Low Serotonin May Trigger Spells of Depression

Wonder why certain people can cope up in stress stressful situations while others may succumb to spells of depression? The answer lies with a certain neurotransmitter called serotonin which is associated to human feelings and happiness. When a group of experts from Duke University's School of Medicine, United States carried out experiments on mice, it was found that mice that were deficient in serotonin were more prone to depression. When exposed to stressful conditions, they failed to respond to the standard anti-depressant, Prozac. Prozac works by boosting serotonin transmission between neighbouring neurons. "Our results are very exciting because they establish that low serotonin could be a contributing factor to the development of depression in response to psycho-social stress in a genetically defined animal model of serotonin deficiency," said senior author Marc Caron from Duke University's School of Medicine, United States. Experts have been studying the role of serotonin with respect to stress and depression. In a previous study the group concluded that lack of serotonin may lead to susceptibility to certain types of stress. They focused more on the role of serotonin and its varying levels on human mental and psychological wellbeing. For the recent study, experts analysed a strain of mouse that was deficient in serotonin. A trans-genic mouse strain called Tph2KI that has only 20-40 percent of normal levels of serotonin in its brain. These mice harbour an extremely rare mutation that was first identified in a small group of people with major depression. The researchers attempted at testing the responses of these mice to a type of psycho-social stress - social defeat stress. These mice were exposed to stressful conditions wherein each was housed with an aggressive stranger mouse briefly every day for 7-10 days. Later, it was examined whether the serotonin deficient mice would avoid interacting with an unfamiliar mouse - a depression-like behaviour. The study concluded that a week of social stress was not sufficient for normal mice to show signs of depression, whereas the serotonin-deficient mice did. However, longer period of exposure to stress adversely affected both normal as well as the mutant mice. It was also seen that a Prozac treatment helped alleviate stress in normal mice while the mutant mice strain remained the same with respect to their stress levels. The study appeared in the journal Proceedings of the National Academy of Sciences and concluded that low levels of serotonin may increase the susceptibility to depression. The research also shed light on the reason behind why some people with depression seem unresponsive to treatment with selective serotonin re-uptake inhibitors (SSRIs), the most common anti-depressant drugs in the market today. Inputs from IANS