The development of day-night differences in sleep and wakefulness in norway rats and the effect of bilateral enucleation
Related Experiment Video
Updated: Jul 5, 2026
A Highly Reproducible and Straightforward Method to Perform In Vivo Ocular Enucleation in the Mouse after Eye Opening
Published on: October 6, 2014
Andrew J Gall1, William D Todd, Baisali Ray
1Program in Behavioral and Cognitive Neuroscience, Department of Psychology, University of Iowa, Iowa City, IA 52242, USA.
Insights
Early light exposure shapes infant rat sleep-wake cycles. Visual system development, via the retinohypothalamic tract (RHT) and suprachiasmatic nucleus (SCN), is crucial for establishing nocturnal behavior in young rats.
Area of Science:
- Neuroscience
- Chronobiology
- Developmental Biology
Background:
- The suprachiasmatic nucleus (SCN) shows circadian rhythmicity in fetal and infant rats.
- The impact of this rhythmicity on infant behavior is not well understood.
Purpose of the Study:
- To investigate the development of circadian sleep-wake patterns in infant rats.
- To determine the role of visual system input in establishing nocturnality.
Main Methods:
- Sleep and wakefulness were monitored in rats at postnatal days 2, 8, 15, and 21.
- Bilateral enucleation was performed at postnatal days 3 and 11 to disrupt photic entrainment.
- Behavioral patterns were assessed post-surgery.
Main Results:
- Day-night differences in sleep-wake activity were observed as early as postnatal day 2.
- Nocturnal wakefulness emerged around postnatal day 15 and was established by postnatal day 21.
- Early enucleation (postnatal day 3) resulted in daytime wakefulness, while later enucleation (postnatal day 11) did not alter the normal nocturnal pattern.
Conclusions:
- Prenatal and postnatal experiences significantly modulate the development of circadian sleep-wake patterns.
- Visual system stimulation via the retinohypothalamic tract (RHT) influences the developing circadian system.
- This visual input is critical for the emergence of species-typical nocturnality.
Abstract:
The suprachiasmatic nucleus exhibits circadian rhythmicity in fetal and infant rats, but little is known about the consequences of this rhythmicity for infant behavior. Here, in experiment 1, the authors measured sleep and wakefulness in rats during the day and night in postnatal day (P)2, P8, P15, and P21 subjects. As early as P2, day-night differences in sleep-wake activity were detected. Nocturnal wakefulness began to emerge around P15 and was reliably expressed by P21. The authors hypothesized that the process of photic entrainment over the 1st postnatal week, which depends on the development of connectivity between the retinohypothalamic tract (RHT) and the SCN, influences the later emergence of nocturnal wakefulness. To test this hypothesis, in experiment 2 infant rats were enucleated bilaterally at P3 and P11, that is, before and after photic entrainment. Whereas pups enucleated at P11 and tested at P21 exhibited increased wakefulness at night, identical to sham controls, pups enucleated at P3 and tested at P21 exhibited the opposite pattern of increased wakefulness during the day. Pups tested at P28 and P35 exhibited this same pattern of increased daytime wakefulness. All together, these results suggest that prenatal and postnatal experience modulates the development of species-typical circadian sleep-wake patterns. Moreover, the authors suggest that visual system stimulation, via the RHT's connections with the SCN, exerts an organizational influence on the developing circadian system and, consequently, contributes to the emergence of nocturnality in this species.
