Volume 17, Number 9,
Issue of May 1, 1997
pp. 3352-3363
Copyright ©1997 Society for Neuroscience
Immunocytochemical Characterization of AMPA-Selective Glutamate
Receptor Subunits: Laminar and Compartmental Distribution in Macaque
Striate Cortex
Received Sept. 16, 1996; revised Jan. 21, 1997; accepted Feb. 19, 1997.
Renee K. Carder
Zanvyl Krieger Mind/Brain Institute, Johns Hopkins University,
Baltimore, Maryland 21218
Subunit proteins that comprise functional AMPA receptors were
localized by immunocytochemical methods in the adult macaque primary
visual cortex (V1). GluR1, GluR2/3/4c, and GluR4 immunoreactivity consisted of rich plexuses of punctate profiles scattered throughout the neuropil, in radial arrays, and outlining the membrane of somata
and proximal dendrites. Cytoplasmic immunoreactivity was limited.
GluR2/3/4c immunostaining was more prominent along the somata surface
and exhibited greater levels of cytoplasmic immunoreactivity than GluR1
and GluR4 immunostaining. The density of AMPA subunit immunoreactive
elements also varied across layers and compartments of macaque V1.
Immunoreactivity for GluR1, GluR2/3/4c, and GluR4 was densest in three
bands that corresponded to layers IVA, IVC, and VI. Immunostaining for
each subunit was also unevenly distributed within many of the layers.
In layers II-III, patches of intense immunostaining coincided with
cytochrome oxidase (CO)-rich blobs. In layer IVA, intense subunit
staining formed a conspicuous honeycomb pattern. In layer IVC, subunit
staining formed a radial lattice. GluR2/3/4c subunit immunostaining was
also preferentially distributed within the CO-rich blobs of layers
V-VI. These findings demonstrate that AMPA subunit immunoreactivity is
densely concentrated in layers and compartments receiving direct
geniculocortical innervation. This distribution, which differs from
that of excitatory synapses, suggests that the density of AMPA
receptors is unevenly distributed at synaptic and possibly
extrasynaptic sites within macaque visual circuits.
Key words:
V1;
area 17;
glutamate;
excitatory neurotransmission;
geniculocortical afferents;
cytochrome oxidase blobs