# Circadian influences on central nervous system barriers and the glymphatic system

## TL;DR

This review explores how circadian rhythms influence key systems that maintain brain health and fluid balance.

## Contribution

It synthesizes recent evidence on the role of circadian rhythms in regulating CNS barriers and fluid systems.

## Key findings

- Circadian rhythms regulate the blood-brain barrier and blood-cerebrospinal fluid barrier.
- The glymphatic system's function is influenced by circadian timing.
- Disruption of circadian rhythms may contribute to neurological disorders.

## Abstract

The central nervous system (CNS), comprising the brain and spinal cord, is fortified by complex barriers that protect the underlying organs and maintain homeostasis. The importance of proper fortification and homeostatic regulation provided by these systems has broad implications for many physiological processes and several pathological conditions are associated with their disruption. Recent studies support the notion that CNS barriers and fluids are regulated by circadian rhythms. Whereas reciprocal associations between the structural and functional integrity of neural barriers and disease states are well-established, the role of circadian rhythms in mediating these relationships remains unspecified. The goals of this review are to provide a general overview of three primary systems responsible for maintaining CNS homeostasis, namely the blood-brain barrier, blood-cerebrospinal fluid barrier, and glymphatic system, and to synthesize recent evidence highlighting the role of circadian rhythms as a critical regulator of CNS fluid and barrier function.

Diagram illustrating the circadian clock's influence on three systems: 1) blood-brain barrier, shown with cellular structures; 2) blood-cerebrospinal fluid barrier, featuring the choroid plexus in a brain diagram; 3) glymphatic system, depicted with interconnected neural pathways.