Alfentanil increases cortical dopamine D2/D3 receptor binding in healthy subjects

Animal studies have shown that opioids modulate the function of dopaminergic neurons. The effect of alfentanil on cortical and thalamic binding of the D2/D3 receptor ligand [(11)C]FLB 457 was evaluated in eight healthy subjects with positron emission tomography. The simplified reference tissue model was used to calculate tracer binding potential (BP) during a baseline condition and target-controlled infusion of alfentanil, and the results were analyzed using a comparison group not receiving opioid. Behavioral and analgesic effects of alfentanil were also evaluated. In the region-of-interest analysis, alfentanil increased the BP of [(11)C]FLB 457 in the medial frontal cortex (P=0.0027), dorsolateral prefrontal cortex (P=0.027) superior temporal cortex (P=0.028), and medial thalamus (P=0.003) These results were confirmed in a voxel-based analysis, which further revealed an opioid-induced increase in [(11)C]FLB 457 BP in the anterior cingulate cortex (P<0.001). Alfentanil induced euphoria (P=0.003) and analgesia (P=0.006) Cheerfulness (r=0.918, P=0.001) and euphoria (r=0.982, P<0.001) were associated with increased BP of [(11)C]FLB 457 in the left posterior cingulate cortex, but the analgesic effect of alfentanil did not correlate with changes in [(11)C]FLB 457 BP. The results of this study demonstrate opioid-dopamine interactions in frontal and temporal cortical regions and the thalamus in healthy subjects. Increased D2/D3 tracer binding during opioid infusion may reflect decreased synaptic dopamine levels. The association of the uplifting effect of alfentanil with increased D2/D3 binding in the posterior cingulate cortex suggests that cortical dopamine may be involved in the behavioral effects of opioids.