Changes in daily activity patterns and the brain’s internal clock after exposure to light cycles shorter or longer than 24 hours

Intrinsic periods of circadian behavior in Per1-luc transgenic mice are significantly shorter in a 10-hour light cycle compared to a 14-hour light cycle.

• Mice exposed to a 10-hour light cycle exhibited significantly shorter intrinsic periods than those exposed to a 14-hour light cycle at all ages.
• Aftereffects from the shorter light cycle decreased in mice older than 3 months, indicating age-related changes in entrainment ability.
• Age did not affect entrainment or aftereffects in the 14-hour light schedule.
• The behavioral period of pups born in constant darkness was influenced by the light cycle experienced in utero, suggesting maternal transference of aftereffects.
• Isolated SCN recordings from young mice showed aftereffects, but a negative correlation was found between behavior periods and SCN activity.
• Enucleation in constant darkness did not alter behavioral aftereffects, suggesting that the eyes are not necessary for expressing these aftereffects.

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