Important role of the eyes controlling the locomotor rhythm in quail

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Abstract
Whether the eye of quail is a driving oscillator or not was studied by examining the locomotor activity rhythm. The circadian rhythmicity was assessed by the actogram and chi‐square periodogram. The bird showed clear diurnal rhythmicity under 24 h light‐dark (LD) condition. By bilateral enucleation, the activity during dark phase increased, and the diurnal rhythmicity became obscure in some birds when the actogram was inspected visually. The periodogram showed, however, that the significant daily rhythm was maintained in all birds examined in this condition. Thus, the brain photoreceptor could mediate LD information responsible for the locomotor activity. Under constant dim light condition, the circadian rhythmicity was found in intact quail. Unilateral enucleation has no substantial effect on these circadian rhythmicities. However, there was a disruption of circadian rhythmicity following bilateral enucleation. These observations suggest that the ocular system of quail may be classified as one of the driving oscillators, and is involved in the expression of the circadian rhythmicity of locomotor activity.