Striatal dopamine transporter availability in unmedicated bipolar disorder

Objectives: Dopamine transmission abnormalities have been implicated in the etiology of bipolar disorder (BPD). However, there is a paucity of receptor imaging studies in BPD, and little information is available about the dopamine system in BPD. Reuptake of synaptic dopamine by the dopamine transporter (DAT) is the principal mechanism regulating dopamine neurotransmission, and is often used as a marker for presynaptic dopamine function. This positron emission tomography (PET) study investigated whether DAT availability differed between BPD and healthy control subjects. Methods: A total of 11 unmedicated BPD patients in either the euthymic or depressed phase and 13 closely matched healthy subjects underwent PET imaging with the DAT-selective radiotracer [C-11]CFT and a structural magnetic resonance imaging (MRI) scan. Striatal binding potential (BPND) was estimated using the multilinear reference tissue model. Region of interest and analyses were conducted to test for differences in [C-11]CFT BPND between groups. Results: Unmedicated BPD subjects had significantly lower DAT availability relative to healthy controls in bilateral dorsal caudate. Conclusions: The results of this study support the hypothesis that there are abnormalities in the dopaminergic system in BPD, and suggest that DAT availability may be related to the neuropathology of BPD. Future studies are needed to determine if DAT availability cycles with disease phase.