Dopamine and Other Neurotransmitters
Though dopamine is the primary neurotransmitter involved by drug use, there’s evidence other neurotransmitters are involved as well. This was demonstrated in a study involving cocaine, which induces a high by interfering with systems designed to remove surplus dopamine.
Dr. Nora Volkow of the Brookhaven National Laboratory, found that a cocaine high’s intensity was directly related to how extensively cocaine tied with a mechanism for removing excess dopamine from circulation: 47% of the sites had to be occupied to produce a high; the most intense high occurred 60% to 80% of the sites were occupied.1
It was originally thought cocaine caused a high only by interfering with dopamine mop-up. However, subsequent studies convincingly questioned this view. Two such studies used “knockout mouse technology,” which investigates a single gene by removing it from a mouse embryo and growing the mouse to maturity to compare it to others who have the gene. Researchers at Duke University produced mice that “knocked out” the gene engineering dopamine. Since the mice couldn’t produce dopamine they could not produce a high, it was thought, and they shouldn’t find drugs rewarding. Yet, they did.2
The rats kept taking cocaine, indicating they were receiving some reward independent of the dopamine system. Dr. Rene Hen, the lead researcher, speculated the reward might be related to serotonin. “We know that serotonin and dopamine cross-talk,” Dr. Hen said. “If you touch one system, you will see repercussions in the other.”3
Accordingly, though dopamine is the primary neurotransmitter involved in drug addiction, it isn’t the only one. Addiction is a complex brain disease implicating more than one neurotransmitter system and multiple brain structures. Many of its workings are yet to be understood, including how altering one neurotransmitter’s function impacts other neurotransmitters.
For the next article in the Addiction Science series, click on Non-dopamine neurotransmitters.
1. Addicted, Time Magazine, May 7, 1997.
2. Broader Treatment May Aid Drug Addicts; San Francisco Chronicle, Oct. 19, 1998.
3. Two Studies Shed New Light on Cocaine’sEffect on Brain; New York Times,May 14, 1998.