2.3. Behavioral Tests

We performed a rotarod, suspension test, pole test, and forced swimming 3 days after the last MPTP injection. The rotarod test is widely used to generally assess motor performance, which was done as described previously and modified a little [15]. Mice were trained for two consecutive days before MPTP injections in acceleration mode (2–20 rpm) over 5 min. The training was repeated at a fixed speed (15 rpm) until the mice were able to stay on the rod for at least 150 s. After MPTP and crocetin treatment, the time falling down from rod was recorded in acceleration mode (2–20 rpm). For suspension experiment, C57BL/6J mice were placed on a horizontal wire of ∼1.5 mm in diameter, suspended 30 cm from the ground, and the hang time was recorded to detect mouse limb coordination. The pole test is used to assess motor function and was done as described previously [16]. Mice were placed facing upwards at the top of a pole (1 cm in diameter, 45 cm in length) that had been covered with surgical tape to provide a rough surface and capped with a flat plastic disc to prevent the mouse from traversing the top of the pole. The times for the mouse to turn and face downwards (turn time) and for the mouse to descend into the home cage (total time) were recorded. Mice were trained on the task for two days before MPTP treatment. The test trial was performed three times per animal, and average values from three examinations were used for each animal. For the forced-swimming test, C57BL/6J mice in each group were dropped individually into glass cylinders (10 × 10 cm) containing 10 cm deep water that maintained at 25 ± 1°C and remained for 6 min. The time of swimming was recorded during the last 4 min of the 6-min testing period, followed by 2 min of habituation.