Less is more: a dose-response mechanistic account of intranasal oxytocin pharmacodynamics in the human brain

The potential of intranasal oxytocin to treat several brain disorders is hampered by questions regarding the most effective dose to engage central targets and the validity of haemodynamic neuroimaging to capture its effects on neuronal activity. Using a dose-response design (9, 18 and 36 IU), we demonstrate that resting oxytocin-induced physiological changes in the amygdala, a key-hub of the brain oxytocin system, are consistent with an inverted-U dose-response curve, with maximal effects for lower doses. Yet, the effects of oxytocin vary by amygdala subdivision, highlighting the need to qualify dose-response curves within region. We further link physiological changes with the density of the oxytocin receptor gene mRNA across brain regions, strengthening our confidence in intranasal oxytocin as a valid approach to target central targets. We also demonstrate that intranasal oxytocin does not disrupt cerebrovascular reactivity, corroborating the validity of haemodynamic neuroimaging to probe its effects on the human brain.