The Comparison of the Effects of Different Transcranial Electrical Stimulation(tES) Paradigms on Beta-Amyloid (Aβ 25-35)-Induced Memory Impairmentupon Morris Water Maze Task in Male Rats

Background: In light of therapeutic limitations in Alzheimer's disease (AD), recent alternative or add-on treatment approaches such as non-invasive brain stimulation through transcranial electrical stimulation (tES) have gained attention. Translational studies have postulated that transcranial direct current stimulation (tDCS) is potentially a novel therapeutic option to reverse or stablize cognitive impairments. The aim of this study was to comparatively evaluate the effects of the four main paradigms of tES, including tDCS, transcranial alternative current stimulation (tACS), transcranial random noise stimulation (tRNS), and transcranial pulse current stimulation (tPCS) on beta amyloid 25-35 (Aβ 25-35)-induced memory impairment in male rats submitted to the Morris water maze (MWM) task. Method: To develop AD model in Sprague-Dawley male rats weighing 250-270, the cannula was implanted bilaterally into the hippocampi. Aβ 25-35 (5 μg/2.5 ml/ day) was microinjected bilaterally for 4 days. Then, tES was applied to the animals for 6 days. Subsequently, rats’ learning and memory function was evaluated on day 11-14 in MWM task. Results: Our findings indicated that tDCS, tACS, tRNS reduced escape latency, while such an effect was not observed in tPCS paradigm. In terms of the duration of animals’ presence in the platform quadrant, tDCS and tACS increased the outcome measure. Conclusion: We conclude that tDCS and tACS are more effective than the other two examined paradigms of tES in ameliorating learning and memory impairments.