Dopamine D-2 receptor availability in opiate-dependent subjects before and after naloxone-precipitated withdrawal

Dopamine may play a role in opiate withdrawal and dependence. We measured dopamine D-2 receptor availability in 11 opiate-dependent subjects using PET and [C-11]raclopride at baseline and during naloxone precipitated withdrawal. Because [C-11]raclopride is sensitive to endogenous dopamine, this strategy enabled us to test whether we could document in humans the DA reductions reported in animal models of opiate withdrawal. Results were compared with values from 11 controls, two of which also received naloxone. The ratio of the distribution volume in striatum to that in cerebellum (B-max/K-d+1) was used as model parameter for D-2 receptor availability. Baseline measures for B-max/K-d were lower in opiatedependent subjects (2.44 +/- 0.4) than in controls (2.97 +/- 0.45, p less than or equal to .009). Naloxone precipitated an intense withdrawal in the abusers but did not change the B-max/K-d ratio. This study documents decreases in D-2 receptors in opiate-dependent subjects but does not document significant changes in striatal DA concentration during acute withdrawal. (C) 1997 American College of Neuropsychopharmacology [Neuropsychopharmacology 16:174-182, 1997]