CIRCADIAN-RHYTHMS OF ROD-CONE DOMINANCE IN THE JAPANESE-QUAIL RETINA

When the Japanese quail is held in constant darkness, retinal response s (ERG b-waves) increase during the animal's subjective night and decr ease during its subjective day. Rod photoreceptors dominate the b-wave responses (lambda(max) = 506 nm) 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 (lambda(ma x), similar to 550-600 nm) during the day regardless of the state of r etinal adaptation. Apparently a circadian oscillator enables cone sign als to block rod signals during the day but not at night. The ERG b-wa ve reflects the activity of bipolar cells that are postsynaptic to rod s and cones. The ERG a-wave reflects the activity of both rods and con es. The amplitude of the isolated a-wave (PIII) changes with lime of d ay, as does that of the b-wave, but its spectral sensitivity does not. The PIII responses are maximal at similar to 520 nm both day and nigh t and may reflect multiple receptor mechanisms. The shift in rod-cone dominance detected with the ERG b-wave resembles the Purkinje shift of human vision but, unlike the Purkinje shift, does not require a chang e in ambient light intensity. The shift occurs in constant darkness, w ith a period of similar to 24 hr indicative of a circadian rhythm in t he functional organization of the retina.