The puzzle of why some people turn to extreme violence may be a step closer to being solved, following the findings of a new study.

Norwegian scientists injected mice with an antibody sourced from the blood of murderers, rapists and gang members.

After being injected, they found that these rodents resorted to violent confrontations with their fellow creatures far more quickly than normal.

This suggests variations in the antibody found between people may be a factor in how aggressively they respond to stress.

The finding could one day lead to a treatment for violent criminals, although researchers warn this is still some way off.

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The puzzle of why some people turn to extreme violence may be a step closer to being solved, after Norwegian scientists injected mice with a protein taken from violent criminals' blood. This image shows different areas of the mice brain reacting to the presence of chemicals

Experts from Akershus University Hospital, just outside the capital Oslo, extracted antibodies from 16 convicts serving time for a range of extreme physical or sexual violent crimes.

Mice were injected with the substance, autoantibodies which react against adrenocorticotropic hormone (ACTH) which is produced by the pituitary gland.

Its key function is to stimulate the production and release of cortisol - the body's main stress hormone.

By introducing the antibody, researchers were interfering with the production process of this stress control hormone.

Mice who received the injections were far quicker to attack other mice who intruded on their territory.

Experts says they are still unclear as to exactly what this antibody does, however.

'The resident would attack the mouse very fast,' lead researcher Sergueï Fetissov, told The Times.

'The implication was that this antibody, which differed between violent and non-violent humans, could be one of the reasons they were violent in the first place.

'The antibodies may predispose people to aggressive behaviour,' said Professor Fetissov.

'But we don't know why the antibodies differ in these groups.'

Mice who received the injections were far quicker to attack other mice who intruded on their territory. This graph shows the reaction time's for aggressive behaviour in the mice who received the chemical

WHAT DOES THE ADRENO-CORTICOTROPIC HORMONE DO? Adrenocorticotropic hormone is produced by the pituitary gland. Its key function is to stimulate the production and release of cortisol - the body's main stress hormone - from the cortex of the adrenal gland. Adrenocorticotropic hormone is made in the corticotroph cells of the anterior pituitary gland. It is secreted in several intermittent pulses during the day into the bloodstream and transported around the body. Like cortisol, levels of adrenocorticotropic hormone are generally high in the morning when we wake up and fall throughout the day. This is called a diurnal rhythm. Once adrenocorticotropic hormone reaches the adrenal glands, it binds on to receptors causing the adrenal glands to secrete more cortisol, resulting in higher levels of cortisol in the blood. It also increases production of the chemical compounds that trigger an increase in other hormones such as adrenaline and noradrenaline. Stress, both physical and psychological, also stimulates adrenocorticotropic hormone production and hence increases cortisol levels. Advertisement

Of the sixteen violent aggressor inmates included in the study, eleven of these had committed at least one murder or had attempted to commit murder.

One inmate had participated in gang-related activity resulting in murder.

Four inmates had committed brutal physical violence with violent sex-related components, such as rape, molestation, or grievous bodily harm.

Inmates who had committed sexual acts with minors were excluded from the study.

All violent male inmates except one were recruited from a high-security prison outside Oslo.

Norwegian scientists injected mice with an antibody sourced from the blood of murderers, rapists and gang members to see how they would react (stock)

The inmates were serving long-term sentences, the majority in preventive detention. None had serious mental illness.

Experts say a far larger sample size will be needed before the mechanism observed during the tests can be better understood.

The researchers also stressed that many members of the general public are likely to have these antibodies without a risk of turning violent.

The full findings of the study were published in the journal Proceedings of the National Academy of Sciences.