Novel Object Recognition (NOR) test.

The NOR test was used to assess recognition memory as previously described [21]. Fifteen days after SE, rats were placed in the OF test chamber for 5 minutes and allowed to explore two similar objects (trial 1). Two hours after trial 1, one of the objects was replaced by a novel object. Then rats were placed back in the testing chamber and were allowed to explore the objects for 5 minutes (trial 2). The placement of the novel and familiar objects was counterbalanced to control for any potential side preferences. All trials were conducted under red light conditions and the arena and objects were thoroughly cleaned with 70% ethanol between trials. Exploration time was defined by the rats’ noses coming within 1 cm of the objects, which was tracked with Any-Maze video tracking system and verified with hand scoring by investigators blinded to treatment groups. Percent of time spent exploring the left versus right (trial 1) or familiar versus novel (trial 2) was compared. Recognition of the familiar object (Recognition Index; RI) was determined by subtracting the time spent with the familiar object during trial 2 (F2) from the time spent with the corresponding object (left or right) in trial 1 (F1) as a proportion of total exploration time [(F1-F2)/(F1+F2)] [27]. Discrimination of novel and familiar objects during trial 2 (Discrimination Index; DI) was determined by subtracting the time spent with the familiar object (F) from the time spent with the novel object (N) [(N-F)/(N+F)] as a proportion of total exploration time during trial 2 [35].