Abuse of drugs such as cocaine, alcohol and marijuana receive a lot of attention from the media and government officials. Often overlooked are the problems caused by inhalant abuse, a practice frequently referred to as 'huffing.' In many countries, children as young as 9 or 10 years old commonly abuse inhalants in the form of glues, paints and varnishes. Kids can obtain them because they're usually cheap, widely available and legal.
Scientists have never really understood how inhalants work or what kinds of long-term effects they have on the brain until now. Researchers from all over the United States worked together to study toluene, the chemical solvent found in most abused inhalants.
Pharmacologist Ed French from the University of Arizona in Tucson says he and his colleagues were able to show that toluene stimulates parts of the brain's reward mechanism, what he calls the reward pathway. "[It's] the same pathway that is turned on by sex and social interactions and many, many other things," French says. "Even computer games will turn this pathway on. So the things that make people feel good and produce what some call euphoria, is mediated through this pathway in the brain, the reward pathway."
French and the other scientists exposed brain cells of rats to various concentrations of toluene and recorded their electrical activity. He says they were surprised to find that low concentrations of toluene were most effective at producing the euphoria associated with the drug. He says they were also surprised to discover that inhalants containing toluene and other solvents were as addictive as other better-known drugs of abuse, such as cocaine, heroin, alcohol and nicotine.
But French points to one important distinction between those drugs and inhalants. "The long-term use of inhalants leads to irreversible damage to the brain," he says, adding he has never seen long-term nicotine use cause such damage. "It certainly can damage the lungs because it's taken in by through smoke. But there's no doubt, the pathology people have seen this for years and years, that people who abuse inhalants for a long period of time, they have irreversible brain damage.
And, French says, there's another reason the solvents in inhalants are so dangerous. "Solvents can sensitize the heart muscle and some people can go into an arrhythmia, which can be fatal." In other words, you can get sudden cardiac arrest from inhaling solvents.
"These things are really dangerous," French says. "The liver gets rotted; the kidneys get rotted; everything goes to hell so to speak."
French says knowing more about the neuro-pharmacology of toluene and other abused solvents may eventually allow scientists to come up with pharmacological treatments for inhalant addiction. The study appears this month in the journal Neuropsychopharmacology.