https://www.cell.com/cell/pdf/S0092-8674(19)31007-4.pdf

Alzheimer Disease: An Update on Pathobiology and Treatment Strategies.

Sharp wave ripples (SPW-Rs) represent the most synchronous population pattern in the mammalian brain. Their excitatory output affects a wide area of the cortex and several subcortical nuclei. SPW-Rs occur during "off-line" states of the brain, associated with consummatory behaviors and non-REM sleep, and are influenced by numerous neurotransmitters and neuromodulators. They arise from the excitatory recurrent system of the CA3 region and the SPW-induced excitation brings about a fast network oscillation (ripple) in CA1. The spike content of SPW-Rs is temporally and spatially coordinated by a consortium of interneurons to replay fragments of waking neuronal sequences in a compressed format. SPW-Rs assist in transferring this compressed hippocampal representation to distributed circuits to support memory consolidation; selective disruption of SPW-Rs interferes with memory. Recently acquired and pre-existing information are combined during SPW-R replay to influence decisions, plan actions and, potentially, allow for creative thoughts. In addition to the widely studied contribution to memory, SPW-Rs may also affect endocrine function via activation of hypothalamic circuits. Alteration of the physiological mechanisms supporting SPW-Rs leads to their pathological conversion, "p-ripples," which are a marker of epileptogenic tissue and can be observed in rodent models of schizophrenia and Alzheimer's Disease. Mechanisms for SPW-R genesis and function are discussed in this review.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/hipo.22488

Hippocampal sharp wave‐ripple: A cognitive biomarker for episodic memory and planning

Compare your culture to one of the cultures discussed in this unit. On a sheet of paper, list the cultures you are comparing and make one column titled “similarities,” and a second column titled “differences.” Now, list as many similarities and differences between the two as you can think of. Are there more similarities or differences between the two cultures you selected? Have you ever met anyone from this culture? How can you use this information to build greater respect between cultures?

Similarities and Differences

Factors other than age and genetics may increase the risk of developing Alzheimer disease (AD). Accumulation of the amyloid-β (Aβ) peptide in the brain seems to initiate a cascade of key events in the pathogenesis of AD. Moreover, evidence is emerging that the sleep-wake cycle directly influences levels of Aβ in the brain. In experimental models, sleep deprivation increases the concentration of soluble Aβ and results in chronic accumulation of Aβ, whereas sleep extension has the opposite effect. Furthermore, once Aβ accumulates, increased wakefulness and altered sleep patterns develop. Individuals with early Aβ deposition who still have normal cognitive function report sleep abnormalities, as do individuals with very mild dementia due to AD. Thus, sleep and neurodegenerative disease may influence each other in many ways that have important implications for the diagnosis and treatment of AD.

Sleep and Alzheimer disease pathology--a bidirectional relationship.

Sleep and Human Aging

Aggregation of β-amyloid (Aβ) in the brain begins to occur years before the clinical onset of Alzheimer's disease (AD). Before Aβ aggregation, concentrations of extracellular soluble Aβ in the interstitial fluid (ISF) space of the brain, which are regulated by neuronal activity and the sleep-wake cycle, correlate with the amount of Aβ deposition in the brain seen later. The amount and quality of sleep decline with normal aging and to a greater extent in AD patients. How sleep quality as well as the diurnal fluctuation in Aβ change with age and Aβ aggregation is not well understood. We report a normal sleep-wake cycle and diurnal fluctuation in ISF Aβ in the brain of the APPswe/PS1δE9 mouse model of AD before Aβ plaque formation. After plaque formation, the sleep-wake cycle markedly deteriorated and diurnal fluctuation of ISF Aβ dissipated. As in mice, diurnal fluctuation of cerebrospinal fluid Aβ in young adult humans with presenilin mutations was also markedly attenuated after Aβ plaque formation. Virtual elimination of Aβ deposits in the mouse brain by active immunization with Aβ(42) normalized the sleep-wake cycle and the diurnal fluctuation of ISF Aβ. These data suggest that Aβ aggregation disrupts the sleep-wake cycle and diurnal fluctuation of Aβ. Sleep-wake behavior and diurnal fluctuation of Aβ in the central nervous system may be functional and biochemical indicators, respectively, of Aβ-associated pathology.

