To elucidate neuroimmune interactions underlying placebo analgesia, we exposed 37 healthy human volunteers to a standardized pain challenge on each of 2 days within a Positron Emission Tomography (PET) neuroimaging paradigm using the MOR selective radiotracer, 11C-Carfentanil (CFN). Unfortunately, current lack of mechanistic clarity obfuscates clinical translation. Validation that neuroimmune interactions involving brain μ-opioid receptor (MOR) activity and plasma IL-18 underlie placebo analgesic expectation could have widespread clinical applications.
Emerging evidence suggests placebo-responsive neurotransmitter systems (e.g., endogenous opioid) regulate immune function by manipulating inflammatory proteins including IL-18, a potent pro-inflammatory, nociceptive cytokine implicated in pathophysiology of various diseases. Placebo, administered under positive expectation in clinical trials, can have potent effects on disease pathology, obscuring active medications.
Behavioral conditioning and expectation can have profound impact on animal and human physiology.
