Maternal separation enhances offensive play-fighting, basal corticosterone and hypothalamic vasopressin mRNA expression in juvenile male rats.

Early life stress is a risk factor for altered adult emotionality including impaired social behavior, enhanced aggression and violence. These behavioral deficits most likely have an earlier onset in life. We recently demonstrated that maternal separation (MS, 3h daily on postnatal day 1-14) increased intermale aggression in adult Wistar rats. Here, we investigated whether MS induced alterations in juvenile play-fighting, which is a precursor of aggression. MS increased offensive play-fighting behaviors in juvenile male rats, as indicated by a twofold increase in the number of nape attacks, a higher frequency of offensive pulling and biting, and a lower frequency of submissive play behaviors. Furthermore, MS rats showed higher plasma corticosterone levels and higher vasopressin mRNA expression in the paraventricular nucleus and the bed nucleus of the stria terminalis compared with control rats during the early dark phase. Thus, MS enhanced aggressive play-fighting accompanied by changes in several relevant neuroendocrine parameters. Taken together with previous findings, the increase in aggressive behaviors both at juvenile and adult age illustrates that exposure to MS alters the way rats cope with social conflict situations throughout life.