SUMMARY We developed a technology (Capturing Activated Neural Ensembles, or CANE) to label, manipulate, and trans-synaptically trace neural circuits that are transiently activated in behavioral contexts with high efficiency and temporal precision. CANE consists of a knock-in mouse and engineered viruses designed to specifically infect activated neurons. Using CANE, we selectively labeled neurons that were activated by either fearful or aggressive social encounters in a hypothalamic subnucleus previously known as a locus for aggression, and discovered that social fear and aggression neurons are intermixed but largely distinct. Optogenetic stimulation of CANE-captured social fear neurons (SFNs) is sufficient to evoke fear-like behaviors in normal social contexts, whereas silencing SFNs resulted in reduced social avoidance. CANE-based mapping of axonal projections and presynaptic inputs to SFNs further revealed a highly distributed and recurrent neural network. CANE is a broadly applicable technology for dissecting causality and connectivity of spatially intermingled but functionally distinct ensembles.

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 (CeA GA neurons). In vivo calcium imaging revealed that different GA drugs activate a shared ensemble of CeA GA neurons. CeA GA neurons also possess basal activity that mostly reflect animals’ internal state rather than external stimuli. Optogenetic activation of CeA GA potently suppressed both pain-elicited reflexive and self-recuperating behaviors across sensory modalities, and abolished neuropathic pain-induced mechanical (hyper-)sensitivity. Conversely, inhibition of CeA GA activity exacerbated pain, produced strong aversion, and cancelled the analgesic effect of low-dose ketamine. CeA GA neurons have widespread inhibitory projections to numerous affective pain-processing centers. Our study points to CeA GA as a potential powerful therapeutic target for alleviating chronic pain.