Gap junction protein connexin43 is heterogeneously expressed among glial cells in the adult rabbit retina.

The immunohistochemical distribution and ultrastructural immunolocalization of connexin43 (Cx43) in the neural retina of the rabbit was investigated. Cx43 immunolabeling appeared in the form of distinct puncta distributed on different kinds of glial cells and exclusively in the myelinated fiber region of the neural retina. Double-label immunohistochemistry showed that the most obvious Cx43 labeling occurred at processes of glial fibrillary acidic protein-positive astrocytes and on vimentin-positive Müller cells. Cx43-immunoreactive puncta were also evident on cell bodies and processes of 2'-3'-cyclic nucleotide phosphodiesterase-labeled oligodendrocytes. As shown by electron microscopy, immunoreactivity to Cx43 was restricted to gap junctions among the macroglial cell population. The homologous interastrocytic and Müller cell-to-Müller cell, as well as the heterologous astrocyte-to-Müller cell and astrocyte/Müller-to-oligodendrocyte gap junctions were symmetrically labeled. Our results indicate a specific expression of Cx43 at gap junctions between macroglial cells located in the myelinated streak. The extensive Cx43 immunolabeling suggests a substantial amount of gap junctional coupling that establishes a macroglial syncytium.