Up-regulation of Alzheimer's disease-associated proteins may cause enflurane anesthesia induced cognitive decline in aged rats

Isoflurane anesthesia can cause post-operative cognitive dysfunction in elderly patients. As an isomer of isoflurane, enflurane may also account for cognitive dys- function. However, the mechanism of enflurane-induced cognitive dysfunction remains obscure. In this study, we investigated the effects of enflurane anesthesia on cognitive function and the possible roles of b-amyloid protein and phosphorylated tau protein in response to enflurane anes- thesia in aged rats. After intraperitoneal injection of enflurane, the Morris water maze and the step-down pas- sive avoidance tests were conducted to test the cognitive ability and memory. The enflurane group showed pro- longed escape latency, extended space exploration time and increased number of errors at early stage after enflu- rane anesthesia, suggesting that enflurane should be responsible for the impairment of cognition in aged rats. In addition, we analyzed the expression level of b-amyloid and phosphorylation level of tau in the hippocampus by immunoblotting. Interestingly, the levels of b-amyloid and phosphorylated tau in the hippocampus increased signifi- cantly at early stage and then restored to pre-anesthetic levels. Taken together, our results suggest that increasing of b-amyloid and phosphorylation of tau are important to cause cognitive decline in aged rats during initial stage after enflurane anesthesia.