Postnatal development of vimentin-positive cells in the rabbit superior colliculus.

The present study examined the postnatal development of the radial glia in the rabbit superior colliculus during the first 40 postnatal days. An antivimentin monoclonal antibody and the carbocyanine fluorescent tracer DiI were used in order to investigate the development of laminar connectivity in the superior colliculus. We focused our study on the superficial gray layer, the intermediate layer, and the deep layers of the superior colliculus, the periaqueductal gray matter (PAGM), and the medial intercollicular region. Vimentin-positive structures of glial lineage consisted of 1) the main radial system, which in the newborn rabbit was made up of wavy fibers that ran from the aqueduct to the pial surface, where they terminated in end-feet. At postnatal day 15, these fibers diminished to 100-200 microns long wavy tracts, which emanated from the aqueduct, and to a few straight or arched fragments in the superficial gray layer; 2) the median ventricular formation, which extends from mesencephalic aqueduct to the intercollicular sulcus, was characterized by a series of ascending, vimentin-positive fibers, some of large caliber, which persisted until postnatal day 40; 3) the tangential fiber system, which was made up of fibers that diverged from the median ventricular formation and of a number of short tracts running perpendicular to the periaqueductal radial fibers; these structures may provide support for migrating subpopulations of neurons; 4) immature and mature-like protoplasmic and fibrous astrocytes, which appeared during the second postnatal week. Thereafter, the number of vimentin-positive astrocytes decreased sharply. Our findings generally support earlier descriptions of the radial glia, except for the persistence, in superficial layers of the superior colliculus, of straight and curved fragments of fibers, which may participate in the organization of visual afferents at this level.