Cocaine and the nervous system.

Cocaine and the nervous system

Len Bias didn't have a chance. Minutes after the University of Maryland basketball player overdosed on cocaine, he developed an erratic, uncontrollable heartbeat. He died June 19, 1986, a casualty of a heart syndrome known as sudden death.

For several years, researchers have studied animal models of cocaine-related sudden death in hopes of finding the causes of this rapid and unpredictable form of heart failure. Scientists have proposed that cocaine exerts its lethal influence by stimulating the sympathetic nervous system, which accelerates heart rate. But a new study of cocaine-infused dogs indicates the drug may have an additional--and more critical--effect on another part of the nervous system. The finding suggests new treatments for cocaine overdose, says biophysicist Stephen S. Hull, who led the study.

Hull and his co-workers at the University of Oklahoma and Corazonix, Inc., in Oklahoma City, found that cocaine appears to inhibit the parasympathetic nervous system, which normally acts as a protective "brake" to slow a rapidly beating heart. "Rather than [just] jazzing the accelerator, cocaine [primarily] acts to release the brake," he explains.

Hull's team detected two clues pointing to cocaine's deadly link with the parasympathetic nervous system. For one, they observed that cocaine caused severe arrhythmia by increasing both blood pressure and heart rate in the 10 dogs under study. Normally, Hull says, elevated blood pressure prompts the brain to stimulate the parasympathetic nervous system and thus to lower the heart rate. He and his colleagues reasoned that the stimulation had little effect because cocaine had disrupted the parasympathetic system.

They also found that the low dose of cocaine used in their study--comparable to about one-thousandth the typical street dose -- markedly reduced the degree of heart rate variation among both healthy dogs and those at high risk for sudden death. Proper functioning of the parasympathetic system, Hull notes, determines the brain's ability to vary heart rate widely--a necessary control for a healthy heart.

Hull says the findings suggest that heart-stabilizing drugs that activate the parasympathetic nervous system may improve survival of overdose victims. Electrical stimulation of the vagus nerve, which contains parasympathetic fibers leading to the heart, may be another possible treatment, he adds. People who overdose on cocaine "should be treated with anti-arrhythmic drugs just as if they were heart attack patients," Hull asserts, "even if they don't appear to have symptoms."