Supplementary Material for: At the head and heart of oxytocin’s stress-regulatory neural and cardiac effects: a chronic administration RCT in children with autism

Introduction. Intranasal administration of oxytocin presents a promising new approach to reduce disability associated with an autism spectrum disorder diagnosis. Previous investigations have emphasized the amygdala as the neural foundation for oxytocin’s acute effects. To fully understand oxytocin’s therapeutic potential however, it is crucial to gain insight into the neuroplastic changes in amygdala circuitry induced from chronic oxytocin administrations, particularly in pediatric populations. Objective. We aimed to examine the impact of a four-week course of intranasal oxytocin on amygdala functional connectivity in children with autism, compared to placebo. Additionally, we investigated whether oxytocin improves cardiac autonomic arousal, as indexed by high-frequency heart rate variability. Methods. Fifty-seven (45 boys, 12 girls) children with autism aged 8-12 years participated in a double-blind, randomized pharmaco-neuroimaging trial involving twice-daily administrations of intranasal oxytocin or placebo. Resting-state fMRI scans and simultaneous, in-scanner heart rate recordings were obtained before, immediately after and four weeks after the nasal spray administration period. Results. Significant reductions in intrinsic amygdala-orbitofrontal connectivity were observed, particularly at the four-week follow-up session. These reductions correlated with improved social symptoms and lower cardiac autonomic arousal. Further, oxytocin’s neural and cardiac autonomic effects were modulated by epigenetic modifications of the oxytocin receptor gene. The effects were more pronounced in children with reduced epigenetic methylation, signifying heightened expression of the oxytocin receptor. Conclusion. These findings underscore that a four-week oxytocin administration course decreases amygdala connectivity and improves cardiac autonomic balance. Epigenetic modulators may explain inter-individual variation in responses to oxytocin.