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J.-J. Pang, F. Gao, S. M. Wu; Light Responses and Morphology of bNOS-Immunoreactive Neurons in the Mouse Retina. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1855. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Nitric oxide (NO), produced by NO synthase (NOS), modulates the function of all retinal neurons and ocular blood vessels and participates in the pathogenesis of ocular diseases. To further understand the regulation of ocular NO release, we systematically studied the morphology, topography and light responses of NOS-containing amacrine cells (NOACs) in dark-adapted mouse retina.
Immunohistological staining for neuronal NOS (bNOS), combined with retrograde labeling of ganglion cells (GCs) with Neurobiotin (NB, a gap junction permeable dye) and Lucifer yellow (LY, a less permeable dye), was used to identify NOACs. The light responses of ACs were recorded under whole-cell voltage clamp conditions and cell morphology was examined with a confocal microscope.
In dark-adapted conditions bNOS-immunoreactivity (IR) was present primarily in the inner nuclear layer and ganglion cell layer. bNOS-IR somas were negative for LY, thus they were identified as ACs; and nearly 6 % of these cells were labeled by NB, indicating that they were dye-coupled with GCs. bNOS-IR somas in the GCL and INL were absent in bNOS knock out mice (Nos1tm1Pl-/- ) (Huang, 1998). Three morphological subtypes of NOACs (NI, NII and displaced) were identified. The cell density, inter-cellular distance and distribution of NOACs were studied in whole retinas. NI cells had a dendritic arbor ramifying near the center of the inner plexiform layer (IPL), while the dendrites of the NII cells ramified primarily in sublamina b of the IPL. Light evoked depolarizing ON-OFF responses in NI cells and OFF responses in NII cells, with the former having high light sensitivity and the latter having lower light sensitivity. Frequent (1 to 2 Hz) or abrupt change of light-intensity was more efficient in evoking transient light responses. The light responses in NOACs were suppressed by DNQX, suggesting that they were mediated by AMPA/KA receptors.
bNOS-IR cells in the mouse retina are ACs, including NI, NII and displaced cells. NOACs are most extensively activated by 1~ 2 Hz flickering light, especially at the light offsets. The depolarizing ON-OFF responses in NI cells and depolarizing OFF responses in NII cells are mediated by AMPA/KA receptors. The transient depolarizing light responses and the expression of Ca++ channels in NOACs suggest that NO is released from NOACs in flickering light and light is likely to quantitatively modulate NO release from NOACs. NOACs cells may thereby play a significant role in retinal diseases associated with NO.
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