Behavioral tests

The rotarod test was performed as previously described, with modifications³⁴. Briefly, 6 days after the last MPTP injection, all mice received four rounds of training on the rotarod (Stoelting Co.). In the first two rounds of training, the rotarod was maintained at a constant speed of 20 r.p.m. for 3 min. In the second two rounds of training, the rotarod reversed rotation direction every three turns at the constant speed of 20 r.p.m. for 3 min. Twenty-four hours after the last round of training, all groups of mice received formal rotarod testing in which the rotarod reversed rotation direction every three turns at the constant speed of 20 r.p.m. Mice were tested ten times at 20 min intervals, and the time that they remained on the rotarod during each test was recorded. Maximum test time (cut-off limit) was 300 s. The motor performance of the mouse was expressed as the latency to fall off the rotarod.

In order to study motor function in M83 mice, rotarod and wire-hang tests were performed at days 1, 45, and 92 of the experiment, in mice that had been previously trained for the tests. For the rotarod test (Bioseb), the speed of the rotating rod gradually increased by 40 r.p.m. every 30 s, for a maximal time of 5 min. For the wire-hang test, a wire (diameter between 2 and 3 mm) was placed horizontally in a plastic box (length 52 cm, width 38 cm, height 34 cm). The mouse was placed on the wire hanging upside down. The latency of fall from the wire was recorded up to a maximal time of 3 min. The behavioral tests were performed in triplicate and the best performance was used for statistical analysis.