Position within the brain
- The dentate gyrus borders with field CA3 of the hippocampal formation.
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. In the near future, an online repository will become available on: www.hippocampome.org. If you are using a wide-screen monitor, the table below will display more optimally when you select a wide-screen layout for this webpage. Click the configuration icon next to the register button and select "Select width: float" (top right icon).
|Layer||Cell type||Cell count||Soma||Dendrites||Axon||Immunoreactivity|
|Molecular Layer - deep.||Basket alike.||-||Multipolar/triangular||Aspiny dendrites that remain primarily in the molecular layer.||Appears to contribute to the basket plexus within the granule cell layer.||Stains positive for vasoactive intestinal polypeptide (VIP).|
|Molecular Layer.||Chandelier alike.||-||Spans molecular layer, basal dendrites absent or not well developed.||Projects to initial segments of granule cell axons.||glutamic acid decarboxylase (GAD), parvalbumin|
|Molecular Layer - deep||Molecular layer perforant path-associated cell||-||Outer two-thirds of the molecular layer|
|Granule cell layer||Granule cell||Estimated between 0.6 x 10e6 to 2.2 x 10e6||Elliptical||Cone-shaped tree of spiny dendrites, branches towards the superficial part of the molecular layer||calbindin|
|Granule cell layer - deep||Basket cell||Not constant; varies over septo-temporal and proximo-distal extent. See: Seress and Pokorny, 1981 and Ribak et al, 1983.||A single, principal aspiny apical dendrite directed towards the molecular layer. Several primary basal dendrites with ramifications in the polymorphic layer.||parvalbumin|
|Granule cell layer - deep||Other cell types||Mainly GABAergic|
|Polymorphic layer/hilus||Mossy cells||-||Triangular / multipolar||Dendrites innvervate the polymorphic layer and at times cross the granule layer to reach the molecular layer. Proximal dendrites have large spines.|
|Polymorphic layer/hilus||Fusiform type | Small, round or multipolar cells.||-||Aspiny dendrites, stellate plexus||Axons have been reported to project into the hippocampus proper|
|Polymorphic layer/hilus||Fusiform type | Long-spined multipolar cells.||-||Spiny dendrites, dendritic tree confined to hilus||Axon have been reported to project outside hippocampus proper|
|Polymorphic layer/hilus||Chandelier cells.||-||Dendritic tree confined to the polymorphic layer||Axons terminitae on initial axon segments of mossy cells|