Novel Object Recognition Test

The NOR test was used here to study non-spatial memory. The test was performed in the same arena employed for the open field test. For habituation, the rat was placed into the open field without stimuli for 10 min for 2 days. For training, two identical objects were placed near the two corners of the open field (15 cm from each adjacent wall). The rat was placed into the center of the open field facing the opposite wall and was allowed 5 min for free exploration of the arena. The test began after a delay of 2 h, with the same object that was used in the training phase (familiar object) and a novel object set into the arena. The rat was placed into the arena and allowed to explore the objects for 3 min. The positions of the objects in the test and the objects used as novel or familiar were counterbalanced between the animals. The time that each rat interacted with the familiar object and the novel object was recorded. The total exploration time (e1) was calculated during the training session for two identical objects. The discrimination index (d1) was calculated as the time spent exploring the novel object minus the time spent exploring the familiar object. The discrimination ratio was calculated as the time spent exploring the novel object minus the time spent exploring the familiar object divided by the total exploration time.