After-effects of Repetitive Anodal Transcranial Direct Current Stimulation on Learning and Memory in a Rat Model of Alzheimer's Disease

Repetitive anodal transcranial direct current stimulation (tDCS) in a rat model of Alzheimer's disease (AD) has been shown to have distinct neuroprotective effects. Moreover, the effects of anodal tDCS not only occur during the stimulation but also persist after the stimulation has ended (after-effects). Here, the duration of the after-effects induced by repetitive anodal tDCS was investigated based on our previous studies. Adult male Sprague-Dawley rats were divided into three groups: a sham group, a β-amyloid (Aβ) group (AD group) and a stimulation group (ATD group). Aβ was injected into the bilateral hippocampi of the rats in the AD and ATD groups to produce the AD model. Rats in the ATD group underwent 10 sessions of anodal tDCS, and the after-effects of repetitive anodal tDCS were evaluated by behavioral and histological analyses. A Morris water maze (MWM) was utilized on a monthly basis to assess spatial learning and memory abilities. The ATD group showed shorter escape latencies and more platform region crossings than the AD group. Hippocampal choline acetyltransferase (ChAT) and glial fibrillary acidic protein (GFAP) immunohistochemical analyses were carried out after the last MWM assessment. The immunohistochemistry results showed notable differences among the groups, particularly between the AD and ATD groups. This study reveals that repetitive anodal tDCS can not only improve cognitive function and memory performance but also has long-term after-effects that persist for 2 months.