Distribution and immunoreactivity of glia in the retina of the rabbit.

Glial markers, namely antibodies to glial fibrillary acidic protein (GFAP), vimentin, galactocerebroside (GC), and 08 antigen, were used to study the occurrence and location of neuroglial cells in adult rabbit retinae. Müllerian glia were vimentin-positive, lacked detectable amounts of GFAP, and were found in all parts of the rabbit retina. The neuronal A-type horizontal cells were labeled by vimentin antibody only in the superior retina and at the medullary rays but not in the inferior retina. They lacked GFAP in all regions. Astroglia showing GFAP and vimentin immunoreactivity were absent from most of the superior and inferior retina, being found only in the myelinated area of the ganglion cell axon bundles, the medullary rays. Thus the rabbit retina differs from the retinae of all mammals studied to date by this restriction of astroglia to just one area. The medullary rays, which are known to be myelinated, were labeled by the antibodies to GC and 08 antigen. Boycott and Hopkins ('84) found, using whole-mounted rabbit retinae stained by the reduced silver method of Richardson, that all neurons in the ganglion cell layer of the rabbit retina have a cilium, while cells that have only a diplosome are either neuroglia or microglia. By using this criterion as a basis to differentiate between neurons and glia, the absence of neuroglia from the nerve fiber layer outside the medullary rays was confirmed in the same silver-stained material. Thus, the data obtained from immunocytochemistry and conventional silver staining agree closely. It has been concluded that, at least in the adult, significant lengths of ganglion cell axons extend without astroglial sheaths.