In this study, Dr. Carpenter and colleagues will examine the interaction between a specific gene and an environmental factor in the development of autistic-like behaviors in a mouse model. The reelin gene is a candidate genetic factor for autism and is important for the development of the cerebral cortex and cerebellum. Mice with reduced levels of expression of this gene have neurodevelopmental defects which result in behavioral abnormalities. This research will examine the effects of an environmental factor hypothesized to be a risk factor for autism (organophosphate exposure during the prenatal period) on the development of autistic behaviors in mice which express low levels of the protein encoded by the reelin gene. It will also determine whether reduced reelin expression in combination with organophosphate exposure leads to changes in the anatomy of brain regions associated with these behaviors.