The effect of cage familiarity on locomotor behavior in the open field. Arrows indicate the time point at which either a familiar container (the rat's home-cage) or an unfamiliar one (a novel cage) was introduced into the open field. Solid and open circles indicate distance traveled in the presence of a familiar and unfamiliar cage, respectively. Lines without symbols indicate the distance of travel before a cage was introduced into the open field and represent the mean of tests before placement of familiar and unfamiliar cages. Left column shows saline-treated rats and right column the quinpirole-treated group. Values are mean and SEM.