Dopamine neurons and depression-related behaviors

In these articles, Tye et. al (2012) and Chaudhury et. al (2012) examined the relationship between both the Ventral Tegmental Area (VTA) and Nucleus Accumbens (NAc) dopamine neurons and depression. Within each paper, similar tests were performed on the animals to determine their levels of depression (such as the sugar preference test). Additionally, Chaudhury et. al (2012) included a social defeat stress/social interaction test, while Tye et. al (2012) used a forced swim test. I found it interesting that one source included a social test of depression, while the other did not. I thought that this additional perspective presented by Chaudhury et. al (2012), as well as their use of both tonic and phasic (the other paper only used phasic) contributed to their paper immensely, however Tye et. al (2012) presented their arguments clearly and went in depth into their analysis, especially of the forced swim test.

In both papers, they observed an increase in sucrose preference with phasic activation of VTA dopamine neurons. This made the claim Tye et. al (2012) made, that phasic activation of VTA dopamine neurons reversed the symptoms of depression in mice exposed to chronic mild stress during the forced swim test and tail suspension test, very convincing. In Chaudhury et. al (2012), however, they found that phasic stimulation increased depression behavior usually exhibited after repeated social defeat stress. They later go on to say that the depression effects were context-specific. Additionally, Chaudhury et. al (2012) mice were exposed to a more stressful paradigm than the chronic mild stress the animals in Tye et. al (2012) experienced. This could account for differences in data since the animals were exposed to two different types of stress, which could have different effects on behavior.

In the future, I think that repeating each set of experiments under the different stress paradigms could help provide a better understanding of some of the results in this paper. In real life, there are many different symptoms of depression, so using two different models to complete all the tests done in both papers may provide a more complete view of how dopamine neurons control depression-related behaviors. Additionally, the behaviors used to induce chronic mild stress were varied - possibly having groups that only used one specific behavior could potentially alter the findings, especially since some mice may not be affected by certain behaviors, and others may have been extremely upset by certain behaviors.