/pdf/disruption-of-the-sleep-wake-cycle-and-diurnal-fluctuation-441wpvg065.pdf

Disruption of the Sleep-Wake Cycle and Diurnal Fluctuation of β-Amyloid in Mice with Alzheimer’s Disease Pathology

Background The amyloid hypothesis predicts that increased production or decreased clearance of β-amyloid (Aβ) leads to amyloidosis, which ultimately culminates in Alzheimer disease (AD). Objective To investigate whether dynamic changes in Aβ levels in the human central nervous system may be altered by aging or by the pathology of AD and thus contribute to the risk of AD. Design Repeated-measures case-control study. Setting Washington University School of Medicine in St Louis, Missouri. Participants Participants with amyloid deposition, participants without amyloid deposition, and younger normal control participants. Main Outcome Measures In this study, hourly cerebrospinal fluid (CSF) Aβ concentrations were compared with age, status of amyloid deposition, electroencephalography, and video recording data. Results Linear increases were observed over time in the Aβ levels in CSF samples obtained from the younger normal control participants and the older participants without amyloid deposition, but not from the older participants with amyloid deposition. Significant circadian patterns were observed in the Aβ levels in CSF samples obtained from the younger control participants; however, circadian amplitudes decreased in both older participants without amyloid deposition and older participants with amyloid deposition. Aβ diurnal concentrations were correlated with the amount of sleep but not with the various activities that the participants participated in while awake. Conclusions A reduction in the linear increase in the Aβ levels in CSF samples that is associated with amyloid deposition and a decreased CSF Aβ diurnal pattern associated with increasing age disrupt the normal physiology of Aβ dynamics and may contribute to AD.

https://jamanetwork.com/journals/jamaneurology/articlepdf/1108053/noc110054_51_58.pdf

Effects of Age and Amyloid Deposition on Aβ Dynamics in the Human Central Nervous System

Objectives To investigate dynamic changes in human plasma β-amyloid (Aβ) concentrations, evaluate the effects of aging and amyloidosis on these dynamics, and determine their correlation with cerebrospinal fluid (CSF) Aβ concentrations. Design A repeated plasma and CSF sampling study. Setting The Washington University School of Medicine in St Louis, Missouri. Participants Older adults with amyloid deposition (Amyloid + ), age-matched controls without amyloid deposition (Amyloid − ), and younger normal controls (YNCs) were enrolled for the study. Main Outcome Measures Hourly measurements of plasma Aβ were compared between groups by age and amyloidosis. Plasma Aβ and CSF Aβ concentrations were compared for correlation, linear increase, and circadian patterns. Results Circadian patterns were observed in plasma Aβ, with diminished amplitudes with aging. Linear increase of Aβ was only observed for CSF Aβ in the YNC and Amyloid − groups, but not in the Amyloid + group. No linear increase was observed for plasma Aβ. No significant correlations were found between plasma and CSF Aβ concentrations. Conclusions Plasma Aβ, like CSF, demonstrates a circadian pattern that is reduced in amplitude with increasing age but is unaffected by amyloid deposition. However, we found no evidence that plasma and CSF Aβ concentrations were related on an hourly or individual basis.

https://jamanetwork.com/journals/jamaneurology/articlepdf/1475602/noc120063_1591_1597.pdf

β-Amyloid Dynamics in Human Plasma

The amyloid-β (Aβ) protein is diurnally regulated in both the cerebrospinal fluid and blood in healthy adults; circadian amplitudes decrease with aging and the presence of cerebral Aβ deposits. The cause of the Aβ diurnal pattern is poorly understood. One hypothesis is that the Amyloid Precursor Protein (APP) is diurnally regulated, leading to APP product diurnal patterns. APP in the central nervous system is processed either via the β-pathway (amyloidogenic), generating soluble APP-β (sAPPβ) and Aβ, or the α-pathway (non-amyloidogenic), releasing soluble APP-α (sAPPα). To elucidate the potential contributions of APP to the Aβ diurnal pattern and the balance of the α- and β- pathways in APP processing, we measured APP proteolytic products over 36 hours in human cerebrospinal fluid from cognitively normal and Alzheimer's disease participants. We found diurnal patterns in sAPPα, sAPPβ, Aβ40, and Aβ42, which diminish with increased age, that support the hypothesis that APP is diurnally regulated in the human central nervous system and thus results in Aβ diurnal patterns. We also found that the four APP metabolites were positively correlated in all participants without cerebral Aβ deposits. This positive correlation suggests that the α- and β- APP pathways are non-competitive under normal physiologic conditions where APP availability may be the limiting factor that determines sAPPα and sAPPβ production. However, in participants with cerebral Aβ deposits, there was no correlation of Aβ to sAPP metabolites, suggesting that normal physiologic regulation of cerebrospinal fluid Aβ is impaired in the presence of amyloidosis. Lastly, we found that the ratio of sAPPβ to sAPPα was significantly higher in participants with cerebral Aβ deposits versus those without deposits. Therefore, the sAPPβ to sAPPα ratio may be a useful biomarker for cerebral amyloidosis.

https://digitalcommons.wustl.edu/cgi/viewcontent.cgi?article=3893&context=open_access_pubs

Yafei Huang

Papers

Disruption of the Sleep-Wake Cycle and Diurnal Fluctuation of β-Amyloid in Mice with Alzheimer’s Disease Pathology

Effects of Age and Amyloid Deposition on Aβ Dynamics in the Human Central Nervous System

β-Amyloid Dynamics in Human Plasma

Diurnal Patterns of Soluble Amyloid Precursor Protein Metabolites in the Human Central Nervous System