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"Thomas, John H"
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Flow of cerebrospinal fluid is driven by arterial pulsations and is reduced in hypertension
Flow of cerebrospinal fluid (CSF) through perivascular spaces (PVSs) in the brain is important for clearance of metabolic waste. Arterial pulsations are thought to drive flow, but this has never been quantitatively shown. We used particle tracking to quantify CSF flow velocities in PVSs of live mice. CSF flow is pulsatile and driven primarily by the cardiac cycle. The speed of the arterial wall matches that of the CSF, suggesting arterial wall motion is the principal driving mechanism, via a process known as perivascular pumping. Increasing blood pressure leaves the artery diameter unchanged but changes the pulsations of the arterial wall, increasing backflow and thereby reducing net flow in the PVS. Perfusion-fixation alters the normal flow direction and causes a 10-fold reduction in PVS size. We conclude that particle tracking velocimetry enables the study of CSF flow in unprecedented detail and that studying the PVS in vivo avoids fixation artifacts.
Arterial pulsations are thought to drive CSF flow through perivascular spaces (PVSs), but this has never been quantitatively shown. Using particle tracking to quantify CSF flow velocities in PVSs of live mice, the authors show that flow speeds match the instantaneous speeds of the pulsing artery walls that form the inner boundaries of the PVSs.
Journal Article
Theoretical analysis of wake/sleep changes in brain solute transport suggests a flow of interstitial fluid
Clearance of protein waste products from the brain is accomplished by a combination of advection and diffusion in cerebrospinal fluid (CSF) and interstitial fluid (ISF). In the glymphatic model, there is a flow of ISF in the interstitial space, and both advection and diffusion occur there. Such a flow of ISF would be slow and difficult to detect directly, and its existence has proved controversial. Waste clearance has been shown to occur mainly during sleep, during which the volume of the interstitial space increases substantially due to ISF emitted from astrocytes. Here I show that this volume increase of the interstitial space, by itself, should lead to a slight reduction of diffusive transport, due to dilution of the waste solute, but to a significant increase in flow rate and advective transport, due to lowered hydraulic resistance. Thus, a flow of ISF together with the observed volume increase of the interstitial space might provide an important mechanism contributing to the enhanced clearance during sleep.
Journal Article
Animation
With an introduction by John Lasseter-- and very little else in the way of words-- this second book in The Artist Series lavishly showcases the most brilliant animation created by such luminaries as Ub Iwerks, Norm Ferguson, Ben Sharpsteen, Hamilton Luske, Dick Huemer, Grim Natwick, Art Babbitt, Fred Moore, Bill Tytla, Frank Thomas, Ollie Johnston, Milt Kahl, Marc Davis, John Lounsbery, Ward Kimball, Eric Larson, Les Clark, Wolfgang Reitherman, John Sibley, Bill Justice, Clyde Geronimi, Ted Berman, Glen Keane, Andreas Deja, Eric Goldberg, Mark Henn and Tony Bancroft. The artwork-- much of which has never before been published-- offers the opportunity to marvel at the those magical lines of pencil that brought life to so many unforgettable Disney characters. Animation represents a rare opportunity to enjoy a glimpse into the truly spectacular trove of treasures from the Walt Disney Animation Research Library.
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Cerebrospinal fluid influx drives acute ischemic tissue swelling
The brain is enveloped in a cushion of cerebrospinal fluid (CSF), which normally provides protection and helps to remove metabolic waste. CSF transport has also recently been shown to play unexpected roles in neurodegeneration and sleep. Mestre et al. used multimodal in vivo imaging in rodents and found that, after a stroke, an abnormally large volume of CSF rushes into the brain, causing swelling (see the Perspective by Moss and Williams). This influx of CSF is caused by constrictions of arteries triggered by a well-known propagating chemical reaction-diffusion wave called spreading depolarization. CSF transport can thus play a role in brain swelling after stroke. Science , this issue p. eaax7171 ; see also p. 1195 In rodent models, the influx of cerebrospinal fluid along the glymphatic pathway swells the brain during ischemic stroke. Stroke affects millions each year. Poststroke brain edema predicts the severity of eventual stroke damage, yet our concept of how edema develops is incomplete and treatment options remain limited. In early stages, fluid accumulation occurs owing to a net gain of ions, widely thought to enter from the vascular compartment. Here, we used magnetic resonance imaging, radiolabeled tracers, and multiphoton imaging in rodents to show instead that cerebrospinal fluid surrounding the brain enters the tissue within minutes of an ischemic insult along perivascular flow channels. This process was initiated by ischemic spreading depolarizations along with subsequent vasoconstriction, which in turn enlarged the perivascular spaces and doubled glymphatic inflow speeds. Thus, our understanding of poststroke edema needs to be revised, and these findings could provide a conceptual basis for development of alternative treatment strategies.
