Objectives: The purpose of this study was to determine the occurrence of changes in the binding of serotonin and dopamine transporters, which are highly selective markers for their respective neuronal systems.
Methods: Twenty male subjects (age 18-26 years; IQ 99.3±18.1) with autism and 20 age-and IQ-matched controls were employed. Participants recruited from the community. Using PET, we measured the binding of brain serotonin and dopamine transporters in each individual with the radioligands [11C](+)McN-5652 and [11C]WIN-35,428, respectively. SPM was used for between-subject analysis and for within-subject correlation analysis with respect to clinical variables.
Results: Serotonin transporter binding was significantly lower throughout the brain in autistic subjects, compared with control subjects (P < .05). Specifically, the reduction in the anterior and posterior cingulate cortices was associated with the impairment of social cognition in autism (P < .05). A significant correlation was also found between repetitive behavior/obsessive interests and the reduction of serotonin transporter binding in the thalamus (P < .05). In contrast, the dopamine transporter binding was significantly higher in the orbitofrontal cortex of the autistic group (P < .05). In the orbitofrontal cortex, the dopamine transporter binding was significantly inversely correlated with serotonin transporter binding (r = –0.61; P = .004).
Conclusions: The brains of people with autism have abnormalities in both their serotonin transporter and dopamine transporter bindings. The current findings indicate that the gross abnormalities in these neurotransmitter systems may underpin the neurophysiology of autism.