Enhanced locomotion of mGluR2–/– KO mice in novel environments. (A) Mice were placed in the open field and distance traveled was measured every 5 min for a 30-min period [(n = 19 (WT) and 17 (KO)]. There is a significant increase in locomotor activity in mGluR2–/– KO mice as compared with WT mice [genotype effect, F(1, 34) = 4.55, P = 0.040] (*, P < 0.05). (B) Distances traveled were measured for a 10-min period in the indicated tests. Data are presented as percentages of average value of WT mice. Differences in distances traveled are not statistically significant between mGluR2–/– KO and WT mice in these tests, but mGluR2–/– KO mice displayed a tendency to increase locomotor activity in all three tests; the light-dark transition test, P = 0.36, n = 21 (WT) and 19 (KO); the elevated-plus maze test, P = 0.25, n = 21 (WT) and 19 (KO); the social interaction test, P = 0.21, n = 10 pairs (WT) and 9 pairs (KO). (C) Distances traveled of mGluR2–/– KO (n = 16) and WT (n = 16) mice in their home cages exposed to a light-dark cycle of 12 h/12 h were measured at each 60-min point. There is no statistical difference between the two genotypes [genotype effect, F(1, 30) = 0.000, P = 0.999].