Dissecting motor cortex modulation of nociception during chronic pain

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Abstract The heavy burden of chronic pain and the Opioid Epidemic has prompted an urgent, worldwide search for alternative, non-addictive methods of analgesia. One promising alternative is non-invasive electrical or magnetic stimulation of the motor cortex (MC). While MC stimulation (MCS) has repeatedly been found to reduce chronic pain in human subjects and to decrease nocifensive behaviors in rodent pain models, major questions remain about the MCS analgesic mechanisms of action, how MC influences activity in nociceptive circuits, and how to improve MCS clinical efficacy. Evidence suggests that MCS antinociceptive efficacy increases when the stimulation targets the region in motor cortex that corresponds to the body part from which nociception originates (somatotopically matched) and that MCS analgesia requires endogenous opioid activity. Here, I propose to use a rodent model of trigeminal neuropathic pain to elucidate the underlying mechanisms of MCS antinociception and to define key MCS features that pain clinicians can use to improve MCS efficacy. To characterize MCS mechanisms, I will 1) quantify the efficacy of somatotopically matched MCS (ssMCS), 2) determine what opioid receptor subtypes are required for MCS antinociception, and 3) identify how endogenous opioids modulate an opioid-sensitive MC descending circuit to the spinal trigeminal nucleus pars caudalis (SpVC) during ssMCS. To ascertain MCS efficacy between matched and off-target MCS in two different nerve constriction models, I will use classic pain behavioral paradigms along with cutting-edge machine learning algorithms to analyze mouse behavioral responses. To interrogate the combined impact of MC somatotopy and endogenous opioid signaling in MCS analgesia, I will focus on the descending projection from MC to SpVC. I will determine where opioid receptor types and endogenous opioid peptides are positioned along this circuit and then assess the impact of ssMCS +/- opioid signaling on MC and SpVC neural activity using cutting-edge calcium imaging techniques in behaving mice. Altogether, this project will determine how MCS modulates nociception through endogenous opioid signaling in somatotopically aligned circuits to guide the optimization of MCS clinical protocols. The results will also provide the first report of neural activity during and after ssMCS at both the target and in an MC output. This project will take place in the lab of Prof. Mark Schnitzer’s (sponsor) lab at Stanford, an ideal environment for innovative neuroscience. Together with the mentorship of leading pain neuroscientists, Profs. Greg Scherrer and Sean Mackey (co-sponsors), the proposed training plan provides an excellent opportunity for me to become an expert in pain and opioid neurobiology while interrogating novel scientific concepts with cutting-edge technology. Further, I will gain valuable clinical knowledge by interacting with Prof. Mackey and his team of clinical pain researchers and physicians. Finally, this project will help me develop into an independent scientist and ideally position me to start my own lab program studying pain circuitry and its intersection with motor circuits.