How exactly are the two related? Stress at a young age permanently alters the expression of a key gene in the brain, resulting in a lifetime of elevated levels of a hormone that contributes to depression, according to a study published this week by the journal Nature Neuroscience. To figure this out, a team of German researchers stressed out baby mice by separating them from their mothers for three hours a day during their first 10 days of life. Other mice were kept with their mothers continuously, to serve as controls. All the animals underwent blood tests at 6 weeks, at 3 months and at 1 year of age. The mice that had been separated from their mothers had higher levels of the stress-related hormone corticosterone circulating in their blood than their counterparts, the researchers found. When the animals were subjected to stressful situations, the traumatized mice also produced more corticosterone than the controls. The researchers, from the Max Planck Institute of Psychiatry in Munich, found behavioral deficits in the stressed-out mice, too. They were more likely to freeze up in forced swim tests and had memory problems with certain tasks. The researchers traced these problems to decreased methylation of a key section of the AVP gene, which prompted the mice to make too much of the hormone arginine vasopressin. To confirm that arginine vasopressin was responsible for the stress, the researchers gave the mice a drug that blocked the hormone's effects in the brain. When the drug was working, the stressed-out mice produced normal levels of corticosterone. 'Our results suggest that adverse events in early life can leave persistent epigenetic marks on specific genes that may prime susceptibility to neuroendocrine and behavioral dysfunction,' they concluded. 