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. 2013 Oct 18;342(6156):373-7.
doi: 10.1126/science.1241224.

Sleep Drives Metabolite Clearance From the Adult Brain

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Free PMC article

Sleep Drives Metabolite Clearance From the Adult Brain

Lulu Xie et al. Science. .
Free PMC article

Abstract

The conservation of sleep across all animal species suggests that sleep serves a vital function. We here report that sleep has a critical function in ensuring metabolic homeostasis. Using real-time assessments of tetramethylammonium diffusion and two-photon imaging in live mice, we show that natural sleep or anesthesia are associated with a 60% increase in the interstitial space, resulting in a striking increase in convective exchange of cerebrospinal fluid with interstitial fluid. In turn, convective fluxes of interstitial fluid increased the rate of β-amyloid clearance during sleep. Thus, the restorative function of sleep may be a consequence of the enhanced removal of potentially neurotoxic waste products that accumulate in the awake central nervous system.

Figures

Fig. 1
Fig. 1. Wakefulness suppresses influx of CSF tracers
(A) Diagram of experimental setup used for two-photon imaging of CSF tracer movement in real time. To avoid disturbing the state of brain activity, a cannula with dual ports was implanted in the cisterna magna for injection of CSF tracers. ECoG and EMG were recorded to monitor the state of brain activity. (B) Three-dimensional (3D) vectorized reconstruction of the distribution of CSF tracers injected in a sleeping mouse and then again after the mouse was awakened. The vasculature was visualized by means of cascade blue-dextran administered via the femoral vein. FITC-dextran (green) was first injected in the cisterna magna in a sleeping mouse and visualized by collecting repeated stacks of z-steps. Thirty min later, the mouse was awakened by gently moving its tail, and Texas red-dextran (red) was administered 15 min later. The experiments were performed mostly asleep (12 to 2 p.m.). The arrow points to penetrating arteries. (C) Comparison of time-dependent CSF influx in sleep versus awake. Tracer influx was quantified 100 μm below the cortical surface; n = 6 mice; *P < 0.05, two-way ANOVA with Bonferroni test. (Right) The tracer intensity within the two arousal states at the 30-min time point was compared. **P < 0.01, t test. (D) ECoG and EMG recordings acquired during sleep and after the mouse was awakened. Power spectrum analysis of all the animals analyzed in the two arousal states (n = 6 mice; *P < 0.05, t test). (E) 3D reconstruction of CSF tracer influx into the mouse cortex. FITC-dextran was first injected in the awake stage, and cortical influx was visualized by means of two-photon excitation for 30 min. The mouse was then anesthetized with ketamine/xylazine (intraperitoneally), and Texas red-dextran was injected intra-cisternally 15 min later. The vasculature was visualized by means of cascade blue-dextran. Arrows point to penetrating arteries. (F) Comparison of time-dependent CSF influx in awake versus ketamine/xylazine anesthesia; n = 6 mice; *P < 0.05, two-way ANOVA with Bonferroni test. (Right) The tracer intensity during the two arousal states at the 30-min time point was compared. **P < 0.01, t test. (G) ECoG and EMG recordings in the awake mouse and after administration of ketamine/xylazine. Power spectrum analysis of all the animals analyzed in the two arousal states; n = 6 mice; *P < 0.05, t test.
Fig. 2
Fig. 2. Real-time TMA+ iontophoretic quantification of the volume of the extracellular space in cortex
(A) TMA+ was delivered with an ion-tophoresis microelectrode during continuous recordings by a TMA+-sensitive microelectrode located a distance of ~150 μm away. The electrodes were filled with Alexa488 and Alexa568, respectively, so that their distance could be determined with two-photon excitation (insert over objective). A smaller extracellular space results in reduced TMA+ dilution, reflected by higher levels of detected TMA+. (B) The extracellular space is consistently smaller (α) in awake than in sleeping mice, whereas the tortuosity remained unchanged (λ); n = 4 to 6 mice; **P < 0.01, t test. (C) Power spectrum analysis of ECoG recordings; n = 6 mice; *P < 0.05, t test. (D) The extracellular space was consistently smaller in the awake state than after administration of ketamine/xylazine in paired recordings within the same mouse, whereas tortuosity did not change after anesthesia; n = 10 mice; **P < 0.01, t test. (Bottom) TMA measurements obtained during the two arousal states compared for each animal. (E) Power spectrum analysis of ECoG; n = 6 mice; *P < 0.05, t test.
Fig. 3
Fig. 3. Sleep improves clearance of Aβ
(A). Time-disappearance curves of 125I-Aβ1-40 after its injection into the frontal cortex in awake (orange triangles), sleeping (green diamonds), and anesthetized (red squares, ketamine/xylazine) mice. (B) Rate constants derived from the clearance curves. (C) Time-disappearance curves of 14C-inulin after its injection into the frontal cortex of awake (orange triangles), sleeping (green diamonds), and anesthetized (red squares, ketamine/xylazine) mice. (D) Rate constants derived from the clearance curves. A total of 77 mice were included in the analysis: 25 awake, 29 asleep, and 23 anesthetized, with 3 to 6 mice per time point. *P < 0.05 compared with awake, ANOVA with Bonferroni test.
Fig. 4
Fig. 4. Adrenergic inhibition increases CSF influx in awake mice
(A) CSF tracer influx before and after intracisternal administration of a cocktail of adrenergic receptor antagonists. FITC-dextran (yellow, 3 kD) was first injected in the cisterna magna in the awake mouse, and cortical tracer influx was visualized by means of two-photon excitation for 30 min. The adrenergic receptor antagonists (prazosin, atipamezole, and propranolol, each 2 mM) were then slowly infused via the cisterna magna cannula for 15 min followed by injection of Texas red-dextran (purple, 3 kD). The 3D reconstruction depicts CSF influx 15 min after the tracers were injected in cisterna magna. The vasculature was visualized by means of cascade blue-dextran. Arrows point to penetrating arteries. (B) Comparison of tracer influx as a function of time before and after administration of adrenergic receptor antagonists. Tracer influx was quantified in the optical section located 100 μm below the cortical surface; n = 6 mice; *P < 0.05, two-way ANOVA with Bonferroni test. (Right) The tracer intensity during the two arousal states at the 30-min time point was compared. **P < 0.01, t test. (C) Comparison of the interstitial concentration of NE in cortex during head-restraining versus unrestrained (before and after), as well as after ketamine/xylazine anesthesia. Microdialysis samples were collected for 1 hour each and analyzed by using high-performance liquid chromatography. **P < 0.01, one-way ANOVA with Bonferroni test. (D) TMA+ iontophoretic quantification of the volume of the extracellular space before and after adrenergic inhibition; n = 4 to 8 mice; **P < 0.01, t test. (E) Power spectrum analysis, n = 7 mice; **P < 0.01, one-way ANOVA with Bonferroni test.

