Isolation rearing induces profound behavioral and neurochemical abnormalities in rodents. However, there is some controversy regarding the effect of isolation rearing on social behaviors and monoamine neurotransmission in mesolimbic and mesocortical areas. In the current study, we aimed to address these issues and demonstrated that isolation rearing from weaning to adulthood resulted in increased playful fighting and social contact behaviors. Isolation-reared rats also manifested increased dopamine and serotonin levels in the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) as well as an increase in serotonin turnover in the NAc. This study provides additional evidence that social isolation induces alterations in behavior and in the brain.