Format

Send to

Choose Destination
Proc Natl Acad Sci U S A. 2017 Jul 3;114(27):E5464-E5473. doi: 10.1073/pnas.1700983114. Epub 2017 Jun 19.

Hypocretin (orexin) is critical in sustaining theta/gamma-rich waking behaviors that drive sleep need.

Author information

1
Center for Integrative Genomics, University of Lausanne, CH-1015 Lausanne, Switzerland; anne.vassalli@unil.ch.
2
Department of Physiology, University of Lausanne, CH-1005 Lausanne, Switzerland.
3
Center for Integrative Genomics, University of Lausanne, CH-1015 Lausanne, Switzerland.

Abstract

Hcrt gene inactivation in mice leads to behavioral state instability, abnormal transitions to paradoxical sleep, and cataplexy, hallmarks of narcolepsy. Sleep homeostasis is, however, considered unimpaired in patients and narcoleptic mice. We find that whereas Hcrtko/ko mice respond to 6-h sleep deprivation (SD) with a slow-wave sleep (SWS) EEG δ (1.0 to 4.0 Hz) power rebound like WT littermates, spontaneous waking fails to induce a δ power reflecting prior waking duration. This correlates with impaired θ (6.0 to 9.5 Hz) and fast-γ (55 to 80 Hz) activity in prior waking. We algorithmically identify a theta-dominated wakefulness (TDW) substate underlying motivated behaviors and typically preceding cataplexy in Hcrtko/ko mice. Hcrtko/ko mice fully implement TDW when waking is enforced, but spontaneous TDW episode duration is greatly reduced. A reformulation of the classic sleep homeostasis model, where homeostatic pressure rises exclusively in TDW rather than all waking, predicts δ power dynamics both in Hcrtko/ko and WT mouse baseline and recovery SWS. The low homeostatic impact of Hcrtko/ko mouse spontaneous waking correlates with decreased cortical expression of neuronal activity-related genes (notably Bdnf, Egr1/Zif268, and Per2). Thus, spontaneous TDW stability relies on Hcrt to sustain θ/fast-γ network activity and associated plasticity, whereas other arousal circuits sustain TDW during SD. We propose that TDW identifies a discrete global brain activity mode that is regulated by context-dependent neuromodulators and acts as a major driver of sleep homeostasis. Hcrt loss in Hcrtko/ko mice causes impaired TDW maintenance in baseline wake and blunted δ power in SWS, reproducing, respectively, narcolepsy excessive daytime sleepiness and poor sleep quality.

KEYWORDS:

brain theta oscillations; hypocretin/orexin; narcolepsy; sleep homeostasis; waking substate

PMID:
28630298
PMCID:
PMC5502606
DOI:
10.1073/pnas.1700983114
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center