Adult susceptibility induced by preweaning shifts of zeitgeber in rats (I).

The exclusive manipulation of "time indicators" (Zeitgeber) early in development gives rise to a specific susceptibility observable in the course of experimental treatment in the adult. Independent groups of rats were submitted to equidistant shifts of the time indicators during three different periods of the postnatal development (days 1-18, 18-35 and 35-53). Apart from these specific episodes, each group remained in the same rearing conditions as the control groups (LD 12:12, temperature 12:12). The effects were evaluated at the adult stage. From day 130 until day 140, the animals were left in individual cages without any other modification in environmental conditions. They were then transported daily in a trolley in their individual cages, for five consecutive days (days 141-145 during three minutes at 15.00 hours). The results indicate that the rats belonging to the 1-18 group show a significant weight loss between the days 130 to 145. Moreover, they present a significant modification of the ultradian components of the circadian rhythms of their locomotor and feeding activity. The conclusion is that the early manipulation of the Zeitgeber before weaning may alone lead to a specific susceptibility which becomes apparent during the experimental treatment of the young adults