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L Li, Q Ren; Dynamics of ERG ON and OFF Responses in Zebrafish: Evidence for Separate Rod and Cone Pathways and the Regulation by Dopamine and Circadian Clock . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1965.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To evaluate rod and cone contributions to the dark-adapted ERG and the effect of dopamine and circadian clock on the process of rod-cone transition during dark adaptation. Methods: Full-field ERGs were recorded at different times of dark adaptation following bright light adaptation. We measured the threshold lights required to evoke threshold ERG ON and OFF responses. We also measured the ON and OFF response V-log I curves. Results: Between early and late dark adaptation, a visual purkinje phenomenon was observed in the ERG ON response but not in the OFF response. At all times of dark adaptation, the OFF channel thresholds to phototopically matched green and red lights were identical; they decreased during the first 20 min of dark adaptation, thereafter, they increased. Over several log units of light intensity, the ON response amplitude increased as a function of the time of dark adaptation, but that of the OFF response decreased. The dark adaptation time required to reach 100 µV of the ON response was about 20 min when measured in the late afternoon but it increased to over 35 min when measured in the early morning. The OFF channel response was gradually lost after 50 min of dark adaptation when measured in either late afternoon or early morning. This pattern of ERG ON-OFF transition persisted in constant light for 2 days and was phase-shifted by a reversed light-dark cycle. Intraocular injections of a dopamine D1 but not D2 receptor antagonist slowed down the process of ERG ON-OFF transition in the early morning but not in the late afternoon. Conclusion: In zebrafish, rod and cone signals may be propagated by different channels. The ON channel processes both the rod and cone signals, and the OFF channel transmits mainly the cone signals. During dark adaptation, the rod function is enhanced whereas the cone sensitivity is suppressed. Under the influence of a circadian clock, dopamine regulates the process of rod-cone transition between the ON and OFF channels.
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