Photomicrographs of the CA3 region of the hippocampus and the dentate gyrus of the macaque monkey. (A) Nissl-stained section showing the major layers of the CA3 region of the hippocampus. Deep to superficial layers include so, stratum oriens; pcl, pyramidal cell layer; sl, stratum lucidum, sr, stratum radiatum, sl-m, stratum lacunosum-moleculare. (B) Section of the CA3 region of the hippocampus stained immunohistochemically with plasma from a representative AU subject. Numerous labeled neurons are observed in the stratum radiatum (black arrows) and the adjacent stratum lacunosum-moleculare (open arrows). Only background level staining is observed in the pyramidal cell layer, but there are a variety of labeled neurons in stratum oriens (white arrows). (C) Nissl-stained section showing the layers of the dentate gyrus. Layers include pl, polymorphic layer; gcl, granule cell layer; and ml, molecular layer. (D) Section of the dentate gyrus stained immunohistochemically with plasma from a child with autism. Numerous labeled neurons (black arrows) are shown in the polymorphic cell layer, whereas fewer positive cells (open arrows) are shown in the molecular layer. Calibration bars, 100 μm. The bar in B applies to A, and the bar in D applies to C.