Lighter compared to deeper isoflurane anaesthesia can affect recognition memory in male C57BL/6 mice

Concerns have been raised about how deeply patients are anaesthetized, and the effects that different depths of anaesthesia may have after recovery. In order to study the anaesthetic drugs per se, and to eliminate the effect of clinical variables, several animal studies have been published. Isoflurane induced transient deficits on spatial memory at low concentrations, affecting the hippocampus. However, the influence of different concentrations of isoflurane on non-spatial memory still needs clarification. Thus, our aim was to study the effects of different depths of anaesthesia (1% and 2% isoflurane) on a non-spatial memory task, the object recognition test, in C57BL/6 adult mice.Twenty-eight 2-month-old C57BL/6 male mice were habituated to the test arena of the object recognition test for 10 min each day over 2 days before anaesthesia. Mice were then randomly allocated in different treatment groups: 1% or 2%, anaesthetized with 1% or 2% of isoflurane, respectively, for 1 h or the control group, which was not anaesthetised. Twenty-four hours after anaesthesia, the animals were placed in an arena with two identical objects and allowed to explore for 10 min-Sample Trial. One hour later, mice were allowed to explore the arena for 10 min in the presence of one of the objects presented in the previous trial (familiar object) and a novel object - Choice Trial. The time spent exploring each object was evaluated by a blinded analysis. The recognition of one object as familiar was detected based on a higher level of exploration of the novel object.Animals that were anaesthetized previously with 2% isoflurane performed at control levels, indicating the recognition of a familiar object in the object recognition task; this contrasted with the results of the group that was anaesthetized with 1% isoflurane.Lighter (1%) rather than deeper (2%) isoflurane anaesthesia may affect non-spatial memory in C57BL/6 male mice. Our results raise awareness of the need for careful consideration of the depth of anaesthesia used, especially the use of light isoflurane anaesthesia, which is often chosen to provide animal immobilization during non-invasive procedures.