Brain glial imaging in chronic pain
Microglia and astrocytes respond to pathological events in the central nervous system, such as strokes, trauma or neurodegenerative diseases, by undergoing a series of cellular responses collectively known as 'glial activation'. As such, glial activation may be a used as a biomarker for neuropathology, as well as a therapeutic target for many conditions. In this talk, I will present a study in which the novel technology of integrated positron emission tomography-magnetic resonance imaging and the recently-developed radioligand [11C]PBR28 was used to show increased brain levels of the translocator protein (TSPO), a marker of glial activation, in patients with chronic low back pain (cLBP). In cLBP patients we observed a significant [11C]PBR28 signal increase in multiple brain regions, including thalamus and the putative somatosensory representations of the lumbar spine and leg. Despite the signal increase in patients, the thalamic levels of TSPO were negatively correlated with clinical pain and levels of circulating proinflammatory cytokines, suggesting that TSPO expression exerts pain-protective/anti-inflammatory effects in humans, by limiting the extent of glial responses. Given the putative role of activated glia in the establishment and or maintenance of persistent pain, the present findings offer clinical implications that may serve to guide future studies of the pathophysiology and management of a variety of persistent pain conditions.