Fig. 2.

Reduced response to AMPH in locomotor activity of R1441C KI mice. (A) Spontaneous activity of KI/KI (n = 14) and +/+ (n = 11) mice at 1 year of age in the open field during 1-h test. Two infrared light arrays measured horizontal movements, and one array measured vertical movements (rearing on hind legs). Repeated sequential breakings of the same beam were scored as occurrences of stereotyped behaviors (scratching, grooming, etc.). (B) Rotarod test. KI/KI and +/+ mice show similar latencies to fall off an accelerating rotating rod. The average time before falling off the rod is shown for each of three consecutive trials. (C) KI/KI and +/+ mice show similar acoustic startle responses at each decibel of loud noise tested. Each mouse was tested 10 times at each decibel level in a semirandom order with a 30-s interstimulus interval, and the startle response was averaged and normalized to body mass. Body mass does not differ between the genotypes. (D) AMPH injection (i.p., 2.0 mg/kg body weight) dramatically stimulates the locomotor activity of WT (+/+), but not that of KI/KI mice during the 1-h test (#, P < 0.05; ns, not significant). The numbers shown in the bars indicate the numbers of mice used for each experiment. Data in all panels are expressed as mean ± SEM.