Distribution of beta-dystroglycan immunopositive globules in the subventricular zone of rat brain

Present study demonstrates a novel localization of beta-dystroglycan in rat brain. Beside the meningeal surface and the cerebral vessels where beta-dystroglycan immunopositivity has been described, now immunopositive solid bodies were found at the basis of ependymocytes. Since they proved to be round in either coronal, sagittal, and horizontal section, revealing their globular shape, they received the term 'globules.' Double immunofluorescent labeling of GFAP (glial fibrillary acidic protein) and beta-dystroglycan revealed that 'globules' are within the 'cordon' of subventricular astrocytes. The 'globules' were found throughout the ventricular system, except the ventral part and floor of the third ventricle. The latter one comprised the median eminence and extended caudally to the inframamillary recess. The area where the 'globules' were missing, corresponded to that where ependymocytes were replaced by GFAP-immunopositive tanycytes. Utrophin and alpha-dystrobrevin were co-localized with dystroglycan, whereas alpha1-syntrophin was detected along the borders of the ependymal cells. Comparing our results to former data, the 'globules' seem to be the anchoring places of the 'fractons' formed by laminin [Mercier et al. (2003) J Comp Neurol 455:324-340], which interconnect the vascular basal lamina and the ependymal layer. The ependymal localization of the 'globules' was proved by pre-embedding electron microscopic immunohistochemistry. The 'globules' proved to be a labyrinthine structure, which seemed to be identical with the 'basal membrane labyrinth' described by Leonhardt [Leonhardt (1970) Z Zellforsch Mikrosk Anat 105:395-404]. The description of the beta-dystroglycan-immunopositive 'globules' contributes to the better understanding of the structure of the subventricular zone where neurogenesis can occur during adulthood and provides an important link to the meningeo-glial network.