Availability of dopamine and serotonin transporters in opioid-dependent users-a two-isotope SPECT study

Rationale and objective The aims of this study were to examine the differences between 32 opioid-dependent users treated with a very low dose of methadone or undergoing methadone-free abstinence and 32 controls. Methods SPECT analysis using [ ^99mTc] TRODAT-1 to assess striatal dopamine transporter (DAT) availability and [ ¹²³I] ADAM to assess midbrain serotonin transporter (SERT) availability were performed. Results Lower striatal DAT and midbrain SERT availabilities were noted in low-dose methadone users. History of metamphatamine use was associated with the lower striatal DAT. The striatal DAT of methadone-free abstainers was also lower than controls. The midbrain SERT availability tended to be higher in the methadone-free abstainers than the low-dose methadone users. The severity of depressive symptoms was negatively correlated with midbrain SERT availability in the opioid users. Conclusion The availability of striatal DAT tended to be, and the availability of midbrain SERT was, lower in the opioid users. History of metamphatamine use may confound the difference in straital DAT between controls and opioid users, as midbrain SERT and depressive symptoms are also associated with opioid use and abstinence.