Previous studies have shown that the expression of glutamate receptor
subunits is developmentally regulated and have been implicated in
processes of cell differentiation during postnatal life. The tissue
localization and developmental pattern of the glutamate receptor 2 subunit
of the α-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate (AMPA)
receptor were investigated by means of immunohistochemistry and
immunoblotting. Labeling of amacrine and ganglion cells and the inner
plexiform layer appeared early during development, while glutamate
receptor 2 subunit expression in the outer plexiform layer started
after the first postnatal week. The distribution of labeling within
the inner plexiform layer changed from nonorganized to laminated
appearance prior to eye-opening. There was an increasing number of
positive amacrine and ganglion cell somata during the first 2 weeks,
but their number decreased considerably as the retina matured and were
seen at least up to 35 days of postnatal development. Little labeling
was found in the ganglion cell layer and in the inner plexiform layer of
late postnatal and adult retina. Labeling in the outer plexiform layer
and of bipolar cell somata appeared to increase in the developing retina.
Glur2 labeling of these cells and the outer plexiform layer became
discernible during the second postnatal week, and this labeling was
present in the adult as well. Immunoblotting showed that GluR2 protein
levels were similar at postnatal days 7 and 10, but slightly decreased
between the second and fourth postnatal weeks. Our data imply that the
immunological expression of glutamate receptor 2 subunit in the inner
plexiform layer decreases as a function of age, and is correlated with
developmental event(s) in the postnatal retina.