Structural Organization of the Rat Hippocampal Formation

Abstract

The review examines historical aspects of hippocampal nomenclature. His anatomical study began with the ancient Greeks, who named the unusual-looking structure the “ram’s horn,” the cornu ammonis. The term “hippocampus” (Ancient Greek: ἱππόκαμπος, from ἵππος “horse” and κάμπος “sea monster” or “seahorse”) was first coined in the 16th century by the anatomist J.C. Arantius. The term “hippocampal formation” is currently applied to a group of cytoarchitectonically distinct adjacent regions, including, along with the hippocampus itself, the dentate gyrus, subiculum, presubiculum, parasubiculum, and entorhinal cortex. The rationale for including these six regions in the hippocampal formation group is that they are connected to each other by unique and largely unidirectional pathways. The review is devoted to the spatial, morphological, and cyto- and myeloarchitectonic organization of all parts of the rat hippocampal formation and the distinctive neuroanatomical characteristics of its parts. The comparative features of the structure of the hippocampal formation of rats, monkeys, and human beings are described. Although the volume of the hippocampus is approximately ten times larger in monkeys and 100 times larger in human beings than in rats, the basic architecture of the hippocampal formation is common, although there are some species differences. The relatively simple organization of the main cell layers, combined with the highly organized laminar distribution of hippocampal neuronal processes, facilitates its use as a model system in modern neurobiology.