Nuclear neurotransmitter molecular imaging of autism spectrum disorder

Autism spectrum disorder (ASD) is a group of developmental disabilities characterized by marked deficits in social communication and interaction, including limited and repetitive patterns of behavior. We selected key nuclear neurotransmitter molecular imaging reports of ASD by combining “autism” AND “positron” AND “dopamine” OR “serotonin” OR “glutamate” OR “GABA” utilizing databases as follows: PubMed, Scopus, Web of Science, Science Direct, and Google Scholar. This review reports important findings in ASD utilizing positron emission tomography (PET) and single-photon emission computed tomography (SPECT). We studied major neurotransmitter systems, dopamine, serotonin, glutamate, and gamma-aminobutyric acid (GABA). Dopamine neurotransmission was decreased in the anterior medial prefrontal cortex in children with autism. Dopamine transporter was increased in the orbital frontal cortex of adults with ASD and decreased in the striatum of children with ASD. Decreased tryptophan metabolism, an estimate of serotonin synthesis, (A) in left frontal cortex correlated with severe language impairment and (B) in the right frontal cortex correlated with left and mixed handedness. Although not confirmed by some investigators, serotonin transporter was decreased in the cingulate, the medial frontal cortex, the midbrain, and the temporal lobes. Serotonin receptors were decreased in the thalamus in individuals with ASD and in the cortices of parents of children with ASD. Metabotropic glutamate receptor subtype 5 (mGluR 5 ) was increased in the post-central gyrus and the cerebellum of men with autism. PET studies for GABA did not differentiate people with ASD from controls. The increasing incidence of ASD and the inconsistent findings of different nuclear molecular imaging studies are evidence for the urgent need for further investigations utilizing nuclear molecular imaging to identify the key neurophysiological mechanisms underlying the pathophysiology of ASD.