Distribution of heavy metals in the hippocampal region of the guinea pig

Summary With the present modification of Timm's sulfide silver method all parts of the hippocampal region show a distinctly stratified staining pattern, suggesting large regional differences in the content of heavy metals.The stain is largely confined to distinct grains, partly associated with neuronal somata and partly dispersed in the neuropil. Work in progress supports the idea that the grains in the neuropil are synaptic boutons, as has been shown previously for the mossy fibre layer.The staining pattern has been compared in detail with the fields and layers of the hippocampal region as delineated by cyto- and fibroarchitectonics. Previous concepts of the subdivision of this cortical region are confirmed and supplemented.The sulfide silver pattern of the guinea pig hippocampal region is fundamentally similar to that of the rat. However, the entorhinal area, the regio inferior hippocampi, and the dentate area show notable differences in the staining pattern between the two species.We are indebted to Mrs. E. Kjaer Hansen, Mrs. L. Knudsen, Mr. B. Krunderup, Mr. A. Meier, Mr. Th. Nielsen, Mrs. B. Sørensen, and Miss M. Sørensen for skilful technical assistance.This study was supported in part by U.S.P.H.S. Grant NS 07998.Permanent address: Anatomical Institute, University of Oslo, Norway