Fig. 1.

The exploratory behavior of mice born to infected mothers is very different from that of mice born to sham-infected mothers. The movements of a typical mouse from each group were traced from a videotape of a 10 min session in an open field subdivided into 25 squares by lines on the bottom of the box. Sites of rearing on hindpaws are illustrated by circles. Although these are not the most extreme examples of the behavior of mice from each group, it is clear that the mouse born to a sham-infected mother (top) responds very differently to the stress of this situation than the mouse born to a virus-infected mother (bottom).