Although the overall cellular composition is quite similar in the dorsal-intermediate entorhinal area (DIE) and the dorsal-lateral entorhinal area (DLE), there are striking and defining differences in the way cells are organized into layers. Layer I of the dorsal-lateral entorhinal area (DLE) is thinner than that of the dorsal-intermediate entorhinal area (DIE). In both areas, layer II contains rather big, rounded neurons that stand as darkly stained in Nissl stained material. However, in DIE these cells are organized in a fairly dense and homogeneously packed layer, while they in DLE tend to be more dispersed and to some extent invade the molecular layer.
A very narrow, relatively acellular band separates layer II from layer
III in much of the DIE extent, which is not seen in DLE. Layer III in
DIE is wide, and clearly presents a narrow, more densely packed outer
zone with its neurons arranged in clusters, and a less densely and
irregularly packed inner zone. In contrast, layer III of DLE is rather
thin, and the cells are organized in horizontal rows, parallel to the
surface curvature of the rhinal fissure. Area DIE does not have a
distinguished layer IV or lamina dissecans whereas in DLE layers III
and V are markedly separated from each other. Layers V and VI do not
show striking architectonic differences. When considering additional
markers it is apparent that whereas layer II of DLE stains rather
strongly for calbindin both in terms of neurons as well as neuropil, in
DIE the neuropil staining is less dense such that the individual
positive neurons are easy to see. In material stained for parvalbumin,
the DIE / DLE border coincides with a gradual loss of the positive
staining in layer III: moderate in DLE, light to absent in DIE.
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