Comment in

  • Neuroscience. Sleep: the brain's housekeeper?
    Underwood E. Underwood E. Science. 2013 Oct 18;342(6156):301. doi: 10.1126/science.342.6156.301. Science. 2013. PMID: 24136944 No abstract available.
  • Neuroscience. Sleep it out.
    Herculano-Houzel S. Herculano-Houzel S. Science. 2013 Oct 18;342(6156):316-7. doi: 10.1126/science.1245798. Science. 2013. PMID: 24136954 No abstract available.
  • Sleep: Sleep: not such a waste.
    Welberg L. Welberg L. Nat Rev Neurosci. 2013 Dec;14(12):816-7. doi: 10.1038/nrn3632. Epub 2013 Nov 8. Nat Rev Neurosci. 2013. PMID: 24201183 No abstract available.
  • Alzheimer disease: Sleep alleviates AD-related neuropathological processes.
    Malkki H. Malkki H. Nat Rev Neurol. 2013 Dec;9(12):657. doi: 10.1038/nrneurol.2013.230. Epub 2013 Nov 12. Nat Rev Neurol. 2013. PMID: 24217519 No abstract available.
  • Wake up with a new brain!
    Hyacinthe C, Ghorayeb I. Hyacinthe C, et al. Mov Disord. 2014 Jan;29(1):33. doi: 10.1002/mds.25765. Epub 2014 Jan 2. Mov Disord. 2014. PMID: 24395717 No abstract available.
  • Sleep tight: a purpose for sleep.
    Kelly KM, Mikell CB, McKhann GM 2nd. Kelly KM, et al. Neurosurgery. 2014 Feb;74(2):N17-8. doi: 10.1227/01.neu.0000442978.07078.e5. Neurosurgery. 2014. PMID: 24435147 No abstract available.

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