Dopamine release during psychological stress in euthymic bipolar I disorder: a Positron Emission Tomography study with [11C]raclopride

•There is evidence that stress susceptibility alters the course of bipolar disorder.•An exaggerated dopamine response to stress has been hypothesized to cause recurrence of manic episodes in bipolar disorder.•We used a validated stress paradigm to assess if dopamine release in response to stress as measured with raclopride binding was different in euthymic patients with BD as compared with healthy controls.•We found a significantly higher dopamine release in the basal ganglia regions during the stress task for all participants, although the magnitude of this release was not different between the groups. Neurochemical mechanisms underlying stress induced relapse of mood episodes in Bipolar I Disorder (BD) remain unknown. This study investigated whether euthymic BD patients have a greater dopamine release in ventral striatum, caudate and putamen in response to psychological stress using Positron Emission Tomography (PET) scanning with the radiotracer [11C]raclopride. Euthymic patients with BD (n = 10) and 10 matched healthy controls underwent two [11C]raclopride PET scans, one during a “stress” and the other in a “no stress” condition separated by at least 24 h. Montreal Imaging Stress Test (MIST) was used to induce stress during stress condition. Participants received an injection of [11C]raclopride over one minute followed by PET scan for 60 min. Participants were assessed for mood symptom severity at baseline, and before and after each scan. The reduction in [11C]raclopride binding in stress condition compared with non-stress rest condition for each subject provided an estimate of dopamine release due to stress. There was a significant effect of stress in reducing the [11C]raclopride binding in the ventral striatum, caudate and putamen; however, no significant effects of group or condition x group interaction were found. Small sample size and recruitment of euthymic patients who may be less vulnerable to stress may limit the generalizability of findings. Our findings showed that psychological stress led to dopamine release in the basal ganglia for all participants but the magnitude of dopamine release during a stress task was not different between euthymic BD patients and healthy controls.