Microglial cells contribute to the negative feeling that comes through neurological diseases

Specific immune cells found in the brain, microglia, play a key role in the processes that cause you to feel unbalanced and depressed in relation to inflammation. This is the conclusion of a study using mice conducted by researchers at Linköping University, Sweden. The results were published in the scientific journal Immunity, and suggests that microglial cells contribute to the negative mood experienced during a number of neurological diseases, and possibly also depression.

David Engblom’s research group at Linköping University has spent several years looking at why inflammation in the body, such as a common cold or flu, causes us to feel poor and disobedient, and why which we feel is like retiring in our shell. The activity of the immune system affects zero cells in some way. However, normal cells of the immune system cannot enter the brain: it is sensitive and must be protected. Instead, the brain has its own special immune cells: microglial cells.

Previous research has shown that microglial cells are activated in a number of neurological diseases, such as Alzheimer’s disease, Parkinson’s disease and stroke. People affected by these conditions also often fall into a negative mood. Other previous research has suggested that inflammatory processes play a role in the development of depression. This prompted the researchers behind the new study to more closely examine whether microglial cells are involved in mood regulation during inflammation.

The study showed that animals feel sick and unbalanced when we activate the microglial cells. We confirm that two signaling molecules, interleukin-6 and prostaglandin E2, are particularly important in these processes. Unsurprisingly, these signaling substances are at the heart of it, but we were a little surprised that it is the microglial cells that release these molecules. “

David Engblom, Professor, Department of Biomedical and Clinical Sciences (BKV), Linköping University

During inflammation, many processes are initiated in several cell types. So one of the challenges in determining the role of a particular cell type in the body, is to differentiate its effects. In this study, the scientists used a technique called chemogenetics, which allowed them to specifically activate the activity in microglial cells in mice. The researchers activated the microglial cells while the mice were kept in a specific type of environment. The mice avoided the type of environment around them, which the researchers describe as showing that the animals did not like the experience. The mice were less interested in a sweet solution, which they usually feel awful.

To examine whether the microglial cells are an important link between the immune system and mood, the researchers studied what happened when microglial cells are blocked. When the microglial cells were not available for activation, the mice did not feel bad, even when they had inflammation. This reinforces the idea that these cells are essential for the process.

“Our findings show that the activity of microglial cells is sufficient to create disorder and negative emotion in mice. It is natural to suggest that similar processes occur in several human diseases. Activated microglia are unlikely to contribute to discomfort and depression in people with inflammatory and neurological diseases, ”says David Engblom.

If further research shows that the biological apparatus described in the study works in the same way in humans, it may be possible in the long run to reduce the symptoms of depression by ‘block this equipment.