By Neil Swan, NIDA NOTES Staff Writer

All drugs of abuse disrupt the normal flow of the neurotransmitter dopamine, stimulating its release and increasing its brain levels. This action is believed to be significantly involved in producing drug-induced feelings of pleasure and reward and, over time, addiction and vulnerability to withdrawal symptoms. Drugs of abuse begin this action by chemically binding to specific molecular sites called receptors, some of which are found on dopamine nerve cells.

Recent findings from several NIDA-funded researchers confirm not only that nicotine is highly addictive but that it also affects the same brain mechanism as other drugs of abuse and increases brain levels of dopamine. The findings also suggest how nicotine abstinence and withdrawal activate the body's stress systems. Two research teams have spotlighted how nicotine, just like heroin or cocaine, activates dopamine-containing nerve cells in the brain's mesolimbic system, which is involved in emotion and behavior. Another group has shown that some brain changes during withdrawal from chronic nicotine use are similar to those that occur during withdrawal from other drugs of abuse.

Dr. John A. Dani of Baylor College of Medicine in Houston and his colleagues have shown that nicotine binds at multiple receptors on dopamine nerve cells, or neurons, to activate the neurons. Theoretically, this activation of dopamine neurons by nicotine begins the response that leads to feelings of pleasure and reward, and then addiction. The researchers examined dopamine nerve cells from the brains of rats that had been exposed to nicotine for prolonged periods. They found that nicotine at levels comparable with those found in human smokers first activates or sensitizes these neurons but then quickly desensitizes them.