Ependymal development, proliferation, and functions: A review

Abstract

A survey of the literature shows that proliferation of ependyma occurs largely during the embryonic and early postnatal periods of development in most species. Differentiation of these cells proceeds along particular regional and temporal gradients as does the expression of various cytoskeletal (vimentin, cytokeratins, glial fibrillary acidic protein) and secretory proteins (S‐100). Turnover declines significantly postnatally, and only low levels of residual activity persist into adulthood under normal conditions. Although the reported response of ependyma to injury is somewhat equivocal, only limited regenerative capacity appears to exist and to varying degrees in different regions of the neuraxis. Proliferation has been most often observed in response to spinal cord injury. Indeed, the ependyma plays a significant role in the initiation and maintenance of the regenerative processes in the spinal cord of inframammalian vertebrates. In the human, however, ependyma appears never to regenerate at any age nor re‐express cytoskeletal proteins characteristic of immature cells. The functions of ependyma including tanycytes, a specialized form of ependymal cell that persists into adulthood within circumscribed regions of the nervous system, are still largely speculative. Fetal unlike mature ependyma is believed to be secretory and is believed to play a role in neurogenesis, neuronal differentiation/axonal guidance, transport, and support. In the adult brain, mature ependyma is not merely an inert lining but may regulate the transport of ions, small molecules, and water between the cerebrospinal fluid and neuropil and serve an important barrier function that protects neural tissue from potentially harmful substances by mechanisms that are still incompletely understood. Microsc. Res. Tech. 41:2–13, 1998 © 1998 Wiley‐Liss, Inc.

Diagnostic value of subependymal pseudocysts and choroid plexus cysts on neonatal cerebral ultrasound: a meta-analysis

“…Ventricular ependymal cells show marked proliferation during the embryonic period 32. During this time the germinal matrix zone is much larger than at term 33.…”

Frontal horn thin walled cysts in preterm neonates are benign

“…Fetal ependyma, unlike mature ependyma, is an active secretory structure for the programming of developmental events,15and plays a role in neurogenesis, neuronal differentiation, axonal guidance, transport, and support 16. Histological examination suggests an ependymal origin of the frontal horn cyst (fig3B).…”

The regulation of brain states by neuroactive substances distributed via the cerebrospinal fluid; a review

“…White matter tracts are guiding tracts for the interstitial fluid flow as well as for the dissemination of primary brain tumors [158]. Diffusion and exchange between cerebrospinal and extracellular fluid compartments may occur in both directions [37,77] through an uninterrupted single-layered lining of the ventricular system, consisting of several types of ciliated ependymal cells [95,159]. Due to the lack of tight junctions between ependymal cells, the CSF-ECF barrier can be described as open or non-existent.…”

“…Those lining the ventral part of the third ventricle have basal processes that extend to the hypophyseal-portal vasculature as well as into the mediobasal hypothalamus, suggesting a role in pituitary and neural control. As reviewed by Bruni [95] and Rodriguez et al . [177], multiple tanycyte functions have been proposed over time.…”