Abstract
Environmental light conditions during development can have long-lasting effects on the physiology and behavior of an animal. Photoperiod, a clear example of environmental light conditions, is detected by and coded in the suprachiasmatic nucleus. It is therefore possible that differences observed in behavior in adulthood after exposure to different perinatal photoperiods are caused by lasting changes in the suprachiasmatic nucleus or alternatively, in other nuclei affected by perinatal photoperiod. It can then be expected that behavior with strong circadian aspects, like rest-activity and sleep, are affected by difference in photoperiod during development as well. To investigate this further, we exposed mice to different photoperiods during their development in the womb until weaning (long: 16 h of light, 8 h of darkness; short: 8 h of light, 16 h of darkness). After weaning, the animals were exposed to a 12 h:12 h light:dark cycle for at least 3 more weeks and some animals were subsequently exposed to constant darkness. We assessed their rest-activity patterns by recording voluntary locomotor activity and used EEG recordings to determine sleep architecture and electroencephalographic spectral density. Perinatal long photoperiod animals showed a shorter duration of locomotor activity than short photoperiod-developed mice in a 12:12 light-dark cycle. This difference disappeared in constant darkness. In the light phase, that is, during the day, perinatal long photoperiod mice spent less time awake and more time in NREM sleep than short photoperiod-developed mice. No effects of perinatal photoperiod were observed in the EEG spectral density or in response to sleep deprivation. We see lasting differences in behavioral locomotor activity and sleep in female and male mice after exposure to different perinatal photoperiods. We conclude that perinatal photoperiod programs a developing mammal for different external conditions and changes brain physiology, which in turn results in long-lasting, possibly even permanent, changes in the sleep and locomotor activity.