Hypothalamic Orexin Input to the Medial Amygdala Links Vigilance to Arousal

Abstract Arousal circuits govern anesthetic state transitions, but emergence is often complicated by agitation, and the neural circuits linking anesthetic arousal to vigilance remain unclear. Here, we identify a lateral hypothalamic orexin-to-medial amygdala pathway (LHA Ox →MeA) that links anesthetic state transitions to vigilance-like behavioral bias. Synaptic labeling and slice recordings revealed dense LHA Ox innervation in the MeA, and RNAscope showed predominant Ox2R expression in MeA GABAergic (MeA vGAT ) neurons. LHA Ox →MeA terminal activation increased local orexin release, promoted arousal from isoflurane anesthesia, delayed loss of righting reflex during induction, and accelerated recovery during emergence. In vigilance assays, stimulation acutely suppressed open-field exploration and produced real-time place preference without conditioned reinforcement. Fiber photometry demonstrated preferential recruitment of MeA vGAT neurons across anesthetic states. Direct MeA vGAT activation recapitulated cortical engagement, arousal, and vigilance phenotypes, whereas TeLC-mediated silencing of MeA vGAT output abolished induction delay and reversed vigilance-like bias while sparing light-anesthesia arousal and emergence acceleration.