Spinal interneurons and pain

Chronic pain is one of the most prevalent and difficult clinical problems. Those affected by chronic pain diseases often experience a multitude of debilitating symptoms such as hyperalgesia, allodynia, and spontaneous pain. Despite high demand for effective therapies, conventional pain medications such as nonsteroidal antiinflammatory drugs and opioids lack significant clinical efficacy or cause serious side effects. Etiology and pathophysiology of chronic pain is multifaceted and complex. Of particular interest is the injury induced maladaptive plasticity within spinal dorsal horn (SDH) circuits where somatosensory information is integrated and processed. These changes have been proposed to underlie the onset and the maintenance of chronic pain. While the field has advanced greatly, the functional and molecular organization of SDH circuits remain poorly understood. This is in part due to the incredible complexity and heterogeneity of interneuron subpopulations that reside within this region of the nervous system. Herein, we describe recent advances in the molecular, anatomical, and functional organization of SDH interneuron populations involved in acute nociceptive processing, as well as chronic pain induced by neuropathic or inflammatory injuries.