Abstract： Objective To explore changes in cognitive and memory function in the Alzheimer's disease (AD) model rats,and also its association with the changes in the expressions of brain-derived neurotrophic factor (BDNF),tyrosine kinase receptor B (TrkB) and synaptophysin in hippocampus,following HBO treatment.Methods The rats were randomly divided into 4 groups:the normal control group,the sham surgical group (5μ1 of saline were injected into bilateral hippocampus),the model control group (5μl of Aβ25-35 were injected into bilateral hippocampus) and the HBO treatment group (5μl of Aβ25-35 were injected into bilateral hippocampus and treated with HBO),each consisting of 10 animals.During the experiment,the rats were fed with conventional clean food and were kept in a space with constant temperature.Two weeks after injection with Aβ25-35,the rats were treated with HBO.Following completion of treatment,the rats of all the groups had the Morris water maze tests,i.e.navigational experiment and space exploration experiment,to detect changes in cognitive and spatial memory.Then,the expression levels of BDNF,TrkB and synaptophys in hippocampus were detected by Western Blot and immunohistochemistry.Results The results of the Morris water maze tests indicated that the number of running across the platform for the rats in the HBO group was 3.3 and the percentage of swimming in the original quadrant accounted for 30％,and statistical significance could be seen when comparisons were made (P ＜ 0.05).It was suggested that HBO could significantly improve spatial memory of the AD model rats,and at the same time it could enhance the expressions of BDNF,TrkB and synaptophysin in hippocampus.Statistical significance could be noted when it was compared with the model control group (P ＜ 0.05).Conclusions HBO might increase the expression levels of BDNF,TrkB and synaptophysin,which were closely associated with memory,thus improving the cognitive function and spatial memory of the AD model rats.