The effects of various lighting schedules upon the circadian rhythms of 23 liver or brain enzymes of C57BL/6J mice.
The activities of 23 brain or liver enzymes were studied in 5-6 week old C57BL/6JNctr male and female mice that had been fed ad libitum and standardized for 2 weeks to either (1) 12 hr of light (0600-1800) alternating with 12 hr of darkness (1800-0600) (LD 12:12), (2) staggered sequences of 12 hr of light and 12 hr of dark (SLD 12:12) or (3) continuous illumination (LL 12:12) for 2 weeks. Mice in the LD 12:12 and LL 12:12 experiments were killed at 4 hr intervals along a 24-hr span in order to sample at six different circadian stages. Lighting schedules for mice in the SLD 12:12 experiment were organized such that six different circadian stages were sampled when all mice were killed at one time of day. All 23 enzymes demonstrated a prominent circadian rhythm in at least one of the experiments. Moreover, about two-thirds of the enzymes in LD and SLD 12:12 had a statistically significant fit to a 24-hr cosine curve, while only one-third of the enzymes in LL 12:12 had significant fits to cosine curves. Peak activities of enzymes from mice in LD 12:12 were clustered at the time of transition from light to dark. This was also the trend for the activities of enzymes from mice in SLD 12:12, but resynchronization did not appear completed within the 2-week span. This, along with the observation that mesors (mean 24-hr activity) were reduced and amplitudes altered, indicated that the 2-week standardization period was not sufficient for some enzymes. Times of peak activities, mesors and amplitudes were affected for most enzymes from mice in the LL 12:12 environment. This suggests that individual mice became desynchronized from one another with respect to the original light-dark schedule and that rhythms were altered or lost because individual mice were free running with frequencies different from 24 hr.
Feuers
R J
RJ
Department of Health and Human Services, Food and Drug Administration, Jefferson, AR 72079.
Delongchamp
R R
RR
Scheving
L E
LE
Casciano
D A
DA
Tsai
T H
TH
Pauly
J E
JE
D000818:Animals; D001921:Brain / Q000201:enzymology*; D002940:Circadian Rhythm; D003624:Darkness; D005260:Female; D008027:Light; D008099:Liver / Q000201:enzymology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL