The short allele of the serotonin transporter gene (5-HTTLPR) is associated with greater negative emotionality. Given that emotion modulates pain, short allele carriers (s-carriers) may also demonstrate altered pain modulation. The present study used a well-validated emotional picture-viewing paradigm to modulate pain and the nociceptive flexion reflex (NFR, a measure of spinal nociception) in 144 healthy genotyped participants. As expected, pain/NFR responses were largest during unpleasant pictures and smallest during pleasant pictures. However, relative to l/l-carriers, s-carriers demonstrated greater pain inhibition during pleasant pictures and greater pain facilitation during unpleasant pictures. Neither emotional modulation of NFR nor NFR threshold was associated with 5-HTTLPR polymorphisms. Results also indicated that men who were s-carriers had a higher pain threshold and tolerance than other participants. Taken together, our results indicate 5-HTTLPR polymorphisms may influence pain modulation at the supraspinal (not spinal) level; however, the influence on pain sensitivity may be sex-specific.
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