The neuropeptide oxytocin (OXT) exerts anxiolytic and prosocial effects in the central nervous system of rodents. A number of recent studies have attempted to translate these findings by investigating the relationships between peripheral (e.g., blood, urinary and salivary) OXT concentrations and behavioral functioning in humans. Although peripheral samples are easy to obtain in humans, whether peripheral OXT measures are functionally related to central OXT activity remains unclear. To investigate a possible relationship, we quantified OXT concentrations in concomitantly collected cerebrospinal fluid (CSF) and blood samples from child and adult patients undergoing clinically indicated lumbar punctures or other CSF-related procedures. Anxiety scores were obtained in a subset of child participants whose parents completed psychometric assessments. Findings from this study indicate that plasma OXT concentrations significantly and positively predict CSF OXT concentrations (r=0.56, P=0.0064, N=27). Moreover, both plasma (r=-0.92, P=0.0262, N=10) and CSF (r=-0.91, P=0.0335, N=10) OXT concentrations significantly and negatively predicted trait anxiety scores, consistent with the preclinical literature. Importantly, plasma OXT concentrations significantly and positively (r=0.96, P=0.0115, N=10) predicted CSF OXT concentrations in the subset of child participants who provided behavioral data. This study provides the first empirical support for the use of blood measures of OXT as a surrogate for central OXT activity, validated in the context of behavioral functioning. These preliminary findings also suggest that impaired OXT signaling may be a biomarker of anxiety in humans, and a potential target for therapeutic development in individuals with anxiety disorders.

Research suggests that children with autism spectrum disorder (ASD) may have reduced empathy, as measured by an impaired contagious yawn response, compared to typically developing (TD) children. Other research has failed to replicate this finding, instead attributing this phenomenon to group differences in attention paid to yawn stimuli. A third possibility is that only a subgroup of children with ASD exhibits the impaired contagious yawn response, and that it can be identified biologically. Here we quantified blood concentrations of the "social" neuropeptide oxytocin (OXT) and evaluated yawning behavior and attention rates during a laboratory task in children with ASD (N = 34) and TD children (N = 30) aged 6-12 years. No group difference in contagious yawning behavior was found. However, a blood OXT concentration × group (ASD vs. TD) interaction positively predicted contagious yawning behavior (F 1,50 = 7.4987; P = 0.0085). Specifically, blood OXT concentration was positively related to contagious yawning behavior in children with ASD, but not in TD children. This finding was not due to delayed perception of yawn stimuli and was observed whether attention paid to test stimuli and clinical symptom severity were included in the analysis or not. These findings suggest that only a biologically defined subset of children with ASD exhibits reduced empathy, as measured by the impaired contagious yawn response, and that prior conflicting reports of this behavioral phenomenon may be attributable, at least in part, to variable mean OXT concentrations across different ASD study cohorts.Lay Summary: People with autism may contagiously yawn (i.e., yawn in response to another's yawn) less often than people without autism. We find that people with autism who have lower levels of blood oxytocin (OXT), a hormone involved in social behavior and empathy, show decreased contagious yawning, but those who have higher blood OXT levels do not differ in contagious yawning from controls. This suggests that decreased contagious yawning may only occur in a biologically defined subset of people with autism.