On two different days, researchers injected two substances known to be safe in humans into 22 healthy subjects and 23 cocaine addicts who had abstained from the drug for one to six weeks. The substances scopolamine and physostigmine act on acetylcholine receptors. On the third day, subjects were given saline. After each injection, subjects underwent brain scans using single photon emission computed tomography (SPECT) to look at blood flow in the limbic region.
"It's a complicated system," said Dr. Adinoff, holder of the Distinguished Professorship in Drug and Alcohol Abuse Research. "The idea was to push it; it didn't matter whether the system was more active or less active, we just wanted to see if it changed."
Both scopolamine and physostigmine induced blood flow changes in limbic brain regions, but the flow patterns were different in cocaine addicts and healthy subjects.
One of the most intriguing areas affected by both substances was the tail of the hippocampus, Dr. Adinoff said. Other research has shown that this section controls environmental cues that may make someone more likely to continue to use cocaine.
"That makes sense," Dr. Adinoff said. "It's a very specific and isolated region with lots of cholinergic receptors."
The amygdala, which is involved with cue-induced cravings, also was affected by pushing the cholinergic system.
"Both of these areas of the brain are relevant to drug cravings and reward, so perhaps we could inhibit desire for a drug by giving medication that would affect these systems," Dr. Adinoff said.
Dr. Adinoff said the next step would be to use functional magnetic resonance imaging (fMRI) to assess how the cholinergic system affects decision-making processes in addicts that heighten the risk of relapse.
|Contact: LaKisha Ladson|
UT Southwestern Medical Center