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M. Sato, K. Makino, T. Ohtsuka; Effect of Nitric Oxide on Cone ERG in the Rat Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2181.
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Nitric oxide (NO) modulates various activities of retinal cells as well as the signal transmission among them. The role of NO is not fully known in the in situ retina. In the previous study (Sato & Ohtsuka, 2008), a conflicting evidence on cone photoreceptors was shown, therefore, we injected excess amounts of NO scavenger into the vitreous body of rat eye, and studied cone ERG in the different light adapting conditions.
Sprague Dawley rat, 8 - 10 wks old, was anesthetized by 20% urethane i.p., with 0.4% procaine-HCl on the cornea and atropine sulfate for dilation. 2 µL of 1 M monosodium glutamate (Glu) was injected into the vitreous body of left eye, which isolated a-wave from ERG for several hours. Then 2 µL of 2 mM carboxy-PTIO (C348, Dojin) in PBS was injected for scavenging NO in the vitreous body. We estimated the vitreal NO, about 1 µM in the daytime (Hoshi et al., 2003), was almost zero for first 1 hour. White LED flash, 350 µW/cm2 at the corneal surface, for 10 msec was used for eliciting cone ERG of Glu-isolated ERG a-wave. Green LED, 3.5 µW/cm2, was used for a backgound adapting light. ERG was recorded from the left eye; the other eye served as reference.
In the light adapted condition, the green background light was illuminated all through the experiment for suppressing the rod activity. Bright test flash (350 µW/cm2) elicited cone ERG; the amplitude decreased about 30% at 20-30 min after injection of carboxy-PTIO. This decrease continued for more than 60 min. While with no background light, the test flash (0.35 µW/cm2) elicited also cone ERG; the amplitude decreased about 30% at 5 min after injection of carboxy-PTIO. Our result suggested the deprivation of intraretinal NO decreased the cone activity either in the dark or light condition.
Various studies have shown the underlying mechanism of light and dark adaptation within the photoreceptors. Our finding suggested the external NO concentration also modulates the adapting level of cone photoreceptors.
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