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Localization of nitric oxide synthase in the tree shrew retina

  • QI-LIN CAO (a1) (a2), HEATHER A. MURPHY (a1) and HEYWOOD M. PETRY (a1) (a3)
    • Published online: 01 May 1999

Nitric oxide (NO) is a novel neuronal messenger that likely influences retinal function by activating retinal guanylyl cyclase to increase levels of cGMP. In the present study, the localization of neuronal nitric oxide synthase (nNOS, Type I NOS) in the cone-dominant tree shrew retina was studied using NADPH-d histochemistry and nNOS immunocytochemistry. Both NADPH-d and nNOS-immunoreactivity (IR) labeled the inner segments of rods and the myoids of a regular subpopulation of cones, with their corresponding nuclei outlined. The labeled cone myoids were co-localized with a marker for short-wave-sensitive (SWS) cones (S-antigen) and also displayed the regular triangular packing and density (7%) characteristic of SWS cones in tree shrew and other mammalian retinas. These measures confirmed the identity of the labeled cones as SWS cones. Photoreceptor ellipsoids of all cones were strongly labeled by NADPH-d reactivity, but lacked nNOS-IR. Another novel finding in tree shrew retina was that both NADPH-d and nNOS-IR labeled Müller cells, which have not been labeled by nNOS-IR in other mammalian retinas. Consistent with findings in rod-dominant retinas, two types of amacrine cells at the vitreal edge of the inner nuclear layer and a subpopulation of displaced amacrine cells at the scleral edge of the ganglion cell layer were labeled by both NADPH-d and nNOS-IR. Processes of these labeled cells were seen to extend into the inner plexiform layer, where dense punctate label was seen, especially in the central sublamina. These results show that localization of NOS in the cone-dominant tree shrew retina shares some common properties with rod-dominant mammalian retinas, but also shows some species-specific characteristics. The new finding of nNOS localization in tree shrew SWS cones and rods, but not in other cones, raises interesting questions about the roles of NO in the earliest level of visual processing.

Corresponding author
Correspondence and reprint requests to: Heywood M. Petry, Department of Psychology, Life Sciences Building, Room 317, University of Louisville, Louisville, KY 40292, USA.
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In an attempt to improve morphological detail, we used postembed immunocytochemistry to visualize nNOS distribution in 2–5 μm sections of retinal tissue embedded in PolyBed812. Although these procedures had previously proven quite adaptable to immunocytochemistry (Petry et al., 1993) and amacrine cell labeling was quite obvious, we never observed any clear photoreceptor labeling in the postembed tissue, even using a variety of nNOS antibodies (INCSTAR; Transduction Labs, Lexington KY; and JH85AP4 a gift of Dr. T.M. Dawson). These difference in labeling in cryostat sections and in embedded sections are likely due to an overall reduction in antigenicity following the embedding process and/or a reduced amount of nNOS in photoreceptors compared to amacrine cells.
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Visual Neuroscience
  • ISSN: 0952-5238
  • EISSN: 1469-8714
  • URL: /core/journals/visual-neuroscience
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