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B. Lei, K. Zhang, B. Chang, G. Yao; Assess OFF Pathway Function in Mice With Electroretinogram (ERG) . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3097.
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© ARVO (1962-2015); The Authors (2016-present)
The OFF–pathway functions at distal retina in rodents are difficult to study by conventional electroretinogram (ERG) because the nocturnal E–type (excitatory) retina does not present the photopic positive OFF–response in ERG. In this study, we examined the OFF–pathway function in mouse by using a modified ERG procedure (Lei and Chang, 2003, ARVO E–abstract).
Conventional scotopic and photopic ERG and 10 Hz scotopic flicker ERG were recorded in C57BL/6 wild–type mice with normal retinal function and in mice that show pure rod (cpfl1/cfpl1) or pure cone ERG responses (rho–/–). Six to eight mice at 6–7 weeks of age were used in each strain. To isolate the OFF responses, glutamate analog APB (2–amino–4–phosphobutyric acid, an ON channel blocker) was injected intravitreally to these animals. Their ERG data were compared with those obtained from mouse models with selective ON–pathway defect (nob1 and nob3).
The ON pathway was selectively blocked in C57BL/6 mice after APB injection, as well as in nob1, nob3 mice. Therefore their scotopic ERG b–waves were absent. However both cone– and rod–driven OFF ERG responses were evident in the flicker ERGs. The amplitudes of cone–driven OFF responses (approximately 1/2 of the total cone–driven responses) were higher than those of the rod–driven OFF responses (approximately 1/3 –1/4 of the total rod–driven responses). At intensities that activate only rod–driven responses, the OFF signals in cpfl1/cfpl1 mice were similar to those acquired in APB injected wild–type mice. Due to the lack of cone functions in cpfl1/cfpl1 mice, these findings suggest that the OFF responses in these animals were conducted via the third rod pathway.
The rod– and cone–driven OFF bipolar cell responses are integrated parts of ERGs in nocturnal E–type retina. By using a modified ERG technique, we demonstrated for the first time that the rod–OFF bipolar cell pathway is functional in the outer retina.
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