Oxytocin is essential in activities of the social brain such as trust and love and in maternal bonding behaviors. It is produced in the brain and secreted into the circulation. Here, by analyzing maternal behaviors of RAGE gene-manipulated mice, oxytocin was found to be transported back to the brain, crossing the blood-brain barrier (BBB), an extremely effective barrier, by binding to the receptor for advanced glycation end-products (RAGE) on capillary endothelial cells of the BBB.