Abstract
In addition to its involvement in motor control and in encoding reward value, increasing evidence also implicates basal ganglia dopaminergic mechanisms in responses to stress and aversive stimuli. Basal ganglia dopamine (DA) neurotransmission may then respond to environmental events depending on their saliency, orienting the subsequent responses of the organism to both positive and negative stimuli. Here we examined the involvement of DA neurotransmission in the human response to pain, a robust physical and emotional stressor across species. Positron emission tomography with the DA D2 receptor antagonist radiotracer [11C]raclopride detected significant activation of DA release in dorsal and ventral regions of the basal ganglia of healthy volunteers. Activation of nigrostriatal (dorsal nucleus caudate and putamen) DA D2 receptor-mediated neurotransmission was positively associated with individual variations in subjective ratings of sensory and affective qualities of the pain. In contrast, mesolimbic (nucleus accumbens) DA activation, which may impact on both D2 and D3 receptors, was exclusively associated with variations in the emotional responses of the individual during the pain challenge (increases in negative affect and fear ratings). These data demonstrate that basal ganglia dopamine D2 receptor-mediated neurotransmission is involved in responses to pain and that it contributes to individual variations in the pain experience at the levels of physical and emotional elements, albeit with different neuroanatomical substrates.