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Why were knockout mice lacking certain serotonin receptors more aggressive?
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Aggressive behaviour
A pair of red deer stags (Cervus elaphus) competing for possession of a female in the rutting season.
In vertebrate species, research indicates that serotonin functions as an aggression-inhibiting biochemical within the limbic system of the brain.12
In genetically engineered "knockout" mice that lack the genes necessary to produce specific serotonin receptors, this inhibitory mechanism is disrupted. Because these receptors are essential for mediating the calming effects of serotonin, their absence leads to markedly higher levels of aggression compared to non-altered mice. This finding confirms that serotonin plays a critical role in suppressing aggressive behavioral patterns in vertebrates.2