| Objective To observe the effect of lipopolysaccharide(LPS)-mediated intrauterine infection on the expression of mineralocorticoid receptor(MR)?glucocorticoid receptor(GR)and the regulatory function of hypothalamus-pituitary-adrenal(HPA)axis,so as to explore the mechanisms of learning and memory deficits of rat offspring which were infected during prenatal period,then to provide scientific experimental evidence for the prevention of intrauterine infection-induced delayed neuropsychiatric sequelae which are based on learning and memory dysfunction.Methods Ten-week-old female Sprague-Dawley rats(n=30)were matched with male rats(1:1).Pregnant rats were randomly divided into control group(n=10)and experimental group(n=20).The pregnant rats in experimental group were treated with LPS(66 ?g/kg,intraperitoneally),and the pregnant rats in control group were intraperitoneally injected with same volume of saline on gestational day 10.On postnatal day 48,(1)open field test was used to detect the ability of exploring new environment;morris water maze test was used to estimate the ability of learning and memory;(2)brain tissues of offspring rat were taken and paraffin sections were stained with hematoxylin eosin(HE)for histological observation of hippocampus;(3)frozen sections were treated with indirect immunofluorescence to observe the expression of MR and GR in hippocampus;(4)fresh hippocampal tissues were collected for western blotting analysis to verify the expression of MR and GR in hippocampus;(5)dexamethasone suppression test was used to test the feedback function of HPA axis.Results(1)In open field test,numbers of lattice span and rearings in the experimental group were significantly lower than that of the control group(t=2.227,2.189,all P<0.05).In morris water maze test,the time of escape latency in experimental group was significantly higher than that of the control group during the training period(F=15.487,P<0.01),and from the third day,the time of escape latency in experimental group was significantly higher than that of the control group(d1: F=13.995,P<0.01;d2:F=4.911,P<0.05;d3: F=13.232,P<0.01),at the same time,the swimming time in the target quadrant and the numbers of crossing platform in experimental group were significantly decreased compared with the control group(time: t=4.575,P<0.01;numbers: t=2.230,P<0.05).(2)HE stain showed that the nerve cells of hippocampus in control group distributed in order,nucleuses were round or oval,nucleoli were obvious,and chromatin were homogeneous;but in the experimental group,cells in area CA1 of hippocampus distributed in disorder and pathological changes were detected obviously,such as necrosis and obvious nuclear pyknosis,and cells distributed sparsely and in disorder in area DG.(3)Immunofluorescence stain showed that MR and GR were expressed in all regions of hippocampus,especially in area CA1.In area CA1,the average optical density(AOD)of MR and GR all decreased significantly in the experimental group compared with the control group(t=2.470,2.398,all P<0.05),and there was no differences between experimental group and control group in MR/GR.In area CA3,the AOD of MR?AOD of GR and MR/GR of experimental group had no differences with the control group.In area DG,the AOD of GR increased significantly in experimental group compared with the control group(t=-3.720,P<0.01),and MR/GR decreased significantly compared with the control group(t=2.151,P<0.05).(4)Western blotting showed that the expression level of MR in area CA1 and area CA3 decreased significantly in experimental group compared with the control group(CA1: t=7.561,P<0.01;CA3: t=3.092,P<0.05).At the same time,the expression level of GR in area CA1 decreased significantly in experimental group compared with the control(t=7.238,P<0.01),but increased significantly compared with the control group in area DG(t=-6.470,P<0.01).(5)There was no difference between the two groups in basal plasma level of corticosterone,and both groups responded to dexamethasone injection with a significant decrease in plasma corticosterone concentration relative to basal concentrations(experimental group: t=8.092,P<0.01;control group: t=13.343,P<0.01).It indicated that HPA axis was suppressed by dexamethasone.Conclusion Offspring rats' ability of exploring new environment and the ability of spatial learning and memory are significantly impaired by intrauterine infection.In experimental group,hippocampal pathology appears the damage of different degree and the expression of MR and GR in hippocampus have different degrees of change,but the regulatory function of HPA axis of experimental group have no difference with control group.The changed expression of MR and GR in hippocampus might be associated with the hippocampus-dependent learning and memory dysfunction which were leaded by LPS-mediated intrauterine infection. |
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