| Learning and memory is a continuous process including memory acquisition, cons-olidation, retrieval and retention phase. Learning and memory impairment is one of t-he most serious problems induced by stress, and the underlying mechanisms remain unclear. The ability of stress paradoxically either to enhance or impair memory conso-lidation and retrieval is a well-documented phenomenon. In particular, the hippocam-pus, an area widely known for its role in learning and memory processing, isvulnerab-le to stress-induced neuroendocrine responses affecting structure and function. The pr-esent findings show hypothalamic-pituitary-adrenal axis participate in the process of stress-induced impairment, and glucocorticoids play a quite crucial role in this process. In the past, numerous studies have dealt with the role of glucocorticoids on process-es of memory acquisition and consolidation in both animals and human, but the litera-ture concerning the actions of glucocorticoids receptor on memory retrieval remains much less. Only a few recent studies addressed the actions of glucocorticoids receptor on memory retrieval. Opiates and opioid receptors are implicated in multiple physiol-ogical functions including learning and memory. Extensive evidence indicates opiate drugs can modulate memory process. When injected after training in a variety of tasks, opiate receptor agonists and antagonists can impair and enhance memory consolidati-on, respectively, and opiate drugs can also inflence on memory retrieval process. Stre-ss-induced learning and memory impairment involved in glucocorticoids system, and lots reports suggested endogenous opioid system can also mediate learning and mem-ory process, but the mechanism of interaction between endogenous opioid system and stress-induced memory impairment is still not clear.Previous findings of our lab indicate that blocking μ opioid receptors can reverse t-he stress-induced spatial reference memory impairment, which performed with stress before 4 days morris water maze training, but previous studies can’t show a single str-ess effect on different phase of memory process and the role of endogenous opioid sy-stem in this process. This study used drugs or stress pre-treatment at different phase of Morris water maze (MWM) to try to solve this problem.The mice were trained in the MWM for twelve consecutive trials at the 1st day, and the probe test was assessed at the 2nd and 5th day respectively with a 60-s free-swim probe trial, so all the process of memory in MWM can be divided into four phases:a-cquisition, consolidation, retrieval and retention phase. The mice were treated with e-lvated platform stress before the 1st day training, after the 1st day trainning and befo-re the 2nd day probe test of MWM, respectively, then we find that, stress before the 1st day training of MWM can damage memory acquisition phase and stress before the 2nd day probe test of MWM can damage memory retrievalphase, but stress after the 1st day training of MWM do not damage memory process. According to the previous positive research results, the mice were pre-treated with naloxone (opioid receptor an-tagonist)/naloxone+stress/CORT (glucocorticoid receptor agonist)/naloxone+CORT/ RU-486 (glucocorticoid receptor antagonist)/RU-486+stress/CTAP (opioid receptor special antagonist)/CTAP+stress respectively before the 2nd day test phase, and the results show that blocking opioid receptor, blocking opioid μ receptor specially or b1-ocking glucocorticoid receptor can reverse the effect of impairment induced by stress in spatial reference memory retrieval phase, and blocking opioid receptor can reverse the effect of impairment induced by the action of glucocorticoid receptor in spatial re-ference memory retrieval. All the findings prove endogenous opioid system can medi-ate the stress-induced impairment, but the interaction mechanisms of endogenous opi-oid system and endogenous glucocorticoid system on spatial reference memory are not well clear, which need to be further explored. |
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