Paul Franken

Associate Professor, University of Lausanne, Schwitzerland

Title: Reassessing the state variables used to study the processes regulating sleep

Abstract: Last year we celebrated the 40th anniversary of the influential two process model. The model postulates that a homeostatic process, modelled on the dynamics of EEG delta activity, and a circadian process, emerging from the rhythmic interaction among clock genes, interact to regulate the distribution and quality of sleep. Our recent analyses in both mice and humans show the existence of two types of delta waves, each with different dynamics not easily reconciled with a homeostatic process but rather suggesting a role for faster delta waves in facilitating the wake-to-sleep transition. Transcriptome dynamics show that circadian rhythms in cortical gene expression, including that of clock genes, is mostly sleep-wake driven and that sleep deprivation causes a long-term disruption of their expression. These and other observations show that clock genes also play a role in the homeostatic aspect of sleep regulation.

Rune Enger

Associate Professor, University of Oslo, Norway

Title: Dynamics of the gliovascular interface across the sleep-wake cycle

Abstract: Perivascular spaces bordered by perivascular endfeet, are important highways for fluid and solute transport in the brain enabling efficient waste clearance during sleep. However, the underlying mechanisms regulating the gliovascular interface and augmenting perivascular flow in sleep are largely unknown.

Using two-photon imaging of naturally sleeping male mice we have demonstrated sleep cycle-dependent vascular dynamics of pial arteries and penetrating arterioles: slow, large-amplitude oscillations in NREM sleep, a vasodilation in REM sleep, and a vasoconstriction upon awakening at the end of a sleep cycle and microarousals in NREM and intermediate sleep. These vascular dynamics are mirrored by changes in the size of the perivascular spaces of the penetrating arterioles: slow fluctuations in NREM sleep, reduction in REM sleep and an enlargement upon awakening after REM sleep and during microarousals in NREM and intermediate sleep.

These data demonstrate large morphological changes to the gliovascular interface coupled to vasoconstrictions and dilations. We believe taking these dynamics into account is imperative for understanding the mechanisms regulating perivascular fluid flow and its driving forces, and also for shedding light on the potential physiological purposes of perivascular endfeet.

Please join us prior to the talk for coffee and cookies.