“…Elevated locomotor activity is one of the more consistent behavioral phenotypic traits of DAT KO mice (Giros et al, 1996;Spielewoy et al, 2000;Gainetdinov et al, 2001); in the present study, these mice exhibited levels of activity in a novel environment, that is, their total distance traveled two to three times those of WT and HT mice. The finding that M100907 can reverse hyperactivity selectively in DAT KO mice, which have elevated synaptic levels of dopamine (Gainetdinov et al, 1999), complements earlier reports that M100907 reverses the behavioral hyperactivity induced by indirect dopamine agonists, such as cocaine, d-amphetamine and GBR 12909, in both rats and mice Carlsson, 1995;Kehne et al, 1996;O'Neill et al, 1999;McMahon and Cunningham, 2001). Although the between-cohorts design of the locomotor tasks in the present study, using different cohorts of mice with different doses, precluded an explicit test of dose-dependency of M100907, the greater relative effect size of the highest dose strongly suggests that behavioral effects were dose related.…”