Objectives: To determine the density and laminar distribution of GABAB receptors, benzodiazepine binding sites, and 5HT1A receptors in the FFG in adult autistic and control cases.
Methods: Single concentration receptor binding autoradiography experiments were completed in the FFG using 3H-CGP54626 as a ligand for GABAB receptors, 3H-flunitrazepam as a ligand for GABAA receptor benzodiazepine (BZD) binding sites, and 3H-8OH-DPAT as a ligand for 5HT1A receptors . Autistic (n=10) and control (n=10) brains were matched for age and post-mortem interval. Optical densities were measured in the superficial and deep layers using the Inquiry program. Data analysis was conducted using Student’s t-test.
Results: GABAB receptor density and BZD binding site density were significantly decreased in the superficial layers (p=0.007; p=0.02, respectively) in autistic cases. In the deep layers there was a significant decrease (p=0.002) in the density of GABAB receptors in the deep layers, but no change in BZD binding site density. Additionally, there were significant reductions in the density of 5HT1A receptors in both the superficial (p=0.02) and deep (p=0.04) layers in autistic cases.
Conclusions: A growing body of evidence suggests that individuals with autism have difficulties in face perception, implicating the FFG. Recognition of persons, and especially their individual faces, is a key part of an individual’s social experience and successful functioning within a social group. This study demonstrates decreased receptor density in the superficial and deep layers of the FFG in two key neurotransmitter systems, GABA and serotonin, in autism. Abnormalities in the superficial layers suggest a disruption in cortiocortical connections, whereas abnormalities observed in the deep layers suggest altered efferent connectivity to sub-cortical regions. This study also provides important evidence regarding abnormalities in the GABAergic and serotonergic receptor systems, which may contribute to abnormal face processing in individuals with autism.
Acknowledgments: Human tissue was obtained from the Harvard Brain and Tissue Resource Center, The Autism Research Foundation, and the NICHD Brain and Tissue Bank for Developmental Disorders.