Circadian variations in the differential blood counts of mice under constant (LL) and alternating (LD) light periods

Summary

Laboratory mice, offspring of CB6 F₁ s, were maintained at a constant temperature of 21.0 ± 1.0° C and in constant light (LL) of 40 lux or under 12 h of light (40 lux) alternating with 12 h of darkness (LD) for 8 consecutive days. During the following 36 h, tail blood was secured from each mouse at 6-h intervals. From those samples, a differential white blood cell count, based on 100 leukocytes, was made for each animal. The relative numbers of eosinophils, basophils, and monocytes did not fluctuate rhythmically under LL or LD. The per cent distributions of lymphocytes and neutrophils did vary with circadian frequency in both LL and LD (Figs. 1, 2) The peak counts of neutrophils were found in blood sampled near midnight; high counts of lymphocytes were made in smears prepared about 6:00 a.m. and 6:00 p.m.