Cytoarchitectonically, the presubiculum (PrS) and the parasubiculum (PaS) are alike in that, with the exception of dorsal portions of PrS, the laminar differentiation between the two layers is not very conspicuous. However, the distinctive differentiation is the cell size. Whereas cells in PaS are fairly large, almost the same size of layer II cells in EC, those in PrS are much smaller. In addition, the latter also stain darker in a Nissl or NeuN stain.
The border in the deep layers V and VI however is impossible to
establish, resulting in the widely accepted custom not to differentiate
between the deep layers at all (similarly, no clear border is generally
indicated between the deep layers of PaS and EC). However, using the
additional information provided by staining with an antibody against
calbindin and parvalbumin, a marked border between the two regions can
be established. PaS has almost no neuropil staining for calbindin,
whereas PrS does show strong staining in neurons and neuropil in layer
II. Parvalbumin staining provides a corresponding border since layers
II and III of PaS stain very dense and almost homogeneously whereas the
deep layers are almost negative. In PrS, staining is dense in layer II,
somewhat weaker in layer III and in addition the superficial portion of
layer V shows positive neuropil with an occasional positive neuron,
whereas the remainder of the deep layers show a slightly less dense
staining.
The PrS, also referred to as Brodman’s area 27 (Brodmann, 1909), is
generally divided into a dorsal and a ventral portion, based on the
different cytoarchitectonic features described above, which coincide
with subtle differences in connectivity (van Groen and Wyss, 1990). The
dorsal portion has been named the postsubiculum, or Brodman’s area 48
as well. The PaS, or Brodman’s area 49 has been subdivided into two
portions (area 49a and 49b,(Brodman, 1909)). Neither the PrS nor the
PaS subdivisions are applied in the present account.
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