In adult monkeys, an antidepressant treatment has induced new nerve cell growth in the hippocampus, a brain area responsible for learning and memory. A similar process may occur in humans, the research suggests, and may help explain the effectiveness of antidepressant treatments. The results, the first from nonhuman primates, are similar to those previously seen in rodents. They suggest that creation of new nerve cells, a process known as neurogenesis, is an important part of antidepressant therapy. Researcher Tarique Perera, MD, at Columbia University, and colleagues observed changes in the number of brain cells in the dentate gyrus region of the hippocampus. The study is published in The Journal of Neuroscience. The growth of new nerve cells in the hippocampus has been suggested as the way antidepressants work in rodents, says Eric Nestler, MD, PhD, of the University of Texas Southwestern Medical Center. "However, the clinical relevance of this action has remained controversial, in part, because of uncertainty as to whether similar neurogenesis occurs in humans," he says. "This finding further supports the potential clinical relevance of changes in neurogenesis seen in rodent models." Perera and the team treated a group of monkeys with electroconvulsive shock (ECS), an animal version of the highly effective clinical antidepressant electroconvulsive therapy. They saw an increase in new nerve cells in the hippocampus. Over four weeks, a majority of these cells became mature neurons. These brain changes were not a response to tissue damage, Perera says, because no evidence of increased cell death was found in the ECS treated animals. In fact, the researchers found that the ECS treatments increased production of a protein (BCL2) that protects neurons from damage. "These findings support the hypothesis that induction of neurogenesis is a necessary component in the mechanism of action of antidepressant treatments," Perera says. ### The study was supported by the National Institute of Mental Health at the National Institutes of Health, the American Psychiatric Association Lilly Research Fellowship Award, and the National Alliance for Research on Schizophrenia and Depression. The Journal of Neuroscience is published by the Society for Neuroscience, an organization of more than 36,500 basic scientists and clinicians who study the brain and nervous system. Contact: Sara Harris