[Neurochemical basis for social encounter-induced hyperactivity in post-weaning isolation-reared mice]

Rearing rodents in social isolation from post-weaning causes abnormal behaviors in adulthood, such as hyper-locomotion, aggression, cognitive impairments, and depression- and anxiety-like behaviors. This social isolation is widely used as a model to study the effects of adverse early-life experiences on behavior and the neural mechanisms associated with neuropsychological development. Previous studies have shown abnormalities of dendritic spine density, synaptic protein levels and amine metabolism in the prefrontal cortex and hippocampus of isolation-reared animals, but the neurochemical basis for induction of abnormal behaviors is not known. We have established a novel methodology for assessing social interaction, focusing on the psychological stressor responsible for induction of abnormal behaviors as a transient environmental factor. This review summarizes the effect of a social encounter with an unfamiliar conspecific on behavior and neurochemistry in isolation-reared mice. The current analysis using the encounter response will provide new strategies to clarify the pathophysiology of psychiatric disorders including schizophrenia, depression and drug dependence.