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E.V. Vukmanic, M.G. Au, M.L. Risner, J. Souza, J. Bilotta; Reduction of the ERG Off–Response Using CNQX Modifies the B–Wave Response in Adult Zebrafish . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2249.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Previous work, across a variety of different vertebrate species, has suggested that the b–wave component of the electroretinogram (ERG) results from the combination of both depolarizing and hyperpolarizing retinal neurons. The purpose of this study was to examine the effects on the ERG of suppressing the responses of hyperpolarizing bipolar cells by blocking AMPA/kainate ionotropic glutamate receptors via intravitreal injections of 6–cyano–7–nitroquinoxaline–2,3–dione (CNQX). Methods: Adult zebrafish (Danio rerio) were injected intravitreally with either 0.25mM CNQX or saline solution. Photopic spectral sensitivity functions were derived from the b–wave component of the ERG response to 200–ms stimuli of various wavelengths (320–640 nm) and irradiances. Sensitivity at each stimulus wavelength was derived from log irradiance versus log response amplitude functions. Results: In general, CNQX increased the amplitude of the b–wave substantially while suppressing the d–wave component. However, these results appear to be wavelength–dependent. Based on the spectral sensitivity functions, CNQX reduced sensitivity to short–wavelength stimuli, suggesting a reduction in the contributions of short–wavelength sensitive cones (S–cones) to the b–wave component. Unlike in the spectral sensitivity functions of the saline–only subjects, the functions of the CNQX subjects did not possess the inhibitory contributions of both major color opponent mechanisms (Long–wavelength sensitive cones inhibited by Middle–wavelength sensitive cones, and Middle–wavelength sensitive cones inhibited by S–cones). Conclusions: CNQX eliminated the d–wave component of the ERG response while amplifying the b–wave response; however, both effects were dependent upon stimulus wavelength. Based on these results, it appears that hyperpolarizing bipolar cells do participate in shaping the b–wave component of the adult zebrafish ERG. The suppression of S–cones in the spectral sensitivity function based on the b–wave component following CNQX administration suggests a relationship between AMPA/kainate receptor function and S–cone sensitivity.
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