Neonatal novelty exposure affects sex difference in open field disinhibition.

Neonatal stimulation induces sexually dimorphic changes at both the levels of behavior and neural systems. The effects of such stimulation on emotional reactivity measured by open field activity have been inconsistent. We found that among 23-day-old rats, neonatal novelty exposure induced an opposite pattern of sex difference in the initial open field disinhibition. This result suggests that the effect of early life stimulation on emotional reactivity is sex-dependent and that this early stimulation modulates the sexual dimorphism in emotional reactivity to a novel environment.