Organization of the ventricular zone of the cerebellum

Abstract

The roof of the fourth ventricle (4V) is located on the ventral part of the cerebellum, a region with abundant vascularization and cell heterogeneity that includes tanycyte-like cells that define a peculiar glial niche known as ventromedial cord. This cord is composed of a group of biciliated cells that run along the midline, contacting the ventricular lumen and the subventricular zone. Although the complex morphology of the glial cells composing the cord resembles to tanycytes, cells which are known for its proliferative capacity, scarce or non-proliferative activity has been evidenced in this area. The subventricular zone of the cerebellum includes astrocytes, oligodendrocytes, and neurons whose function has not been extensively studied. This review describes to some extent the phenotypic, morphological, and functional characteristics of the cells that integrate the roof of the 4V, primarily from rodent brains.

Keywords: Bergmann glia; astrocytes; choroid plexus; ependymal glial cells; fourth ventricle.

Figure 1

Camera lucida drawings of main cell types of the SVCC. (A) Cells located in the lateral region of the SVCC have an elongated soma (diameter 32.506 ± 0.808 μm), long processes that project toward the middle region and processes that extend ventrally. (B) Star-shaped soma cells (diameter 36.957 ± 0.774 μm) with a long lateral process and one that projects ventrally. (C) Small cells (diameter 17.728 ± 2.223 μm), with two processes projecting ventrally and a short lateral process.

Figure 2

Blood vessels respond to hypoxic preconditioning. The surface of the roof of the 4V is profusely irrigated by blood vessels and arteries. These confocal microscope images show the vessels stained with DiI and the surface of the lobule I exposed by the whole mount preparation, before and four days after hypoxic pre-conditioning, where vessel dilation can be observed.

Figure 3

Cellular organization of the ventricular zone of the cerebellum. The drawing summarizes the main cell types found in the roof of the 4V. BG cells (green) surrounds and covers the dendritic trees of Purkinje neurons (brown). The end-feet of Bergmann glia borders the dorsal side of the SVZ, where the subventricular cellular cluster is located (SVCC, gray blue) which is ventrally bordered by multiciliated ependymal glial cells (orange cells). The ventromedial cord (VMC, purple), is integrated by local subventricular neurons and glial cells and contacted by local astrocytes (blue). Ependymal biciliated cells (red) are in the midline at the periventricular layer-zone (PVZ), facing the lumen of the ventricle. Two sets of axons transverse contralaterally the roof of the 4V, subventricular axons (SV axons, red) from the fastigial nucleus and supraventricular axons (SupraV axons, green) form the vellum medularis that project from the IV cranial nerve.