Ventromedial prefrontal neurokinin 1 receptor availability is reduced in chronic pain

Neurokinin 1 (NK1) receptors are involved in pain and anxiety behaviors in animals, but little is known about central alterations in this receptor system in human pain. With positron emission tomography, using a [11]-Carbon labeled NK1 receptor antagonist, we demonstrate attenuated NK1 receptor availability in frontal, insular and cingulate cortex, as well as the hippocampus, amygdala and the periaqueductal gray area in patients with chronic pain. The reduced availability was most pronounced in the ventromedial prefrontal cortex (vmPFC), where attenuations correlated to measures of fear and avoidance of movement. Further, vmPFC NK1 levels also displayed opposing influences in patients as compared to controls on regional cerebral blood flow in the anterior cingulate. We conclude that the central NK1 receptor system is altered in human chronic pain. The results suggest that NK1 receptors in the vmPFC modulate motor inhibition, and contribute to fear and avoidance of movement.