Melatonin and light induce phase shifts of circadian activity rhythms in the C3H/HeN mouse.
This study examines the effect of light pulses and administration of the pineal hormone melatonin on the circadian activity rhythm of C3H/HeN mice. Mice were housed in constant dark in cages equipped with running wheels. Phase shifts in the circadian rhythm of wheel-running activity were measured following treatment with a 15-min pulse of light (300 lux) or administration of vehicle (ethanol/saline) or melatonin (90 micrograms, sc). Light treatment induced phase changes in circadian activity rhythms; specifically, delays during early subjective night (circadian time [CT] 12.5 to CT 18.5) and advances during late subjective night (CT 0.5). A single dose of melatonin administered at various CTs had no consistent effect on free-running circadian activity rhythms. By contrast, melatonin administration for 3 consecutive days at the same clock time induced advances in circadian activity rhythms by more than 1 h when the first dose was administered at CT 10 and induced delays in circadian activity rhythms by up to 1 h when the first dose was administered between CT 24 and CT 2. With the caveat that multi- ple melatonin treatments are required to induce phase shifts, the results suggest that the circadian timing system controlling the rhythm of wheel-running activity in the C3H/HeN mouse is responsive to both light and melatonin.
Benloucif
S
S
Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, Chicago, IL 60611, USA.
Dubocovich
M L
ML
D000204:Activity Cycles / Q000187:drug effects / Q000528:radiation effects; D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects / Q000528:radiation effects; D003624:Darkness; D008027:Light; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D051379:Mice; D008809:Mice, Inbred C3H; D009043:Motor Activity / Q000187:drug effects / Q000528:radiation effects
D008550:Melatonin