Table 1.
Participants.
Figure 1.
Conditioned pain modulation scores (CPM-scores).
To control for individual variation with regard to baseline values, the proportion of difference from baseline was used rather than the difference of raw values. This was done to control for individual variation in baseline measures and gives positive CPM-scores for pain inhibition and negative ones for facilitation, as compared to the baseline. To enable a comparison of VAS-ratings with threshold values, we define our CPM-scores as q(b–c)/b where b = baseline value (in kPA, mm or mA) and c = value during CPM. q = 1 for heat-pain VAS-ratings and q = −1 for thresholds ratings.
Figure 2.
Baseline values for test-pain stimuli.
A. Pressure pain thresholds (PPTs) in kPA, assessed by algometry, at baseline. Genotype did not have a significant effect on the baseline level [U = 247, z = −0.14, p = 0.90]. B. No significant differences were found on the basis of genotype [U = 211, z = −0.95, p = 0.35] between the individualized temperatures used as test-stimuli. C. Average of the two baseline NFR-threshold measurements in mA. No significant differences were found between groups, F<1.
Figure 3.
The low 5-HTT-expressing group, as compared with the high 5-HTT group, had a significantly diminished conditioned pain modulation with regard to pressure pain thresholds [F(1,41) = 5.99, p = 0.02] and heat at 30 seconds [U = 145.5, z = −2.44, p = 0.02, r = −0.36]. There were no significant differences between groups with regard to tonic pain-mediated increase in the threshold for the nociceptive flexion reflex (NFR), F<1.
Figure 4.
Interaction between pain-ratings for suprathreshold noxious heat and genotype.
Mean VAS-ratings for suprathreshold noxious heat, applied to the right ventral forearm, are shown for the low 5-HTT-expressing and high 5-HTT-expressing genotype groups, respectively. The interaction between temperature level and genotype on the VAS-rating was significant [F(1.60, 65.51) = 4.10, p = 0.03].