Journal of Neuroscience, Vol 14, 7641-7654, Copyright © 1994 by Society for Neuroscience
Nitric oxide synthase in Muller cells and neurons of salamander and fish retina
BA Liepe, C Stone, J Koistinaho and DR Copenhagen
Department of Ophthalmology, University of California, San Francisco 94143.
Nitric oxide synthase (NOS) is the biosynthetic enzyme of the signaling
molecule nitric oxide (NO). NO donors have been reported to modulate
conductances in cell types throughout the retina, from photoreceptors to
ganglion cells. Previously, NOS immunoreactivity has been reported in
amacrine cells and cells within the ganglion cell layer. Here, we have
examined the cellular localization of NOS in the retinas of salamander,
goldfish, and catfish using both an affinity-purified antiserum to brain
NOS and NADPH diaphorase (NADPHd) histochemistry. These markers indicate
that an NOS-like enzyme is localized not only to presumptive amacrine cells
but also, depending on the species, to photoreceptor ellipsoids, to somata
within the ganglion cell layer, and to horizontal cells. In addition to
these neurons, our results indicate that Muller cells, the radial glia of
the retina, also contain an NOS- like enzyme. In support of this latter
conclusion, cells morphologically similar to Muller cells were positive for
NADPHd staining in all three species. In salamander, NOS-like
immunoreactivity, NADPHd staining, and binding of anti-GFAP (a marker for
glia) were localized to cells that were morphologically indistinguishable
from Muller cells. In goldfish, reactivity to both anti-NOS and
anti-vimentin (a marker for glia) colocalized to radial processes extending
through the inner retina to the inner limiting membrane. These observations
are the first to indicate the presence of an NOS-like enzyme in Muller
cells and suggest that these glia could be a ready source of NO for target
neurons throughout the retina.
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