Oxytocin signaling bidirectionally modulates serotonergic and dopaminergic neurons in the dorsal raphe nucleus.

The involvement of oxytocin in social behavior is well established, yet its interaction with neuromodulatory systems, such as serotonin and dopamine, remains incompletely understood. Here, we utilized immunohistochemistry, anatomical tracing, chemogenetic, and ex vivo electrophysiological approaches primarily in male mice, with female mice used only for an additional anatomical tracing control experiment, investigate how oxytocin modulates serotonergic and dopaminergic neuronal populations. Employing the dual-eGRASP tool, we visualized oxytocinergic projections from the paraventricular nucleus (PVN) to the serotonergic and dopaminergic neurons in dorsal raphe nucleus (DRN). Blocking oxytocin receptors in the DRN attenuated social interaction behavior. Additionally, analysis of c-Fos levels and neuronal excitability revealed that oxytocin inhibits serotonergic neurons while activating dopaminergic neurons in the DRN. Our findings suggest a bidirectional regulatory role of oxytocin signaling in the DRN serotonergic and dopaminergic neurons.Significance Statement Social behavior relies on interactions among neuromodulatory systems, yet how oxytocin communicates with serotonin and dopamine circuits remains unclear. We identify the DRN as a functionally relevant target of hypothalamic oxytocin neurons during social approach. Using dual-eGRASP, we visualize contacts from PVN oxytocin neurons onto both serotonergic and dopaminergic DRN. Blocking oxytocin receptors in the DRN reduces social interaction without affecting locomotion. Moreover, oxytocin suppresses serotonergic neuronal activity while increasing dopaminergic neuronal activation, revealing opposing control of two prosocial neuromodulatory populations within the same region. These findings provide a circuit framework for how oxytocin coordinates social behavior through bidirectional modulation of dorsal raphe neuromodulators.