The dorsal-lateral entorhinal area (DLE) forms a strip of cortex closely related to the rhinal fissure, and therefore it is the only entorhinal field entirely located on the lateral aspect of the rat’s cerebral hemisphere. At caudal levels it occupies both banks of the rhinal fissure, while anteriorly it lies medial or ventral to the rhinal fissure. It is positioned between the perirhinal cortex dorsally and the dorsal-intermediate entorhinal area (DIE) ventrally.
Similar to DIE, DLE extends along most of the rostrocaudal extent of
the entorhinal cortex, as is seen in coronal sections. Layer I is thin,
and differs characteristically from what is seen in all other
subdivisions of the entorhinal cortex in that it is populated by
neurons that look like displaced layer II cells. Layer II is rather
thin and densely packed with darkly stained elongated, big neurons. The
long axis of many of these neurons runs parallel to the outer surface
of the ventral bank of the rhinal fissure. Layer III is also thin, and
the cells are organized in horizontal rows, parallel to the surface
curvature of the rhinal fissure. The outer portion of this layer has a
higher cell density than the inner one. A cell sparse layer IV
separates layers III and V.
Layer V has a few very big and darkly stained neurons, while the
remaining neurons are medium-sized. Layer VI is more compact than layer
V, and its cells larger than the layer VI cells of the immediately
adjacent DIE. Layer VI is obliquely oriented, so that the long axes of
the neurons are parallel to the surface of the medial bank of the
rhinal fissure. Overall, both layers V and VI make an oblique and in
some instances slightly curved border with the adjacent perirhinal
cortex.
Field DLE has previously not been defined as a separate division of rat
entorhinal cortex, although Steward (1976) described a
’transitional’ field that corresponds to the presently
defined field. In all other available descriptions, DLE is included
into the lateral or the dorsolateral entorhinal cortex (Krettek and
Price, 1977; Ruth et al., 1982).
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