EFFECTS OF A SHELTER ON OPEN-HELD ACTIVITY OF RATS (RATTUS-NORVEGICUS) AND MICE (MUS MUSCULUS)

Effects of a shelter on open-field activity of rats and mice were exam ined. Subjects were both sexes of Wistar-Imamichi/Iar and F344/DuCrj s train rats and BALB/c and C57BL/6 strain mice. They were individually tested in three situations in a random order: (1) a standard open fiel d, where the subject was first placed in a start box at a corner of th e field (forced situation: FO); (2) an open field with a shelter, wher e the shelter was used as the start box (free situation: FR); and (3) an open field with a shelter, where a start box was used (forced-free situation: FF). Both species were less active in the FR and FF situati ons than in the FO situation, indicating that the presence of a shelte r suppressed open-held activity of the animals. Data did not support t he thesis that a shelter provides security to animals. For example, a few rats in the FF situation did not enter the shelter, although they showed enough ambulation to reach it. Also, many mice in the FR and FF situations left it hastily or hesitated to enter it. Behavioral diffe rences by species, strain, and sex were also discussed.