Neonatal exposure to atypical Zeitgeber in the Wistar rat. Effects on development of circadian rhythms of drinking and motor activities

The data described concern the maturation of circadian motor and drinking rhythms immediately after weaning. We ran two experiments in both of which mother rats and their litters were subjected to either an atypical Zeitgeber or to standard conditions from the birth of the young up to weaning on the 19th day. In the experimental groups, the light and the temperature cycles were permanently in phase opposition and were shifted by 12 hours every 3 days. In the control groups, the cycles were the same except that they were in phase and were never shifted. In the first experiment, after weaning the young were subjected to an LD cycle; in the second experiment to constant conditions. The results of both experiments showed that the circadian rhythms of drinking and locomotor activities appeared with a delay of ten days in the experimental rats. These rats kept an ultradian structure for a longer time. During the constant conditions, a lengthening (around 25 min.) of the free-running period was observed. In conclusion, atypical environmental cycles during early neonatal life affect the development of the circadian system.