The confronting cisternae in the hippocampal neurons of rats and Japanese monkeys.

The ultrastructure of the neurons in the hippocampal formation of Wistar rats and Japanese monkeys was investigated. Confronting cisternae were observed in the cytoplasm of pyramidal neurons and granule cells. The structures were composed of closely apposed parallel cisternae, presumably continuous with the cisternae of the rough endoplasmic reticulum. The cytoplasmic matrix between the confronting cisternae contained electron dense flocculent material. In the pyramidal neurons irregular confronting cisternae were also observed. Possible functions of the confronting cisternae are discussed.