Insights into paradoxical (REM) sleep homeostatic regulation in mice using an innovative automated sleep deprivation method

Identifying the precise neuronal networks activated during paradoxical sleep (PS, also called REM sleep) has been a challenge since its discovery. Similarly, our understanding of the homeostatic mechanisms regulating PS, whether through external modulation by circadian and ultradian drives or via intrinsic homeostatic regulation, is still limited, largely due to interfering factors rendering the investigation difficult. Indeed, none of the studies published so far were able to manipulate PS without significantly altering slowwave sleep and/or stress level, thus introducing a potential bias in the analyses. With the aim of achieving a better understanding of PS homeostasis, we developed a new method based on automated scoring of vigilance states-using electroencephalogram and electromyogram features-and which involves closed-loop PS deprivation through the induction of cage floor movements when PS is detected. Vigilance states were analyzed during 6 and 48 h of PS deprivation as well as their following recovery periods. Using this new automated methodology, we were able to deprive mice of PS with high efficiency and specificity, for short or longer periods of time, observing no sign of stress (as evaluated by plasma corticosterone level and sleep latency) and requiring no human intervention or environmental changes. We show here that PS can be homeostatically modulated and regulated while no significant changes are induced on slow-wave sleep and wakefulness, with a PS rebound duration depending on the amount of prior PS deficit. We also show that PS interval duration is not correlated with prior PS episode duration in the context of recovery from PS deprivation. Statement of Significance A large body of controversial literature has been produced trying to reveal the nature of paradoxical sleep (REM sleep) homeostatic regulation. In these studies, paradoxical sleep was challenged by different means, using total sleep deprivation, more or less specific PS deprivation, and most of the time inducing a fair amount of stress. Here we report using an innovative method allowing to highly specifically deprive mice of paradoxical sleep without significantly modifying other vigilance states, that paradoxical sleep homeostatic regulation depends only on the prior amount of paradoxical sleep deficit. Gaining a better understating on how paradoxical sleep is regulated is crucial in helping to treat its comorbid dysregulation in diseases such as anxiety disorders.