Confocal microscopic study of glial-vascular relationships in the retinas of pigmented rats

Astroglia are interposed between the cerebral vasculature and neurons, wher e they may mediate the transfer of substances from the circulation to neuro ns and couple changes in neuronal activity to changes in cerebral blood flo w. The retina is a particularly advantageous model system for studying glia l-vascular interactions in situ. Confocal microscopy and three-dimensional image reconstruction were used to study the anatomical relationships betwee n glia and the surface vasculature in retinas acutely isolated from adult p igmented rats. Retinas were immunostained using antibodies directed against the basal lamina surrounding the vasculature as well as antibodies directe d against glial fibrillary acidic protein. Surface vessels of all calibers were contacted by the processes of astrocytes. The vitreal surfaces of the large retinal vessels were covered by a meshwork of immunoreactive astrocyt e processes of a variety of shapes, whereas the scleral surfaces of the ves sels were supported by thick bundles of astrocyte processes. In addition, g lial cells were filled intracellularly with the gap junction-permeable trac ers Lucifer yellow and Neurobiotin. Intracellular fills dearly demonstrated the presence of astrocytes with somata that were closely apposed to the la rge retinal vessels. Tracer-filled astrocytes displayed a variety and compl exity of shapes that was not apparent in immunostained material. Gap juncti onal coupling was stronger between astrocytes adjacent to the same artery t han between periarterial astrocytes and astrocytes located away from arteri es. Significantly fewer Muller cells were labeled when Neurobiotin was inje cted into astrocytes associated with arteries than when Neurobiotin was inj ected into astrocytes that were distant from arteries. J. Comp. Neurol. 429 :253-269, 2001. (C) 2001 Wiley-Liss, Inc.