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M. Sato, T. Ohtsuka; Effect of Intravitreal Nitric Oxide on the Rat Electroretinogram. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2206. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The intraretinal concentration of nitric oxide (NO) is increased by light adaptation; the intravitreal NO concentration in the rat eye is ~0.5 µM during nighttime, but ~1 µM during daytime (Hoshi et al., 2003). To investigate the role of this NO increase in visual information processing, we recorded the electroretinogram (ERG) after injecting the NO donor, S-nitroso-N-acetylpenicillamine (SNAP), into the vitreous body of the rat eye.
Sprague Dawley rats, 8 - 10 wks old, were used. The dark-adapted rat was anesthetized by 20% urethane i.p., with 0.4% procaine-HCl on the cornea and atropine sulfate for dilation. 2 µL of SNAP (#346-070771, Dojin), 5 mM in PBS, was injected into the vitreous body by a microsyringe. Since the half-time for release of NO from SNAP is 5 hr, the estimated intravitreal NO concentration was ~3 µM for the first hr. 2 µL of 1M monosodium glutamate (Glu) was injected alone or prior to SNAP for isolation of ERG a-wave. ERG to a green LED light, 70 µW/cm2 at the corneal surface, was recorded from the left eye; the right eye served as reference.
10 min after SNAP injection, the ERG a-wave decreased by ~40% and the b-wave by ~30%. This decrease lasted >4 hrs. The amplitudes of oscillatory potentials also decreased by ~50%. Glu decreased the b-wave gradually until only the a-wave remained after 30 min; the b-wave was suppressed completely for >90 min and then recovered gradually. SNAP injection 30 min after Glu had no effect on the ‘cone a-wave’, but reduced the ‘rod a-wave’ amplitude by ~30%; the suppressed ‘rod a-wave’ was gradually replaced by the recovering b-wave after 90 min.
Our in situ experiment showed that NO selectively suppressed the rod a-wave, but not the cone a-wave. This suggests that the release of NO in the retina may mediate the suppression of rod activity during light-adaptation, thus expanding the dynamic range of cone input to second-order neurons.
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