A PET [18F]altanserin study of 5-HT2A receptor binding in the human brain and responses to painful heat stimulation

There is a large body of evidence that serotonin [5-hydroxytryptamine (5-HT)] plays an important role in the transmission and regulation of pain. Here we used positron emission tomography (PET) to study the relationship between baseline 5-HT2A binding in the brain and responses to noxious heat stimulation in a group of young healthy volunteers. Twenty-one healthy subjects underwent PET scanning with the 5-HT2A antagonist, [18F]altanserin. In addition, participants underwent a battery of pain tests using noxious heat stimulation to assess pain threshold, pain tolerance and response to short-lasting phasic and long-lasting (7-minute) tonic painful stimulation. Significant positive correlations were found between tonic pain ratings and [18F]altanserin binding in orbitofrontal (r = 0.66; p = 0.005), medial inferior frontal (r = 0.60; p = 0.014), primary sensory-motor (r = 0.61; p = 0.012) and posterior cingulate (r = 0.63; p = 0.009) cortices. In contrast, measures of regional [18F]altanserin binding did not correlate with pain threshold, pain tolerance, or suprathreshold phasic pain responses. These data suggest that cortical 5-HT2A receptor availability co-varies with responses to tonic pain. The correlation between [18F]altanserin binding in prefrontal cortex and tonic pain suggests a possible role of this brain region in the modulation and/or cognitive-evaluative appreciation of pain.