Background: Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive and behavioral impairment. Currently, medication is the main management for patients with AD but pharmacologic treatments are accompanied by adverse effects and the response is limited. Recently, transcranial alternating current stimulation (tACS) has been used as a non-invasive methods in various disease to improve cognitive function. Previous studies have shown reduced activity of gamma oscillations in hippocampus and entorhinal cortex in AD transgenic mouse, which are key regions in the formation of memory. Also, it is known that tACS can manipulates the intrinsic oscillations of the brain. However, there are little evidence whether tACS improves congnitive function in AD. So, we conducted a tACS experiment in transgenic mouse of AD to find out its effectiveness on cognitive function.
Method: Twenty mice of 4 months old were devided into 4 groups of five mice each ; 5xFAD mouse with no stimulation (AD-NT group), 5xFAD mouse receiving tACS (AD-T group), wild type mouse with no stimulation (WT-NT group) and wild type mouse receiving tACS (WT-T group). Stimulation group was received tACS with gamma frequency (40Hz), 200μA over F3 and F4 (bilateral frontal lobe) area for 20 minutes across 2 weeks (5 times a week). As a behavior test, Y-maze was performed to assess working memory for 7 mintues. In this test, the spontaneous alternation ratio was used and calculated as [(number of alternations) / (total arm entries − 2)] × 100. After 2 weeks of stimulation, mices’s hippocampus was extracted and analyzed through Western blot (BDNF, CREB and pCREB). BDNF is a critical regulator of synaptic plasticity which is mediated by CREB and pCREB. Excitatory postsynaptic potential (EPSP) recording was performed to investigate synaptic plasticity of the hippocampus. Since the experiment with two mices of AD-NT group was not completed, the results were analyzed with eighteen mice.
Result : The spontaneous alternation ratio was AD-NT group (61.57±3.75), AD-T group (65.74±6.47), WT-NT group (63.26±5.65) and WT-T group (63.76±3.93) (Fig. 1). Although there were no significant difference between groups, the spontaneous alternation ratio of AD-T group was higher than that of AD-NT group. The level of BDNF, CREB and pCREB of AD-T group was higher than that of AD-NT group in the result of Western blot (Fig. 2). In particular, the level of BDNF significantly higher in AD-T group compared the AD-NT group (p<0.05). The EPSP result showed AD-NT group (120.94±6.37), AD-T group (159.56±44.54), WT-NT group (158.80±22.81) and WT-T group (144.61±9.39) (Fig. 3). The EPSP significantly increased in AD-T group compared the AD-NT group (p<0.01).
Conclusion: In this study, we confirmed improvement of cognitive function in transgenic mouse of AD via behavior test, electrophysiologic test and western blot analysis throught stimulation of gamma tACS in frontal lobe. |
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Fig 1. Y-maze test and spontaneous alternation ratio.
Fig 2. Western blot analysis of CREB, pCREB and BDNF; (a) representative bands of CREP, pCREB and BDNF. (b) quantitiative BDNF expression level. (c) quantitiative CREB expression level. (d) quantitiative pCREB expression level.
Fig 3. The field EPSP (fEPSP) responses in each group; we recorded the hippocampal long term potentiation (LTP) in each group of mice that either received tACS or no stimulation.
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