Two 'Happy' Hormone Regulators May Cause Intense Rage

The hormone regulating neurotransmitters glutamate and serotonin have long been associated with happiness, with serotonin in particular being the subject of many reward-based behavioral studies. However, a new study has found that if a male mouse is exposed to high levels of these transmitters, they become exceptionally aggressive and violent.

Now researchers are suggesting that because of the many similarities in the neurobiology of aggression between rodents and humans, investigations into serotonin and glutamate could help experts better understand violent and antisocial tendencies in psychopathic patients.

That's at least according to a study recently published in The Journal of Neuroscience, which details how an international team of researchers (including Swiss, Japanese, American, and Taiwanese affiliations) paid special attention to serotonin in the dorsal raphe nucleus (DRN) - located in the most 'primitive' part of the brain. Here, you can find the largest clusters of serotonin-producing neurons in humans and mice alike.

This production is traditionally regulated by several neurotransmitters, including glutamate, γ-aminobutyric acid (GABA) and even more serotonin. Past studies have found that chronic problems like intense anxiety and depression can often be linked to imbalances in the DRN, but they often have to do with too little serotonin production, not too much.

In a one-of-a-kind approach, the team implanted tiny probes into the brains of controlled mice subjects that can both microinject drugs into the DRN and collect fluid samples from it. They then exposed their test subjects to a situation that would prompt aggression, such as the invasion of one male into another male's territory. (Scroll to read on...)

The researchers then compared brain levels with their behavior. For instance, normal aggressive behavior such as threatening posture was found to be associated with notable changes in glutamate, but not serotonin.

That all changed when things escalated to hyper-aggression - including biting with a potential intent to kill the invader. During these intense encounters, the mice were found to have heightened levels of glutamate which triggered a brief-but-powerful surge in serotonin, suggesting that this is critical for escalating aggressive behavior.

The team now hopes that this revelation will lead to new discoveries concerning human behavior - ones that could potentially revolutionize the treatment of psychotically aggressive patients.

[With materials from the University of Tsukuba]

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