Figure 2.

Locomotor hyperactivity of M₄R KO mice. (A-D) M₄R KO mice displayed an increase in novelty-induced locomotor hyperactivity in the open field test. (A) M₄R KO mice traveled significantly longer than wild-type mice during the whole experimental period. Locomotor hyperactivity of M₄R KO was detected in the earlier (1-10 min) part of the experiment but not in the middle (11-20 min) or later (21-30 min) parts of the experimental period. No significant differences were observed between genotypes in vertical activity (B) or margin time (C). (D) M₄R KO mice demonstrated a significant increase in stereotypic behavior counts. M₄R KO, n = 19; wild-type mice, n = 27. (E-H) M₄R KO mice exhibited locomotor hyperactivity in the light/dark transition test. (E) M₄R KO mice traveled significantly longer than wild-type mice in the dark box but not in the light box. No significant difference was observed between genotypes in time spent in the light box (F), the number of transitions between the light and dark sides (G), or latency to entering the light box (H). M₄R KO mice, n = 28; wild-type mice, n = 28.