Protective effects of astragalosides on dexamethasone and Aβ25-35 induced learning and memory impairments due to decrease amyloid precursor protein expression in 12-month male rats

Alzheimer's disease (AD) is a chronic neurodegenerative disorder of the elderly characterized by learning and memory impairment. Stress level glucocorticoids (GCs) and beta-amyloid (A beta) peptide deposition are found to be correlated with dementia progression in patients with AD. The astragalosides (AST) was extracted from traditional Chinese herb Astragalus membranaceous. In this study, 12 months male rats were treated with A beta(25-35) (10 mu g/rat, hippocampal CA1 injection) and dexamethasone (DEX, 1.5 mg/kg, ig) and AST (8, 16 and 32 mg/kg, ig) or ginsenoside Rg1 (Rg1, 5 mg/kg, ig) for 14 days. We investigated the protective effect of AST against DEX + A beta(25-35) injury in rats and its mechanisms of action. Our results indicate that DEX + A beta(25-35) can induce learning and memory impairments and increase APP and A beta(1-40) expression. AST (16, 32 mg/kg) or Rg1 (5 mg/kg) treatment significantly improve learning and memory, down-regulate the mRNA levels of APP and beta-secretase, decrease expression of APP and A beta(1-40) in hippocampus. The results indicated that DEX might increase hippocampal vulnerability to A beta(25-35) and highlight the potential neuronal protection of AST. (C) 2012 Elsevier Ltd. All rights reserved.