The Effects Of Memantine Combined With Enriched Environment On The Expression Of Synaptic Plasticity-related Proteins In Hippocampus And The Learning And Memory Ability Of Senescence Accelerated Mouse Prone8

BackgroundAlzheimer’s disease (AD)，one of the most prevalent age-dependent neurodegendegenerative disorders, is characterized by synaptic dysfunction and synapticplasticity impairment in specific brain regions. At the early course of AD, the diseasegradually affects memory and learning abilities, and language skills, causes cognitiveimpairment,interferes with the individual’s ability to perform daily activities, andultimately leads to death. The AD brain is marked by extracellular amyloid plaques,and by intracellular neurofibrillary tangles, along with multiple secondary pathologiessuch as inflammation, oxidative stress, and ionic imbalance.Some animal models of AD were established to research the molecularmechanisms of AD, and to evaluate potential therapeutic interventions, such astransgenic model, destroyed model, autoimmune model and ageing model.Senescence-accelerated mouse prone-8(SAMP8), a substrain of SAMP, shows earlyonset of learning and memory deficits along with Amyloid accumulation andhyperphosphorylation of microtubule-associated protein tau in the hippocampus.Therefore, the SAMP8strain is a suitable model for studying memory and learning abilities,moreover to be applied in pathogenesis and therapeutic studies of AD.Memantine is an uncompetitive, moderate-affinity antagonist of N-methyl-D-aspartate receptor, which was approved by the Food and Drug Administration forthe treatment of moderate to severe Alzheimer’s disease. Studies have demonstratedthat Memantine improved cognitive impairment and reduced overproduction ofsoluble A beta and abnormal hyperphosphorylation of tau in transgenic mice, as wellas in the postmortem brains of patients with AD. Recently, there is growing interest inthe potential beneficial effects of Enriched environments on aging and aged animals.Environmental enrichment can improve cognitive abilities, synaptic plasticity, andrestores impaired hippocampal neurogenesis in some transgenic mouse models ofAlzheimer’s disease.Evidences strongly suggest that representative synaptic plasticity–relatedproteins are critical for spatial memory and synaptic plasticity of AD, such as brainderived neurophic factor (BDNF) and tyrosine kinase receptor B (TrkB),Synaptophysin（SYP）and Postsynaptic density protein（PSD-95）.The relativedecreased expressions of four representative synaptic plasticity–related proteins caninduce dysfunction of synaptic function and synaptic structure which may contributeto the cognitive decline.In this study, we used SAMP8mice as AD model to study whether Memantinecombined with Enriched environment could improve the spatial learning and memoryability in SAMP8mice. Furthermore, the cellular and molecular mechanismsinvolved in the improvment were also studied.0bjectiveTo observe the effects of Memantine combined with enriched environment (EE)on the expression of brain derived neurophic factor (BDNF) and tyrosine kinase receptor B (TrkB)、 Synaptophysin （SYP） and postsynaptic density protein（PSD-95）in hippocampus and the learning and memory ability of senescenceaccelerated mouse prone8(SAMP8).Methods24male SAMP8mouse (6-month-old) were divided randomly into standardenvironment (SE) group、treated with enriched environment (EE) group、treated withMemantine(SM) group and Mematine combined with enriched environment (EM)group，6mouse in each group. After8-week-treatment，Morris water maze test wasperformed to evaluate improvement of spatial learning and memory ability,and Openfield test was performed to measure the general locomotor activity as well as anxiety.The expression of BDNF、TrkB、SYP and PSD-95protein and mRNA were detectedby Western blotting and Real-time PCR separately。ResultsMWM：①Compared with SE group, the overall mean escape latency of EE group, SMgroup was significantly shorten since the third day, and which of EM group wasshorten since the second day (P<0.05~0.01); and the mean escape latency of EMgroup was shorter than EE group and SM group in the fourth day (all P<0.05)②Compared with SE group, the frequencies of crossing platform in the other3groups were significantly increased(P<0.05~0.01); and the frequencies of crossingplatform in the ME group was more than EE group and SM group(all P<0.05). TheSE control mouse spent significantly less time in the target quadrant than SM and EMmouse (P<0.05~0.01). However, EE and SM groups showed no difference from EMgroup (P>0.05). Open field test：①Compared with SE group,The number of square crossings and rearings of SEwas significantly lower than the other3groups (P<0.05~0.01), However, no markeddifferences were observed among SM、 EE and EM groups in locomotoractivity(P>0.05);②Compared with SE group,the numble of fecal boluses andgroomings in the other3groups decreased significantly (P<0.05~0.01). And EMgroup had a lower number of fecal boluses than control group (P<0.01). However,there was also no significant difference among SM、EE and EM group(P>0.05).Real-time PCR：Compared with control group，the levels of BDNFmRNA、SYPmRNA andPSD-95mRNA in SM、EM groups were significantly increased (P<0.01)，moreover inEM group，the level of BDNFmRNA was significantly more than the EE group andSM group (P<0.05). And the levels of BDNFmRNA and SYPmRNA in EE groupwere also significantly more than control group. However，the level of TrkBmRNA inthe other3groups were increased but had no statistical significance(P>0.05),compared with control group.Western blotting：Compared with SE group，the levels of BDNF、trkB、SYP and PSD-95proteinsin SM、EM groups were significantly increased (P<0.05~0.01). And the levels ofBDNF、trkB and SYP proteins in EE group were also significantly more than SEgroup (P<0.05~0.01). However，the level of PSD-95protein in EE group wasincreased but had no statistical significance(P>0.05), compared with control group.Moreover in EM group，the levels of BDNF、trkB and PSD-95proteins weresignificantly more than the EE group and SM group (P<0.05~0.01).Conclusions1、The Memantine and enriched environment can improve the learning and memory ability of SAMP8mouse, and increase significantly the locomotor activityand decrease the emotional reactivity of SAMP8mouse. The treatment of Memantinecombined with enriched environment has more advantage on improving the spatiallearning and memory ability of SAMP8mice than the treatment of Memantine orenriched environment alonely．2、The Memantine and enriched environment can increase the expressions of theBDNF、trkB、SYP and PSD-95in hippocampus. And the effects can be enhancedwhen Memantine combined with enriched environment；in our studies we supposethat Memantine and enriched environment improve cognitive abilities of SAMP8mouse by the molecule mechanism that they increase the expressions of the BDNF、trkB、SYP and PSD-95in hippocampus.