The Study Of The Mechanisms Of The Chronic Multiple Stress-induced Learning And Memory Impairment

Stress is a nonspecific response of the body to any demand placed upon it.Now it is customary to speak of a stressor as an event or experience thatthreatens the ability of an individual to adapt and cope. As a result, the stressorevokes a stress response, which involves the release of hormones and othercellular mediators that can promote adaptation when the response is efficientlyturned on and shut off, but which can also promote path-physiological processeswhen the response is overused or deregulated. The brain is the central in theadaptation to stress, it is also a target of stress, with animal models showingstress-induced remodeling of brain structure, such as dendritic atrophy and lossof dendritic spines in neuronal populations.Chronic multiple stress could have some bad effects on multisystem，especially on central never system by affecting the hypothalamic-pituitary-adrenal axis, glutamine and its receptor release, and the structure and the synaptic plasticity.Microglia, the resident immune cells of the mammalian central nervoussystem (CNS), play a pivotal role in both physiological and pathologicalconditions such as the restoration of CNS integrity and the progression ofneurodegenerative disorders. Extensive data have demonstrated that theneuroinflammation induced by microglia activation has detrimentalconsequences on the developing and mature brain. Our previous study foundthat exposure to chronic multiple stress can induce the microglia activation andinhibition of the microglia activation may play an important role in learning andmemory decline induced by chronic multiple stress.[Aim]：1. To study the effects of chronic multiple stress on hippocampal neuronsactivities, hippocampal microglia activities, learning and memory capacity inRats.2. To investigate the effects and mechanisms of microglia activation onchronic multiple stress-induced neuronal injury.3. To proclaim the regulatory mechanisms of Erk signal pathway, andprovide some experiment base for the prevention for stress impairment.[Methods]：1．Forty male SD rats were randomly divided into four group：control group,stress group, control+minocycline group, stress+minocycline group. Theanimal model of chronic multiple stress was established by exposing to one outof seven stressors every day, including food or water deprivation，day nightreverse，cage tilt45degrees，single cage alone，restraint，4℃cold exposure，and forced swim for3weeks. 2．The ability of spatial memory was determined by Morris Water mazeexperiments; LTP was recorded by the patch-clamp technique.3．The morphological changes of microglia and hippocampal neurons wereobserved by a fluorescence microscope. Detection of the expression of IL-1βand TNF-α by ELISA, The number of apoptotic cells was determined byTUNEL in situ assay kit．Western blot was performed to determine theexpression and phosphorylation of MAPKs、GluR1in hippocampal of the brain．[Results]：1. Chronic multiple stress impaired the learning and memory function in Rats.The chronic multiple stress animal models were established by exposing to oneout of seven stressors for3weeks. Hidden platform test suggested that incomparison to the control group, the latency was significantly longer in chronicmultiple stress group (p<0.05); the probe test showed that compare to the controlgroup, the explore time of target quadrant was significantly shorter in chronicmultiple stress group (p<0.05);LTP induction was significantly shorter inchronic multiple stress group through the patch-clamptechnique(p<0.05).chronic multiple stress induced the activation of microgliaand cell apoptosis of neuron in hippocampus in Rats.2. The results of fluorescence showed the stress resulted in more apoptotic cellsand activated microglia compared with the control group (p<0.05),accompanying significantly higher IL-1β and TNF-α levels in chronic multiplestress group (p<0.05).3．Chronic multiple stress resulted in declined expression of p-Erk1/2andGluR1in Hippocampus in Rats.4. Western blot demonstrated that the stress resulted insignificantly decreased p-Erk1and GluR1level in Hippocampus (P<0.05)．5. Minocycline decreases the productions of the activated microglia, andreversed the down-regulated P-Erk1and GluR1levels in Hippocampus.Following the treatment of minocycline, the activation of microglia wassignificant suppressed（P<0.05）, the expression of TNF-α、IL-1β was significantincreased; the expression of p-Erk1/2、GluR1recovered and had no statisticalsignificant difference compared with the stress group（P<0.05).6. Inhibition of the microglia activation could protect the neuron inhippocampus, and increased the learning and memory function and LTPinduction.Following the treatment of minocycline, the number of apoptotic cellsapoptosis was reversed, LTP induction was significant increased compared withthe stress group（P <0.05）, The spatial memory function was significant higherthan that of the stress group（P>0.05).[Conclusions]：1. Chronic multiple stress induced the activation of microglia and cell apoptosisof neurons in hippocampus and impaired the learning and memory function inrats.2. Chronic multiple stress may activate the microglia, and then induce the cellapoptosis in hippocampus, and impaired the learning and memory function.3. Microglia may suppress the expression of phosphorylation of Erk1/2andGluR1in hippocampus neurons, and then suppress the LTP induction and theneuron apoptosis, leading to the impaired learning and memory.