Positron emission tomography imaging with the radiotracer [11C]ABP688 was used to measure mGluR5 binding and magnetic resonance spectroscopy was used to measure glutamate-glutamine levels in the striatum of cocaine-addicted participants (n = 15) compared with healthy control subjects (n = 15). Following the scans, the cocaine-addicted volunteers performed cocaine self-administration sessions to investigate the correlation between cocaine-seeking behavior and mGluR5 receptor binding.
The results of the study showed that cocaine addiction was associated with a 20% to 22% reduction in [11C]ABP688 binding in the striatum. A secondary analysis of cortical and subcortical regions other than the striatum showed a similar reduction in [11C]ABP688 binding, suggesting that the decrease was widespread. No between-group differences were seen in the magnetic resonance spectroscopy measures of glutamate-glutamine in the left striatum. In addition, no correlation was seen between [11C]ABP688 binding in the striatum and the choice to self-administer cocaine.
Overall, these results show that long-term cocaine use is associated with a decrease in mGluR5 availability compared with matched healthy control subjects and suggests that this receptor may serve as a viable target for treatment development for this disorder.