General anesthetics activate a potent central pain-suppression circuit in the amygdala.

Abstract

General anesthesia (GA) can produce analgesia (loss of pain) independent of inducing loss of consciousness, but the underlying mechanisms remain unclear. We hypothesized that GA suppresses pain in part by activating supraspinal analgesic circuits. We discovered a distinct population of GABAergic neurons activated by GA in the mouse central amygdala (CeAGA neurons). In vivo calcium imaging revealed that different GA drugs activate a shared ensemble of CeAGA neurons. CeAGA neurons also possess basal activity that mostly reflects animals' internal state rather than external stimuli. Optogenetic activation of CeAGA potently suppressed both pain-elicited reflexive and self-recuperating behaviors across sensory modalities and abolished neuropathic pain-induced mechanical (hyper-)sensitivity. Conversely, inhibition of CeAGA activity exacerbated pain, produced strong aversion and canceled the analgesic effect of low-dose ketamine. CeAGA neurons have widespread inhibitory projections to many affective pain-processing centers. Our study points to CeAGA as a potential powerful therapeutic target for alleviating chronic pain.