We have experimentally developed a photoperiod-controllable clean rack for SPF rats. The effectiveness of this clean rack in preventing the infection was attested to by the fact that the SPF rats and nude mice housed in this rack maintained SPF conditions after six months. And we investigated circadian rhythms of water intake and blood corticosterone levels in rats kept in the rack under various lighting conditions. Both rat groups under diurnal and reversed lighting conditions manifested significant increase in both water and blood corticosterone levels, showing a reversed phase relationship of the circadian rhythms between the two groups. These facts indicate the usefulness of the rack newly developed in the studies on circadian rhythms, reproductive physiology and behavior.
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