Figure 4.

Locomotor activity. Performances in an open field of 24-week-old En1+/− and WT mice expressed as the mean ± SD of distance traveled in centimeters (A), number (mean ± SD) of rearings (B), and time spent in the central zone (C); **p < 0.01. D, Effect of amphetamine (2 mg/kg) on the distance traveled in the open field (in centimeters; mean ± SD) by WT and En1+/− mice during the 30 min that follow injection. Mice are 32–33 weeks old at the time of the test. Animals receive either saline (Sal) or amphetamine (Amph). Differences (Student's t test): En1+/− versus WT, *p < 0.05; Amph versus Sal, ^#p < 0.05 and ^##p < 0.01. Amphetamine administration at a dose of 5 mg/kg induces hyperactivity in both WT and En1+/− mice (data not shown). E, Rotarod performances of 27-week-old En1+/− and WT mice expressed as the mean ± SD of latency (s) to fall (average of 3 trials). Although the same trend (decreased performance for En1+/− mice) was observed at all speeds, the difference did not reach significance because of the abnormally high performances of one mutant mouse of 10 (see Results).