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H. Heikkinen, F. Vinberg, S. Nymark, A. Koskelainen; Adaptation of Mouse Cones to Steps of Light After Suppression of Rods, Measured With Electroretinogram from Isolated Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2172.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effects of background illumination and repetitive flash stimulation on the amplitude, kinetics and sensitivity of mouse cone photoresponses (fast PIII) after pharmacological removal of the b-wave and the slow PIII from the transretinal electroretinogram (ERG).
Flash responses of mouse cones in the dark-adapted state or during 10-15 s steps of background lights were recorded as transretinal ERG across isolated retinas with the pigment epithelium removed. 2mM aspartate and/or 50µM APB was added to abolish the b-wave by suppressing synaptic transmission especially through the ON-pathway. Dark-adapted cone photoresponses were isolated with 2ms flashes preceded by a rod-saturating preflash. Flash pairs were delivered either at long intervals, allowing the rods as well as the cones to recover between pairs, or at <1 sec intervals, allowing only cones to recover.
Dark-adapted APB or APB/Asp isolated cone photoresponses were similar to those published earlier1,2, although they were slightly faster (tp ca. 40 ms). However, under an adapting background or a series of intense flashes (keeping rods saturated but allowing the cones to recover), their amplitude grew >1.5 fold, while the response waveform slowed down, became biphasic and generally exhibited additional components of possibly postreceptoral origin. The initial activation phase up to ca. 6-10 ms maintained its original kinetics and form. Also the sensitivity parameter extracted from thus "enhanced" cone photoresponse families remained close to its dark-adapted value, decreasing in Weber-like fashion with a sensitivity halving intensity of 40000-60000 photons / µm2s at max (ca. 3000-5000 Rh*/s) when steps of background light were applied.
Photopic mouse ERG recorded under rod-saturating conditions (steady background or rod-saturating preflashes) will yield cone driven responses affected both by the initial enhancement due to the rod-saturating conditions and Weber-like desensitization by the background.1 Nikonov et al (2006), J. Gen. Physiol. 127:359-742 Heikkinen et al (2008), Vis. Res. 48:264-72
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