Abstract
We developed a unique protocol where transcranial direct current stimulation (tDCS) of the motor cortex is performed during positron emission tomography (PET) scan using a μ-opioid receptor (μOR) selective radiotracer, [11C]carfentanil. This is one of the most important central neuromechanisms associated with pain perception and regulation. We measured μOR non-displaceable binding potential (μOR BPND) in a trigeminal neuropathic pain patient (TNP) without creating artifacts, or posing risks to the patient (e.g., monitoring of resistance). The active session directly improved in 36.2% the threshold for experimental cold pain in the trigeminal allodynic area, mandibular branch, but not the TNP patient’s clinical pain. Interestingly, the single active tDCS application considerably decreased μORBPND levels in (sub)cortical pain-matrix structures compared to sham tDCS, especially in the posterior thalamus. Suggesting that the μ-opioidergic effects of a single tDCS session are subclinical at immediate level, and repetitive sessions are necessary to revert ingrained neuroplastic changes related to the chronic pain. To our knowledge, we provide data for the first time in vivo that there is possibly an instant increase of endogenous μ-opioid release during acute motor cortex neuromodulation with tDCS.
Highlights
Pain is described as a complex experience affecting the sensory, and the affective and cognitive systems (Merskey and Bogduk, 1994)
We developed a unique protocol where transcranial direct current stimulation of the motor cortex is performed during positron emission tomography (PET) scan using a μ-opioid receptor selective radiotracer, [11C]carfentanil
Each electrode was positioned inside a 35 cm2 sponge, that was soaked with approximately 12 mL of saline solution (6 mL per Frontiers in Psychiatry | Neuropsychiatric Imaging and Stimulation transcranial direct current stimulation (tDCS) effects on μ-opioid receptors side) before the PET and up to 12 mL during the procedure
Summary
Pain is described as a complex experience affecting the sensory, and the affective and cognitive systems (Merskey and Bogduk, 1994). We developed a unique protocol where transcranial direct current stimulation (tDCS) of the motor cortex is performed during positron emission tomography (PET) scan using a μ-opioid receptor (μOR) selective radiotracer, [11C]carfentanil. The single active tDCS application considerably decreased μORBPND levels in (sub)cortical pain-matrix structures compared to sham tDCS, especially in the posterior thalamus.
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