快猫短视频

DRUG abusers hooked on 鈥渟peed鈥� risk brain damage, even months after they
quit. A new study shows that methamphetamine is more toxic to the brain than
heroin, cocaine or alcohol, and could put people at high risk for
neurodegenerative diseases such as Parkinson鈥檚.

Methamphetamine is an addictive drug that boost levels of dopamine, a
neurotransmitter that stimulates brain cells, enhancing mood and making people
more animated. But previous studies of animals given speed have suggested that
the drug also sabotages the dopamine system, reducing levels of molecules called
dopamine transporters that shuttle the feel-good neurotransmitter around the
brain. 鈥淭hose studies in animals were very dramatic鈥攚e needed to know
whether the same thing happens in humans,鈥� says Nora Volkow, a psychiatrist at
Brookhaven National Laboratory in New York state.

To find out, Volkow鈥檚 team recruited 15 methamphetamine addicts who had
abused speed for at least two years, then stayed off the drug for at least two
weeks. The scientists carried out positron emission tomography (PET) scans to
measure levels of dopamine transporters in the brains of the former addicts and
18 volunteers who had never taken speed.

Levels of dopamine transporters in the former drug abusers鈥攅ven those
who had been clean for almost a year鈥攚ere more than 20 per cent lower than
normal in two key areas of the brain involved in movement, concentration and
motivation. This reduction mimics the effects of ageing: levels of dopamine
transporters naturally fall by between 5 and 6 per cent each decade, causing
people to slow down and impairing their movement and memory. 鈥淲hat we see is the
equivalent of 40 to 50 years鈥� ageing in the brains of these people鈥攖hat鈥檚
a huge amount,鈥� says Volkow.

Not surprisingly, the former drug abusers also had impaired movement and
found it difficult to remember lists of words given to them by the researchers
when compared with 18 people who had never taken speed. Volkow warns that if the
damage doesn鈥檛 reverse itself speed addicts might be prone to Parkinson鈥檚
disease, in which levels of dopamine transporters are hugely depleted.

Volkow and her team also measured the uptake of glucose in the volunteers鈥�
brains, a measure of brain activity. They found that the rate was around 14 per
cent higher in the speed addicts than in people who had never taken the drug.
This unusually high activity can follow brain damage from injuries or radiation
exposure and may reflect inflammation of the brain.

Volkow concludes that speed could cause long-term damage to the dopamine
system. 鈥淚n that respect, speed is much more damaging than cocaine or alcohol,鈥�
she says. Her team plans to monitor the former addicts over several years to
find out if the damage is permanent.