Cindy West
The Gadsden Times

Scientists say addiction changes brain chemistry

A 28-year-old Blount County woman spent all her teenage years and her entire adulthood on drugs.
She said she got to a point where she knew something was wrong, but she didn't know how to get off the roller-coaster of drug abuse. "I was using even when I didn't want to," she said. "I would do a shot and kind of hope I wasn't going to die. Then I'd say, 'I'm not going to do this tomorrow.'"

Addicts have found that quitting alcohol, cigarettes or other illegal drugs isn't as simple as saying they are going to quit, however.

Rochelle Schwartz-Bloom studies how drugs affect the brain and educates the public about them. A professor at Duke University Medical Center's Department of Pharmacology and Cancer Biology in Durham, N.C., she and a colleague have developed a videotape showing the process using animation.
She and other scientists explained how drugs affect the brain during a conference in Canada in June. Called the Addiction Studies Program for Journalists, the program is presented several times each year to help reporters explain to the general public how addiction works.

The brain functions because messages are sent from one neuron to another. The process starts as an electric signal in one neuron. When it is being transferred from one neuron to another, the electrical impulse changes to a chemical signal involving neurotransmitters, such as dopamine.
The connection between neurons is called a synapse, and that is where the chemical process takes place. The electrical impulse in the first neuron causes neurotransmitters - dopamine, for instance - to be released. "When the dopamine is released, it travels to dopamine receptors on a nearby receiving neuron, where it causes ions to flow across the cell membrane," Schwartz-Bloom said. "The movement of charged particles across the membrane creates an electrical current in the receiving neuron. This is called synaptic transmission. Thus, the receiving neuron receives the message to change the rate at which it fires an electrical impulse."

Drugs modify synaptic transmission, changing the way neurons communicate with each other. A drug that affects dopamine synaptic transmission can increase the dopamine that reaches the receiving neuron. "Amphetamines increase the release of dopamine from a neuron," Schwartz-Bloom said.
"Cocaine binds to the dopamine transporter, keeping the transporter from taking up dopamine," Schwartz-Bloom said. That leaves too many dopamine molecules in the synaptic space because they haven't been taken up into the neurons properly. The excess of dopamine in the synaptic space increases the electrical signal generated in the receiving neuron.

"Nicotine activates acetylcholine receptors," Schwartz-Bloom said. Acetylcholine is another neurotransmitter. "The nicotine binds with sites on the acetylcholine receptor to increase neural firing.
"Drugs can affect this communication process in many different ways," she said.

How a drug is taken can also affect the brain in different ways, something that addicts learn early on. To get the quickest effect, drugs are smoked or injected into the bloodstream.

"If someone snorts it or takes a pill, then all of that (the effect) is slowed down even more," Schwartz-Bloom said. "It depends on how much they're taking. If they take more, it's going to have a longer effect on the brain.

"Take cocaine and crack cocaine, for example. The compound is the same compound it always was. It's just that people have invented new ways of getting it to their brain faster and in higher quantities without killing themselves."

When a person uses drugs, that person's brain learns to function in the presence of those drugs. When the person quits using drugs, the brain doesn't immediately start to function the way it did before the drug use.

Some drugs, such as methamphetamine, are toxic. A single, high dose of methamphetamine has been shown to damage nerve terminals in the dopamine-containing regions of the brain, according to the National Institute on Drug Abuse Web site.

"Now (scientists) have started to look at recovering addicts up to 12 months after they've gotten clean," Friedman said. "What they see is that some of those (brain) changes do, in fact, persist. The brain of an addict 12 months after he's stopped using drugs is not the same as the brain of a normal person."
The process by which we learn to enjoy something occurs between the prefrontal cortex of the brain, the part of the brain responsible for higher reasoning, and the limbic system, the older part of the brain responsible for primitive urges. The nucleus accumbens and ventral tegmental area are part of the limbic system. If a drug interferes with the dopamine flow to the ventral tegmental area, that changes the chemical message that flows to the nucleus accumbens and the prefrontal cortex, making it a different message than what would have normally been sent.

David Friedman is professor at Wake Forest School of Medicine's Department of Physiology and Pharmacology in Winston-Salem, N.C. Friedman said that in the 1950s scientists electrically stimulated the pathway from the nucleus accumbens and the ventral tegmental area in humans. The test subjects reported feeling pleasure.

All drugs of abuse except hallucinogens release dopamine into a part of the brain called the nucleus accumbens, Friedman said.

Changes in the way the brain works aren't the only processes involved in drug addiction. Behavior conditioning also plays a part.

Scientists know that humans find rewarding the things we need to do to survive, such as eat and reproduce. We learn to repeat any action that we find rewarding, which is called operant conditioning. The neural circuit -- the pathway to reward - includes the ventral tegmental area, nucleus accumbens and prefrontal cortex and is the structure involved in the reward principle. Drugs activate the brain's reward system. "Relief from stress is just as important as getting pleasure," Friedman said.

When that reward pathway is activated, that teaches us to repeat the behavior that activated.