Dopamine neurons in the dorsal raphe nucleus may modulate social dominance in mice

Social hierarchy is a fundamental organizational structure in group-living animals, influencing individual health and behavior. Dopaminergic (DA) systems, particularly in the ventral tegmental area (VTA) and dorsal raphe nucleus (DR), are implicated in motivation and competition, but their distinct roles in social dominance remain unclear. Here, we investigated the contributions of VTA and DR DA neurons to social dominance in sexually naive male C57BL/6J mice. Using the tube test to establish stable social hierarchies, we observed increased c-Fos expression in both dominant and subordinate mice within the VTA and DR post-test. Notably, only dominant mice exhibited significantly higher c-Fos expression in DR DA neurons relative to subordinate counterparts. Fiber photometry results showed that both VTA and DR DA neurons were activated during proactive push behaviors and inhibited during passive retreats, with DR neurons showing stronger activation during dominance-related actions. Chemogenetic manipulation results revealed that inhibiting DR DA neurons in dominant mice reduced their social rank, while activating these neurons in subordinates increased their rank. In contrast, chemogenetic modulation of VTA DA neurons had no significant effect on social dominance. Furthermore, modulation of DA neurons in both regions exerted rank-dependent effects on specific anxiety-like behavioral phenotypes. These findings highlight the distinct roles of DR and VTA DA neurons in social hierarchy, suggesting that DR DA neurons may play a more critical role in modulating social dominance. This study advances our understanding of neural mechanisms underlying social hierarchy and highlights the functional significance of region-specific DA neuronal populations.