2.4. Novel object recognition test

The novel object recognition test (NOR) was performed to measure the ability of animals to identify a novel object in a familiar environment as previously described.²⁴ In the NOR test, each rat is subjected to three tasks over 3 consecutive days. On day 1, the habituation phase, each rat was acclimated to the experimental area (50 × 50 × 40 cm) for 10 minutes once daily in the absent of any behavioral stimulus. On day 2, the training phase, two identical objects were placed into the area, and each animal was permitted to explore the objects for 5 minutes. On day 3, the retention phase, one of the old objects was replaced with a novel one, and each rat explored the novel object for 5 minutes. Exploration was referred to touching the novel object with the nose and/or pointing the nose to it at a distance <1 cm. To eliminate the odor cues, the field and the objects were fully decontaminated with 70% alcohol, dried, and ventilated between two tests. The time spent exploring each object was recorded using a video‐assisted tracking system. The cognitive function of rats was presented as the discrimination index (DI) [= (novel object exploration time − familiar object exploration time)/total exploration time × 100%].