A few excerpts.
“We found that cervical lymph nodes drain CSF macromolecules (Extended Data Fig. 3f), and multisensory 40 Hz stimulation increased amyloid accumulation in cervical lymph nodes (Extended Data Fig. 3g,h). These findings indicate that amyloid is cleared from the brain following multisensory 40 Hz stimulation in part via glymphatic routes.”
“Gamma stimulation promotes arterial pulsation
Arterial vasomotion regulates CSF movement2,9 and is entrained by the envelope of gamma rhythms20. Thus, we explored whether changes in CSF influx by multisensory 40 Hz stimulation may be owing to arterial pulsatility….To evaluate whether gamma stimulation increases arterial pulsatility in awake mice, we administered multisensory stimulation for 1 h, then imaged arterial vasomotion (Fig. 2c). After quantifying arterial vasomotion peaks (Extended Data Fig. 6c), we found that multisensory 40 Hz stimulation increased arterial pulsations compared with non-40 Hz control stimulations (Fig. 2d)….We speculate that stimulation itself may increase vasomotion during the stimulation period (Extended Data Fig. 6d), and we attribute the sustained increase in vasomotion following the end of stimulation to the long-lasting effects of sustained peptide signalling on vascular changes.”
“We found that multisensory 40 Hz stimulation increased meningeal lymphatic vessel diameter compared with control stimulation in 6-month-old 5XFAD mice (Extended Data Fig. 7b,c). High-resolution volumetric 3D reconstruction analysis revealed that the volume of lymphatic vessels increased following multisensory 40 Hz stimulation (Extended Data Fig. 7d,e and Supplementary Video 3). These results suggest that gamma stimulation increases lymphatic diameter in the dural meninges.”
“Discussion
Following the observation that optogenetic gamma stimulation can attenuate amyloid burden5, we found that sensory gamma stimulation promotes 40 Hz neural activity in multiple brain regions including the prefrontal cortex6,7,16. Sensory gamma stimulation also attenuates Alzheimer’s disease-related pathology5, ameliorates neurodegeneration7 and morphologically transforms astrocytes6 and microglia5,6,7 in models of Alzheimer’s disease. These observations have been replicated and extended45,46,47,48, but the cellular processes by which sensory stimulation attenuates amyloid load in the brain have remained incompletely resolved. In this study, we investigated the role of glymphatic clearance during multisensory gamma stimulation. Given that the glymphatic system clears parenchymal amyloid3 and is regulated by neural rhythms18, we hypothesized that glymphatic clearance might account for amyloid reduction by sensory gamma stimulation. Gamma rhythms may be relevant to aspects of glymphatic clearance as gamma may be involved in aspects of sleep49,50 and neuronal synchrony. Moreover, the envelope of gamma rhythms entrains arterial pulsatility20, which is thought to govern CSF influx. Leveraging a variety of imaging modalities to monitor multiple aspects of the glymphatic pathway, as well as genetic and molecular interventions, we found that gamma stimulation promoted the influx of CSF into the cortex and the efflux of ISF, which was associated with increased arterial pulsatility, increased AQP4 polarization, and dilation of meningeal lymphatic vessels. Our findings support observations indicating that brain rhythms govern CSF dynamics1,18,51. Our experiments also suggest that aspects of gamma rhythms, such as arterial pulsatility20 and peptide signalling, may contribute to CSF dynamics. The long-lasting nature of peptide signalling may explain in part why increased vasomotion persists following the end of stimulation.
Glymphatic influx is attributed to the sleeping state. A recent report suggests that noninvasive sensory stimulation modulates CSF outflow in awake humans52, potentially suggesting that CSF and glymphatic pathways can be modulated in the awake brain. Our findings suggest that multisensory 40 Hz stimulation promotes amyloid clearance and activates glymphatic pathways. Future work may disentangle how cellular pathways regulating glymphatic systems in various arousal states are modulated.
The meningeal lymphatic drainage network, arterial-driven CSF movement and neuronal network dysfunction contribute to amyloid pathology in Alzheimer’s disease14. Our observations suggest that brain rhythms contribute to arterial regulation of CSF clearance and meningeal lymphatic drainage. We found that multisensory gamma stimulation increased arterial pulsatility in a VIP interneuron-dependent manner. Consistent with prior results highlighting electrophysiological and haemodynamic coupling of CSF dynamics9,51, our experiments highlight an interconnected relationship between glial, neuronal and vascular cells in the regulation of CSF dynamics. Transcriptional responses to gamma stimulation—which we highlighted using both snRNA-seq and in situ hybridization—further indicate that transcriptional responses related to ion channels may have a critical role in linking neural oscillations with glial and vascular responses governing fluid transport. Our results also suggest that vasoactive signals from neurons act on glial and vascular cells during neural oscillations to drive CSF clearance. Future work further defining factors linking brain rhythms and vasoactive clearance may enhance the therapeutic potential of recruiting glymphatic transport for the treatment of neurodegenerative disorders associated with the accumulation of amyloid peptides and potentially other pathogenic extracellular proteins.”
