The effect of viscous loading on brain ependymal cilia

Ependymal cilia line the ventricular system moving cerebral spinal fluid close to the brain surface. They may be exposed to fluid of increasing viscosity in certain pathological conditions such as bacterial meningitis. Our aim was to determine the effect of increasing viscosity on ciliary function. Ciliated ependyma was exposed to solutions of different viscosities (1-60 cP) and ciliary function assessed by high-speed digital imaging. The mean (SD) ciliary beat frequency (CBF), measured after 30 minutes incubation in Medium 199 at 37oC, was 34.9 (2.9) Hz. Increased viscous loading was followed by a rapid decrease in ciliary beat frequency compared to baseline readings (p<0.001). After 15 minutes of exposure to the increased viscous load, CBF reached a new stable level while the viscous load was maintained. Compared to baseline measurements of CBF, viscous loading of 3.7cP caused a 16%, 10.4cP at 34% and 24cP a 70% decrease in beat frequency. Further viscous loading at levels up to 60cP resulted in no further reduction of ependymal CBF. Solutions of 24cP and 40cP had no effect on ciliary amplitude. An increase in viscosity to 60cP caused a significant (30%: p = 0.001) decrease in the ciliary beat amplitude.