Adolescent mice subjected to three months of social isolation developed anxiety, depression, and severe social memory deficits, but intranasal oxytocin treatment completely reversed these changes while restoring prefrontal cortex protein expression (MAP-2, PSD-95) and normalizing gut microbiota composition. The intervention also reduced neuroinflammation and corrected abnormally elevated oxytocin receptor levels in isolated animals. This finding bridges decades of research showing oxytocin's prosocial effects with emerging evidence that social isolation fundamentally rewires brain development during critical adolescent periods. The multi-system approach—tracking neural markers, immune responses, and microbiome changes simultaneously—represents a significant methodological advance in understanding how social environments shape brain health. For adults experiencing prolonged isolation, this suggests oxytocin-based interventions might address not just immediate mood symptoms but underlying neurobiological damage. However, the three-month isolation period in mice represents extreme social deprivation that may not translate directly to human social isolation patterns. The intranasal delivery method, while promising for clinical application, would need extensive safety testing in humans. Most critically, this work positions the gut-brain-social axis as a unified therapeutic target rather than treating psychiatric symptoms in isolation.