“We found that cervical lymph nodes drain CSF macromolecules (Extended Data Fig. 3f), and multisensory 40 Hz stimulation increased amyloid accumulation in cervical lymph nodes (Extended Data Fig. 3g,h). These findings indicate that amyloid is cleared from the brain following multisensory 40 Hz stimulation in part via glymphatic routes.”
“Gamma stimulation promotes arterial pulsation
Arterial vasomotion regulates CSF movement2,9 and is entrained by the envelope of gamma rhythms20. Thus, we explored whether changes in CSF influx by multisensory 40 Hz stimulation may be owing to arterial pulsatility….To evaluate whether gamma stimulation increases arterial pulsatility in awake mice, we administered multisensory stimulation for 1 h, then imaged arterial vasomotion (Fig. 2c). After quantifying arterial vasomotion peaks (Extended Data Fig. 6c), we found that multisensory 40 Hz stimulation increased arterial pulsations compared with non-40 Hz control stimulations (Fig. 2d)….We speculate that stimulation itself may increase vasomotion during the stimulation period (Extended Data Fig. 6d), and we attribute the sustained increase in vasomotion following the end of stimulation to the long-lasting effects of sustained peptide signalling on vascular changes.”
“We found that multisensory 40 Hz stimulation increased meningeal lymphatic vessel diameter compared with control stimulation in 6-month-old 5XFAD mice (Extended Data Fig. 7b,c). High-resolution volumetric 3D reconstruction analysis revealed that the volume of lymphatic vessels increased following multisensory 40 Hz stimulation (Extended Data Fig. 7d,e and Supplementary Video 3). These results suggest that gamma stimulation increases lymphatic diameter in the dural meninges.”
“Discussion
Following the observation that optogenetic gamma stimulation can attenuate amyloid burden5, we found that sensory gamma stimulation promotes 40 Hz neural activity in multiple brain regions including the prefrontal cortex6,7,16. Sensory gamma stimulation also attenuates Alzheimer’s disease-related pathology5, ameliorates neurodegeneration7 and morphologically transforms astrocytes6 and microglia5,6,7 in models of Alzheimer’s disease. These observations have been replicated and extended45,46,47,48, but the cellular processes by which sensory stimulation attenuates amyloid load in the brain have remained incompletely resolved. In this study, we investigated the role of glymphatic clearance during multisensory gamma stimulation. Given that the glymphatic system clears parenchymal amyloid3 and is regulated by neural rhythms18, we hypothesized that glymphatic clearance might account for amyloid reduction by sensory gamma stimulation. Gamma rhythms may be relevant to aspects of glymphatic clearance as gamma may be involved in aspects of sleep49,50 and neuronal synchrony. Moreover, the envelope of gamma rhythms entrains arterial pulsatility20, which is thought to govern CSF influx. Leveraging a variety of imaging modalities to monitor multiple aspects of the glymphatic pathway, as well as genetic and molecular interventions, we found that gamma stimulation promoted the influx of CSF into the cortex and the efflux of ISF, which was associated with increased arterial pulsatility, increased AQP4 polarization, and dilation of meningeal lymphatic vessels. Our findings support observations indicating that brain rhythms govern CSF dynamics1,18,51. Our experiments also suggest that aspects of gamma rhythms, such as arterial pulsatility20 and peptide signalling, may contribute to CSF dynamics. The long-lasting nature of peptide signalling may explain in part why increased vasomotion persists following the end of stimulation.
Glymphatic influx is attributed to the sleeping state. A recent report suggests that noninvasive sensory stimulation modulates CSF outflow in awake humans52, potentially suggesting that CSF and glymphatic pathways can be modulated in the awake brain. Our findings suggest that multisensory 40 Hz stimulation promotes amyloid clearance and activates glymphatic pathways. Future work may disentangle how cellular pathways regulating glymphatic systems in various arousal states are modulated.
The meningeal lymphatic drainage network, arterial-driven CSF movement and neuronal network dysfunction contribute to amyloid pathology in Alzheimer’s disease14. Our observations suggest that brain rhythms contribute to arterial regulation of CSF clearance and meningeal lymphatic drainage. We found that multisensory gamma stimulation increased arterial pulsatility in a VIP interneuron-dependent manner. Consistent with prior results highlighting electrophysiological and haemodynamic coupling of CSF dynamics9,51, our experiments highlight an interconnected relationship between glial, neuronal and vascular cells in the regulation of CSF dynamics. Transcriptional responses to gamma stimulation—which we highlighted using both snRNA-seq and in situ hybridization—further indicate that transcriptional responses related to ion channels may have a critical role in linking neural oscillations with glial and vascular responses governing fluid transport. Our results also suggest that vasoactive signals from neurons act on glial and vascular cells during neural oscillations to drive CSF clearance. Future work further defining factors linking brain rhythms and vasoactive clearance may enhance the therapeutic potential of recruiting glymphatic transport for the treatment of neurodegenerative disorders associated with the accumulation of amyloid peptides and potentially other pathogenic extracellular proteins.”
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