Depression: Developing a Biological Basis

As Dr. Silton mentioned during her lecture, depression is a widespread and well-known psychological disorder. It is the leading cause of disability and around 17% of adults experience one major depressive episode in their life. It relates to other health problems; for example, it leads to an earlier onset and a more severe case of cardiovascular disease. It predicts longer recovery from other health problems. Furthermore, 50-90% of people who commit suicide do so during a depressive episode or while they’re recovering from one. With all that being said, it is very clear that depression is a very prevalent disorder and it can have serious and sometimes irreversible effects.

However, despite its effects and it’s prevalence, diagnosing a patient with depression can be a challenge. The process of diagnosing a potential patient is a little murky in terms of what specifically qualifies a person to be considered depressed. Being depressed entails having a cluster of signs and symptoms, but there’s not very much biology behind such a diagnosis. This is partly due to the DSM-V manner of diagnosis– which is currently being replaced by a developing new system – the RDoC. Dr. Silton mentioned the shift to RDoC is aiming to focus more on discovering biological bases for psychological disorders. In other words, current diagnosis is based on more subjective measures, while the new system will be more based off objective measures. This new focus on discovering biological bases for psychological disorders opens a completely new door for researchers. There is a very conscious effort to try and discover more biological markers for these disorders.

Such efforts include the research on depression that’s being done at the Icahan School of Medicine at Mount Sinai. More specifically, they did research on a biological marker that can regulate the vulnerability to depression. They experimented with mice to see the effect of a pro-inflammatory immune chemical called interleukin-6. They found that mice with elevated levels of this chemical showed depression-like behaviors. This suggested that differences in the peripheral immune system could contribute to the vulnerability of developing depression.

In order to more directly analyze the role for immune responses in depression-like behaviors, “the investigators used irradiation to lesion the immune system of mice.” They transferred bone marrow to replace the immune system with one from mice that showed either low or high levels of interleukin-6. They found that mice that had received transplants from high-responding donors had a lot more depression-like behaviors when compared to those who got their transplants from low-responding donors.

This finding shows us that “circulating immune chemicals that can act in the brain may influence vulnerability to depression.” This could add a biological component in diagnosing depression because if a patient has high levels of this chemical, it means they are more susceptible to depression. This is exactly the kind of basis that could be added to the RDoC. Even though this is only shows a higher susceptibility to depression, it is still a biological basis that can direct doctors in the right path. Hopefully more research like this can be done to discover more specific biological markers that indicate depression, markers that provide much more solid evidence than the current more subjective cluster of symptoms and signs. 

http://www.sciencedaily.com/releases/2013/12/131212100045.htm