Visualizing flow in an intact CSF network using optical coherence tomography: implications for human congenital hydrocephalus

Abstract

Cerebrospinal fluid (CSF) flow in the brain ventricles is critical for brain development. Altered CSF flow dynamics have been implicated in congenital hydrocephalus (CH) characterized by the potentially lethal expansion of cerebral ventricles if not treated. CH is the most common neurosurgical indication in children effecting 1 per 1000 infants. Current treatment modalities are limited to antiquated brain surgery techniques, mostly because of our poor understanding of the CH pathophysiology. We lack model systems where the interplay between ependymal cilia, embryonic CSF flow dynamics and brain development can be analyzed in depth. This is in part due to the poor accessibility of the vertebrate ventricular system to in vivo investigation. Here, we show that the genetically tractable frog Xenopus tropicalis , paired with optical coherence tomography imaging, provides new insights into CSF flow dynamics and role of ciliary dysfunction in hydrocephalus pathogenesis. We can visualize CSF flow within the multi-chambered ventricular system and detect multiple distinct polarized CSF flow fields. Using CRISPR/Cas9 gene editing, we modeled human L1CAM and CRB2 mediated aqueductal stenosis. We propose that our high-throughput platform can prove invaluable for testing candidate human CH genes to understand CH pathophysiology.

The role of motile cilia in the development and physiology of the nervous system

“…Sensory regions in olfactory organs are coloured dark green, while non-sensory regions are light green. Three-dimensional renderings of brain ventricular systems of (a') a two-day old zebrafish [32], (a'') a threemonth-old zebrafish [33], (b') a stage 45 Xenopus tropicalis [34], (c') an average adult mouse [35], and (d') an adult human [36] are shown. TV = telencephalic; DV = diencephalic ventricle; TeV = tectal ventricle; RV = rhombencephalic ventricle; LV = Lateral ventricle; 3V = 3rd ventricle; MV = mesencephalic ventricle; 4V = 4th ventricle.…”

“…Since many physiological parameters impact the bulk flow, and are difficult to measure with high spatial and temporal resolution, most studies focus on the cilia-mediated flow along the ventricular walls. The contribution of motile cilia in CSF flow is clearly demonstrated in zebrafish [32,110], clawed frog [34,133], rodents [e.g. 123,137,139,163,164], pigs [163] and humans [123].…”

In Xenopus ependymal cilia drive embryonic CSF circulation and brain development independently of cardiac pulsatile forces

“…Recent work by Faubel et al showed a network of streams driven by MCCs along the lateral ventricle of mouse suggesting the existence of a complex polarization along the ventricular surfaces [ 32 ]. The significance of this organization remains to be a daunting puzzle yet it is known that functional cilia are crucial for early brain development [ 33 ] (mouse, rat, pig [ 32 ], zebrafish [ 21 ], Xenopus [ 34 ], human [ 35 ]). Overall, the role of cardiac and ciliary forces in CSF circulation continues to be an area of intense research although limited by the availability of model systems and technical difficulties accessing the embryonic CNS in vivo.…”

“…Xenopus tadpole brains, although architecturally simpler, share the distinct compartmentalization of the mammalian brain with two lateral ventricles, third and fourth ventricle, but have the additional advantage of being semi-transparent during development. We have previously exploited this feature to demonstrate that the developing Xenopus brain is ciliated and to demonstrate a genetic hydrocephalus model with established hydrocephaly genes [ 34 ]. Here, we use this model to test the role of cardiac and ciliary forces on Xenopus embryonic CSF circulation as well as their role in Xenopus neurodevelopment.…”

Optical coherence tomography as a noninvasive 3D real time imaging tool for the rapid evaluation of phenotypic variations in insect embryonic development

“…For example, early mouse and rat embryos as the model of mammalian were imaged using OCT to assess structural and functional birth defects [15]. Cerebrospinal fluid flow in the brain ventricles of Xenopus tropicalis was measured with OCT to study the congenital hydrocephalus pathophysiology [17]. Cerebrospinal fluid flow in the brain ventricles of Xenopus tropicalis was measured with OCT to study the congenital hydrocephalus pathophysiology [17].…”