Journal Article
Aquaporin-4-dependent glymphatic solute transport in the rodent brain
The glymphatic system is a brain-wide clearance pathway; its impairment contributes to the accumulation of amyloid-β. Influx of cerebrospinal fluid (CSF) depends upon the expression and perivascular localization of the astroglial water channel aquaporin-4 (AQP4). Prompted by a recent failure to find an effect of Aqp4 knock-out (KO) on CSF and interstitial fluid (ISF) tracer transport, five groups re-examined the importance of AQP4 in glymphatic transport. We concur that CSF influx is higher in wild-type mice than in four different Aqp4 KO lines and in one line that lacks perivascular AQP4 (Snta1 KO). Meta-analysis of all studies demonstrated a significant decrease in tracer transport in KO mice and rats compared to controls. Meta-regression indicated that anesthesia, age, and tracer delivery explain the opposing results. We also report that intrastriatal injections suppress glymphatic function. This validates the role of AQP4 and shows that glymphatic studies must avoid the use of invasive procedures.
Journal Article
From sci-fi to sci-fact: the state of robotics and AI in the hospitality industry
Purpose
This paper aims to review the extant hospitality and tourism literature on the state of robotics and artificial intelligence (AI) in the service industry. The aim was to highlight the current areas of research on this emerging topic and identify areas for future application and study.
Design/methodology/approach
A list of hospitality and tourism journals was used to identify articles related to AI and robotics using the terms AI, robots, robotics, hospitality and tourism, and several combinations thereof. Additional sources were identified through the literature reviews from the identified works.
Findings
The findings revealed several studies on the current state of robotics and AI in hospitality and tourism. Additional research examines and discusses implications for internal and external customer service, legal and ethical issues and theory.
Originality/value
This paper provides a compilation of the current studies that examine the impact of robotics and AI in hospitality and tourism. It offers scholars an overview of the current knowledge in the field on this rapidly emerging and evolving topic.
论酒店行业中机器学和AI的发展
摘要
研究目的
本文审阅了有关服务行业中机器学和智能技术（AI）发展的相关文献。其研究目的在于强调有关这个新兴话题的研究领域和指出未来研究方向。
研究设计/方法/途径
本文样本包括有关AI和机器学的期刊文献，关键搜索词包括AI、机器人、机器学、酒店管理、旅游，以及几项关键词组合。本文还通过文献综述审阅了多个数据源。
研究结果
研究结果描述了目前酒店旅游行业机器学和AI有关领域的研究状态。此外本文还研究和提出对于内部和外部客户服务、法律伦理问题、以及理论等领域做出研究启示。
研究原创性/价值
本文对目前有关机器学和AI酒店旅游学术研究进行系统梳理。为学者对其相关领域的现状提供全局视角，并且显示这个新兴话题的迅速发展。
关键词
文献综述、AI、机器学、酒店科技
Journal Article
Bulk flow of cerebrospinal fluid observed in periarterial spaces is not an artifact of injection
Cerebrospinal fluid (CSF) flowing through periarterial spaces is integral to the brain’s mechanism for clearing metabolic waste products. Experiments that track tracer particles injected into the cisterna magna (CM) of mouse brains have shown evidence of pulsatile CSF flow in perivascular spaces surrounding pial arteries, with a bulk flow in the same direction as blood flow. However, the driving mechanism remains elusive. Several studies have suggested that the bulk flow might be an artifact, driven by the injection itself. Here, we address this hypothesis with new in vivo experiments where tracer particles are injected into the CM using a dual-syringe system, with simultaneous injection and withdrawal of equal amounts of fluid. This method produces no net increase in CSF volume and no significant increase in intracranial pressure. Yet, particle-tracking reveals flows that are consistent in all respects with the flows observed in earlier experiments with single-syringe injection.
Journal Article