Study finds link between meth, loss of muscle control

By: GARY WARTH - Staff Writer | Saturday, August 25, 2007 12:17 AM PDT ∞

Some young methamphetamine abusers may be in danger of developing Parkinson's diseaselike symptoms later in life, according to research findings released last week.

The symptoms may occur because meth can damage a part of the brain that protects and repairs neurotransmitters related to movement control, the study found.

The Medical University of South Carolina conducted the study and published the findings Wednesday in the Journal of Neuroscience.

In a phone interview from South Carolina, university researcher Dr. Jacqueline McGinty cautioned against concluding that the study, conducted on young molecularly altered mice, could be applied to all humans.

The findings might, however, be relevant to a portion of the population already deficient in the protein that protects certain neurotransmitters. With no way of knowing who has the protein deficiency, meth users have no way of knowing if they are at risk.

"It's kind of a Russian roulette thing," she said.

The study, paid for by the U.S. Army and the National Institutes of Health, was conducted on specially bred mice that partially lacked a protein called glial derived neurotrophic factor (GDNF), which protects and repairs the neurotransmitter dopamine in areas of the brain related to movement control.

Healthy neurotransmitters are key to the body's motor functions because they relay nerve impulses over a synapsis to muscles, glands or other nerves. If a neurotransmitter is damaged or missing, the brain can lose its movement control.

The tremors, slow movements and other symptoms of Parkinson's disease occur because of degeneration of the part of the brain that produces dopamine transmitters.

Similar symptoms may occur if something were to happen to the protein GDNF.

The studied used mice that were 2 1/2 months old, the equivalent of adolescents in humans. Some mice were bred to have a partial GDNF gene deletion while others had the full gene. Both were given either methamphetamine or saline injections four times over an eight-hour period.

Researchers found that the effects of meth were more severe in mice with the GDNF deletion. More foreboding, a comparison of all mice injected with meth showed that one year later the GDNF-depleted mice moved significantly slower than the genetically normal mice.

For humans born with GDNF depletion, the study may mean that early meth use can result in muscular disorders years later.

"Methamphetamine intoxication in any young adult may have deleterious consequences later in life, although they may not be apparent until many decades after the exposure," McGinty said in a prepared statement last week. "These studies speak directly to the possibility of long-term public health consequences resulting from the current epidemic of methamphetamine abuse among young adults."

McGinty said future studies may examine why mice with the GDNF depletion were more vulnerable to the effects of meth.

While the study focused specifically on the protein depletion, McGinty said there might be other abnormalities in the brain that could make meth users predisposed to other unknown symptoms caused by the drug.

Other long-term effects of meth on the brain have been known for years, according to research compiled this year by the California Department of Alcohol and Drug Programs.

Meth unleashes a rush of dopamine, which is the brain's primary pleasure chemical and important in memory, judgment and emotions. Continued use of meth causes a depletion of dopamine, leaving users with anhedonia, or the inability to experience pleasure naturally.

It also substantially affects serotonin, a brain chemical that plays a major role in sleep, appetite, sexual behavior and aggression.

Imaging studies have shown damage to the brain's areas that control memory, judgment, impulse control and moods. Much of the damage is reversible, but recovery is a long process.

Researchers have found memory deficits recover after a few weeks of abstinence from meth, but sleep patterns and dream states are disrupted for months, and anhedonia lasts at least four months.

Contact staff writer Gary Warth at (760) 740-5410 or gwarth@nctimes.com.