The Effects of Constant Light and Running-Wheel Access in Middle-Aged Female C57BL6/J Mice.

Objective  Chronic light exposure is associated with poorer mental and physical health. Many groups are chronically exposed to light due to their work schedule, including night-shift nurses. The present study aims to determine if middle-aged female mice have an increased vulnerability to chronic light exposure compared with younger individuals. Materials and Methods  Young and middle-age female mice were housed in cages with or without running wheels and were exposed to either a 12:12-hour light:dark cycle or constant light (LL). All mice were assayed for circadian locomotor activity and anxiety-like behaviors, and weight, food consumption, and estrogen receptor beta (ERβ) levels were measured. Results  Middle-aged mice exhibited longer circadian periods in LL, reduced circadian power, and increased food consumption compared with young mice. LL increased novelty-induced activity and reduced ERβ regardless of age. Discussion  These results indicate that middle-aged females may have an increased susceptibility to the negative circadian consequences caused by constant bright light exposure.