Light and electron microscopic data on field CA1 of the hippocampus of the squirrel monkey, Saimiri sciureus

Data are presented on the structure and ultrastructure of field CA1 of the hippocampus of Saimiri sciureus. In Saimiri, as in other higher primates, the pyramidal layer of this field expands into the stratum oriens and shows an extensive neuropil between the perikarya. This neuropil is composed mainly of strong horizontal and oblique side branches of the apical dendrites of the pyramidal cells and a large number of terminal boutons forming predominantly asymmetric contacts on these dendritic profiles. Candidates for pathways which may terminate here are the association fibers from field CA3 (Schaffer collaterals) and the projections from the septum, entorhinal cortex and neocortex. However, previous experimental support exists only for the latter of these projections.