A scanning and transmission electron microscopic analysis of the cerebral aqueduct in the rabbit

Abstract

An examination of the surface of the cerebral aqueduct with the scanning electron microscope revealed that the walls of the cerebral aqueduct were so heavily ciliated that most of the ependymal surface was obscured, yet certain specialized supraependymal structures could be discerned lying on (or embedded within) this matt of cilia. These structures were determined by transmission electron microscopy and Golgi analysis to be either macrophages, supraependymal neurons, dendrites from medial periaqueductal gray neurons, or axons of unknown origin. Some axons, which were found to contain vesicles, appeared to make synaptic contacts with ependymal cells. Using the transmission electron microscope, the ependymal lining was found to consist of two different cell types: normal ependymal cells and tanycytes which have a long tapering basal process that was observed to contact blood vessels or, more rarely, seemed to terminate in relation to neuronal elements. While there have been previous reports on the structure of the third and lateral ventricles in other species, there are limited reports in the rabbit. The present report is not only the first description for the rabbit, but it is the first complete scanning and transmission electron microscopic analysis of the cerebral aqueduct in any species.

The methodology for labeling the distal cerebrospinal fluid-contacting neurons in rats

“…An optimal tracer (Ishihara et al, 1991;Klara and Brizzee, 1977;Köbbert et al, 2000;Meller and Dennis, 1993;Wang and Zhang, 1992) must be used to trace CSF-CNs. When it was injected into the ventricle of the brain, it could not pass through the spaces of the ependyma into the parenchyma of the brain but could label CSF-contacting structures.…”

The ependyma: A protective barrier between brain and cerebrospinal fluid

“…The secretory product of ventricle-lining cells in embryonic chicks includes a chondroitin sulfate proteoglycan postulated to maintain expansion of the developing neural tube (Gato et al, 1993). In the adult rabbit, aqueductal ependymal cells possess surface blebs and vesicles of various sizes (Meller and Dennis, 1993). Some authors, however, consider ependymal blebs in adult pigeons to be a fixation artifact (Mestres and Rascher, 1994).…”

“…Varicosities with serotonin-and gamma amino butyric acid (GABA)-containing vesicles are widespread on the ependymal surface. However, synapse-like formations between serotonergic endings and ependymal cells have been observed only on the subcommissural organ and in the cerebral aqueduct (Didier-Bazes et al, 1993;Meller and Dennis, 1993). Although the destruction of supraependymal axons can influence the shape of ependymal cells under some circumstances (Bjugn et al, 1988;Cupedo and de Weerd, 1988;Ribas, 19771, their function remains unclear.…”

Ependymal development, proliferation, and functions: A review

“…[Reproduced with permission from Bruni et al (1974) Brain Res., 73:145-150. ] ined extensively by using conventional light and electron microscopic techniques, and the regional differences have been well documented (Bruni, 1974;Del Brio et al, 1991;Meller and Dennis, 1993;Millhouse, 1971Millhouse, , 1975Peters et al, 1976). This extensive literature will not be examined here, however; for reviews on the subject readers are referred to Flament-Durand and Brion (1985) and Bruni et al (1985).…”