Motor Cortex as a Research and Therapeutic Target in TMD

Chronic temporomandibular joint disorders (TMD) represent clinical problems in which empirical treatments offer uncertain relief for a large number of patients. Many conventional therapies are ineffectual, leading to persistent treatment failure and/or poor iatrogenic-induced results; which raises the possibility that the cause for their pain endurance may also lie in the brain milieu. Although MRI-based techniques have provided insights into some neuroplastic mechanisms of TMD in humans, many questions regarding its molecular mechanisms in vivo are still unanswered. First, how are endogenous μ-opioid mechanisms in the brain, known to be centrally involved in pain regulation, affected by acute and chronic TMD pain? Second, how can they be directly modulated to provide analgesic effect on pain measures? Finally, what are the neuroplastic effects in the brain after continuous modulation of those molecular mechanisms? The understanding of these processes is crucial to determine the mechanisms engaged in the persistence and, most important, the alleviation of TMD.

Preliminary studies from our center, using positron emission tomography (PET) with [11C] carfentanil, a selective radiotracer for mu-opioid receptor (muOR), have demonstrated that there is a decrease in μOR availability (non-displaceable binding potential -BPND) in key pain-related structures in the brains of chronic trigeminal pain patients, which correlated with their clinical pain measures. We propose to demonstrate that acute (masseteric pain challenge) and chronic clinical pain measures in TMD patients are correlated with μ-opioid receptor (µOR) non-displaceable binding potential (BPND) in the thalamus and other pain-related regions.