PET study shows oxytocin failing to aid serotonin in the autistic brain

The “cuddle hormone” and neurotransmitter oxytocin, which has been shown to improve social skills in individuals with autism spectrum disorders (ASD), does not boost beneficial serotonin activity in these patients as it clearly does in their non-autistic peers, according to a PET-based study conducted at the Institute of Cognitive Sciences in Lyon, France.

While disappointing, the neuroimaging finding may lead to research aimed at better understanding the oxytocin-serotonin connection.

The study was published online Oct. 17 in Cerebral Cortex.

Lead author Arthur Lefevre, PhD, senior author Angela Sirigu, PhD, and colleagues mapped the effects of nasally inhaled oxytocin on serotonin in 18 patients with ASD and 24 healthy controls.

All participants underwent one PET scan with the oxytocin nasal spray and one scan without (for baseline).

The researchers used the radiotracer 18F-MPPF to mark the serotonin 1A receptor (serotonin-1AR) and measured the binding potential of the tracer.

This measurement provided an indication of how well the oxytocin had modulated the receptor.

The team found that, at baseline, the ASD patients did not differ from controls for serotonin-1AR concentration and distribution.

However, the oxytocin significantly increased MPPF binding potential in several brain regions of the healthy controls—but did not change the binding potential at all in the ASD group.

Serotonin serum concentration analysis corroborated these results, the authors report.

“Our findings suggest a disturbed oxytocin-serotonin interaction in autism,” they write. “This may limit the potential benefits of oxytocin in these patients and open the ways to investigate combined oxytocin-serotonin treatments.”