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Depression has been linked to the hormone serotonin found in the brain for years. Doctors and researchers have developed treatment options that directly influence the levels of serotonin. New research, however suggests that depression might actually be caused by the miscommunication between brain cells. Based from this finding, the researchers suggest that treatment for depression might have to be changed.

Senior author Scott M. Thompson, PhD., a professor and interim chair of the Department of Physiology at the University of Maryland School of Medicine wanted to observe the effects of serotonin on depressed patients. Although it has been known that serotonin can make depressed patients feel happier, it has never been proven that the lack of serotonin leads to depression, and current drugs today take that approach in treating people. The researchers analyzed the effects of different levels of serotonin in rats and mice after the team introduced the animals to stressful conditions that were considered to be similar to the psychological stressors linked to depression in humans.

The mice were given the choice of either drinking plain water or sugar water, the latter being the more desirable. After the stressful conditions, the mice no longer cared for the sugary water, indicating that they suffered from a similar human condition known as anhedonia. Anhedonia is a symptom of depression in which the person no longer gets the reward or pleasure emotion that he/she previously got from a certain hobby, task, or interaction. Based from this finding, the researchers analyzed the levels of serotonin in both the control group and the stressed group of mice. They found that the levels of serotonin did not play a factor in causing anhedonia. Instead, they noted that the excitatory connections, the transmissions between brain cells, were different.

"In the depressed brain, serotonin appears to be trying hard to amplify that cocktail party conversation, but the message still doesn't get through," Thompson concluded.

Current antidepressants such as Prozac, Zoloft and Celexa inhibit brain cells from absorbing serotonin, which results in an increased concentration of the hormone in the brain. This study suggests that current antidepressants, which are roughly 50 percent effective, need to be revamped. The researchers believe that antidepressants need to focus on fixing the miscommunications between brain cells by enforcing the ability of serotonin in promoting excitatory connections.

According to the U.S. Centers for Disease Prevention and Control (CDC), depression afflicts one in every 10 Americas, appearing two times as much in women than men. The World Health Organization (WHO) stated that by 2020, depression could be the second leading disability experienced globally. It is currently the leading contributing risk factor for suicides.

The study was published in Nature Neuroscience.