The distortion of dentate gyrus development detected in two autistic subjects was reflected in granule cell migration into the molecular layer and formation of an additional granule cell layer. Distortion of the shape of the dentate granule cell layer with the formation of irregular circles and loops appears to be another piece of evidence suggesting abnormal neuronal migration and networking. Numerous factors up-regulate neurogenesis in the hippocampus [32], including seizures [70, 71], antidepressant drugs [59, 72] and lithium [18]. Several areas of dysplastic changes with significant deficits of pyramidal neurons were found in the CA1 sector in three autistic subjects, but thickening of the pyramidal layer and an increased packing of dysplastic neurons in the CA1 sector of the 56-year-old subject suggests a diversity of CA dysplasia patterns in autism. The lack of gliosis indicates that the observed pathology is a sign of microdysgenesis rather than an effect of hypoxic neuronal loss. A significant deficit of mature pyramidal neurons and the presence of small irregular or poorly differentiated oval neurons suggest the defect of neuronal maturation in autism.
