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Researchers have always thought that only neurons, the major type of brain cells, control behavior. But we now know that's not entirely correct, according to new research. A minor type of brain cells known as microglia also influences behavior -- specifically anxiety-related behaviors.
You see, anxiety isn't inherently defective in itself. Anxiety is an emotional state that prepares us against danger, or that prompts us to put in our best into a given task we're "anxious" about. The problem arises when anxiety spirals out of control and becomes overwhelming. We become paralyzed and stuck in that state.
So, if anxiety is an inherent natural behavior, it's logical to assume that a part of the brain would be responsible for triggering this behavior. And when that trigger gets faulty, we might expect a disorder like anxiety disorder, OCD, or obsessive-compulsive spectrum disorder (OCSD).
This trigger that has always eluded the prying eyes of scientists is microglia. The study was conducted in mice.
The study demonstrated that specific populations of microglia, acting like buttons on a game controller, can either activate or suppress anxiety and OCSD behaviors.
The findings can result in more targeted treatments for these disorders.
Mice exhibiting behaviors resembling OCSD cannot resist compulsively grooming themselves. They can lick their bodies nonstop, trying hard to keep themselves as clean as can be.
In a previous study, the team identified that a mutation in a gene called Hoxb8 led to chronic anxiety symptoms and excessive grooming in mice. Surprisingly, they discovered that the source of these behaviors was microglia, a type of immune cell.
Microglia make up only 10% of the brain's cells and were traditionally regarded as the brain's "trash collectors," responsible for eliminating dying neurons and abnormal proteins.
Nevertheless, how microglia accomplish these tasks remained a mystery. To uncover more information, Naveen Nagajaran Ph.D., the lead study author, went ahead to experiment with mice.
Using laser, he selectively stimulated specific regions of microglia in the brain.
To the team's greatest amazement, he was able to trigger anxiety-like behaviors like a switch, simply by stimulating specific regions of Microglia.
When they stimulated a subpopulation of microglia called Hoxb8 microglia, the mice became more anxious. In other brain regions, the laser activation of Hoxb8 microglia induced excessive grooming. Targeting Hoxb8 microglia in another location produced multiple effects: increased anxiety, excessive grooming, and freezing, a sign of fear. Stopping the laser stimulation immediately halted these behaviors.
Also, they noticed that neurons close to the stimulated microglia displayed heightened activity, indicating that these two types of cells communicate with each other to drive distinct behaviors.
There's more.
A regional population of microglia does not exhibit the characteristics of Hoxb8. Simultaneously stimulating these "non-Hoxb8" microglia and Hoxb8 microglia prevented the onset of anxiety and OCSD-like behaviors.
This suggests that the two populations of microglia function as a balance system, acting as both an accelerator and a brake. Under normal circumstances, they regulate each other to keep things in equilibrium. Hence, an imbalance in their signals can lead to a disorder.
By understanding these interactions in the brain, researchers may uncover targeted treatment methods for managing excessive anxiety.
