A large literature has documented the importance of oxytocin in affiliation. This nonapeptide hormone has also been found to attenuate the stress response in both rats and humans (see Lee et al., 2009, for a review). Intracerebral oxytocin has been shown to inhibit the responsiveness of the hypothalamic-pituitary-adrenal axis in rats (Neumann, 2002), and intranasal administration of oxytocin has been associated with decreased amygdalar activation in response to threatening scenes in humans (Kirsch et al., 2005). Importantly, researchers have found that oxytocin biology is associated with the quality of parental environments. Adult female rats that received lower levels of maternal licking and grooming as pups subsequently exhibited decreased oxytocin receptor binding in several brain regions (Francis et al., 2000). Adverse early parental environments have been associated with lower oxytocin concentrations in cerebrospinal fluid (Winslow et al., 2003; Heim et al., 2008) and disruption of oxytocin biology in regulating stress-related cortisol responses in adult men (Meinlschmidt and Heim, 2007). These findings suggest that disruption of oxytocin biology is one mechanism through which early adverse environments lead to greater vulnerability to stress and stress-related psychosocial outcomes.
