Research Abstract

Circadian Rhythms of Rod-Cone Dominance in the Japanese Quail Retina

Mary K. Manglapus, Hiroyuki Uchiyama, Japanese quail
Neal F. Beulow, and Robert Barlow

When the Japanese quail is held in constant darkness, retinal responses (ERG b-waves) increase during the animal's subjective night and decrease during its subjective day.Rod photoreceptors dominate the b-wave responses to all stimulus intensities at night but only to those intensities below the cone threshold during the day.Above the cone threshold, cones dominate b-wave responses during the day regardless of the state of retinal adaptation.Apparently a circadian oscillator enables cone signals to block rod signals during the day but not at night.

 ERG responses to test wavelengths spanning the visible spectrum were measured in dark-adapted animals day and night.

        

Spectral sensitivity changes with time of day

Figure ERG responses to test wavelengths spanning the visible spectrum were measured in dark-adapted animals day and night.The spectral sensitivity of the b-wave shifts from day to night with its amplitude peaking at intermediate wavelengths (~500 nm; filled circles) at night and to longer wavelengths (~550 ö600 nm; open circles) during the day.The smooth curve is a nomogram for a rod photopigment based on microspectrophotometric measurements.In the vicinity of 610 nm, the spectral sensitivity of the b-wave does not change significantly from day to night, indicating that this is an isosbestic region.The shift of peak spectral sensitivity to longer wavelengths during the day is associated with an approximately sixfold or 0.8 log unit decrease in sensitivity.More than 100-fold decreases in sensitivity were detected for the responses to shorter wavelength flashes.

Constant darkness, the ERG b-wave exhibits a circadian rhythm of rod-cone dominance.Rods dominate at night while cones dominate during the day.ERGs were recorded from a single eye.