Changes of learning and memory in aged rats after isoflurane inhalational anaesthesia correlated with hippocampal acetylcholine level.Ann Fr Anesth Reanim 2012; 31(3):e61-6AF
BACKGROUND AND PURPOSE
It has not been clearly described for mechanisms of postoperative cognitive dysfunction (POCD), but not yet for narcotic in connection with POCD. Acetylcholine plays important roles in learning and memory especially in elderly people. It is not very clear that cholinergic changes in the hippocampus are in relation to spatial memory impairment. The effects of isoflurane, a commonly used inhalation anaesthetic, as well as acetylcholine on learning and memory in the brain tissue of aged rats were observed in present study. We investigated the inhalation anaesthesia drug's effect on cholinergic system to examine whether the regional and progressive cholinergic changes may lead to POCD.
Seventeen-month-old rats were randomly assigned to either an isoflurane anaesthesia group (n=17) or propofol anaesthesia group (n=17). In isoflurane anaesthesia experiment group, isoflurane (1.4 to 1.7% for 2 hours) was delivered via a ventilator to make freely moving microdialysis model. In propofol group, propofol was administered by continuous infusion via a tail vein catheter to make freely moving microdialysis model. They were all mechanically ventilated. Morris Water Maze test was used to assess the learning and memory abilities of all the two groups' rats twice a day for 5 days. Microdialysis was performed on the freely moving rats to determine the levels of acetylcholine in the brain tissues immediately after each Water Maze test.
The isoflurane anaesthesia treatment increased the escape latency contrast to propofol anaesthesia group. The isoflurane anaesthesia's rats were then divided into isoflurane-induced severe learning/memory impairment group (n=6, mean escape latency is 1.96 times more than that of in propofol anaesthesia group) and the isoflurane-induced mild learning/memory impairment group (n=11, mean escape latency is equal or less than 1.96 times of that in propofol anaesthesia group). The results demonstrated that those rats that were categorized in the isoflurane-induced severe learning/memory impairment group had decreased levels of acetylcholine in the brain tissue as compared to those rats categorized in the mild learning/memory impairment group and in propofol anaesthesia group.
The results indicated that isoflurane may impair learning and memory in aged rats.