A pharmaco-fMRI study on pain networks induced by electrical stimulation after sumatriptan injection

Sumatriptan, a drug widely used to alleviate migraine headaches, has several somatosensory adverse effects, including tactile allodynia. To understand whether sumatriptan affects sensory and affective circuitries simultaneously, we investigated the responses of 12 healthy volunteers to electrical stimuli after infusion with either sumatriptan or saline. Using a double-blind crossover study design, we used functional magnetic resonance imaging (fMRI) to measure brain activation in different areas during electrical stimulation. The visual analog scale (VAS) and short-form McGill pain questionnaire (SF-MPQ) were used to rate stimulation-evoked sensations and affections after drug administration. VAS rating, SF-MPQ, and block fMRI were all performed in each subject during sumatriptan and saline injection. Echo-planar imaging sequences were used to determine the whole-brain blood oxygenation level-dependent signal of the entire brain. Our results showed that sumatriptan predominantly activated regions in the medial pain system and smaller regions in the lateral pain system. These regions included the secondary somatosensory cortex (SII), anterior insular cortex, orbitofrontal cortex, medial thalamus, cerebellar supravermis, dentate nucleus, and the majority of the anterior cingulate cortex (ACC). In contrast, activation following saline administration was observed primarily in the lateral pain system, including the primary sensory cortex, lateral SII, posterior insular cortex, anterior ACC, and lateral thalamus. Importantly, we found that VAS ratings and MPQ scores were increased after sumatriptan infusion, but not after saline administration. Our fMRI, VAS, and SF-MPQ findings suggest that sumatriptan plays a significant role in the affective dimension of pain and a minor role related to sensory discrimination.