Play is indispensable for an adequate development of coping with social challenges in the rat

In this study, young rats were deprived of early social interactions during weeks 4 and 5 of life. Different behavior al tests were conducted in adult hood to study the behavioral responses of rats lacking ear ly social experi ences. Juvenile deprivation resulted in decreased social activity and an al tered sexual pattern, but did not affect locomotor activity or the performa nce in the elevated plus maze. Furthermore, behavioral and neuroendocrine r esponses of juvenile isolated rats were dramatically altered when they were confronted with territorial aggression. Juvenile deprived rats did not rea dily display a submissive posture in response to the resident and showed no immobility behavior after being returned to the resident's territory, whil e their plasma corticosterone and adrenaline concentrations;were significan tly increased compared to nonisolated controls. In contrast, behavioral res ponses in the shock prod test were not affected by previous isolation. The results suggest that early social experiences are vital for interactions wi th conspecifics later in life, i.e., aggression, sexual, and social interac tions; (C) 1999 John Wiley & Sons, Inc.