Research carried out at Emory University found links between the reduced release of dopamine in the brain, and the inflammatory reaction in the body. The research found the possibility that this is part of the body’s effort to optimize its energy expenditure during inflammatory episodes.
Low-grade chronic inflammation interferes with the dopaminergic signaling system in the brain that motivates and links between the reduced release of dopamine in the brain. The possibility that this is the body’s effort to optimize energy expenditure when having inflammatory attacks.
The research hypothesis is that when the body needs energy to heal a wound or overcome an infection, both of which cause low-grade inflammation, to ensure that energy is available, the brain uses a technique to reduce the drive to perform other tasks which could potentially drain away the energy needed for healing. This is a recalibration of the reward neurons in the motivation center of the brain, causing ordinary tasks no longer feel like they’re worth doing.
Andrew Miller, a co-author of the study, explains: “If our theory is correct, then it could have a tremendous impact on treating cases of depression and other behavioral disorders that may be driven by inflammation. It would open up opportunities for the development of therapies that target energy utilization by immune cells, which would be something completely new in our field.”
It is known that immune cells use cellular signaling molecules called cytokines, influencing the functioning of the dopamine-releasing neurons called the mesolimbic system. This system boosts our willingness to work hard for a reward.
A recent discovery that immune cells use a unique capability to change from various metabolic states, which other cells cannot. This could affect cytokine release patterns in such a way as to signal the brain to conserve available energy for the use of the immune system.
This discovery is the foundation of the hypothesis, which refers to evolutionary changes. In the hypothetical early environment, the immune system facing huge microbial and predatory battles used tremendous amounts of energy. It therefore had its own mechanism to signal other body systems, using the mesolimbic dopamine system, to control the use of energy when the organism was experiencing severe or sudden stress.
In our modern society with very low physical activity, low-grade inflammation is caused by chronic stress, metabolic syndrome, aging, and other poor lifestyle choices. This inadvertently causes the mesolimbic dopamine neurons to produce less dopamine. Lower dopamine levels decrease the motivation for work, by reducing the perception of reward while increasing the perception of effort involved. This causes the conservation of energy for use by the immune system.
Other studies by Miller and other scientists have shown that high levels of immune functioning together with low levels of dopamine and low motivation characterizes some cases of schizophrenia, depression and other mental health conditions.
The scientists do not think these disorders are caused by the low-grade inflammation, but that some people who have these problems are hypersensitive to immune cytokines. This could in turn cause them to lose motivation for daily living and bring on depression.