Infantile (handling) stimulation and behavior in young Roman high- and low-avoidance rats.

The effect of infantile handling stimulation on exploratory and emotional behavior of Roman high- and low-avoidance (RHA/Verh and RLA/Verh) weanling rats was investigated. Postnatally handled and nonhandled, 4-week-old males and females from both psychogenetically selected lines were exposed to a hexagonal tunnel maze, including an illuminated central arena. Postnatal handling increased exploratory behavior and decreased emotional reactivity as expressed by increased entries into the central arena and a reduction in defecations in both lines of rats. These effects were more pronounced in the RLA/Verh rats. In agreement with earlier studies using nonselected adult rats, the females of both lines (especially those from the RHA/Verh line) were more sensitive than males to the positive influences of early stimulation.