Oxytocin receptor neurons in the paraventricular thalamus as a nexus for social behaviour and fear.

Oxytocin has been implicated in regulating social behaviour and emotional responses; however, the underlying neural circuits remain incompletely understood. Neurons expressing oxytocin receptors (OTRs) in the paraventricular thalamus (PVT) are emerging as a potential modulator of these processes. In this study, we investigated the specific role of OTR-expressing PVT neurons in sociability and fear-related behaviours. Using chemogenetic approaches, we found that bidirectional manipulation of these neurons significantly modulated social behaviour and fear extinction in mice. Inhibition of OTR-expressing PVT neurons impaired sociability and fear extinction, whereas activation selectively enhanced early extinction learning without affecting sociability. Electrophysiological analyses revealed that oxytocin increases tonic firing in PVT neurons, suggesting a mechanism for heightened excitability. In contrast, manipulation of OTR-expressing neurons in the medial prefrontal cortex had no effect on sociability. In a complementary human dataset, salivary oxytocin levels were modestly associated with thalamic microstructure and autism spectrum disorder trait severity. Although the experimental paradigms differed across species, these findings collectively suggest that OTR-expressing PVT neurons may contribute to social and emotional behaviours through circuit-specific mechanisms. These findings may have implications for psychiatric conditions such as autism spectrum disorder and anxiety. Future translational studies should explore the therapeutic potential of targeting oxytocin-related PVT function to treat social and fear-related deficits. Overall, these findings advance our understanding of the role of oxytocin in brain function and its relevance to mental health.