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Effects of feeding and light cycles on activity rhythms of maternally isolated rat pups
Insights
Early-life environmental cues like light-dark and feeding cycles help synchronize circadian activity rhythms in infant rats. Mother-reared pups showed more robust rhythms than isolated pups, highlighting the importance of social and environmental factors.
Area of Science:
- Neuroscience
- Chronobiology
- Developmental Biology
Background:
- Circadian rhythms are fundamental biological processes.
- Understanding the early development of these rhythms is crucial for developmental neuroscience.
- Environmental factors significantly influence the entrainment of biological rhythms.
Purpose of the Study:
- To investigate the emergence and synchronization of circadian motor activity rhythms in infant rat pups.
- To determine the influence of light-dark (LD) cycles, feeding cycles, and temperature cycles on these rhythms.
- To compare the activity patterns of mother-reared versus isolated pups.
Main Methods:
- Continuous motor activity monitoring of infant rat pups from postnatal day 3 to 18.
- Manipulation of environmental cycles including LD, feeding, and temperature.
- Comparative analysis between mother-reared and isolated pup groups.
Main Results:
- Mother-reared pups exhibited significant circadian activity rhythms by postnatal day 5.
- Isolated pups showed less persistent and lower amplitude rhythms, though some synchronization occurred under specific LD and feeding cycles.
- Naturalistic nursing rhythms enhanced nocturnal activity partitioning in isolated pups.
- Constant light with a feeding cycle led to activity during the decreased food intake interval.
- Nocturnal cooling further reduced nocturnal activity proportions.
Conclusions:
- Both light-dark and feeding cycles play a role in synchronizing early postnatal activity rhythms in rats.
- Maternal presence and naturalistic feeding patterns appear to be important for robust rhythm development.
- Environmental cues are critical for entraining circadian behavior even in early development.
Abstract:
Motor activity of infant rat pups was measured continuously between days 3 and 18 of postnatal age. Mother-reared rats on a 12:12 LD cycle exhibited significant rhythmic activity in the circadian range as early as day 5 of postnatal age. Some of the pups reared in isolation from maternal and sibling contact and kept on 12:12 LD cycles, feeding cycles, or combinations of feeding, temperature, and LD cycles also showed rhythmic activity but it was less persistent and of a lower amplitude than the rhythms of the mother-reared group. In the isolated rat pups nocturnal partitioning of activity was strengthened in the presence of both a light-dark cycle and a feeding cycle but only when the feeding resembled more natural nursing rhythms. In animals kept on constant light and a feeding cycle, activity occurred slightly more often during the 12-hr interval of decreased food intake. The addition of a temperature cycle--cooler nocturnal temperature--decreased the proportions of nocturnal motor activity. These results indicate that feeding and light-dark cycles may contribute to the synchronization of activity rhythms during the early postnatal period.