RESUMEN
Risperidone is an antipsychotic drug approved for use in children, but little is known about the long-term effects of early-life risperidone treatment. In animals, prolonged risperidone administration during development increases forebrain dopamine receptor expression immediately upon the cessation of treatment. A series of experiments was performed to ascertain whether early-life risperidone administration altered locomotor activity, a behavior sensitive to dopamine receptor function, in adult rats. One additional behavior modulated by forebrain dopamine function, spatial reversal learning, was also measured during adulthood. In each study, Long-Evans rats received daily subcutaneous injections of vehicle or 1 of 2 doses of risperidone (1.0 and 3.0 mg/kg per day) from postnatal Days 14 to 42. Weight gain during development was slightly yet significantly reduced in risperidone-treated rats. In the first 2 experiments, early-life risperidone administration was associated with increased locomotor activity at 1 week postadministration through approximately 9 months of age, independent of changes in weight gain. In a separate experiment, it was found that the enhancing effect of early-life risperidone on locomotor activity occurred in males and female rats. A final experiment indicated that spatial reversal learning was unaffected in adult rats administered risperidone early in life. These results indicate that locomotor activity during adulthood is permanently modified by early-life risperidone treatment. The findings suggest that chronic antipsychotic drug use in pediatric populations (e.g., treatment for the symptoms of autism) could modify brain development and alter neural set points for specific behaviors during adulthood.