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

Stereotyped behaviors (e.g., body rocking) occur at high rates in individuals with mental retardation (e.g., Down syndrome). To determine if spontaneous stereotypy occurs in a murine model of Down syndrome, the home cage behavior of Ts65Dn and control mice was monitored during the dark cycle. Motor activity was further assessed in novel automated test chambers, with acoustic startle and rotor rod paradigms providing additional environmental challenges. Spontaneous stereotypy (repetitive jumping and cage top twirling) was observed in the home cage in approximately half of the Ts65Dn mice, compared with approximately 10% of diploid controls. Repetitive jumping was observed exclusively in the Ts65Dn mice. In the open field, although no differences were found between Ts65Dn and control mice, stereotypic Ts65Dn mice exhibited significantly less locomotor activity and rearing relative to control 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 animals. The Ts65Dn model may aid in identifying genes associated with the development and expression of stereotypy.

Development of spontaneous stereotyped behavior in deer mice: effects of early and late exposure to a more complex environment.

Abnormal repetitive behaviors such as stereotypies are associated with neurodevelopmental disorders and are often observed under conditions of environmental restriction, particularly early in development. Few studies, however, have systematically assessed the effects of environmental enrichment and almost no information is available as to whether a sensitive period exists for such enrichment effects. We hypothesized that spontaneous stereotypies exhibited by deer mice housed under standard laboratory conditions were the result of environmental restriction and that a sensitive period exists for the development/prevention of stereotypies. Exposure to a more complex environment early in the post-weaning period resulted in substantially less stereotypy in the complex environment. Importantly, this outcome was maintained even after mice were housed in standard cages for an identical period of time. Later exposure to the more complex environment also resulted in significantly lower levels of stereotypy compared to controls. These effects were observed in the experimental housing condition as well as in a standard test context. The effects of early and late enrichment support the importance of environmental restriction in the genesis of stereotype and provide support for the efficacy of early and late enrichment in the prevention of stereotypies.