Wiring diagram of oxytocin system in the mouse brain

Oxytocin (OT) neurons in the brain make direct connection with discreet brain regions to regulate social behavior and physiological responses. Despite significance, we lack comprehensive wiring diagram of OT neurons to understand their synaptic input, axonal output, and relationship with OT receptor (OTR) throughout the entire brain. Here, we systematically map the input and output connectivity of OT neurons in the paraventricular nucleus of the hypothalamus (PVH) and the supraoptic nucleus (SO), and OTR expression via a brain-wide quantitative analysis method at cellular resolution. First, we create 2D flatmap to understand spatial arrangement of OT neurons intuitively. Then, we utilize knock-in Ot-Cre mice injected with Cre dependent retrograde monosynaptic rabies viruses and anterograde adeno associated virus to understand input-output patterns. We find that OT neurons in the PVH showed broader input-output patterns than the SO. Moreover, reciprocally connected brain regions (e.g., the hypothalamus, the thalamus) are closely related to cognitive brain functions, while unidirectional output areas (the midbrain, the hindbrain) are associated with physiological functions. Lastly, we compare OT output and OTR expression using Otr-Venus reporter mice across the brain. We find no significant quantitative correlation, suggesting largely non-synaptic neuronal modulation by OT signaling except few well-overlapped areas (e.g., the paraventricular nucleus of thalamus). In summary, our oxytocin wiring diagram provides a resource to understand anatomical foundation for OT signaling to exert diverse behavioral function in the brain.