A recent study has uncovered a link between paradoxical sleep and genes involved in brain cell death and survival.
Increased Rapid eye movement sleep (REM) is one of the most distinctive features of daily mild stress. According to the study, this can be associated with genes involved in cell death and survival.
REM sleep, also known as paradoxical sleep, is the sleep state during which we have most of our dreams and is involved in the regulation of emotions and memory consolidation. REM sleep disturbances are common in mood disorders, such as depression. However, little was known about how sleep changes are linked to molecular changes in the brain.
During this nine-week-long study, mice were intermittently exposed to a variety of mild stressors, such as the odour of a predator. Mice exposed to mild stressors developed signs of depression; they were less engaged in self-care activities; were less likely to participate in pleasurable activities such as eating appetising food, and became less social and interested in mice they hadn't encountered before.
Monitoring their sleeping patterns, researchers identified an increase in the duration and continuity of REM sleep and specific brain oscillations characteristic of REM sleep, whereas 'deep' sleep, or non-REM sleep, did not change. The changes in REM sleep were very tightly linked to the deficiency in the regulation of the stress hormone corticosterone. Mild stress also caused changes in gene expression in the brain.
Findings of the study were published in the Journal of Proceedings of the National Academy of Sciences.
To further understand the link between stress, the stress hormone, REM sleep, and gene expression, researchers undertook a novel machine-learning approach, which identifies groups of genes that can predict the observed sleep, behavioural and hormonal characteristics.
This revealed that REM sleep, the regulation of the stress hormone and a behavioural sign of depression were closely associated with molecular pathways involved in the death and survival of cells in the brain, primarily in the hippocampus.
These data suggest that an increase in REM sleep can activate signalling pathways in the brain which allow it to change in response to 'mildly stressful' waking experiences. The findings may provide a better understanding of how stress leads to mood disorders and how changes in sleep may contribute to this.
"The comprehensive analysis of the behavioural changes in combination with the sleep and gene expression analyses make a strong case for the important role of REM sleep in the brain response to stress," said Mathieu Nollet.
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