Pineal and hypothalamic pacemakers: Their role in regulating circadian rhythmicity in Japanese quail

Summary Neither pinealectomy nor administration of melatoninvia silastic capsules had any effect on free-running circadian rhythms of locomotor activity in Japanese quail (Coturnix coturnix japonica). The quail, like the chicken, therefore differs from sparrows and starlings in which pinealectomy dramatically disrupts free-running rhythms. Nevertheless, it seems unlikely that there are fundamental differences in circadian organisation within the Class Aves. The effects of lesions within the supraoptic region (SOR) of the hypothalamus were similar to those which follow the ablation of the suprachiasmatic nuclei (SCN) in sparrows, rats and hamsters, causing the breakdown of free-running rhythms of locomotor activity, but not necessarily an arrhythmic state. The SOR and SCN appear then to have homologous functions in birds and mammals. Differences in circadian organisation, such as the degree of influence of the pineal gland and the particular photoreceptors used for entrainment, may therefore be modifications peripheral to the fundamental components of the circadian clock.Abbreviations POR preoptic area - SOR supraoptic region - SCN suprachiasmatic nuclei