Behavioral effects of neonatal herpes simplex type 1 infection of mice.

Neonatal infection with a mutant herpes simplex type 1 virus produced hyperactivity in mice. Activity was measured throughout a 24 hour period during adulthood, and the elevation of activity occurred during the period of the day when mice are normally inactive. In a second experiment, infected mice showed deficits in learning to inhibit behavior in a passive avoidance task, but no deficit in learning a complex spatial task. Virus was detected in the brain by 5 days of age. The peak percentage of mice infected was reached at 10 days of age and declined thereafter. Mortality due to the virus declined with age at which the mouse was infected, but rates of hyperactivity were not different when injection occurred within the first 4 days of life. The viral infection produced no deficit in body weight in suckling mice. Thus we have shown that a mild neonatal virus infection can produce specific behavioral deficits.