shown that it has a regulatory effect on the 5-HT neural pathway,and the abnormality of the 5-HT neural pathway is an important pathological feature of depression.In the CORT regulated 5-HT neural pathway,the raphe-hippocampal pathway is the most important.In this pathway,the 5-HT neuron cell body is located in the raphe nucleus and the axon is projected into the hippocampus,which is involved in the establishment of learning and memory and the subcortical center of emotion regulation.Studies have shown that there are three regions within the hippocampus: dentate gyrus(DG),CA3,and CA1,which have regional specificity in the regulation of 5-HT from the raphe nuclei.Therefore,we firstly have proposed specific regions within the hippocampus as the unit.To study the complete change of 5-HT neurotransmission within this pathway after corticosterone administration.The distribution density of axons from the raphe nucleus is highest in the CA3 region.Therefore,we use CA3 as the target region.The release and reuptake of 5-HT in CA3 is the pivot of 5-HT nerve conduction in the hippocampus.The specific changes in this area after the drug is also bound to change the core of 5-HT nerve conduction in the hippocampus.Microdialysis technology is a new research method developed in recent years.Its unique feature is that it can collect the concentration of local free analytes in deep tissues.It has the characteristics of in vivo,in-situ sampling,real-time,online,etc.Continuous sampling for a long time,with high time and spatial resolution,can get a lot of information while saving animals.Microdialysis helps to study the specificity of the brain regions of trace substances and helps to study the correlation between neurochemical changes and epigenetics.The forced swimming test(FST)and the tail suspension test(TST)in the epiphythology experiment indirectly reflect the existence of depression state by measuring the immobility time of the mice,and the FST and TST can be jointly formed "Behavioral Syndrome" to evaluate the efficacy of antidepressants.Our experiments placed microdialysis probes in the hippocampal CA3 subregion to investigate whether dynamic changes in 5-HT concentrations correspond to apparent behavioral quiescence time in terms of time and whether there is a potential correlation.In summary,based on the role of CORT in neuroendocrine regulation,our group focused on the role of CORT in the regulation of nerve conduction in the 5-HT neural pathway.This experiment was targeted at acute CORT administration,laying the foundation for the establishment of a depression model for the next chronic CORT administration to study the pathogenesis of depression.In this experiment,the dynamic changes of 5-HT concentrations(the sum of release and reuptake)in the raphehippocampal CA3 pathway were measured in vivo,serially,and periodically by microdialysis using an acute subcutaneous injection of CORT.Simultaneously,the change of immobility time in the forced swimming test and tail suspension test was determined,to clear the neurochemical and neurobehavioral changes of 5-HT neurotransmitters in the raphe-hippocampal pathway after administration of acute corticosterone.Methods: One hundred and eight male CD-1 mice(5-8 weeks of age)were respectively tested for microdialysis and epigenetic behavior.In the microdialysis experiment,they were randomly divided into 3 groups,in a group as saline control(5 ml/kg,n=4/group)was given;the other two groups were given subcutaneous injections of mice CORT(20 mg/kg,n=6/group)or vehicle(5 ml/kg,n=4/group).Surgical implantation of the cannula,positioning hippocampal CA3 region,Microdialysis probe placed in experimental mice with surgically embedded cannula(microdialysis probe at 2.7mm-4.5mm department).Continuous collection of dialysate samples,Electrochemical detection real-time,in vivo,quantitative analysis of complete changes in 5-HT concentrations in dialysis samples.In the forced swimming test,there were 17 CORT-treated group,13 vehicle-treated group and 16 saline-treated group.In the tail suspension test,there were 20 CORTtreated group,13 vehicle-treated group and 15 saline-treated group.The immobility time of the mice was measured at basal,60 min,140 min,and 200 min after the administration.SPSS12.0 software was used for multivariate statistical analysis.The level of significance was set at P <0.05.Results: 1.Chromatographic separation and time The 5-HT in standard and dialysate samples was well separated and the 5-HT peak retention time was 15.2 min.2.5-HT standard curve The peak area integral number of 5-HT concentration plot,draw 5-HT standard curve.It can be seen that the linear relationship between the two is good.3.Mouse microdialysis experiment Only use animal data for the correct position of the microdialysis probe.There was a significant interaction between the time and treatment variables(time × treatment: F(30,176)=2.179,P<0.05).The treatment had a significant effect on 5-HT concentrations in mice,but time had no significant effect on 5-HT concentrations(treatment: F(2,176)=14.030,P<0.05;time: F(15,176)=1.288,P>0.05).In the CORT group,the 5-HT concentration in the raphe-hippocampal CA3 region began to increase at 120 min after administration,peaked at 140 min,and increased approximately 60% compared with the 5-HT concentration in the basal state.Continue for 40 minutes,and then 5-HT concentration is reduced to the base level.4.Forced swimming test Before administration,there was no significant difference in immobility time in forced swimming test between CORT-treated group,vehicle-treated group and salinetreated group.Compared with vehicle-treated group and saline-treated group,after acute subcutaneous injection of CORT,the immobility time of forced swimming test in mice was obviously shortened at 140 min.5.Tail suspension test Before administration,there was no significant difference in immobility time in tail suspension test between CORT-treated group,vehicle-treated group and saline-treated group.Compared with vehicle-treated group and saline-treated group,after acute subcutaneous injection of CORT,the immobility time of tail suspension test in mice was obviously shortened at 140 min.Conclusion: Positioning of hippocampal CA3 subregions in male CD-1 mice using microdialysis techniques,with acute subcutaneous CORT administration,5-HT concentration(the sum of release and reuptake)in the raphe-hippocampal pathway starts to increase at 120 min after administration.At 140 min,it reached a peak,which was approximately 60% higher than the 5-HT concentration in the basal state,and the duration was 40 min,and then decreased to the basal level.In addition,when the 5-HT concentration reached the highest peak,the immobillity time in the forced swimming test and tail suspension test was significantly shortened,further illustrating the increase of 5-HT concentration in the raphe-hippocampus CA3 region corresponding to the decrease of immobolity time in the epigenetic behavior.This may lay the foundation for the study of the pathogenesis of the mouse depression model established by chronic corticosterone administration. |
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