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A Novel Continuously Recording Approach for Unraveling Ontogenetic Development of Sleep-Wake Cycle in Rats

Guang-Fu Cui¹, Min Hou^1,2, Yu-Feng Shao¹

¹Departments of Neuroscience, Anatomy, Histology, and Embryology, Key Laboratory of Preclinical Study for New Drugs of Gansu Province, School of Basic Medical Sciences, Lanzhou University, Lanzhou, China.

Frontiers in Neurology

|August 29, 2019

Insights

Researchers developed a novel method for continuous polysomnographic (PSG) recording in infant rats, enabling detailed study of sleep-wake cycles. This study reveals significant developmental changes in sleep patterns from infancy to adulthood in rats.

Area of Science:

Neuroscience
Developmental Biology
Sleep Science

Background:

Sleep-wake development in early life reflects brain maturation.
Infant rats, being altricial, present challenges for continuous sleep monitoring due to their dependence on maternal care and need for controlled environments.
Existing methods are insufficient for uninterrupted polysomnographic (PSG) recording in developing rats.

Purpose of the Study:

To develop and validate a novel approach for continuous PSG recording in infant rats.
To investigate the ontogenetic features and developmental trajectory of sleep-wake cycles in rats from postnatal day 11 (P11) to P75.
To characterize the evolution of electroencephalogram (EEG) and electromyogram (EMG) activities across different sleep-wake states during postnatal development.

Main Methods:

Development of a specialized system including two types of EEG electrodes, a milk-feeding system, and a temperature-controlled incubator for infant rats.
Continuous PSG recording was performed on rats from P11 to P75 during both light and dark phases.
Analysis of sleep-wake states (REM sleep, NREM sleep, wakefulness), EEG power spectra, and episode durations.

Main Results:

The novel system allowed for reliable continuous PSG recording without adverse effects on pup weight gain or behavior compared to dam-reared pups.
Significant ontogenetic changes in sleep architecture were observed: Rapid Eye Movement (REM) sleep proportion decreased, while Non-REM (NREM) sleep and wakefulness increased with age.
Dramatic shifts in sleep-wake cycles occurred within the first postnatal month, with increased NREM sleep and prolonged slow-wave activity in EEG, alongside decreased episode frequency and increased duration of vigilance states.

Conclusions:

The developed methodology is reliable and valid for continuous PSG recording in infant rats, overcoming previous technical limitations.
The study successfully characterized the ontogenetic features of the rat sleep-wake cycle, highlighting critical developmental changes in the first month of life.
Findings provide a foundational understanding of sleep maturation in a rodent model, relevant for studying brain development and neurological disorders.

Read full analysis

Abstract:

Sleep-wake development in postnatal rodent life could reflect the brain maturational stages. As the altricial rodents, rats are born in a very undeveloped state. Continuous sleep recording is necessary to study the sleep-wake cycle profiles. However, it is difficult to realize in infant rats since they rely on periodic feeding before weaning and constant warming and appropriate EEG electrodes. We developed a new approach including two types of EEG electrodes and milk-feeding system and temperature-controlled incubator to make continuously polysomnographic (PSG) recording possible. The results showed that there was no evident difference in weight gaining and behaviors between pups fed through the milk-feeding system and warmed with temperature-controlled incubator and those kept with their dam. Evolutional profiles of EEG and electromyogram (EMG) activities across sleep-wake states were achieved perfectly during dark and light period from postnatal day (P) 11 to P75 rats. The ontogenetic features of sleep-wake states displayed that the proportion of rapid eye movement (REM) was 57.0 ± 2.4% and 59.7 ± 1.7% and non-REM (NREM) sleep was 5.2 ± 0.8% and 4.9 ± 0.5% respectively, in dark and light phase at P11, and then REM sleep progressively decreased and NREM sleep increased with age. At P75, REM sleep in dark and light phase respectively, reduced to 6.3 ± 0.6% and 6.9 ± 0.5%, while NREM correspondingly increased to 37.5 ± 2.1% and 58.4 ± 1.7%. Wakefulness from P11 to P75 in dark phase increased from 37.8 ± 2.2% to 56.2 ± 2.6%, but the change in light phase was not obvious. P20 pups began to sleep more in light phase than in dark phase. The episode number of vigilance states progressively decreased with age, while the mean duration of that significantly increased. EEG power spectra in 0.5-4 Hz increased with age accompanied with prolonged duration of cortical slow wave activity. Results also indicated that the dramatic changes of sleep-wake cycle mainly occurred in the first month after birth. The novel approaches used in our study are reliable and valid for continuous PSG recording for infant rats and unravel the ontogenetic features of sleep-wake cycle.

Keywords:

infant rats milk-feeding ontogeny of sleep polysomnographic recording sleep-wake states temperature-controlled

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