Interglial cell gap junctions increase in urethane-induced photoreceptor degeneration in rats

Gap junctions are found between astrocytes in the inner retina of normal rats, but they are rare between Müller cells or between astrocytes and Müller cells in the inner retina. After photoreceptor degeneration induced by urethane treatment of newborn animals, morphologic alterations of glial cells occur in the inner retina. The Müller cells withdraw from the inner limiting membrane, and the astrocytes hypertrophy and occupy the vitread surface of the inner limiting membrane. The frequency and size of the gap junctions between astrocytes increases with time in rats with urethane-induced photoreceptor degeneration, to a greater extent than expected from elaboration of additional astrocyte plasma membrane. The gap junction-profile length per glial cell membrane-contact length is 2.8 +/- 1.1 microns/1000 microns of membrane in 8-week-old normal animals; it increases to 18.9 +/- 9.4 microns/1000 microns of membrane at 56 weeks of age in urethane-treated animals. The average size of the gap junction-profile length doubles during this same period. To the authors' knowledge this is the first study demonstrating pathologic changes in gap junctions in central nervous system tissue. The authors speculate that this up-regulation of gap junctions occurs in response to an altered extracellular ionic composition in an attempt to increase the lateral spatial buffering of K+ by these cells. The relative location of glial cells in retina can determine, in part, the vulnerability of the retina to edema.