Research On The Learning And Memory Mechnism Of Novelty Acquisition And Effect Of Stress On Synaptic Plasticty In Rats

Learning and memory are one of the important role in brain,and hippocamou is a crucial structure.In 1949,a famous hypothesis that Hebb postulated activity-dependent synaptic plastity is beilived to the cellur mechnism of learning and memory.Synaptic plastity in hippocanpus is cellur and molecular mechnism of learning and memory and a direct material fundment.Therefore,synaptic plastity which reflected the level of information transmission is an important index studied learning and memory.Novelty environmental exploration is one of the model that spatial exploration in rats.Thus,we studied the mechnism of learning and memery,and effect of stress on process of learning and memory.Recordings were taken from freely moving rats,that had undergone chronic implantation of a recording electrode in the hippocampal CA1 area,and stimulated Schaffer collateral-commissural pathway,and recorded the excitatory post synaptic potentiatials(EPSPs) in hippocampal CA1 area stratum radiatum.Without any high or low-frequency induction,we investivated mechanism of learning and memory at 0h and memory retrival at 24h during exploration of novelty environment,and furthermore, hippocampus that expressed enrichmentally in mineralcorticoid receptors and glucocorticoid receptors was sensitived to stress,and so we studied stress impaired learning and memory in some degree.The main results were as follow:Without any induction,input/output curve which rats have adjusted to grasp decreased sharply compared to explore novelty environment before.Novelty exploration induced to decreased amplitudes of EPSP at four stimualte intensities(3.5,4.5,5.0V,P＜0.01;4V, P＜0.05,n=8).Baseline also decreased sharply(74.32±3.58%,P＜0.01,T test,n=9) and generated LTD,This stratuated that rats acquisitioned novelty information by LTD. However,grasp stress disrupted novelty learning process and impaired the novelty acquisition in hippocampus by blocking LTD.Baseline which rats have grasped increased signficantly(133.01±7.04,P＜0.01,T test,n=7) in hippocampal CA1 area and generated LTP.This illustrated that grasp stress disrupted significantly learning procress by LTE At 24h,input/output curve significantly rose,EPSP amplitudes increased sharply at two stimulate intensities(4.0V,P＜0.05;5.0V,P＜0.01,n=6),baseline significantly increased too(132.66±7.46%,P＜0.05,T test,n=6).The results confirmed that memory retrivaled by LTP;However,grasp stress not only disrupted learning procress,but also impaired memory retrival too.When animals that have grasped retrivaled memory at 24h,input/output curve during memory retrival had not difference (P＞0.05,n=3),and baseline also had a descent trend(88.50±4.82%,P＞0.05,T test,n=5). This phenonmen straterated that grasp impaired 24h short-term memory retrival by blocking LTP;After 1h familiar environment adaption at 48h,input/output curve had not significantly difference(104.56±3.40%,P＞0.05,T test,n=4),and baseline had not distinction too(P＜0.05,T test,n=4).The results illustrated that animals have adapted to novelty environment,and synaptic plastity did not change;When animals explored novelty objects at 72h in familiar environment A,baseline decreased significantly (54.72±11.60%,P＜0.05,T test,n=5) and generated LTD,this results confirmed the result of novelty acquisition at 0h once again.When rats were place in anther novelty environment B at 72h,baseline also decreased signficantly(78.71±4.73%,P＜0.05,T test,n=4) and generated LTD,the results confirmed that novelty acquisition storaged information by LTD in hippocampus at three times.At the same,the mechnism of the learning and memory of novelty acquisition were dopamine-dependent.D1/D5 receptor antagonist SCH23390 blocked behaviors of learning and memory during exploring novelty environment activity,baseline and input/output curve decreased at the same time.Those findings supported an important role for dopamine-regulated synaptic plasticity in the storage of unpredicted information and stress demaged the learning and memory progress in hippocampus CA1 area.Furthermore,grasp stress impaired process of learning and memory dopamine-dependent in some degree.