Orchestrating brain fluid dynamics: circadian regulation of CSF, glymphatic exchange, and waste clearance

The brain relies on cerebrospinal fluid (CSF) and the glymphatic system to maintain its delicate internal environment. We explored through a literature search the complex interplay and circadian regulation of CSF production and glymphatic system exchanges attempting to delineate an integrated and innovative view of their activities. We focused on how biological clocks, present at various levels of the finely tuned CSF/interstitial fluid/glymphatic exchange chain, orchestrate these activities. A key aspect is exploring their relationship with the neurovascular unit (NVU), which acts as a crucial regulator of fluidic control and exchanges at the neuron/astrocyte/endothelium interface. While the daily cycling activity of the glymphatic waste system is supported by increasing experimental evidence in animal models, the precise coordination and the primary location of the underlying biological clocks remain subjects of ongoing discussion. We provided a comprehensive discussion addressing these unanswered questions regarding the synchronization and primary regulatory mechanisms governing brain fluid dynamics. Understanding the circadian orchestration of CSF and glymphatic system activities, and their intricate connections with the NVU, is paramount for comprehending brain homeostasis and disease. Further research into the precise localization and function of these biological clocks is crucial for advancing our knowledge of brain fluid dynamics.