Investigation and Modulation of the Mu-Opioid Mechanisms in Migraine (in Vivo)

Migraine is a debilitating chronic condition that affects most of the patient's existence, from childhood to late adulthood. During frequent headache attacks, its sufferers show marked increased sensitivity to noxious (hyperalgesia) and even non-noxious stimuli, a phenomenon called cutaneous allodynia that affects 63% of the patients. Although MRI-based techniques have provided insights into some brain mechanisms of migraine, many questions regarding its molecular impact in the brain are still unanswered. The overall goal of this project is to provide a detailed understanding of the µ-opioid receptor mediated transmission in the brain of migraine patients, one of the most important central pain regulatory systems in humans, with the long-term objective of developing more focused neuromechanism-driven methods for migraine research and therapy. Preliminary studies from an earlier project (NINDS-NIHK23 NS0629946) using positron emission tomography (PET) with \[11C\] carfentanil, a selective radiotracer for μ-opioid receptor (μOR), have indicated that there is a decrease in µOR availability (non-displaceable binding potential; BPND) in the brain of migraine patients during the headache attacks and allodynia, including areas like thalamus and periaqueductal gray matter (PAG). µOR BPND is an objective measurement, in vivo, of endogenous μ-opioid availability, and its acute reduction reflects the activation of this neurotransmitter system. This is arguably one of the neuromechanisms most centrally involved in pain regulation, affecting multiple elements of the pain experience. Moreover, MRI-based reports have found that those findings co-localize with neuroplastic changes in migraine patients. Conventional therapies are unable to selectively target those dysfunctional brain regions, and there is a paucity of data on how to reverse embedded neuroplastic molecular mechanisms when available medications and surgical therapies fail. Several studies with motor cortex stimulation (MCS) have shown that epidural electrodes in the primary motor cortex (M1) are effective in providing analgesia in patients with refractory central. The rationale for MCS stimulation is based in part on the thalamic dysfunction noticed in chronic pain and migraine, and also on studies demonstrating that MCS significantly changes thalamic activity. Evidently, the invasive nature of such a procedure limits its indication to highly severe chronic pain disorders. New non-invasive brain neuromodulatory methods for M1, such as transcranial direct current stimulation (tDCS), can now safely modulate and activate the µOR system, providing relatively lasting pain relief in chronic pain patients and migraine. However, the electric fields generated by its most conventional analgesic montage are widely spread across the brain, lacking specificity on the pain-related structures directly targeted. Recently, a novel high-definition tDCS (HD-tDCS) montage created by our group was able to reduce exclusively "contralateral" sensory-discriminative clinical pain measures (pain intensity/area) in chronic patients by targeting more precisely the putative M1 region. It is hoped that this montage will provide durable relief of pain for this episodic migraine population. This is a phase 2, single center, two-arm, double-masked, randomized investigation and modulation of the µ-opioid mechanisms in migraine (in vivo). We will enroll 60 patients with episodic migraine (30 for the active M1 HD-tDCS group and 30 for a sham group). Each participant will undergo a sequence of events and evaluations that will include baseline assessments, 10 days of HD-tDCS, pre- and post-PET and MRI scans, and questionnaires to evaluate pain and quality of life.