SPECT imaging revealed that cocaine addicted subjects and control subjects differ in subcortical, limbic and cortical response to cholinergic probes in areas relevant to craving, learning and memory; findings that could result in new treatment options for individuals addicted to cocaine, according to a study published in the June issue of Neuropsychopharmacology.
The changes in the brain's cholinergic system, which involves the neurotransmitter acetylcholine and its receptors, or docking points, on brain cells to which the chemical attaches was studied by Bryon H. Adinoff, MD, professor of psychiatry at University of Texas Southwestern Medical Center at Dallas, and colleagues.
The researchers looked at how alterations in the cholinergic system affected the limbic region in the brain of cocaine-addicted subjects. The limbic region of the brain supports functions such as emotions, behavior, learning and long-term memory. It includes brain structures such as the hippocampus and amygdala.
On two different days, researchers injected scopolamine and physostigmine which act on acetylcholine receptors in humans into 22 healthy subjects and 23 cocaine addicts who had abstained from the drug for one to six weeks. On the third day, subjects were given saline. After each injection, subjects underwent brain scans using SPECT to look at regional cerebral blood flow in the limbic region.
Both scopolamine and physostigmine induced blood flow changes in limbic brain regions, but the flow patterns were different in cocaine addicts and healthy subjects, according to Adinoff and colleagues.
One of the most intriguing areas affected by both substances was the tail of the hippocampus, said Adinoff. Other research has shown that this section controls environmental cues that may make someone more likely to continue to use cocaine.
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," added Adinoff.
Adinoff said the next step would be to use functional MRI to assess how the cholinergic system affects decision-making processes in addicts that heighten the risk of relapse.