Seiriki, K.; Maeda, S.; Kojima, L.; Fujimoto, Y.; Baba, T.; Rokujo, H.; Nitta, T.; Nakazawa, T.; Kasai, A.; Hikida, T.; Hashimoto, H.

Individuals experience varying magnitudes of stress in their daily lives. Although stress responses facilitate adaptive processes to cope with changing environments, severe stress can lead to traumatic learning and anxiety disorders. However, the neuronal mechanisms underlying the influence of stress severity on these processes remain unclear. Here, we show that traumatic social stress engages anatomically distinct locus coeruleus noradrenergic (LCNA) subpopulations that exhibit dynamic responses scaled to aversive salience. Using whole-brain activity and axonal projection mappings, we identified projectome subtypes of LCNA neurons, which are differentially recruited by single versus consecutive aversive social experiences. While hippocampus-projecting LCNA neurons responded to general social contacts, thalamus-projecting LCNA neurons tracked the aversive salience of social stimuli. Functional manipulations revealed a bidirectional role of thalamus-projecting LCNA neurons in social avoidance learning. These findings reveal the functional architecture of LCNA subsystems that regulate traumatic social learning via dynamic scaling to aversive salience.