In this description of the stratification/lamination of the dentate gyrus, the most superficial layer, close to the pial surface of the brain comes first, followed by the layers below.
- The most superficial layer is referred to as the molecular layer or stratum moleculare. It lies closest to the hippocampal fissure. Because of the connectional inputs from the entorhinal cortex, this layer is often subdivided in three: the outer, middle and inner part.
- The granule cell layer or stratum granulosum forms the principle cell layer of the DG. Typically, it is divided in three sections. Adjacent to CA1 lies the section called enclosed blade (or suprapyramidal blade/limb). The opposite section is called free/exposed blade (or infrapyramidal blade/limb). The section where the two blades connect is called the crest.
- The polymorphic layer or stratum multiforme is sometimes referred to as CA4 (suggested by Lorente de No, 1934), but in a calbindin staining the polymorphic layer and proximal part of CA3 can easily be distinguished. The polymorphic layer is often referred to as hilus.
In-between the granule cell layer and the polymorphic layer lies a narrow strip of cells that is termed the subgranular zone. The cells in the subgranular zone are linked to adult neurogenesis. See: Steven A Goldman & Zhuoxun Chen, 2011
For a review of the ultrastructure and synaptic connectivity of cell types in the adult rat dentate gyrus, see: Ribak et al, 2007. Another good overview, more tailored towards interneurons is given by Freund and Buzsaki, 1996. An online repository is available at: www.hippocampome.org.
Goldman, S.A., & Chen, Z. (2011). Perivascular instruction of cell genesis and fate in the adult brain. Nature neuroscience, 14(11), 1382–1389. Resolve DOI
Ribak, C.E., & Sharpiro, L.A. (2007). Ultrastructure and synaptic connectivity of cell types in the adult rat dentate gyrus. Progress in brain research, 163, 155–163. Resolve DOI