Behavioral outcome after prenatal exposure to phenytoin in rats.

The long-term behavioral outcome subsequent to prenatal exposure to phenytoin was examined in an animal model for the Fetal Hydantoin Syndrome. Behavioral outcome was determined by two different techniques--the residential maze, which provided a 24-hour measure of horizontal movement frequency in a group of animals, and time-lapse photography, which allowed quantification of frequency, duration, distribution, and sequencing of 15 motor acts performed by individual rats. Phenytoin induced significant, sex-related changes in motor behavior. Ten-week-old females exposed in utero to phenytoin displayed hypoactivity comprised of a longer duration, greater frequency, and more random distribution of grooming behaviors. Prenatally exposed males at that age displayed an opposite effect of hyperactivity consisting of a longer duration and greater frequency of exploratory behaviors. It appears that prenatal exposure to phenytoin may affect normal maturational changes in motor behavior so that immature activity levels are maintained in the adult animal.