Spontaneous stereotypy in an animal model of Down syndrome: Ts65Dn mice

Stereotyped behaviors (e.g., body rocking) occur at high rates in individua ls with mental retardation (e.g., Down syndrome). To determine if spontaneo us stereotypy occurs in a murine model of Down syndrome, the home cage beha vior of Ts65Dn and control mice was monitored during the dark cycle. Motor activity was further assessed in novel automated test chambers, with acoust ic startle and rotor rod paradigms providing additional environmental chall enges. Spontaneous stereotypy (repetitive jumping and cage top twirling) wa s observed in the home cage in approximately half of the Ts65Dn mice, Compa red with approximately 10% of diploid controls. Repetitive jumping was obse rved exclusively in the Ts65Dn mice. In the open field, although no differe nces were found between Ts65Dn and control mice, stereotypic Ts65Dn mice ex hibited significantly less locomotor activity and rearing relative to contr ol and nonstereotypic Ts65Dn mice. Ts65Dn mice attained significantly lower rotor rod speeds but did not differ from controls in the amplitude of the acoustic startle response. These environmental challenges did not increase stereotypy over home cage rates but induced stereotypy in two additional an imals. The Ts65Dn model may aid in identifying genes associated with the de velopment and expression of stereotypy.