BEHAVIORAL-ASSESSMENT OF THE TS65DN MOUSE, A MODEL FOR DOWN-SYNDROME - ALTERED BEHAVIOR IN THE ELEVATED PLUS-MAZE AND OPEN-FIELD

The Ts65Dn mouse carries a partial trisomy for mouse chromosome 16 in a region that has high homology to the Down syndrome (DS) region of hu man chromosome 21 and is, thus, a potential animal model of DS. The fo cus of the present study was to begin to characterize the behavioral p henotype of this mouse to assess its usefulness as a model of aspects of the DS phenotype. The behavior of Ts65Dn and littermate control mic e was assessed in the elevated plus maze, lighted and dark open held, and a step-down passive avoidance task. The behavior of Ts65Dn mice in these tests differed considerably from the nontrisomic controls. In t he elevated plus maze, Ts65Dn had more total arm visits than controls, showed a higher percentage of arm visits to the open arms than contro l mice, and showed no preference for the closed arms. Ts65Dn mice were more active in both open-held situations, regardless of light conditi on, and ventured into the center of the arena more than controls. Ligh ting in the open field had moderate effects on the activity of the Ts6 5Dn mice, but control mice were, as expected, much more active in the dark than the light. The trisomic mice learned and retained the step-d own passive avoidance task in the same number of trials as the control s. Overall, these data indicate that Ts65Dn mice are more active than control mice in two testing situations. Most striking is the finding t hat the Ts65Dn mice were much less responsive to variations in environ mental cues to which normal mice are quite sensitive. These data not o nly begin to characterize systematically the Ts65Dn phenotype, but als o raise several interesting issues about the sources of the aberrant b ehaviors observed in these mice.