DYE-COUPLING BETWEEN SPINAL-CORD OLIGODENDROCYTES - DIFFERENCES IN COUPLING EFFICIENCY BETWEEN GRAY AND WHITE-MATTER

Oligodendrocytes express two gap junction proteins, connexin32 (Cx32) and Cx45. To test for functional coupling between oligodendrocytes, ce lls were filled with the (Cx32-permeable) dyes Lucifer Yellow (LY) and Neurobiotin(R). Cells in slices from rat spinal cord were dialyzed vi a the patch pipette containing the dye while recording with the patch- clamp technique. The dye-labeled cells were identified as oligodendroc ytes by their characteristic pattern of membrane currents and by morph ology. In gray matter, 18% of the injected cells (N = 94) were coupled to more than three adjacent cells (slices from postnatal day 1 to 19) . In contrast, in white matter, the dye was restricted to the injected cell (N = 63 for Lucifer Yellow injection only; N = 11 for LY and Neu robiotin(R)) indicating a lack of functional coupling. Immunolabeling of Cx32 in mature oligodendrocytes of white matter revealed that the g ap junction protein is localized on the cell bodies and abaxonal proce sses which occupy non-overlapping territories. In immature white matte r and gray matter, Cx32 is mostly concentrated in the somatic region o f the cells. In addition to Cx32, we have obtained immunocytochemical data that oligodendrocytes can express Cx45 with a labeling pattern di fferent from the Cx32 expression. Two alternative interpretations of t he coupling data are discussed: 1) that the presence of Cx32 in mature white, matter oligodendrocytes does not serve for communication betwe en cells, but rather for communication within oligodendrocytes in the sense of autocellular coupling, or 2) that the glial syncytium is furn ished with a high degree of functional rectification at the oligodendr ocytic side. GLIA 24:108-120, 1998. (C) 1998 Wiley-Liss, Inc.