| PURPOSEIn the current study we investigated whether a long-term progesterone(PROG) injection could have beneficial effects in promoting the learning and memory capability in ovariectomized mice.In addition,we also made a detection of some biochemical indicators which is related to the learning and memory capability and a histological analyses of hippocampus tissue to determine if PROG have a neuroprotective effect in ovariectomized mice.METHODSPART 1:60 female Kunming mice served as sham control or received bilateral ovariectomy followed by a 90-day regimen of different PROG(50mg/kg,100mg/kg, 200mg/kg,respectively) or normal saline(10ml/kg) beginning 2 weeks after ovariectomy operation,PROG injections was given once per 5 days by intraperitoneal injection.At the end of the administration,we first test the acquisition and retrieval of an avoidance learning task using Y-maze,and then the spatial learning ability was also tested on a Morris water maze(MWM) spatial navigation task.PART 2:After the learning and memory performance of mice,we executed them all and took out the total brain tissue;some of them were used for determining the levels of Superoxide Dismutase(SOD),Maleic Dialdehyde(MDA),Acetylcholine Esterase(ACHE) and Total Antioxygen Capability(T-AOC) in hippocampus tissue; the other brains were made into coronal slices stained by Cresyl violet after paraffin imbedding,Subsequent morphological observation and histological analyses of hippocampus tissue were conducted to determine quantitatively the amount of neuron and the thickness of pyramidal layer in the region CA1,CA3 and granular layer in DG region in hippocampus.RESULTSPART 1:THE RESULTS OF THE TEST ON LEARNING AND MEMORY CAPABILITY IN EACH GROUP1.The main results of Y-maze behavior examination are as follows:After the performance of the acquisition and retrieval of an avoidance learning task using Y-maze,compared with the Sham control group,the ovariectomized(OVX) group has low correct trials in the stage of acquisition and retrieval(P＜0.05); compared with the OVX group,the correct trials in high-dose progesterone treated (HP) group is higher(P＜0.05) in the stage of retrieval;these indicate that HP can enhance the avoidance learning capability in ovariectomized mice.2.The main results of spatial learning ability test on a MWM spatial navigation task:①Place navigation:Compared with the OVX group,the escape latency to the hidden platform was significantly shortened in HP group in the 3rd,5th day during which the escape latency degraded fast in each group(P＜0.05);and the platform memory percentage is much higher(P＜0.05) in the 5th,7th day.②Spatial probe test:Compared with the OVX group,the Sham control group and HP group have a higher time(distance) percentage of the original platform quandrant(P＜0.05).PART 2:THE RELATIONSHIP BETWEEN PROG AND HIPPOCAMPUS TISSUE.1.The results of biochemistry detections in hippocampus tissue:①the comparison result of AchE level in hippocampus tissue among all groups: Compared with the Sham control group,other groups all have a lower level of AchE (P＜0.05),and there is no significant difference among OVX,LP,MP and HP group. ②The comparison result of SOD level in hippocampus tissue among all groups: Compared with the OVX group,MP,SOD level in HP group and Sham control group is much higher(P＜0.05) in hippocampus tissue.③The comparison result of MDA level in hippocampus tissue among all groups: Compared with the OVX group,MDA level in HP group and Sham control group is significantly high(P＜0.05) in hippocampus tissue.④The comparison result of T-AOC in hippocampus tissue among all groups: Compared with the OVX group,the T-AOC in HP group and sham control group is much higher in hippocampus tissue(P＜0.05).2.Quantitative analysis of slices from hippocampus tissue①The comparison result of the neuron amount in pyramidal layer of CA1,CA3 and granular layer of DG in hippocampus:In the region CA1:Compared with the OVX group,the amount of neuron in HP and sham control groups is much higher(P＜0.05).other groups have no significant difference in this region.In the region CA3:Compared with the OVX group,only the neuron amount in Sham control group is significantly high(P＜0.05),the other groups have no significant change in this region.In the region DG:after the comparison between the 5 groups,we found the result was similar to what we had found in CA3.②The comparison result of thickness of pyramidal layer in the region CA1,CA3 and granular layer in region DG in hippocampus:In the region CA1:Compared with the OVX group,the thickness of pyramidal layer is much higher(P＜0.05) in HP and Sham control groups.In the region CA3:Compared with the OVX group,only sham control group have a more thickness in pyramidal layer. In the region DG:Compared with the OVX group,HP and Sham control groups' thickness of granular layer is much higher.③Morphological observation on histological section of hippocampus:Compared with the OVX group(×40 &×100),the neurons of pyramidal layer or granular layer in HP group were arranged orderly,and the layers which is formed by neurons is clearer,moreover,the demarcation between hippocampus and cerebral cortex is more distinct.Compared with the OVX group(×400),in HP group most of the neurons are plesiomorphism and were colored more equally,the boundary among neurons is much clearer and the endochylema more plentiful.In the neurons,Nissle body can be saw more easily and the nucleolus is clear and located in the center of neurons.ConclusionDeficiency of estrogen and progesterone can cause a descent in learning and memory capability in adult female mice,which can be retrieved by a long-term regimen of progesterone(200mg/kg).One of the mechanism of action from PROG in promoting the learning and memory capability in ovariectomized maybe attributed to the antioxidation capacity of PROG.we found that Free radical-induced lipid membrane peroxidation in hippocampus tissue can be inhibited by PROG,which is important in sustaining normal texture and function of hippocampus.PROG has neuroprotective effect and trophic action on the neuron of hippocampus in ovariectomized mice.
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