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DA Cameron; Spectral Sensitivity of Zebrafish Predicted by Cone Fractions, Absorption Spectra, and Neuronal Mechanisms . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3764.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine if first-order physical characteristics of cone photoreceptors can predict second-order neurophysiological aspects of cone processing in the zebrafish retina. Methods: A model for estimating the spectral sensitivity of the photopic ERG b-wave in adult zebrafish (Danio rerio), based upon one originally presented by Hughes et al. (Vis Neurosci 15, 1029; 1998), was developed. The model function involved a same- or opposite-signed combination of the "output" from two spectral cone types, and was applied to three non-overlapping segments of the visual spectrum. Each "output" term included parameters for the fractional abundance of that spectral cone type across the retina (empirically derived) and the relevant cone pigment absorption spectrum (derived with MSP) and one variable, a linear gain. The model estimated the photopic b-wave data for adult zebrafish reported by Hughes et al. (1998). Results: MSP yielded cone absorption spectra consistent with A1-based visual pigments with λmax of 407 (S), 473 (M), and 564 (L) nm; evidence for a UV pigment (U) was also observed. The model yielded four distinct cone processing channels that provided good estimates of the b-wave data: U, S, S-M, and M-L. Although the U and S cones are at relatively low abundance the model revealed that their gains are substantially greater than the gains for M and L cones. These gains were dependent upon cone type but independent of the processing channels (e.g., the M cone gains were equivalent for the S-M and M-L channels, but were always different than the S cone gains). Cone pigment absorption data from earlier reports resulted in good but less accurate matches to the b-wave data. Conclusion: At the level of ON-type bipolar cells (a dominant contributor to the b-wave) the adult zebrafish processes cone-derived signals via four distinct channels, two of which are opponent in nature. These channels may provide neuronal mechanisms for heightened luminance contrast sensitivity at short wavelengths and heightened chromatic contrast sensitivity at long wavelengths.
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