Higher Cortical Facilitation and Serum BDNF Are Associated with Increased Sensitivity to Heat Pain and Reduced Endogenous Pain Inhibition in Healthy Males.

Background: Although the brain-derived neurotrophic factor (BDNF) has been intensively investigated in animal models of chronic pain, its role in human pain processing is less understood. Objective: To study the neurophysiology of BDNF modulation on acute experimental pain, we performed a cross-sectional study. Methods: We recruited 20 healthy male volunteers (19-40 years old) and assessed their serum BDNF levels, quantitative sensory testing, and cortical excitability parameters using transcranial magnetic stimulation. Results: Linear regression models demonstrated that the BDNF (ß = -5.245, P = 0.034) and intracortical facilitation (ß = -3.311, P = 0.034) were inversely correlated with heat pain threshold (adjusted R2 = 44.26). The BDNF (ß = -3.719, P ≤ 0.001) was also inversely correlated with conditioned pain modulation (adjusted R2 = 56.8). Conclusions: Our findings indicate that higher serum BDNF and intracortical facilitation of the primary motor cortex are associated with increased sensitivity to heat pain and high serum BDNF with reduced pain inhibition during noxious heterotopic stimulation.

Combined neuromodulatory interventions in acute experimental pain: assessment of melatonin and non-invasive brain stimulation.

Transcranial direct current stimulation (tDCS) and melatonin can effectively treat pain. Given their potentially complementary mechanisms of action, their combination could have a synergistic effect. Thus, we tested the hypothesis that compared to the control condition and melatonin alone, tDCS combined with melatonin would have a greater effect on pain modulatory effect, as assessed by quantitative sensory testing (QST) and by the pain level during the Conditioned Pain Modulation (CPM)-task. Furthermore, the combined treatment would have a greater cortical excitability effect as indicated by the transcranial magnetic stimulation (TMS) and on the serum BDNF level. Healthy males (n = 20), (aged 18-40 years), in a blinded, placebo-controlled, crossover, clinical trial, were randomized into three groups: sublingual melatonin (0.25 mg/kg) + a-tDCS, melatonin (0.25 mg/kg) + sham-(s)-tDCS, or sublingual placebo+sham-(s)-tDCS. Anodal stimulation (2 mA, 20 min) was applied over the primary motor cortex. There was a significant difference in the heat pain threshold (°C) for melatonin+a-tDCS vs. placebo+s-tDCS (mean difference: 4.86, 95% confidence interval [CI]: 0.9 to 8.63) and melatonin+s-tDCS vs. placebo+s-tDCS (mean: 5.16, 95% CI: 0.84 to 8.36). There was no difference between melatonin+s-tDCS and melatonin+a-tDCS (mean difference: 0.29, 95% CI: -3.72 to 4.23). The mean change from the baseline on amplitude of motor evocate potential (MEP) was significantly higher in the melatonin+a-tDCS (-19.96% ± 5.2) compared with melatonin+s-tDCS group (-1.36% ± 5.35) and with placebo+s-tDCS group (3.61% ± 10.48), respectively (p < 0.05 for both comparisons). While melatonin alone or combined with a-tDCS did not significantly affect CPM task result, and serum BDNF level. The melatonin effectively reduced pain; however, its association with a-tDCS did not present an additional modulatory effect on acute induced pain.