Depression affects more than a quarter of all U.S. adults at some point in their lives, and the World Health Organization predicts that by 2020 it will be the second leading cause of disability worldwide. Depression is also the leading risk factor for suicide, which causes twice as many deaths as murder, and is the third leading cause of death for 15-24 year olds.
The first major finding of the study was the discovery that serotonin has a previously unknown ability to strengthen the communication between brain cells. "Like speaking louder to your companion at a noisy cocktail party, serotonin amplifies excitatory interactions in brain regions important for emotional and cognitive function and apparently helps to make sure that crucial conversations between neurons get heard," says Dr. Thompson. "Then we asked, does this action of serotonin play any role in the therapeutic action of drugs like Prozac?"
To understand what might be wrong in the brains of patients with depression and how elevating serotonin might relieve their symptoms, the study team examined the brains of rats and mice that had been repeatedly exposed to various mildly stressful conditions, comparable to the types of psychological stressors that can trigger depression in people.
The researchers could tell that their animals became depressed because they lost their preference for things that are normally pleasurable. For example, normal animals given a choice of drinking plain water or sugar water strongly prefer the sugary solution. Study animals exposed to repeated stress, however, lost their preference for the sugar water, indicating that they no longer found it rewarding. This depression-like behavior strongly mimics one hallmark of human depression, called anhedonia, in which patients no longer feel rewarded by the pleasures of a nice meal or a good
|Contact: Karen Robinson|
University of Maryland Medical Center