Journal of Neuroscience, Vol 9, 667-682, Copyright © 1989 by Society for Neuroscience
Interlaminar and lateral excitatory amino acid connections in the striate cortex of monkey
ZF Kisvarday, A Cowey, AD Smith and P Somogyi
1st Department of Anatomy, Semmelweis University Medical School, Budapest, Hungary.
The intrinsic excitatory amino acid pathways within the striate cortex of
monkeys were studied by autoradiographic detection of retrogradely labeled
somata following microinjections of D-3H-aspartate (D-3H-Asp) into
different layers. The labeled amino acid was selectively accumulated by
subpopulations of neurons and, to a small extent, by glial cells, the
latter mainly in the supragranular layers. Immunocytochemical detection of
neurons containing GABA showed that, apart from a few cells exclusively in
layer I, GABAergic neurons do not accumulate D-3H-Asp. Several lines of
evidence suggest that D-3H-Asp uptake occurred only at nerve terminals;
thus, the pattern of perikaryal labeling allowed the delineation of
interlaminar and lateral projections. Neurons in layer I probably project
laterally, and layer I receives wide-ranging projections from layer IVB and
layer V from cells up to 1300 microns laterally. Some neurons in layer II
send a focused projection to lower layer VI. Some neurons in layers II/III
project up to 1 mm laterally within their own layer, but relatively few
neurons can be labeled in these projections. Similarly, in layers II/III
few neurons can be retrogradely labeled from layers V and upper VI, and
this projection is organized such that cells closer to the pia project
deeper in layer V/VI. The connections of layer IVA could not be revealed
separately because of the difficulty of confining injections to this thin
sublamina. Neurons in layer IVB project up to 1300 microns within IVB
itself. A small number of cells from IVB also project to layers III,
IVC-alpha, V, and VI with much more restricted lateral spread. Neurons in
upper IVC-alpha send axons to layer IVB with at least 600-800 microns
lateral spread. Neurons in lower IVC-alpha/upper IVC-beta project to layer
III with at least 300-500 microns lateral spread. The bottom 50-80 microns
of layer IVC-beta contains neurons with a very focused projection,
apparently exclusively to the layer III/IVA border region. Both layers IVC
alpha and beta have rich connections within themselves, the beta sublayer
having more restricted lateral connections. Some neurons in layer IVC-beta
give a laterally restricted small input to layers IVC-alpha and IVB. Both
IVC-alpha and - beta project to layers V and VI, and these projections are
spread at least 400 microns laterally. Neurons in layer V project to all
layers, but the projection to layers I-III and within layer V itself spread
much further laterally than the projections to layers IV and VI.(ABSTRACT
TRUNCATED AT 400 WORDS)
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