Is psychological stress in man associated with increased striatal dopamine levels?: A [11C]raclopride PET study.

In rodents, stress causes rapid increases in extracellular dopamine (DA) concentration in cortical and subcortical brain regions, and positron emission tomography (PET) studies in healthy humans have suggested psychological and pharmacological stressors are associated with increased DA concentration in the striatum. In this experiment, we measured the effect of stress, induced by difficult mental arithmetic, on [11C]raclopride binding in order to index striatal DA release. To refine measurements and facilitate interpretation of results a combination of head movement correction, a carefully designed control condition and bolus infusion administration of [11C]raclopride were employed. Fourteen healthy volunteers were scanned using [11C]raclopride PET. Physiological and psychological responses to the task were consistent with a stress response with changes in cardiovascular, hormonal, and subjective state indices. No change of ventral or dorsal striatal [11C]raclopride binding was found in the stress condition compared to nonstress. This negative result suggests that significant DA release does not occur in the striatum in healthy humans after mild, psychological stress.