Isoflurane causes neocortical but not hippocampal-dependent memory impairment in mice.

Background: The aim of this study is to investigate the effect of general anaesthesia induced by isoflurane with buprenorphine on hippocampus-dependent and neocortex-dependent memory, respectively, in mice, and in addition, to compare the effects of such anaesthesia on these memory processes with the effects induced by lipopolysaccharide (LPS) administration on the same memory processes.

Methods: To assess hippocampus-dependent memory, isoflurane (for 15 min) after buprenorphine injection, or LPS 100 μg/kg (intraperitoneally) was administered 24 h before or after fear conditioning. The effect of these treatments on hippocampus-dependent memory was assessed using contextual fear-conditioning tasks at day 4. To assess neocortex-dependent memory, isoflurane anaesthesia or LPS was given 72 h after contextual fear conditioning. Neocortex-dependent memory assessment was performed at day 32.

Results: Unlike LPS injection, isoflurane with buprenorphine-induced anaesthesia does not impair freezing responses in hippocampus-dependent fear-conditioning memory tasks. On anterograde amnesia assessment: 49.67 ± 6.87% for the anaesthesia group and 54.5 ± 4.12% for the control group. On retrograde amnesia assessment: 47.16 ± 8.71% for the anaesthesia group and 54.5 ± 4.12% for control group; P > 0.05. Thus, neither isoflurane nor buprenorphine impair hippocampus-dependent memory. However, on the neocortex-dependent memory task, both isoflurane-induced anaesthesia and LPS-induced inflammation result in reduced freezing responses: 62.13 ± 5.80% for the anaesthesia group, 74.63 ± 5.69% for the LPS group, and 81.75 ± 3.26% for the control group; P < 0.05 compared with control group.

Conclusion: General anaesthesia induced by isoflurane with buprenorphine may result in impairment of neocortex-dependent memory in mouse. However, general anaesthesia so induced does not impair hippocampus-dependent memory in mouse in our experimental conditions.