A rodent model of spontaneous stereotypy: Initial characterization of developmental, environmental, and neurobiological factors

Stereotypies are patterns of motor behavior that are repetitive, excessive, topographically invariant, and that lack any obvious function or purpose. In humans, stereotyped behaviors are associated with psychiatric, neurologi cal, and developmental disorders. In animals, stereotypy has been frequentl y associated with adverse environmental circumstances and often related to alterations in striatal dopamine. To assess the development of stereotyped behaviors and to test the hypothesis that these behaviors are associated wi th environmental restriction, deer mice were housed in either standard labo ratory cages or larger, enriched cages, and the development of stereotypy w as followed from weaning over a 17-week period. Standard-caged deer mice en gaged in stereotyped behaviors at a higher rate and developed these behavio rs more quickly when compared to animals in enriched caging. Additionally, enriched caging was associated with higher rates of patterned running, wher eas jumping and backward somersaulting were typically observed in standard cages. In addition, there was a significant effect of litter, but no effect of sex or cage, on the time to develop stereotypy. No differences were fou nd in the density of either striatal D-1 or D-2 dopamine receptors or the c oncentration of striatal dopamine or its metabolites as a function of reari ng condition or as a function of whether the animals developed stereotypy. These results characterize the development of stereotypies in this species, demonstrate the importance of environmental conditions in the genesis of s tereotypy, and suggest that alterations in striatal dopamine content or dop amine receptor density do not account for the expression of stereotyped beh aviors in this model. (C) 1999 Elsevier Science Inc.